ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Other Sources  (826)
  • ASTRONOMY
  • ASTROPHYSICS
  • EARTH RESOURCES AND REMOTE SENSING
  • 1995-1999  (826)
  • 1
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: Ground-based solar observational programs are discussed. The Birmingham (U.K.) solar oscillation network (BiSON) program, the Crimean (Ukraine) low degree program, the Stanford (California) low degree program, the Tenerife (Spain) group program, the South Pole program, the Mount Wilson (California) program, the international research on the interior of the sun (IRIS) network program, the high-l helioseismometer instrument, the ground luminosity oscillations imager (LOI) program, and the Taiwanese oscillation network (TON) program, are outlined.
    Keywords: ASTRONOMY
    Type: ESA, Proceedings of 4th SOHO on Helioseismology. Volume 1: Invited Reviews and Working Group Reports; p 107-111
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2011-08-24
    Description: The second guide star catalog (GSC-2) is a project that aims to create a complete catalog of stars and galaxies to about the 18th magnitude, and would contain colors, magnitudes, positions and proper motions. The catalog would provide an object list for the construction of an input catalog for possible future astrometric satellites, such as the global astrometric interferometer for astrophysics (GAIA) satellite. With a schedule that is compatible with the projected timeframe of GAIA, the GSC-2 could be available in time to support the preparatory astrophysical observations for an input catalog. The availability of the digitalized images for the preparation of finding charts would improve the efficiency of this task.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 137-141
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: The UBV variability of classical T Tauri stars is investigated using a large data set compiled by Herbst et al. (1994). The analysis is based on the covariance of the UBV colors, which is independent of the obscuration and the temporal sampling, and is a powerful tool for finding trends that otherwise would be hidden in the complex time-dependence of the data. I find that there are two types of UBV variability and introduce the nomenclature 'ortho-' and 'para-UBV' variations, or in short 'type-O' and 'type-P' variations. Objects with a predominance of ortho-UBV variability show strong variability in both the Balmer and Paschen continua, whereas objects dominated by para-UBV changes vary mostly in the Paschen continuum. I show that type-O variations can be explained in terms of rotating spots, variable obscuration, or changes intrinsic to the source that obey the law Delta T(sub S)/T(sub S) varies as Delta n(sub H)/n(sub H), where T(sub S) and n(sub H) are, respectively, the gas temperature and the number density of hydrogen nuclei. Type-P variations can be explained only by changes intrinsic to the source with Delta T(sub S)/T(sub S) varies as - Delta n(sub H)/n(sub H), and I speculate on a possible origin for these changes. The covariance ellipse of the UBV colors is a versatile tool for studying the connection between variability and other spectral signatures of classical T Tauri stars; its use for this purpose is illustrated by studying the correlation between the presence of CO first-overtone bands in emission and the type of variability. I find that objects with CO band emission are also those with type-P variability and propose an observational test to validate this conclusion.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 444; 2; p. 818-830
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2011-08-24
    Description: We present radio observations of the gravitational lens PKS 1830-211 at 8.4 and 15 GHz acquired using the Very Large Array. The observations were made over a 13 month period. Significant flux density changes over this period provide strong constraints on the time delay between the two lensed images and suffest a value of 44 +/- 9 days. This offers new direct evidence that this source is indeed a gravitational lens. The lens distance is dependent upon the model chosen, but reasonable limits on the mass of the lensing galaxy suggest that it is unlikely to be at a redshift less than a few tenths, and may well be significantly more distant.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 444; 2; p. 561-566
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2011-08-24
    Description: We present the results of a first attempt to employ multiaperture masks to obtain spectrophotometry of H II regions in nearby galaxies. A total of 97 H II regions in six southern spiral galaxies were observed using a combination of multiaperture masks and conventional long-slit spectrophotometry. The oxygen abundances derived from the multiaperture mask observations using the empirical abundance diagnostic R(sub 23) are shown to be consistent with those from long-slit spectra and generally show better reproducibility and object definition. Although the number of objects that can be observed simultaneously with this particular system is still quite limited compared with either imaging spectrophotometry or fiber-fed spectrographs, the spectral resolution offered and high throughput in the blue help make multiaperture spectrophotometry a competitive technique for increasing the sampling of H II regions in both radial distance and luminosity. There is still no clear trend of abundance gradient with either the galaxy's luminosity or its Hubble type, although the extrapolated central abundance does appear to correlate with galaxy luminosity/mass. In order to avoid difficulty in choosing an appropriate normalizing radius, we instead plot the oxygen abundance against the underlying I-band surface brightness at the radial distance of the H II region and confirm the existence of a local metallicity-surface brightness reltaionship within the disks of spiral galaxies. Although the simple closed-boc model of galaxy evolution predicts almost the right form of this relationship, a more realistic multizone model employing expnentially decreasing gas infall provides a more satisfactory fit to the observational data, provided the expected enriched gas return from dying low-mass stars shedding their envelopes at late epochs is properly taken into account. This same model, with a star formation law based upon self-regulating star formation in a three-dimensional disk (Dopita & Ryder 1994), is equally capable of accounting for the observed relationship between recent massive star formation and stellar surface brightness (Ryder & Dopita 1994).
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 444; 2; p. 610-631
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2011-08-24
    Description: The power laws are approximately f(exp -1.9), f(exp -1.9), and f(exp -2.1) respectively for the Grigg-Shjellerup (GS), Giacobini-Zinner (GZ), and Halley (H) comets. Other than similarities in the power spectra, the magnetic field turbulence is considerably different at the three comets. Phase steepening is demonstrated to occur at the trailing edges of the GS waves. This is probably due to nonlinear steepening plus dispersion of the left-hand mode components, i.e., the turbulence is whistler-mode. This too can be explained by nonlinear steepening plus dispersion of the magnetosonic waves. At the level of GS and GZ turbulence development when the spacecraft measurements were made, classical three-wave processes, such as the decay or modulation instabilities do not appear to play important roles. It is most likely that the nonlinear steepening and dispersive time scales are more rapid than three-wave processes, and the latter had not had time to develop for the relatively new turbulence. The wave turbulence at Halley is linearly polarized. The exact nature of this turbulence is still not well understood. Several possibilities are suggested, based on a preliminary analyses.
    Keywords: ASTROPHYSICS
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 9; p. 1149-1152
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2011-08-24
    Description: We report new high-resolution near-infrared imaging observations of the planetary nebula J900, in broadband J, H, and K, and narrowband 2.122 micrometers (for H2 1-0 S(1)), Brackett-gamma, and continuum filters. The H2 images reveal a remarkable set of outward-extending features not detected in any previous observations of theis object. In the northwest lobe of the inner bipolar region, the H2 emission, Brackett-gamma emission, and underlying continuum are spatially resolved. The relative positions of the peaks of the line emission suggest an ionization front seen edge-on. The continuum emission, apparently located nearer to the central star, is likely due to transiently heated small dust grains. The extended H2 emission features are probably excited either by oblique shocks caused by material ejected from the nebula, or by radiation leaking from holes in the opacity surrounding the ionized shell.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 109; 3; p. 1173-1180
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2011-08-24
    Description: A study of X-ray emission from five short-period Algol-type binaries based on observations with Advanced Satellite for Cosmology and Astrophysics (ASCA) and ROSAT is presented. We have observed RZ Cas with both satellites, and beta Per, U Cep, delta Lib, and TW Dra with ROSAT. Significant intensity variations are seen in the X-ray emission from RZ Cas, U Cep, TW Dra, and delta Lib. These variations seem unrelated to the eclipsing behavior of these systems and are probably due to either rotational modulation of compact active regions on the surfaces of the chromospherically active secondary components or to flaring activity in the systems. The spectra of all but one of the systems require the presence of at least two discrete plasma components with different temperatures (0.6 - 0.7 keV, and approximately 2 keV) and the abundances of the medium-Z elements 20% - 50% of the solar photospheric values. The high resolving power and signal-to-noise ratio of the ASCA spectra allow us to individually constrain the coronal abundances of O, Ne, Mg, Si, S, and Fe in RZ Cas. We demonstrate that, if we use the elemental abundances and temperatures obtained from the analysis of their ASCA spectra as (fixed) inputs, to fit the ROSAT PSPC spectra well requires the presence of a third component (kT approximately 0.2 - 0.3 keV) in RZ Cas and beta Per. A continuous emission measure model of the power-law type (EM(T) variesas (T/T(sub max)(sup alpha)) generally gives a poor fit to the ASCA and ROSAT data on most sources. Circumstellar or circumbinary absorbing matter seems to be present in some of these systems, as indicated by the variable total column density needed to fit their X-ray spectra.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 840-854
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2011-08-24
    Description: Recent ROSAT Position Sensitive Proportional Counter (PSPC) observations for the first time unequivocally reveal the presence of a compact source of hard X-ray emission centered on the peculiar star eta Car. These observations also show a dramatic change in the hard-band (E greater than 1.6 keV) counting rate by about a factor of 2 in a 4 month interval. Thus, strong variability, which is a characteristic of eta Car in radio through IR and visible-band wavelengths, is also observed at X-ray energies. The increase in hard X-ray emission could be the result of a tripling of the mass-loss rate in less than 4 months.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 445; 2; p. L21-L24
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2011-08-24
    Description: Using data extracted from the ROSAT archive we have discovered a recurrent supersoft X-ray transient RX J0045.4+4154 in M31. The first outburst began on 1992 February 2 and continued for at least 4 days, until the end of the observation sequence. A second outburst that lasted more than 6 days was seen to begin on 1993 January 7. The X-ray spectrum on both occasions yields a characteristic blackbody temperature of approximately 90 eV. For a range of plausible continuum models, the hydrogen column density is (0.8-1.5) x 10(exp 21)/sq cm and is consistent with the source being located in M31. This implies an unabsorbed 0.1-2.0 keV peak luminosity of approximately 10(exp 38) ergs/sec. This is the first recurrent X-ray transient to be found in M31 and is particularly notable because it is much softer than the bright X-ray transients seen in our Galaxy. The spectrum is characteristic of the supersoft class of X-ray sources, which are thought to be accreting white dwarfs that have a hydrogen-burning surface layer. A fit to a white dwarf model atmosphere gives a temperature of 10(exp 6)K, the hottest found so far. This high temperature is consistent with a white dwarf mass of 1.3-1.4 solar mass, approaching the Chandrasekhar limit, and burning close to the nuclear stability limit.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 445; 2; p. L25-L28
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 11
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: The life of 18th century astronomer, craftsman, and partriot David Rittenhouse is detailed. As a craftsman, he distinguished himself as one of the foremost builders of clocks. He also built magnetic compasses and surveying instruments. The finest examples of his craftsmanship are considered two orreries, mechanical solar systems. In terms of astronomical observations, his best-known contribution was his observation of the transit of Venus in 1769. Rittenhouse constructed the first diffraction grating. Working as Treasurer of Pennsylvania throughout the Revolution, he became the first director of the Mint in 1792. Astronomical observations in later life included charting the position of Uranus after its discovery.
    Keywords: ASTRONOMY
    Type: Sky & Telescope (ISSN 0037-6604); 89; 5; p. 38-41
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 12
    Publication Date: 2011-08-24
    Description: Using high-resolution spectroscopic data taken with the Goddard High Resolution Spectrographic (GHRS) aboard the Hubble Space Telescope (HST) and with the International Ultraviolet Expolorer (IUE) satellite, we compare the profiles of the Mg II h and k lines seen in stars with spectral types ranging from early K through mid-M and luminosities from giants to supergiants. For all of these stars the lines are broad emission features with a central absorption. When plotted on a velocity scale the absorption features of the h and k lines agree very well in both shape and position, as do the blue wings of the emission component. The red wings of the emission, however, show a pronounced difference, with the k line wing consistently shifted to the red of the h line wing. At present the reason for this discrepancy is unknown, but we suggest several possibilities, including radiative transfer effects and high-speed stellar winds.
    Keywords: ASTRONOMY
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 442; 1; p. 328-336
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 13
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: The X-ray observatory Advanced Satellite for Cosmology and Astrophysics (ASCA) (Astro-D) was launched in Feb 1993 and is now providing excellent spectro-imaging observations of objects from virtually every astronomical class. This paper reviews the scientific capabilities of ASCA using some of the first results from X-ray binaries, cataclysmic variables, and stars.
    Keywords: ASTRONOMY
    Type: Advances in Space Research (ISSN 0273-1177); 16; 3; p. 29-39
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 14
    Publication Date: 2011-08-24
    Description: A close examination of the 0.7- to 23-micron infrared data base acquired by Gehrz and Ney (1992), suggests that the nucleus of Comet P/Halley 1986 III emitted a burst of small dust grains during a 3-day period commencing within hours of perihelion passage on 1986 February 9.46 UT. The outburst was characterized by significant increases in the coma's grain color temperature T(sub obs), temperature excess (superheat: S = T(sub obs)/T(sub BB)), infrared luminosity, albedo, and 10-micron silicate emission feature strength. These changes are all consistent with the sudden ejection from the nucleus of a cloud of grains with radii of approximately 0.5 micron. This outburst may have produced the dust that was responsible for some of the tail streamers photographed on 1986 February 22 UT. The peak of the dust outburst occurred about 3 days before a pronounced increase in the water production rate measured by the Pioneer Venus Orbiter Ultraviolet Spectrometer. We suggest that jets that release large quantities of small particles may be largely responsible for some of the variable infrared behavior that has been reported for P/Halley and other comets during the past two decades. Such jets may also account for some of the differences IR Type I and IR Type II comets.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 113; 1; p. 129-133
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 15
    Publication Date: 2011-08-24
    Description: The 183-GHz water vapor line was tentatively detected on Mars in January 1991, with the IRAM 30-m millimeter antenna, under extremely dry atmospheric conditions. The measurement refers to the whole disk. The spectral line, although marginally detected, can be fit with a constant H2O mixing ratio of 1.0 x 10(exp -5), which corresponds to a water abundance of 1 pr-microns; in any case, an upper limit of 3 pr-microns is inferred. This value is comparable to the very small abundances measured by Clancy (1992) 5 weeks before our observation and seems to imply both seasonal and long-term variations in the martian water cycle.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 113; 1; p. 110-118
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 16
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: Titan's large free eccentricity results in significant tidal dissipation. This can be used to constrain the existence and depth of hydrocarbon oceans. A hydrodynamical-numerical 2 deg ocean tide model has been constructed to investigate this connection. The model allows some simple land configurations. The results indicate that existence of such an ocean over the age of the solar system is hard to explain, as is the existence of the large eccentricity itself. If such an ocean exists, it is likely to be more than 500 m deep, ignoring the influence of land masses.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 113; 1; p. 39-56
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 17
    Publication Date: 2011-08-24
    Description: The age relations between 36 impact craters with dark paraboloids and other geologic units and structures at these localities have been studied through photogeologic analysis of Magellan SAR images of the surface of Venus. Geologic settings in all 36 sites, about 1000 x 1000 km each, could be characterized using only 10 different terrain units and six types of structures. Mapping of such units and structures in 36 randomly distributed large regions shows evidence for a distinctive regional and global stratigraphic and geologic sequence. On the basis of this sequence we have developed a model that illustrates several major themes in the history of Venus. Most of the history of Venus (that of its first 80% or so) is not preserved in the surface geomorphological record. The major deformation associated with tessera formation in the period sometime between 0.5-1.0 b.y. ago (Ivanov and Basilevsky, 1993) is the earliest event detected. Our stratigraphic analyses suggest that following tessera formation, extensive volcanic flooding resurfaced at least 85% of the planet in the form of the presently-ridged and fractured plains. Several lines of evidence favor a high flux in the post-tessera period but we have no independent evidence for the absolute duration of ridged plains emplacement. During this time, the net state of stress in the lithosphere apparently changed from extensional to compressional, first in the form of extensive ridge belt development, followed by the formation of extensive wrinkle ridges on the flow units. Subsequently, there occurred local emplacement of smooth and lobate plains units which are presently essentially undeformed. The major events in the latest 10% of the presently preserved history of Venus are continued rifting and some associated volcanism, and the redistribution of eolian material largely derived from impact crater deposits. Detailed geologic mapping and stratigraphic synthesis are necessary to test this sequence and to address many of the outstanding problems raised by this analysis.
    Keywords: ASTRONOMY
    Type: Earth, Moon, and Planets (ISSN 0167-9295); 66; 3; p. 285-336
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 18
    Publication Date: 2011-08-24
    Description: A number of planetary objects exhibit large radar reflectivity and polarization ratios, and more recently, a similar behavior has been observed over a vast portion of the Earth's surface: the percolation facies of the Greenland Ice Sheet. Surface-based ranging radar data and snow stratigraphy studies demonstrated that the radar properties of that portion of Greenland are caused by enhanced scattering from massive, large, solid-ice bodies buried in the top few meters of the dry, cold, clean snowy surface of the ice sheet and created by seasonal melting and refreezing events. Here, we model the icy inclusions as randomly oriented, discrete, noninteracting, dielectric cylinders embedded in a transparent snow medium. An exact analytical solution is used to compute the scattered field from the cylinders. Using this model, we correctly predict the polarimetric radar observations gathered by an airborne imaging system at three wavelengths (5.6, 24, and 68 cm), between 19 deg and 65 deg incidence angle. The diameter and number density of the cylinders that are inferred from the radar data using the model are consistent with in situ observations of the icy inclusions. The large radar reflectivity and polarization ratios are interpreted as arising internal reflections of the radar signals in the icy inclusions that first-order external reflection models fail to predict. The results compare favorably with predictions from the coherent backscatter or weak localization theory and may provide a complementary framework for interpreting exotic radar echoes from other planetary objects.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; E5; p. 9389-9400
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 19
    Publication Date: 2011-08-24
    Description: We obtained the first high-dispersion IUE spectrum, and an additional low-dispersion spectrum of the very young planetary nebula He 3-1357 and its central star SDAO 244567. In 1988, it showed a very strong C IV lambda-1549 P Cygni profile which diminished and has disappeared by 1994, but C IV absorptions are seen in a high-resolution spectrum. The electron density from the C III F(lambda 1907)/F(lambda 1909) emission ratio is log N(sub e) = 4.1/cc. The older IUE data were reprocessed, and emission-line fluxes vary greatly for the period 1988-1994. The high-dispersion data show a rich Fe V and Fe VI absorption spectrum.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 443; 1; p. 245-248
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 20
    Publication Date: 2011-08-24
    Description: 24 years of Lunar Laser Ranging (LLR) observations and 16 years of Very Long Baseline Interferometry (VLBI) observations are combined in a global analysis to yield improved estimates of the Earth's precession and nutation. The correction to the International Astronomical Union (IAU) (1976) precession constant inferred from this joint VLBI/LLR analysis is -3.00 +/- 0.20 milliarcsec/yr (mas/yr). A significant obliquity rate correction of -0.20 +/- 0.08 mas/yr is also found. In all, 32 forced nutation coefficients are estimated. These coefficients confirm that the IAU (1980) nutation theory is in error by several mas. The estimated nutation coeficients are found to vary by as much as several tenths of mas, depending on the a priori nutation model used to analyze the VLBI and LLR data. Forced circular nutations derived from this analysis agree with the ZMOA-1990-2 nutation theory at the 0.2 mas level for the 18.6 yr terms, and at the 0.05 mas level for the other terms (periods less than or = 1 yr). A retrograde free core nutation with an amplitude of 0.20 mas is also detected. Its phase is found to be very sensitive to the precise value of the free core nutation period used in the solution. Separate analyses of four independent subsets of the LVBI data indicate no significant variations of the free core nutation since 1988. The pre-1988 estimates of the free core nutation are consistent with the post-1988 estimates but are not accurate enough to rule out possible variations of the free core nutation at these earlier epochs.
    Keywords: ASTROPHYSICS
    Type: The Astronomical Journal (ISSN 0004-6256); 109; 1669; p. 418-427
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 21
    Publication Date: 2011-08-24
    Description: We have observed seven narrow-linedd Seyfert 1 (NLS1) galaxies and one high-ionization Seyfert 2 galaxy with the Very Large Array (VLA). Combining these observations with published data, we summarize the radio properties of the NLS1 galaxies for which spectropolarimetry was reported by Goodrich. Fifteen of these 17 objects now have published radio observations of high sensitivity, and only nine of those have been detected. For a Hubble parameter of 75 km/s/Mpc, the 6 cm radio powers range from 10(exp 20) to 10(exp 23) W/Hz, within the range previously found for other types of Seyfert galaxy. The median radio size of the nine VLA-detected galaxies is no larger than 300 pc, similar to the median size found by Ulvestad & Wilson for a distance-limited sample of Seyfert galaxies. Of the six NLS1 galaxies known to have significant intrinsic optical polarization, three have measurable radio axes. Two of those three galaxies have radio major axes close to 90 deg from their polarization position angles, while the third has an inner radio axis that may be nearly parallel to the polarization position angle. The former relationship is expected for a Seyfert 1 in a unified model of Seyfert galaxies, assuming no intrinsic continuum polarization.
    Keywords: ASTRONOMY
    Type: The Astronomical Journal (ISSN 0004-6256); 109; 1669; p. 81-86
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 22
    Publication Date: 2011-08-24
    Description: The Ulysses spacecraft has gathered data from within flows from the Sun's southern polar coronal hole, the first in situ measurement of this region. We present a brief analysis of the heliospheric magnetic field data from this region, using a fractal method. As is the case near the ecliptic, estimated spectral exponents are near 5/3 on spacecraft scales of seconds to minutes. On longer time scales, however, there appears to be a significantly different population in polar flows, which is similar to that found by the Helios spacecraft in fast solar wind flows at 0.3 AU.
    Keywords: ASTROPHYSICS
    Type: Annales Geophysicae (ISSN 0992-7689); 13; 1; p. 105-107
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 23
    Publication Date: 2011-08-24
    Description: We have performed multiband photopolarimetry toward stars behind the molecular cloud L1457 (MBM 12). This cloud is the nearest known molecular cloud (65 pc) and thought to be contained within the local 'hot bubble.' The polarization shows a regular structure, indicating that the cloud is threaded by an ordered magnetic field. The wavelength dependence of the polarization seems to indicate that the grains in L1457 have higher indices of refraction than normal for interstellar clouds. However, the wavelength of maximum polarization indicates that their size distribution is close to normal.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 443; 1; p. L49-L52
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 24
    Publication Date: 2011-08-24
    Description: Using Viking Orbiter images, detailed photoclinometric profiles were obtained across 10 irregular depressions, 32 fretted fractures, 40 troughs and pits, 124 solitary scarps, and 370 simple grabens in the north Tharsis region of Mars. These data allow inferences to be made on the shallow crustal structure of this region. The frequency modes of measured scarp heights correspond with previous general thickness estimates of the heavily cratered and rigded plains units. The depths of the flat-floored irregular depressions (55-175 m), fretted fractures (85-890 m), and troughs and pits (60-1620 m) are also similar to scarp heights (thicknesses) of the geologic units in which these depressions occur, which suggests that the depths of these flat-floored features were controlled by erosional base levels created by lithologic contacts. Although the features have a similar age, both their depths and their observed local structural control increase in the order listed above, which suggests that the more advanced stages of associated fracturing facilitated the development of these depressions by increasing permeability. If a ground-ice zone is a factor in development of these features, as has been suggested, our observation that the depths of these features decrease with increasing latitude suggests that either the thickness of the ground-ice zone does not increase poleward or the depths of the depressions were controlled by the top of the ground-ice zone whose depth may decrease with latitude.
    Keywords: ASTRONOMY
    Type: Icarus (ISSN 0019-1035); 114; 2; p. 403-422
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 25
    Publication Date: 2011-08-24
    Description: A calculation, employing a detailed model of neutral oxygen, is carried out to give fluorescent line intensities expected in a long-proposed photoexcitation by accidental resonance (PAR) process in which hydrogen Lyman-beta photoexcites the oxygen spectrum. The results pertain to the optically thin case but provide an upper limit to the fluorescent intensities which can be attained. They are applied to analyze line ratios involving the strong 8446 A line observed in classical novae during the diffusion-enhanced and Orion phases. Operation of the PAR process in the novae is verified. It is found that photoexcitation rates in the ejecta reach values greater than 0.1/sec, corresponding to hydrogen Lyman-beta radiation field intensities greater than 1250 ergs/cm/sec/sr.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 1; p. 346-356
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 26
    Publication Date: 2011-08-24
    Description: We report the detection of a broad absorption feature near 2166/cm in the spectrum of the Taurus cloud cource Elias 18. This pre-main-sequence source is the second in Taurus, the third in our survey, and the fifth known in the sky to show the broad 2166/cm absorption feature. Of equal importance, this feature is not seen toward several other embedded sources in our survey, nor is it seen toward the source Elias 16, located behind the Taurus cloud. Laboratory experiments with interstellar ice analogs show that such a feature is associated with a complex C triple bonded to N containing compound (called X(C triple bonded to N)) that results from high-energy processing (ultraviolet irradiation or ion bombardment) of simple ice components into more complex, organic components. We find a nonlinear anticorrelation between the abundance of X(C triple bonded to N) and frozen CO components in nonpolar lattices. We find no correlation between the abundance of X(C triple bonded to N) and frozen CO in polar lattices. Because the abundances of frozen CO and H2O are strongly correlated with each other and with visual extinction toward sources embedded in and located behind the Taurus molecular cloud, these ice components usually are associated with intracloud material. Our results indicate that X(C triple bonded to N) molecules result from chemical processing of dust grains dominated by nonpolar icy mantles in the local environments of pre-main-sequence stars. Such processing of icy grains in the early solar system may be an important source of organic compounds observed in minor solar system bodies. The delivery of these organic compounds to the surface of the primitive Earth through comet impacts may have provided the raw materials for prebiotic chemistry.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 1; p. 279-287
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 27
    Publication Date: 2011-08-24
    Description: We have investigated the properties of the OMC-2 and OMC-3 cores in the Orion giant molecular cloud using high spatial spectral resolution observations of several transitions of the (13)CO, C(18)O, C(S-32) and C(S-34) molecules taken with the SEST telescope. The OMC-2 core consists of one clump (22 solar mass) with a radius of 0.11 pc surrounded by a cluster of 11 discrete infrared sources. The H2 column density and volume density in the center of this clump are 2 x 10(exp 22)/sq cm and 9 x 10(exp 5)/cu cm respectively. From a comparison between physical parameters derived from C(18)O and C(S-32) observations we conclude that the molecular envelope around the core has been completely removed by these sources and that only the very dense gas is left. OMC-3 shows a more complex elongated structure in C(18)O and CS than OMC-2. The C(S-32) and C(S-34) maps show that the denser region can be separated into at least sub-cores of roughly equal sizes (radius approximately equals 0.13 pc), with n(H2) = 6 x 10(exp 5)/cu cm, and a mass of 10 solar mass (from C(S-32)). The very different masses obtained for the central core from C(18)O and C(S-32) (55 and 12 solar mass respectively) indicate that a massive envelope is still present around the very dense sub-cores. We report the first detection of several molecular outflows in OMC-3. The presence of an IRAS source and the first detection of these outflows confirm that star formation is going on in OMC-3. Based on the different physical properties of these regions compared with OMC-1, OMC-2 appears to be in an intermediate evolutionary stage between OMC-1 and OMC-3.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 294; 3; p. 835-854
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 28
    Publication Date: 2011-08-24
    Description: Theoretical electron density sensitive emission-line ratios, determined using electron impact excitation rates calculated with the R-matrix code, are presented for R = I(2s(sup 2) (1)S-2s2p 3P(sub 2))/I(2s(sup 2) (1)S-2s2p 3P(sub 1) = 1(1483 A)/I(1486 A) in N IV. These are found to be up to an order of magnitude different from those deduced by previous authors, principally due to the inclusion of excitation rates for transitions among the 2s2p (3)p fine-structure levels. The observed values of R for several planetary nebulae, symbiotic stars and the Cygnus Loop supernova remnant, measured from spectra obtained with the International Ultraviolet Explorer (IUE) satellite and the Hopkins Ultraviolet Explorer (HUT), lead to electron densities which are in excellent agreement with those deduced from line ratios in other species. This provides observational support for the accuracy of the atomic data adopted in the present calculations.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 1; p. 500-503
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    Publication Date: 2011-08-24
    Description: The depletion of condensable elements onto grains in gaseous nebulae can provide evidence that dust is well mixed with the ionized gas. Al and CA are two of the most depleted elements in the general interstellar medium, and it is therefore important to measure their abundances within the ionized region of nebulae. We compute a large grid of photoionization models and identify sets of line ratios which are relatively insensitive to stellar and nebular parameters, and are thus excellent diagnostics for determining relative abundances. Based on the absence of the ((Ca II) lambda lambda 291, 7324 doublet and the detection of Al II) lambda lambda 2660, 2669 in the ultraviolet, we determine the extent of aluminum and calcium depletion onto grains in NGC 7027 and the Orion Nebula. Our results show a approximately 0.3 dex depletion for Al, but a depletion of more than two and a half orders of magnitude for Ca. A similar calculation based on Mg II lambda 2798 yields roughly a 0.8 dex depletion for Mg. This reaffirms the discrepancy between depletion determined from high and low ionization Mg lines. We also find evidence for a 'depletion gradient' in Ca in NGC 7027, since the calcium depletion we infer for the outer, more neutral regions using (Ca II) is somewhat higher than that inferred for the inner high-ionization region, using (Ca v). This gradient can test current models of the survival of grains within hot ionized gas.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 2; p. 793-799
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 30
    Publication Date: 2011-08-24
    Description: Synthetic-aperture radar (SAR) interferograms produced from ESA's ERS-1 satellite, provide the first synoptic view of ice flow dynamics of the western sector of the Greenland Ice Sheet. Glacial motion is detected in the radar ranging direction at millimetric scales, across a complete sequence of snow accumulation and melting regimes, despite significant varations in their radar scattering properties. Ice flow evolves from a slow, regular motion at the higher elevations. At lower elevations, motion is strongly convoluted by meter-scale undulations in surface topography, which have a unique interferometric signature that enables a novel approach for retrieving flow direction. Inferred flow directions, combined with surface displacements in the radar ranging direction, yield ice velocity estimates that are within 6% of in-situ measurements gathered along a 40 km survey line. Application of repeat-pass SAR interferometry to the entire Greenland Ice Sheet should enable precise mapping of its ice flow dynamics at an unprecedented level of spatial detail.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 5; p. 575-578
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 31
    Publication Date: 2011-08-24
    Description: The Advanced Satellite for Cosmology and Astrophysics (ASCA) instrument uses identical conical foil X-ray mirrors for its four telescopes. One of the major advantages of ASCA's telescopes is the first time ever use of X-ray imaging over a broad energy band and high throughput for conducting astronomical spectroscopy. Nested thin foil reflectors make possible a large effective area up to 10 keV, even under the tight weight restriction of the ASCA spacecraft. The expected characteristics of the ASCA mirrors are summarized based on ray tracings and pre-flight calibrations. The total effective area of four telescopes at 1 and 7 keV are approximately 1200 and 600 sq cm, respectively. The image size (half power diameter: HPD) is about 3 min. The field of view is 24 min and 16 min full width at half maximum for 1 and 7 keV, respectively. Observations of several X-ray sources from space during the performance verification phase have confirmed those performances as well as the alignment of the optical systems.
    Keywords: ASTRONOMY
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 47; 1; p. 105-114
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 32
    Publication Date: 2011-08-24
    Description: The modern scenario of evolution of massive binary systems predicts the existence of a subclass of binary radio pulsars (PSRs) with black holes (BHs). Their Galactic number was evaluated as approximately 1 per 1000 single pulsars (Lipunov et al. 1994b). Distinctive properties of such binaries would be (1) mass of the unseen companion M(sub c) greater than 3-4 solar mass and (2) absence of eclipses of the pulsar radiation with no distinctive variance of the dispersion measure along the pulsar orbit. The pulsars themselves must be similar to standard isolated ones. The recently discovered binary 1 s pulsar PSR B0042-73 = PSR J0045-7319 in the Small Magellanic Cloud (SMC) with a massive companion in a highly elongated (eccentricity e =0.8) 51 day orbit (Kaspi et al. 1994) may be the first such pulsar with a BH. The paradoxical fact that the first pulsar discovered in the SMC proved to be in a binary system can be naturally understood if its companion actually is a 10-30 solar mass black hole. We illustrate this fact by the numerical calculation of evolution of radio pulsars after a star formation burst.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 2; p. 776-778
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 33
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: We calculate the structure of an effectively optically thin and geometrically thin accretion disk in the Kerr geometry, including electron-positron pairs. We show that the properties of the disk solutions are strongly dependent on the angular momentum of the central black hole. We find that close to a rapidly rotating hole there can be an appreciable pair density even for modest accretion rates. Pair critical accretion rates recently discovered in Newtonian disk models are also shown to be present in the general relativistic models, and we show that the geometrically thin disk approximations easily break down for rapidly rotating holes.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 2; p. 765-769
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 34
    Publication Date: 2011-08-24
    Description: We examine the hydrodynamic origin of relativistic outflows in active galactic nuclei (AGN). Specifically, we propose that the presence of a population of relativistic hadrons in the AGN 'central engine' and the associated neutron production suffices to produce outflows which under rather general conditions could be relativistic. The main such condition is that the size of the neutron production region be larger than the neutron flight path tau(sub n) approximately 3 x 10(exp 13) cm. This condition guarantees that the mean energy per particle in the proton fluid, resulting from the decay of the neutrons outside their production region, be greater than the proton rest mass. The expansion of this fluid can then lead naturally to a relativistic outflow by conversion of its internal energy to directed motion. We follow the development of such flows by solving the mass, energy as well as the kinetic equation for the proton gas in steady state, taking into account the source terms due to compute accurately the adiabatic index of the expanding gas, and in conjunction with Bernoulli's equation the detailed evolution of the bulk Lorentz factor. We further examine the role of large-scale magnetic fields in confining these outflows to produce the jets observed at larger scales.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 2; p. 521-532
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 35
    Publication Date: 2011-08-24
    Description: The topology of the magnetic field in the heliosheath is illustrated using plots of the field lines. It is shown that the Archimedean spiral inside the terminal shock is rotated back in the heliosheath into nested spirals that are advected in the direction of the interstellar wind. The 22-year solar magnetic cycle is imprinted onto these field lines in the form of unipolar magnetic envelopes surrounded by volumes of strongly mixed polarity. Each envelope is defined by the changing tilt of the heliospheric current sheet, which is in turn defined by the boundary of unipolar high-latitude regions on the Sun that shrink to the pole at solar maximum and expand to the equator at solar minimum. The detailed shape of the envelopes is regulated by the solar wind velocity structure in the heliosheath.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; A3; p. 3463-3471
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 36
    Publication Date: 2011-08-24
    Description: Data from the Diffuse Infrared Background Experiment (DIRBE) instrument aboard the Cosmic Background Explorer Satellite (COBE) spacecraft have been used to examine the near and far infrared signatures of the interplanetary dust (IPD) bands. Images of the dust band pairs at ecliptic latitudes of +/- 1.4 deg and +/- 10 deg have been produced at DIRBE wavelengths from 1.25 to 100 micrometers. The observations at the shorter wavelengths provide the first evidence of scattered sunlight from particles responsible for the dust bands. It is found that the grains in the bands and those in the smooth IPD cloud have similar spectral energy distributions, suggesting similar compositions and possibly a common origin. The scattering albedos from 1.25 to 3.5 micrometers for the grains in the dust bands and those in the IPD cloud are 0.22 and 0.29, respectively. The 10 deg band pair is cooler (185 +/- 10 K) than the smooth interplanetary dust cloud (259 +/- 10 K). From both parallactic and thermal analyses, the implied location of the grains responsible for the peak brightness of the 10 deg band pair is 2.1 +/- 0.1 AU the Sun A parallactic distance of 1.4 +/- 0.2 AU is found for the peak of the 1.4 deg band pair.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal (ISSN 0004-637X); 442; 2, Pa; p. 662-667
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 37
    Publication Date: 2011-08-24
    Description: We report a new component of Jovian radio emission observed by the Ulysses spacecraft when Ulysses was at high Jovigraphic latitudes (greater than or approximately = 30 deg north or south of the Jovian magnetic equator). This bursty high-latitude emission is elliptically polarized in the right-hand sense when observed from northern latitudes and in the left-hand sense when observed from southern latitudes, consistent with extraordinary mode. The orientation of the polarization ellipse is observed to systematically vary with time relative to the observer. It is argued that the elliptically-polarized nature of the emission is intrinsic to the source region.
    Keywords: ASTRONOMY
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 4; p. 345-348
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 38
    Publication Date: 2011-08-24
    Description: SN 1987A hard X-ray continuum spectra obtained on 1987 October 29, 1988 April 9-10, and 1988 November 11 from balloon-flight measurments are presented. The spectra, spanning the energy range from 25 keV to 300 keV, have been analyzed using a detector response matrix inversion technique that converts the spectra form counts/s/sq cm keV to photons/s/sq cm keV allowing direct comparison with theoretical models. The results indicate that the bulk of the (56)Co is mixed moderately through the inner regions of the supernova envelope but they do not preclude the mixing of a small amount of the (56)Co farther out into the envelope necessary to account for the observed (56)Co line fluxes. The effect of the ratio (57)Co to (56)Co on the 1988 November 11 continuum spectrum is discussed.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 2; p. 963-975
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 39
    Publication Date: 2011-08-24
    Description: The UV line profile structure of high-ionization resonance lines found with the International Ultraviolet Explorer (IUE) in the brightest of four multiply imaged sources (images-A) in the candidate gravitational lens UM 425 = QSO 1120+019 indicates broad absorption line (BAL) structure. The deep-broad trough associated with the O IV line extends to velocities approiximately -12,000 km/s, and contains disrete features that suggest multicomponent velocity structure. This structure may include contributions from C IV absorption from the early-type galaxy that is believed to lens UM 425. A strong absorption feature in the blue wing of the Lyman-alpha lambda 1216 emission line may be a Lyman alpha absorption system at a Z(sub Ly alpha) = 1.437 +/- 0.003, or it may be formed by the superposition of the broad N V lambda lambda 1238, 1242 absorption trough on the extended blue emission wing of the QSO Lyman-alpha line. We obtained a redshift of Z(sub QSO) = 1.471 +/- 0.003 from Lyman-alpha lambda 1215, consistent with the redshift found by Meylan and Djorgovski in the optical. The Lyman-alpha line appears unusally weak due to the presence of N V lambda 1240 BAL absorption. A Lyman-limit absorption system at lambda 912 was not observed in the QSO rest frame. The detection of BAL structure in the other weaker ground-state resonance lines of N II (l) and S IV (l) was not found, suggesting these lines are formed in a region that is distinct from the BAL component. Detection of BAL structure in the other fainter images in this system with Hubble Space Telescope (HST) instrumentation, similar to structure observed here in image A, could provide evidence that UM 425 is a gravitational lens.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 2; p. 599-603
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 40
    Publication Date: 2011-08-24
    Description: We investigate the physical basis for the timescale of impulsive-phase, redshifted Lyman-alpha emission in stellar flares on the assumption that it is determined by energy losses in a nonthermal proton beam that is penetrating the chromosphere from above. The temporal evolution of ionization and heating in representative model chromospheres subjected to such beams is calculated. The treatment of 'stopping' of beam protons takes into account their interactions with (1) electrons bound in neutral hydrogen, (2) nuclei of neutral hydrogen, (3) free electrons, and (4) ambient thermal protons. We find that, for constant incident beam flux, the system attains an equilibrium with the beam energy input to the chromosphere balanced by radiative losses. In equilibrium, the beam penetration depth is constant, and erosion of the chromosphere ceases. If the redshifted, impulsive-phase stellar flare Lyman-alpha emission is produced by downstreaming hydrogen formed through charge exchange between beam protons and ambient hydrogen, then the emission should end when the beam no longer reaches neutral hydrogen. The durations of representative emission events calculated on this assumption range from 0.1 to 14 s. The stronger the beam, the shorter the timescale over which the redshifted Lyman-alpha emission can be observed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 1; p. 385-399
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 41
    Publication Date: 2011-08-24
    Description: The high-energy diffuse gamma-ray emission from the interstellar gas in Orion was studied using observations from the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory (CGRO) and radio surveys of the H I and CO emission. The good correlation of the gamma-ray emission with the atomic and molecular gas permits determination of the gamma-ray emissivity per nucleon in the interstellar medium and the molecular mass calibrating ratio N(H2)/W(sub co) in Orion. The integral gamma-ray emissivity is (1.7 +/- 0.1) x 10(exp -26)/s/sr for E greater than 100 MeV, in good agreement with expectations from studies of the diffuse emission on larger scales. The N(H2)/W(sub co) ratio is (1.06 +/- 0.14) x 10(exp 20)/sq cm/(K km/s), approximately 40% less than the commonly adopted Galactic average. We find no evidence for variations of the cosmic-ray density or N(H2)/W(sub co) ratio in Orion at the sensitivity and resolution of EGRET.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 1; p. 270-280
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 42
    Publication Date: 2011-08-24
    Description: We compare observations of BL Lac megaparsec-scale clustering environments with those for F-R I radio galaxies V and R image data are used to show that the strengths of the clustering measured via spatial cross-correlation amplitude are similar for the two types of galaxies and are consistent with Abel richness class 0. We discuss the implications this has for the origin of the BL Lac phenomena. We also examine the evolution of clustering environments of F-R I radio galaxies and BL Lac objects with redshift.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 441; 1; p. 113-119
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 43
    Publication Date: 2011-08-24
    Description: Through analysis of available optical spectrophotometric data and radio flux density measurements in the literature, it is demonstrated that a good correlation exists between the radio power and bolometric luminosity of the optically-selected OSOs in the Bright Quasar Sample (BOS) of Schmidt and Green (1983). We have recently used VLBI measurements of a sample of ultraluminous infrared galaxies to infer the likely existence of radio-quiet Active Galactic Nuclei (AGNs) deeply enshrouded in dust within their nuclei (Lonsdale, Smith, and Lonsdale 1993). We employ the radio-bolometric luminosity correlation for the BQS quasars to test whether these hypothetical buried AGNs can be energetically responsible for the observed far-infrared luminosities of the ultraluminous infrared galaxies. The ultraluminous infrared galaxies are shown to follow the same relation between radio core power and bolometric luminosity as the radio-quiet QSOs, suggesting that buried AGNs can account for essentially all the observed infrared luminosity, and raising the possibility that any starburst which may be in progress may not be energetically dominant. The broader implications of the radio-optical correlation in quasars for AGNs and luminous infrared galaxy models and the use of radio astronomy as a probe of the central powerhouse in radio quiet AGNs and luminous infrared galaxies are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 2; p. 623-642
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 44
    Publication Date: 2011-08-24
    Description: The proposed design and construction of the Fizeau astrometric mapping explorer (FAME), a small astrometric instrument for use on an artificial satellite, is reported on. The instrument and spacecraft are designed to slowly spin and will repeatedly scan great circles on the sky so that, over a period of time, it will cover the complete sky and repeat in a manner similar to that of the Hipparcos satellite. The instrument will use the two fixed dilute aperture telescopes to measure a fixed angle between stars and detect the positions, magnitude and color of all stars crossing its field of view to a visual magnitude of approximately 15 mag. The aim of the instrument is to obtain a catalog of positions, proper motions and parallaxes of all stars down to about 15 mag, with a magnitude dependent accuracy of positions of 20 to 800 micro arcsec, proper motions of 20 to 800 micro arcsec per year and parallaxes of 20 to 800 micro arcsec.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 187-189
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 45
    Publication Date: 2011-08-24
    Description: The concepts related to the operation and design of the global astrometric interferometer for astrophysics (GAIA) bring together solutions chosen for the astrometry satellite and interferometric techniques. Like the Hipparcos satellite, GAIA is a continuously scanning instrument for which the integration time on any observed object is limited by the field of view of the detector. If a final astrometric accuracy of 10 microarcsec is aimed at, a field of 1 deg in diameter is needed. A design is presented for the proposed 2.6 m baseline Fizeau interferometer with two 40 cm apertures and overall dimensions compatible with the size of the Ariane 5 payload shroud. It has a 0.9 deg diffraction limited field of view. The response of the optical system to small perturbations on each optical element is given in terms of the fringe visibility, which is shown to be dependent on the sub-aperture spot separation. The robustness of the design to thermal, mechanical and manufacturing errors is discussed. The unavoidable distortion present in wide field optical systems is analyzed in terms of displacement of the interference fringes.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 241-249
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 46
    Publication Date: 2011-08-24
    Description: A direct link to an extragalactic reference system is considered as being a principle aim of the global astrometric interferometer for astrophysics (GAIA) mission. The data available from an extragalactic data base and a quasi stellar object (QSO) catalog were used to obtain an estimation of the number of QSO link candidates. The quality of presently available data and the expected accuracy of the extragalactic link are discussed. It is concluded that at least 150 QSO's must be observed by GAIA in order to guarantee an accuracy of better than 1 microarcsec/year for the link. New observations will be needed before the GAIA launch in order to reduce uncertainties in the positions, magnitudes and redshifts for some known quasars. The variability of QSO's with magnitudes near the GAIA observation limit can raise a potential problem. The motions of nearby QSO's are expected to be much smaller than 2 microarcsec/year, and therefore, will not affect the accuracy of the link in the proposed GAIA mission.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 127-129
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 47
    Publication Date: 2011-08-24
    Description: We present a grid of stellar classification spectra of moderate resolution (R approximately 1500) in the range lambda lambda 5600-9000 A, compiled from high signal-to noise spectra of 275 stars, most in the open clusters Praesepe and M67. The grid covers dwarfs from types B8 through M5, giants from G8 through M7, and subgiants from F5 through K0. We catalog atomic and molecular absorption features useful for stellar classification, and demonstrate the use of luminosity-sensitive features to distinguish between late-type dwarf and giant stars. The entire database is made available in digital format on anonymous ftp and through the World Wide Web.
    Keywords: ASTRONOMY
    Type: Astronomical Journal (ISSN 0004-6256); 109; 3; p. 1379-1390
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 48
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: In the past two centuries, alert amateur and professional meteor astronomers have documented 35 outbursts of 17 individual meteor streams well enough to allow the construction of a homogeneous set of activity curves. These curves add to similar profiles of the annual streams in a previous paper (Paper 1). This paper attempts to define the type and range of phenomena that classify as meteor outbursts from which the following is concluded: Outbursts are associated with the return of the comet to perihelion (near-comet type outbursts), but occur also when the parent comet is far from perihelion and far from the Earth (far-comet type). All outbursts of a given type only, depending on encounter geometry. The activity curves, expressed in terms of Zenith Hourly Rates (ZHR), have a shape that is generally well described by: ZHR = ZHR(sub max) 10(sup(-B (the absolute value of lambda (sub dot in a circle) - lambda (sup max) (sub dot in a circle))). The steepness of the slopes varies from an exponent of B = 7 to B = 220 per degree of solar longitude, with a typical value of B = 30. In addition, most near-comet type outbursts have a broader component underlying the main peak with B approximately 1 - 7.The duration Delta t is approximately 1/B of the main peak is almost independent of location near the comet, while the background component varies considerably in duration and relative intensity from one return to another. The two components in the activity curve are due to two distinct structures in the dust distribution near the parent comet, where the main component can be due to a sheet of dust that emanates from the IRAS dust trail. This brings the total number of distinct structures in meteor streams to four, including the two structures from the annual stream activity in Paper 1.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 295; 1; p. 206-235
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 49
    Publication Date: 2011-08-24
    Description: We present interferometric observations of ice-sheet motion in western Greenland based on pairs of ERS-1 synthetic aperture radar (SAR) images. These observations provide the first detailed regional view of ice motion associated with dynamically supported topography near the margin of an ice sheet. The interferograms of this area are much more complicated than other interferograms of ice sheets presented to date. We devote the largest part of this paper to explaining the source of the complexity in these interferograms. A synthetic interferogram based on a simple model helps to illustrate the effects of different components of the ice velocity field in interferometric data and suggests a method for estimating the large-scale ice velocity field from such data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Geophysical Research Letters (ISSN 0094-8276); 22; 5; p. 571-574
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 50
    Publication Date: 2011-08-24
    Description: We report on large-scale ab initio multiconfiguration Hartree-Fock calculations for the UV0.01 multiplet, 2s(sup 2)2p(sup 2)P(sub J) - 2s2p(sup 2 4)P(sub J prime), in N III. The resulting transition probabilities agree very well with recent semiempirical calculations, and the lifetimes for two of the three upper levels agree with experiments. The deviation for the third level is discussed. Comparisons made with the highest quality IUE echelle spectra available -- those of RR Tel and V1016 Cyg (both photoionized sources with electron densities below 10(exp 8)/cu cm) -- show that computed branching ratios of lines sharing a common upper level are in agreement with observations to within uncertainties of +/- 10%. High-quality solar limb data or stellar data from the Hubble Space Telescope (HST) could, in principle, be used to determine whether the theoretical or measured lifetimes for the discrepant level are in error. Unfortunately, stellar data for high-density plasmas (N(sub e) greater than 10(exp 11)/cu cm are needed) do not yet exist, and existing solar data lack the photometric precision to address this problem.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 1; p. 457-464
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 51
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: Thermal drag, a variant of the Yarkovsky effect, may act on small asteroids with sizes from a few meters to a few tens of meters. Yarkovsky thermal drag comes from an asteroid's absorbing sunlight in the visible and reradiating it in the infrared. Since the infrared photons have momentum, by action-reaction, they kick the asteroid when they leave its surface. The reradiation, which is asymmetric in latitude over the asteroid, gives a net force along the asteroid's pole. Due to the asteroid's thermal inertia, averaging this force over one orbital period produces a net drag if the spin axis has a component in the orbital plane. Thermal drag tends to circularize orbits. It can increase or decrease orbital inclinations. An object whose spin axis points in random directions over its lifetime displays little change in orbital inclination. Thermal drag appears to have little to do with the delivery of chondrites from the asteroid belt; the thermal drag timescale (10(exp 8) years for meter-sizzed objects) is long compared with their cosmic ray exposure ages, and aphelia in the asteroid belt are not expected for mature thermal drag orbits. However, Yarkovsky thermal drag may act on the recently discovered near-Earth asteroids, which have radii of 10-30 m. Asteroid 1992 DA, for instance, might have its orbit shrunk by 0.1 AU in 3 x 10(exp 7) years, removing it from an Earth-crossing orbit. The near-Earth asteroids also tend to have small to moderate orbital eccentricities, as expected for highly evolved thermal drag objects. However, the time needed to bring them in from the asteroid belt (about 10(exp 9) years) is long compared with the collisonal and dynamical lifetimes (both about 10(exp 8) years) for Earth-crossing objects, arguing against their emplacement by thermal drag.
    Keywords: ASTROPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 100; E1; p. 1585-1594
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 52
    Publication Date: 2011-08-24
    Description: High-contrast peaks in the cosmic microwave background (CMB) anisotropy can appear as unresolved sources to observers. We fit simluated CMB maps generated with a cold dark matter model to a set of unresolved features at instrumental resolution 0.5 deg-1.5 deg to derive the integral number density per steradian n (greater than absolute value of T) of features brighter than threshold temperature absolute value of T and compare the results to recent experiments. A typical medium-scale experiment observing 0.001 sr at 0.5 deg resolution would expect to observe one feature brighter than 85 micro-K after convolution with the beam profile, with less than 5% probability to observe a source brighter than 150 micro-K. Increasing the power-law index of primordial density perturbations n from 1 to 1.5 raises these temperature limits absolute value of T by a factor of 2. The MSAM features are in agreement with standard cold dark matter models and are not necessarily evidence for processes beyond the standard model.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 441; 1; p. L5-L7
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 53
    Publication Date: 2011-08-24
    Description: We have simulated full-sky maps of the cosmic microwave background (CMB) anisotropy expected from cold dark matter (CDM) models at 0.5 deg and 1.0 deg angular resolution. Statistical properties of the maps are presented as a function of sky coverage, angular resolution, and instrument noise, and the implications of these results for observability of the Doppler peak are discussed. The rms fluctuations in a map are not a particularly robust probe of the existence of a Doppler peak; however, a full correlation analysis can provide reasonable sensitivity. We find that sensitivity to the Doppler peak depends primarily on the fraction of sky covered, and only secondarily on the angular resolution and noise level. Color plates of the simulated maps are presented to illustrate the anisotropies.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 441; 1; p. L1-L4
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 54
    Publication Date: 2011-08-24
    Description: On five occasions between 1992 June 29 and 1994 May 3, we have used the Australia Telescope Compact Array (ATCA) to image Eta Carinae at a wavelength of 3 cm and a resolution of 1 arcsec. These observations have revealed remarkable activity. Since 1992 June, the total flux density has increase from 0.8 to 2.2 Jy, and the original single compact source has grown to a complex of sources spread over an area of about 16 sq arcsec. Strong hydrogen recombination-line spectral emission has appeared at the site of the strongest of these new sources. This recombination emission has the largest spectral width ever observed from a star, +/- 250 km/s, and reveals gas with turbulent velocities as great as 250 km/s approaching us at an average velocity of about 200 km/s. We believe that this radio outburst has been caused by a more than threefold increase of ultraviolet luminosity, and consequent ionization of previously neutral gas clouds.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 441; 2; p. L73-L76
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 55
    Publication Date: 2011-08-24
    Description: The bright quasar Kaz 102, which lies in the vicinity of the North Ecliptic Pole, was monitored during the ROSAT All Sky Survey for 121.5 days from 1990 July 30 to 1991 January 25. In the course of the survey, optical photometry with various filters was peformed at several epochs, together with UV (IUE) and optical spectrophotometry. The spectral energy distribution in the 3 x 10(exp 14) -3 x 10(exp 17) Hz range is obtained simultaneously among the various frequencies to less than or = 1 day. No clear case of variability can be made in the X-rays, while in the optical and UV variability of 10%-20% is apparent. An analysis of IUE and Einstein archives indicates a doubling timescale of years for the UV and soft X-ray flux. The X-ray photon index, which in 1979 was rather flat (Gamma = 0.8(+0.6 -0.4), in 1990/1991 was found to be Gamma = 2.22 +/- 0.13, a typical value for radio-quiet quasars in this energy range. The overall energy distribution and the variability are discussed.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal (ISSN 0004-637X); 442; 2, Pa; p. 589-596
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 56
    Publication Date: 2011-08-24
    Description: This paper describes the calibration of the two solid-state Si(Li) X-ray detectors and the X-ray telescopes that flew as part of Goddard Space Flight Center's Broad Band X-Ray Telescope (BBXRT) experiment on board the space shuttle Columbia in 1990 December. During the 9 day shuttle mission, BBXRT performed approximately 150 observations of 82 celestial sources. The content of the archive is summarized here. Although BBXRT had a relatively short life, it stands as a milestone in X-ray astronomy as being the first instrument to offer moderate spectral resolution over a wide bandpass (0.3-12.0 keV). Among other things, this paper discusses the effective area calibration of the instrument, the flux calibration and flux corrections for off-axis observations, the detector background, and optimal background subtraction techniques. The on-axis effective area calibration for the central detector elements was performed using data from the Crab Nebula, while other carefully selected targets were used for calibration of the outer detector elements. The remaining systematic uncertainties in the effective area calibration for point sources observed both on and off axis are generally less than 5%-10%. The energy scale is known to better than 0.5% at 6.0 keV for both detectors. The results presented here have an impact on the calibration of other medium resolution X-ray experiments such as the CCDs on board ASCA (Astro-D) as well as the Advanced X-Ray Astrophysics Facility detectors.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 96; 1; p. 303-324
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 57
    Publication Date: 2011-08-24
    Description: Soft gamma repeaters are characterized by recurrent activity consisting of short-duration outbursts of high-energy emission that is typically of temperature less than 40 keV. One recent model of repeaters is that they originate in the environs of neutron stars with superstrong magnetic fields, perhaps greater than 10(exp 14) G. In such fields, the exotic process of magnetic photon splitting gamma yields gamma gamma acts very effectively to reprocess gamma-ray radiation down to hard X-ray energies. In this Letter, the action of photon splitting is considered in some detail, via the solution of photon kinetic equations, determining how it limits the hardness of emission in strongly magnetized repeaters, and thereby obtaining observational constraints to the field in SGR 1806-20.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 440; 2; p. L69-L72
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 58
    Publication Date: 2011-08-24
    Description: The COMPTEL sky map of the 1.8 MeV line emission from Al-26 shows an extended diffuse distribution along the Galactic plane with a peculiar large scale asymmetry about the Galactic center (GC) and a clumpy structure with several noticeable hot spots. The most prominent hot spot at the GC appears shifted to positive longitude by about 2 deg. Nearby supernova remnants or Wolf-Rayet stars are plausible explanations for individual hot spots such as in the Vela region. We show that the global asymmetry and most hot spots can be understood by a more general model: the Al-26 sources are confined in the spiral arms of our Galaxy, and coagent star formation is responsible for additional clumpiness. The off-centered GC hot spot is probably due to the observed asymmetrically distributed circumnuclear molecular gas interacting with a central stellar bar, whose existence has been inferred from IR observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 440; 2; p. L57-L60
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 59
    Publication Date: 2011-08-24
    Description: Two dimensional spectral types for each of the stars observed in the global astrometric interferometer for astrophysics (GAIA) mission would provide additional information for the galactic structure and stellar evolution studies, as well as helping in the identification of unusual objects and populations. The classification of the large quantity generated spectra requires that automated techniques are implemented. Approaches for the automatic classification are reviewed, and a metric-distance method is discussed. In tests, the metric-distance method produced spectral types with mean errors comparable to those of human classifiers working at similar resolution. Data and equipment requirements for an automated classification survey, are discussed. A program of auxiliary observations is proposed to yield spectral types and radial velocities for the GAIA-observed stars.
    Keywords: ASTROPHYSICS
    Type: ESA, Future Possibilities for Astrometry in Space; p 169-172
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 60
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: We consider the evolution and heating of dust embedded in the hot interstellar medium of isolated elliptical galaxies. We first construct a new set of galaxy models spanning a decade in luminosity which we use to study the evolution of dust as it is ejected by stellar sources, merges and flows with the interstellar gas, and is sputtered away due to the presence of the hot gas. We find that although grains can flow a considerable distance from the parent star in some cases before being sputtering away, the grain size distribution at a given location is accurately determined by assuming in situ sputtering of dust grains as they are ejected by the parent star. We find that dust heating is dominated by absorption of ambient starlight. Heating due to collisions with energetic electrons in the hot gas and absorption of thermal X-rays is smaller by orders of magnitude. We also find that for the largest galaxy considered (L(sub B) approximately 10 (exp 11) solar luminosity) the energy lost from the hot gas due to electronic collisions with the dust is about an order of magnitude less than that lost due to thermal emission in X-rays. The gas in smaller galaxies loses even less of its energy via heating of grains. In deriving this result, we find that the inclusion of grain sputtering is a crucial ingredient of the calculation. The presence of dust grains is therefore energetically unimportant for elliptical galaxy cooling flow models.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 177-180
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 61
    Publication Date: 2011-08-24
    Description: Near-infrared images of the Galactic bulge at 1.25, 2.2, 3.5, and 4.9 microns obtained by the Diffuse Infrared Background Experiment (DIRBE) onboard the Cosmic Background Explorer (COBE) satellite are used to characterize its morphology and to determine its infrared luminosity and mass. Earlier analysis of the DIRBE observations (Weiland et al. 1994) provided supporting evidence for the claim made by Blitz & Spergel (1991) that the bulge is bar-shaped with its near end in the first Galactic quadrant. Adopting various triaxial analytical functions to represent the volume emissivity of the source, we confirm the barlike nature of the bulge and show that triaxial Gaussian-type functions provide a better fit to the data than other classes of functions, including an axisymmetric spheroid. The introduction of a `boxy' geometry, such as the one used by Kent, Dame, & Fazio (1991) improves the fit to the data. Our results show that the bar is rotated in the plane with its near side in the first Galactic quadrant creating an angle of 20 deg +/- 10 deg between its major axis and the line of sight to the Galactic center. Typical axis ratios of the bar are (1:0.33 +/- 0.11:0.23 +/- 0.08), resembling the geometry of prolate spheroids. There is no statistically significant evidence for an out-of-plane tilt of the bar at 2.2 microns, and marginal evidence for a tilt of approximately equal 2 deg at 4.9 microns. The introduction of a roll around the intrinsic major axis of the bulge improves the `boxy' appearance of some functions. A simple integration of the observed projected intensity of the bulge gives a bulge luminosity of 1.2 x 10(exp 9), 4.1 x 10(exp 8), 2.3 x 10(exp 8), and 4.3 x 10(exp 7) solar luminosity, respectively, at 1.25, 2.2, 3.5, and 4.9 microns wavelength for a Galactocentric distance of 8.5 kpc. The 2.2 microns luminosity function of the bulge population in the direction of Baade's window yields a bolometric luminosity of L(sub bol) = 5.3 x 10(exp 9) solar luminosity. Stellar evolutionary models relate this luminosity to the number of main-sequence progenitor stars that currently populate the red giant branch. Combined with the recent determination of the main-sequence turnoff mass for the bulge by the Hubble Space Telescope (Holtzman et al. 1993) we derive a photometrically determined bulge mass of approximately equal to 1.3 x 10(exp 10) solar mass for a Salpeter initial mass function extended down to 0.1 solar mass.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 716-730
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 62
    Publication Date: 2011-08-24
    Description: We report the results from observations of National Radio Astronomy Observatory (NRAO) 140 carried out in the X-ray band using ROSAT and Advanced Satellite for Cosmology and Astrophysics (ASCA) in 1992 and 1994. We find the source to be absorbed by an effective hydrogen column density of approximately 3 x 10(exp 21) atoms/sq cm during both epochs, consistent with the combined atomic and molecular column inferred from radio measurements along this line of sight through the Perseus cloud complex. We compare these results with previous X-ray absorption measurements and briefly comment upon the origin of the excess absorption which has been seen toward this source. We find the ASCA spectrum of NRAO 140 is well described by a power law of energy index alpha = 0.73 +/- 0.03 and also yields the tightest constraint to date on Fe K-shell emission, with 90% confidence upper limits of 38 and 31 eV for a narrow line at a rest frame energy of 6.4 and 6.7 keV respectively. This, along with a lack of hardening towards higher energies, suggests that either NRAO 140 is devoid of cold reprocessing material, the reprocessing material has a geometry in which the imprinted features are weak, and/or the X-ray emission is relativistically beamed towards us. We also report the detection of a serendipitous source in both the Advanced Satellite for Cosmology and Astrophysics Gas Imaging Spectrometer (ASCA GIS) and ROSAT fields of view. We identify this source as the binary star system IX Per and find its spectrum to be well fitted by a two-temperature Raymond-Smith plasma.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 660-665
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 63
    Publication Date: 2011-08-24
    Description: We have produced two-dimensional maps of the intensity ratio, Q(sub 60), of 60 micron infrared to 20 cm radio continuum emission, for a set of 25 nearby galaxies, mostly spirals. The ratio maps were obtained from infrared images made using IRAS data with the maximum correlation method, and radio images made using VLA data. Before taking the ratio, the radio images were processed so as to have the same resolution properties as the infrared images; the final spatial resolution in all cases is approximately 1 min, corresponding to 1 - 2 kpc for most galaxies. This resolution represents a significant improvement over previous studies. Our new high-resolution maps confirm the slow decrease of Q(sub 60) with increasing radial distance from the nucleus, but show additional structure which is probably associated with separate sites of active star formation in the spiral arms. The maps show Q(sub 60) to be more closely related to infrared surface brightness than to the radial distance r in the galaxy disk. We note also that the Q(sub 60) gradients are absent (or at least reduced) for the edge-on galaxies, a property which can be attributed to the dilution of contrast due to the averaging of the additional structure along the line of sight. The results are all in qualitative agreement with the suggestion that the radio image represents a smeared version of the infrared image, as would be expected on the basis of current models in which the infrared-radio correlation is driven by the formation of massive stars, and the intensity distribution of radio emission is smeared as a result of the propagation of energetic electrons accelerated during the supernova phase.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 445; 2; p. 599-606
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 64
    Publication Date: 2011-08-24
    Description: The BL Lacertae object OJ 287 was intensively monitored with the IUE satellite from 1993 March 15 to 20 in the 2000-3000 A wavelength region. The very low emission state of the source hampered the detection during part of the 23 performed exposures. The light curve at 2650 A constructed with the 11 best images exhibits a variable trend with a factor is less than or approximately 2 enhancement of the flux in about 3 hours. Simultaneous ground based observations show an optical flux variability of smaller amplitude, but correlated with the UV light curve without any apparent lag. The radio light curve is nearly constant. The UV emission state is the weakest observed in 15 years for this flaring blazard, being a factor of less than orapproximately 20 lower than the maximum recorded one.
    Keywords: ASTRONOMY
    Type: Advances in Space Research (ISSN 0273-1177); 16; 3; p. 57-60
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 65
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: The twin Voyager spacecraft, launched nearly two decades ago, continue to operate and are now searching for the edge of our solar system, the heliopause. Voyager's giant-planet flybys of Jupiter, Saturn, Uranus, and Neptune have provided data that are likely to remain the definitive data set for the foreseeable future and have led to many ongoing discoveries. As the spacecraft move toward the heliopause, they are also providing data on the structure of the heliosphere. This article discusses the discoveries resulting from the flyby and heliosphere data that have been made within the past five years.
    Keywords: ASTRONOMY
    Type: Planetary Report (ISSN 0736-3680); 15; 4; p. 4-9
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 66
    Publication Date: 2011-08-24
    Description: The U-B color has been suggested as a predictor of the presence of water of hydration on asteroids. Photometry from the Eight-Color Asteroid Survey (ECAS) was used to test this concept. An overlap in U-B color prevents this magnitude difference from distinguishing between surface material that was thermally processed at higher temperatures and surface material that was aqueously altered. Two tests of the presence of water of hydration using visible spectral region photometry failed to flag those few higher albedo M- and E-class asteroids having photometry that shows a 3.0-micrometers water of hydration absorption. These asteroids probably contain little or no oxidized iron in their surface material.
    Keywords: ASTROPHYSICS
    Type: Icarus (ISSN 0019-1035); 115; 1; p. 217-218
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 67
    Publication Date: 2011-08-24
    Description: Echelle mode spectra obtained with the Goddard High Resolution Spectrograph (GHRS) onboard the Hubble Space Telescope (HST) have been used to determine the abundances of the heavy elements Pt, Au, and Hg in the chemically peculiar HgMn-type stars kappa Cancri and chi Lupi. The abundances were determined by fitting observed line profiles with synthetically generated spectra and are found to be enhanced relative to solar system values by between three and five orders of magnitude in both stars. The Hg isotope mixture in kappa Cancri is found to resemble the terrestrial mixture while that of chi Lupi is dominated by the heaviest isotope. As determined from multiple ionization states, the abundances place constraints upon theories attempting to explain the large superficial abundances of heavy elements.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 444; 1; p. 438-451
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 68
    Publication Date: 2011-08-24
    Description: The Goddard High Resoulution Spectrograph (GHRS) on the Hubble Space Telescope (HST) has been used to obtain medium (R = 20,000) and high (R = 85,000) resoultion UV spectra of chromosphere emission features for the M3.4 III star gamma Cru. Small Science Aperture (SSA) G270M and Echelle-B spectra of selected regions in the 2300-2850 A range were obtained to determine the kinematics of the chromosphere using lines of C2), Fe2, Co2, Si1/2), Ni2, Mn2, and Mg2. Profiles of C2) (UV 0.01) lines and fluorescently excited lines of low optical depth indicate average turbulent velocities (Doppler FWHM) of 30.2 +/- 1.3 and 28.8 +/- 1.3 km/s, respectively. The fluorescent emission lines (mean RV = 21.3 +/- 0.9 km/s) and the wings of the emission components of Fe2 lines (mean RV = 22.8 +/- 0.4 km/s) are approximately at rest relative to the radial velocity of the star (21 km/s), while the C2) lines show a modest inflow (mean RV = 23.1 +/- 0.9 km/s). The more opaque lines of Fe2 and Mg2 exhibit complex profiles resulting from line formation in an optically thick, extended expanding atmosphere. The emission wings of these lines are broadened by multiple scattering, and they are centered near the photospheric radial velocity. Closer to line center, these strong lines show a strong blueshifted self-absorption feature (already seen in IUE data), indicative of formation in an expanding chromosphere, and a previously unseen dip in the profiles on the red side of line center. The absorption components, when extracted using simple Gaussian fits, show strong correlations with the relative optical depths of the lines. The derived absorption flow velocities converge to the photospheric velocity as one examines spectra features formed deeper in the atmosphere. The blueward abosrption velocity increases in magnitude from about 7 to 14 km/s with increasing line optical depth - the strong absorptions directly map the acceleration of the outflowing stellar wind, while the interpretation of the weaker redshifted abosrptions is more ambiguous, indicating either an inflow of material or formation in an extended, spherically expanding outflow. The Mg2 and Fe2 profiles, taken together, imply that the wind speed decreases between the atmospheric layers where the Mg2 and Fe2 self-absorption components are formed. Interstellar absorptions are seen in the resonance lines of Mg2 (UV 1) and Fe2 (UV1) with zero-volt lower levels, at about -3 km/s, consistent with models of the interstellar medium in the direction of gamma Cru. Finally, we have detected the Mg2 'satellite lines' seen in solar spectra obtained above the limb. In gamma Cru these lines are probably fluorescently excited by H Ly beta.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 444; 1; p. 424-437
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 69
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: Scientists are still trying to piece together what exactly occurred when comet fragments from Shoemaker-Levy 9 impacted with Jupiter last year. Several theories have been from the data received from Galileo and the Hubble Space Telescope (HST) together with the modeling of the impacts using supercomputers, scientists hope to discover the answers to their questions and perhaps to resolve the differences that have arisen between the different model simulations.
    Keywords: ASTRONOMY
    Type: Planetary Report (ISSN 0736-3680); 15; 2; p. 12-14
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 70
    Publication Date: 2011-08-24
    Description: The Monte Carlo technique of simulating diffusive particle acceleration at shocks has made spectral predictions that compare extremely well with particle distributions observed at the quasi-parallel region of the earth's bow shock. The current extension of this work to compare simulation predictions with particle spectra at oblique interplanetary shocks has required the inclusion of significant cross-field diffusion (strong scattering) in the simulation technique, since oblique shocks are intrinsically inefficient in the limit of weak scattering. In this paper, we present results from the method we have developed for the inclusion of cross-field diffusion in our simulations, namely model predictions of particle spectra downstream of oblique subluminal shocks. While the high-energy spectral index is independent of the shock obliquity and the strength of the scattering, the latter is observed to profoundly influence the efficiency of injection of cosmic rays into the acceleration process.
    Keywords: ASTROPHYSICS
    Type: Advances in Space Research (ISSN 0273-1177); 15; 8-9; p. 397-400
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 71
    Publication Date: 2011-08-24
    Description: A standard problem in gamma-ray astronomy data analysis is the decomposition of a set of observed counts, described by Poisson statistics, according to a given multicomponent linear model, with underlying physical count rates or fluxes which are to be estimated from the data. Despite its conceptual simplicity, the linear least-squares (LLSQ) method for solving this problem has generally been limited to situations in which the number n(sub i) of counts in each bin i is not too small, conventionally more than 5-30. It seems to be widely believed that the failure of the LLSQ method for small counts is due to the failure of the Poisson distribution to be even approximately normal for small numbers. The cause is more accurately the strong anticorrelation between the data and the wieghts w(sub i) in the weighted LLSQ method when square root of n(sub i) instead of square root of bar-n(sub i) is used to approximate the uncertainties, sigma(sub i), in the data, where bar-n(sub i) = E(n(sub i)), the expected value of N(sub i). We show in an appendix that, avoiding this approximation, the correct equations for the Poisson LLSQ (PLLSQ) problems are actually identical to those for the maximum likelihood estimate using the exact Poisson distribution. We apply the method to solve a problem in high-resolution gamma-ray spectroscopy for the JPL High-Resolution Gamma-Ray Spectrometer flown on HEAO 3. Systematic error in subtracting the strong, highly variable background encountered in the low-energy gamma-ray region can be significantly reduced by closely pairing source and background data in short segments. Significant results can be built up by weighted averaging of the net fluxes obtained from the subtraction of many individual source/background pairs. Extension of the approach to complex situations, with multiple cosmic sources and realistic background parameterizations, requires a means of efficiently fitting to data from single scans in the narrow (approximately = 1.2 keV, HEAO 3) energy channels of a Ge spectrometer, where the expected number of counts obtained per scan may be very low. Such an analysis system is discussed and compared to the method previously used.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 1; p. 322-340
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 72
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: Four spectral emission features of the N(sub KK) = 4(sub 04) -3(sub 13) rotational transition of methylene (CH2) have been detected at signal levels 5-7 sigma above noise toward the hot core of the Orion-KL nebula and the molecular cloud in proximity to the continuum source W51 M. Specifically, in both sources we have resolved the F = 6-5, 5-4, and 4-3 hyperfine transitions of the J = 5-4 fine-structure levels and detected the blended hyperfine structure of the J = 4-3 fine structure levels. At the J = 3-2 fine-structure levels, we have observed new transitions of NS, a known interstellar molecule, which severely contaminates the search for CH2 hyperfine transitions. These new sensitive observations finally confirm the existence of interstellar CH2 which was tentatively reported by us some years ago.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 1; p. 259-264
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 73
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2011-08-24
    Description: A brief discussion on the characteristics of pulsars is given followed by a review of millisecond pulsar discoveries including the very first, PRS B1937+21, discovered in 1982. Methods of timing millisecond pulsars and the accuracy of millisecond pulsars as clocks are discussed. Possible reasons for the pulse residuals, or differences between the observed and predicted pulse arrival times for millisecond pulsars, are given.
    Keywords: ASTRONOMY
    Type: Sky & Telescope (ISSN 0037-6604); 89; 4; p. 18-23
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 74
    Publication Date: 2011-08-24
    Description: We present data on the galactic X-ray source 1E 1740.7-2942 from the Oriented Scintillation Spectrometer Experiment (OSSE) on board NASA's Compton Gamma Ray Observatory (CGRO). Episodes of increased low-energy gamma radiation have been reported from this source, including 1-day events in 1990 October and 1992 September. These events, of intensity 7 x 10(exp -3) and 4 x 10(exp -3) photons/sq cm/s, respectively, have been interpreted as broadened and redshifted positron annihilation radiation. OSSE conducted observations of the Galactic Center region during a 21-day interval from 1992 September 17 thru 1992 October 8. This includes the time of increased 200-450 keV emission from 1E 1740.7-2942 reported by SIGMA. The OSSE observations do not confirm this event. For the specific outburst recorded by SIGMA, 1992 Sep. 19.42-20.58 (UT), OSSE data provide an upper limit (3 sigma) of 2.4 x 10(exp -3) photons/sq cm/s.
    Keywords: ASTRONOMY
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 295; 2; p. L23-L26
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 75
    Publication Date: 2011-08-24
    Description: The star, Altair (A7 IV-V), is clearly shown to have Lyman-alpha emission of chromospheric origin, while no evidence is found for the Mg II emission reported in previous investigations. We present non-Local Thermodymanic Equilibrium (non-LTE) semiempirical models incorporating partial redistribution of the chromosphere of Altair that reproduce the observed Lyman-alpha emission and the Mg II resonance absorption at 2800 A. We unambiguously establihed that chromospheres exist at spectral types as early as A7 on the main sequence, and we also demonstrate that it very unlikely that the observed emission originates in a corotating expanding wind. This result represents a new challenge for chromospheric heating theories. It may indicate that both differential rotation and convection layers, at least near the equator, exist in this fast rotating (v sin i = 220 km/s) star.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 439; 2; p. 1011-1020
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 76
    Publication Date: 2011-08-24
    Description: We use the two-point correlation function of the extrema points (peaks and valleys) in the Cosmic Background Explorer (COBE) Differential Microwave Radiometers (DMR) 2 year sky maps as a test for non-Gaussian temperature distribution in the cosmic microwave background anisotropy. A maximum-likelihood analysis compares the DMR data to n = 1 toy models whose random-phase spherical harmonic components a(sub lm) are drawn from either Gaussian, chi-square, or log-normal parent populations. The likelihood of the 53 GHz (A+B)/2 data is greatest for the exact Gaussian model. There is less than 10% chance that the non-Gaussian models tested describe the DMR data, limited primarily by type II errors in the statistical inference. The extrema correlation function is a stronger test for this class of non-Gaussian models than topological statistics such as the genus.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 439; 2; p. L29-L32
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 77
    Publication Date: 2011-08-24
    Description: X-ray observations of Abell 548 reveal that the hot gas in this cluster is at least as complex as the galaxy distribution. Our ROSAT Position Sensitive Proportional Counter (PSPC) image is used in conjunction with optical data from the Minnesota plate-scanning project and redshift data in the literature to investigate the degree of substructure in the intracluster medium and the galaxy distribution. A548 has several X-ray components: hot gas associated with clumps of galaxies, individual sources, and a newly discovered diffuse component. This diffuse component may be promordial gas falling into the cluster for the first time. The optical data suggest that this cluster consists of four major components, not three (as indicated when velocity data are ignored). Simple models of the orbital dynamics suggest that the cluster may not yet have reached its turnaround radius.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 440; 1; p. 48-59
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 78
    Publication Date: 2011-08-24
    Description: During its full-sky survey, the Energetic Gamma Ray Experiment Telescope (EGRET) high-energy instrument aboard the Compton Gamma-Ray Observatory detected gamma-ray emission in the energy range above 30 MeV from a source identified as the blazar PKS 0420-014. This object was observed during two separate viewing periods in 1992 February/March and May/June. An intensity decrease above 100 MeV of a factor of at least 1.5 from a maximum of (5.0 +/- 1.4) x 10(exp -7) photons 1 sq cm/s was observed during that time interval indicating extensive variability. The photon spectrum in the range between 30 and 10,000 MeV at the time of the maximum intensity is well represented by a power law with an exponent of -1.9 +/- 0.3. Some similarities with other EGRET detected blazars are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 438; 2; p. 659-662
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 79
    Publication Date: 2013-08-31
    Description: Get-Away Special (GAS) G-301, named the Flying Falcon and scheduled for launch on the STS-77 Space Shuttle in April, 1996, is being prepared to perform an experiment designed by the Department of Geology, Bowling Green State University (BGSU). The experiment will employ a new type of infrared imager designed and built by a consortium of Teltron Technologies Inc., Hudson Research Inc., and BGSU that is an uncooled, quantrum ferro-electric, infrared return beam vidicon (IRBV) camera capable of detecting thermal infrared radiation throughout the 2.0-50.0 micron wavelength region, and to which an integral, unable Fabry-Perot filter and a telescopic lens have been added. The primary objectives in the experiment include the mapping of methane plumes from solid waste landfills and wetlands in the midwestern U.S., the mapping of methane plumes offshore in the Gulf of Mexico and in the Middle East, brief monitoring for precursors of volcanoes or earthquakes in the South China sea and the East Pacific Rise (about 300 km west of Easter Island), and the mapping of silica content in exposed outcrops and residual soils of the southwestern U.S. and Middle East.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: NASA. Goddard Space Flight Center, The 1995 Shuttle Small Payloads Symposium; p 231-240
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 80
    Publication Date: 2013-08-31
    Description: For the past 20 years, the 91 cm telescope in NASA's Kuiper Airborne Observatory (KAO) has enabled scientists to observe infrared sources which are obscured by the earth's atmosphere at ground-based sites, and to observe transient astronomical events from anywhere in the world. To augment this capability, the United States and German Space Agencies (NASA and DARA) are collaborating in plans to replace the KAO with a 2.5 meter telescope installed in a Boeing 747 aircraft: SOFIA - The Stratospheric Observatory for Infrared Astronomy. SOFIA's large aperture, wide wavelength coverage, mobility, accessibility, and sophisticated instruments will permit a broad range of scientific studies, some of which are described here. Its unique features complement the capabilities of other future space missions. In addition, SOFIA has important potential as a stimulus for development of new technology and as a national resource for education of K-12 teachers. If started in 1996, SOFIA will be flying in the year 2000.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 707-773
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 81
    Publication Date: 2013-08-31
    Description: We have obtained images of the Orion Bar region through narrow-band filters at 6.2 and 7.8 mu m to determine whether the emission observed at these wavelengths arises from C-C modes in polycyclic aromatic hydrocarbons (PAH's). Morphologically, the distribution of the emissions are similar, but appear different in detail. Quantitative comparisons of these band intensities with previous data at 8.4 and 11.3 mu m indicates that they are indeed consistent with emission from fluorescently excited PAH molecules.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 63-66
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 82
    Publication Date: 2013-08-31
    Description: Monitoring spatial and temporal changes of soil moisture are of importance to hydrology, meteorology, and agriculture. This paper reports a result on study of using L-band SAR imagery to estimate soil moisture and surface roughness for bare fields. Due to limitations of the Small Perturbation Model, it is difficult to apply this model on estimation of soil moisture and surface roughness directly. In this study, we show a simplified model derived from the Integral Equation Model for estimation of soil moisture and surface roughness. We show a test of this model using JPL L-band AIRSAR data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 51-54
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 83
    Publication Date: 2013-08-31
    Description: In the tropical rain forests of Manu, in Peru, where forest biomass ranges from 4 kg/sq m in young forest succession up to 100 kg/sq m in old, undisturbed floodplain stands, the P-band polarimetric radar data gathered in June of 1993 by the AIRSAR (Airborne Synthetic Aperture Radar) instrument separate most major vegetation formations and also perform better than expected in estimating woody biomass. The worldwide need for large scale, updated biomass estimates, achieved with a uniformly applied method, as well as reliable maps of land cover, justifies a more in-depth exploration of long wavelength imaging radar applications for tropical forests inventories.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 39-41
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 84
    Publication Date: 2013-08-31
    Description: Radar backscatter intensity as measured by calibrated synthetic aperture radar (SAR) systems is primarily controlled by three factors: local incidence angle, wavelength-scale roughness, and dielectric permittivity of surface materials. In order to make adequate use of radar observations for geological investigations of surface type, the relationships between lithology and the above characteristics must be adequately understood. In arid terrains weathering signatures (e.g. fracturing, debris grain size and shape, slope characteristics) are controlled to some extent by lithologic characteristics of the parent bedrock. These textural features of outcrops and their associated debris control radar backscatter to varying degrees. The quad-polarization JPL AIRSAR system allows sampling of textures at three distinct wavelength scales: C-band (5.66 cm), L-band (23.98 cm), and P-band (68.13 cm). This paper presents a discussion of AIRSAR data using recent field observations of weathered felsic and basaltic volcanic rock units exposed in the southern part of the Lunar Crater Volcanic Field, in the Pancake Range of central Nevada. The focus is on the relationship of radar backscatter at multiple wavelengths to weathering style and parent bedrock lithology.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 43-46
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 85
    Publication Date: 2013-08-31
    Description: Silicic (silica-rich) lava flows, such as rhyolite, rhyodacite, and dacite, possess unique physical properties primarily because of the relatively high viscosity of the molten lava. Silicic flows tend to be thicker than basaltic flows, and the resulting large-scale morphology is typically a steep-sided dome or flow lobe, with aspect ratios (height/length) sometimes approaching unity. The upper surfaces of silicic domes and flows are normally emplaced as relatively cool, brittle slabs that fracture as they are extruded from the central vent areas, and are then rafted away toward the flow margin as a brittle carapace above a more ductile interior layer. This mode of emplacement results in a surface with unique roughness characteristics, which can be well-characterized by multiparameter synthetic aperture radar (SAR) observations. In this paper, we examine the scattering properties of several silicic domes in the Inyo volcanic chain in the Eastern Sierra of California, using AIRSAR and TOPSAR data. Field measurements of intermediate-scale (cm to tens of m) surface topography and block size are used to assess the mechanisms of the scattering process, and to quantify the unique roughness characteristics of the flow surfaces.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 35-38
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 86
    Publication Date: 2013-08-31
    Description: The replacement of semidesert grassland by woody shrubland is a widespread form of desertification. This change in physiognomy and species composition tends to sharply reduce the productivity of the land for grazing by domestic livestock, increase soil erosion and reduce soil fertility, and greatly alter many other aspects of ecosystem structure and functioning. Remote sensing methods are needed to assess and monitor shrubland encroachment. Detection of woody shrubs at low density would provide a particularly useful baseline on which to access changes, because an initially low shrub density often tends to increase even after cessation of the disturbance (e.g., overgrazing, drought, or fire suppression) responsible for triggering the initial stages of the invasion (Grover and Musick, 1990). Limited success has been achieved using optical remote sensing. In contrast to other forms of desertification, biomass does not consistently decrease with a shift from grassland to shrubland. Estimation of green vegetation amount (e.g., by NDVI) is thus of limited utility, unless the shrubs and herbaceous plants differ consistently in phenology and the area can be viewed during a season when only one of these is green. The objective of this study was to determine if the potential sensitivity of active microwave remote sensing to vegetation structure could be used to assess the degree of shrub invasion of grassland. Polarimetric Airborne Synthetic Aperture Radar (AIRSAR) data were acquired for a semiarid site containing varied mixtures of shrubs and herbaceous vegetation and compared with ground observations of vegetation type and other landsurface characteristics. In this preliminary report we examine the response of radar backscatter intensity to shrub density. The response of other multipolarization parameters will be examined in future work.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 31-34
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 87
    Publication Date: 2013-08-31
    Description: Conventional representations of polarization response are referred to a horizontally and vertically polarized basis. Recent studies by Freeman and Durden, van Zyl, and others suggest that alternative polarimetric features which more easily resolve the contributions of simple scattering mechanisms such as odd-bounce, even-bounce, and diffuse scattering could offer several advantages in terrain classification. The circular polarization covariance matrix is a potential source of such features. In this paper, we derive its relationship to the Stokes matrix, describe some of its properties, and compare the utility of linear and circular polarimetric features in classifying an AIRSAR scene containing urban, park, and ocean terrain.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 27-30
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 88
    Publication Date: 2013-08-31
    Description: The relationship between habitat area, spatial dynamics of the landscape, and species diversity is an important theme in population and conservation biology. Of particular interest is how populations of various species are affected by increasing habitat edges due to fragmentation. Over the last decade, assumptions regarding the effects of habitat edges on biodiversity have fluctuated wildly, from the belief that they have a positive effect to the belief that they have a clearly negative effect. This change in viewpoint has been brought about by an increasing recognition of the importance of geographic scale and a reinterpretation of natural history observations. In this preliminary report from an ongoing project, we explore the use of remote sensing technology and geographic information systems to further our understanding of how species diversity and population density are affected by habitat heterogeneity and landscape composition. A primary feature of this study is the investigation of SAR for making more rigorous investigations of habitat structure by exploiting the interaction between radar backscatter and vegetation structure and biomass. A major emphasis will be on the use of SAR data to define relative structural types based on measures of structural consolidation using the vegetation surface area to volume ratio (SA/V). Past research has shown that SAR may be sensitive to this form of structural expression which may affect biodiversity.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 17-20
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 89
    Publication Date: 2013-08-31
    Description: Landforms in arid regions record the interplay between tectonic forces and climate. Alluvial fans are a common landform in desert regions where the rate of uplift is greater than weathering or sedimentation. Changes in uplift rate or climatic conditions can lead to isolation of the currently forming fan surface through entrenchment and construction of another fan either further from the mountain front (decreased uplift or increased runoff) or closer to the mountain front (increased uplift or decreased runoff). Thus, many alluvial fans are made up of a mosaic of fan units of different age, some older than 1 million years. For this reason, determination of the stages of fan evolution can lead to a history of uplift and runoff. In an attempt to separate the effects of tectonic (uplift) and climatic (weathering, runoff, sedimentation) processes on the shapes of alluvial fan units, a modified conic equation developed by Troeh (1965) was fitted to TOPSAR digital topographic data for the Trail Canyon alluvial fan in Death Valley, California. This allows parameters for the apex position, slope, and radial curvature to be compared with unit age.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 9-12
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 90
    Publication Date: 2013-08-31
    Description: During recent years signature analysis, classification, and modeling of Synthetic Aperture Radar (SAR) data as well as estimation of geophysical parameters from SAR data have received a great deal of interest. An important requirement for the quantitative use of SAR data is the accurate estimation of the backscattering coefficient sigma(exp 0). In terrain with relief variations radar signals are distorted due to the projection of the scene topography into the slant range-Doppler plane. The effect of these variations is to change the physical size of the scattering area, leading to errors in the radar backscatter values and incidence angle. For this reason the local incidence angle, derived from sensor position and Digital Elevation Model (DEM) data must always be considered. Especially in the airborne case, the antenna gain pattern can be an additional source of radiometric error, because the radar look angle is not known precisely as a result of the the aircraft motions and the local surface topography. Consequently, radiometric distortions due to the antenna gain pattern must also be corrected for each resolution cell, by taking into account aircraft displacements (position and attitude) and position of the backscatter element, defined by the DEM data. In this paper, a method to derive an accurate estimation of the backscattering coefficient using NASA/JPL AIRSAR data is presented. The results are evaluated in terms of geometric accuracy, radiometric variations of sigma(exp 0), and precision of the estimated forest biomass.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 13-16
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 91
    Publication Date: 2013-08-31
    Description: An empirical model was developed to infer soil moisture and surface roughness from radar data. The accuracy of the inversion technique is assessed by comparing soil moisture obtained with the inversion technique to in situ measurements. The effect of vegetation on the inversion is studied and a method to eliminate the areas where vegetation impairs the algorithm is described.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 5-8
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 92
    Publication Date: 2013-08-31
    Description: In 1993 NASA's Jet Propulsion Laboratory Airborne Synthetic Aperture Radar system (AIRSAR) was deployed to South America to collect multi-parameter radar data over pre-selected targets. Among the sites targeted was a series of wind streaks located in the Altiplano of Bolivia. The objective of this investigation is to study the effect of wavelength, polarization, and incidence angle on the visibility of wind streaks in radar data. Because this is a preliminary evaluation of the recently acquired data we will focus on one scene and, thus, only on the effects of wavelength and polarization. Wind streaks provide information on the near-surface prevailing winds and on the abundance of winderodible material, such as sand. The potential for a free-flyer radar system that could provide global radar images in multiple wavelengths, polarizations, and incidence angles requires definition of system parameters for mission planning. Furthermore, thousands of wind streaks were mapped from Magellan radar images of Venus; their interpretation requires an understanding of the interaction of radar with wind streaks and the surrounding terrain. Our experiment was conducted on wind streaks in the Altiplano of Bolivia to address these issues.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 3: AIRSAR Workshop; p 1-4
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 93
    Publication Date: 2013-08-31
    Description: The Thermal Infrared Multispectral Scanner (TIMS) was flown on the NASA C-130 aircraft for a series of 12 flights during HAPEX-Sahel at altitudes ranging from 0.25 to 6 km (0.6 to 15 m resolution). TIMS provides coverage of the 8 to 12 micrometer thermal infrared band in 6 contiguous channels. Thus it is possible to observe the spectral behavior of the surface emissivity over this wavelength interval.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 2: TIMS Workshop; p 37
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 94
    Publication Date: 2013-08-31
    Description: Thermal Infrared Multispectral Scanner (TIMS) data were acquired over the McDowell Mountains northeast of Scottsdale, Arizona during August 1994. The raw data were processed to emphasize lithologic differences using a decorrelation stretch and assigning bands 5, 3, and 1 to red, green, and blue, respectively. Processed data of alluvium flanking the mountains exhibit moderate color variation. The objective of this study was to determine, using a quantitative approach, what environmental variable(s), in the absence of bedrock, is/are responsible for influencing the spectral properties of the desert alluvial surface.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 2: TIMS Workshop; p 39-42
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 95
    Publication Date: 2013-08-31
    Description: In mineral exploration, the ability to distinguish and map petrochemical variations of magmatic rocks can be a useful reconnaissance tool. Alkalinity is one such petrochemical parameter and is used in the characterization of granitoid rocks. In quartz normative plutonic rocks, alkalinity is related to the composition and abundance of feldspars. Together with quartz abundance, knowledge of feldspar modes allows the classification of these igneous rocks according to the Streckeisen diagram. Alternative classification schemes rely on whole rock geochemistry instead of mineral identifications. The relative ease of obtaining whole rock analyses means that geochemical classifications tend to be favored in exploration geology. But the technique of thermal infrared spectroscopy of rocks yields information on mineralogy and is one that can be applied remotely. The goal of the current work then is to establish whether data from TIMS can be used to distinguish the mineralogical variations that relate to alkalinity. An ideal opportunity to test this thesis arises from the work presented in a paper by Dewitt (1989). This paper contains the results of mapping and analysis of Proterozoic plutonic rocks in north-central Arizona. The map resulting from this work delineates plutons according to alkalinity in an effort to establish a trend or polarity in the regional magmatism. Also contained within this paper are brief descriptions of the mineralogy of half of the region's plutons. This combination of mineralogical and geochemical information was the rationale behind choosing this area as a site for TIMS over flights. A portion of the region centered on the northern Bradshaw Mountains was selected because it contains plutons of all three alkalinity classifications (alkali-calcic, calc-alkalic, and calic) present on DeWitt's map within a relatively small area. The site was flown in August of 1994 and the data received a few days before the writing of this manuscript. Most of this paper is devoted to the description of laboratory based spectroscopy and spectral simulations. These are required to gain insight into the correct procedures for enhancing the relatively small differences in the low spectral resolution TIMS data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 2: TIMS Workshop; p 33-36
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 96
    Publication Date: 2013-08-31
    Description: This paper describes an empirical method to correct TIMS (Thermal Infrared Multispectral Scanner) data for atmospheric effects by transferring calibration from a laboratory thermal emission spectrometer to the TIMS multispectral image. The method does so by comparing the laboratory spectra of samples gathered in the field with TIMS 6-point spectra for pixels at the location of field sampling sites. The transference of calibration also makes it possible to use spectra from the laboratory as endmembers in unmixing studies of TIMS data.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 2: TIMS Workshopp 9-12 (SEE N95-33789 12-42); JPL, Summaries of th
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 97
    Publication Date: 2013-08-31
    Description: Remote sensing is a tool that, in the context of aeolian studies, offers a synoptic view of a dune field, sand sea, or entire desert region. Blount et al. (1990) presented one of the first studies demonstrating the power of multispectral images for interpreting the dynamic history of an aeolian sand sea. Blount's work on the Gran Desierto of Mexico used a Landsat TM scene and a linear spectral mixing model to show where different sand populations occur and along what paths these sands may have traveled before becoming incorporated into dunes. Interpretation of sand transport paths and sources in the Gran Desierto led to an improved understanding of the origin and Holocene history of the dunes. With the anticipated advent of the EOS-A platform and ASTER thermal infrared capability in 1998, it will become possible to look at continental sand seas and map sand transport paths using 8-12 mu m bands that are well-suited to tracking silicate sediments. A logical extension of Blount's work is to attempt a similar study using thermal infrared images. One such study has already begun by looking at feldspar, quartz, magnetite, and clay distributions in the Kelso Dunes of southern California. This paper describes the geology and application of TIMS image analysis of a less-well known Holocene dune field in south central Oregon using TIMS data obtained in 1991.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 2: TIMS Workshop; p 13-16
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 98
    Publication Date: 2013-08-31
    Description: A research program has been initiated between Arizona State University and the City of Scottsdale, Arizona to study the potential applications of TIMS (Thermal Infrared Multispectral Scanner) data for urban scene classification, desert environmental assessment, and change detection. This program is part of a long-term effort to integrate remote sensing observations into state and local planning activities to improve decision making and future planning. Specific test sites include a section of the downtown Scottsdale region that has been mapped in very high detail as part of a pilot program to develop an extensive GIS database. This area thus provides excellent time history of the evolution of the city infrastructure, such as the timing and composition of street repavement. A second area of study includes the McDowell intensive study by state and local agencies to assess potential sites for urban development as well as preservation. These activities are of particular relevance as the Phoenix metropolitan area undergoes major expansion into the surrounding desert areas. The objectives of this study in urban areas are aimed at determining potential applications of TIMS data for classifying and assessing land use and surface temperatures. Land use centers on surface impermeability studies for storm runoff assessment and pollution control. These studies focus on determining the areal abundance of urban vegetation and undeveloped soil. Highly experimental applications include assessment and monitoring of pavement condition. Temperature studies focus on determining swimming pool area and temperature for use in monitoring evaporating and urban water consumption. These activities are of particular relevance as the Phoenix metropolitan area undergoes major expansion into the surrounding desert area.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 2: TIMS Workshop; p 5-8
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 99
    Publication Date: 2013-08-31
    Description: Remote sensing of sand dunes helps in the understanding of aeolian process and provides important information about the regional geologic history, environmental change, and desertification. Remotely sensed data combined with field studies are valuable in studying dune morphology, regional aeolian dynamics, and aeolian depositional history. In particular, active and inactive sands of the Kelso Dunes have been studied using landsat TM and AIRSAR. In this report, we describe the use of AVIRIS data to study the Kelso dunes and to compare the AVIRIS information with that from TM and AIRSAR.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: JPL, Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 1: AVIRIS Workshop; p 159-161
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 100
    Publication Date: 2013-08-31
    Description: Vulcano Island is part of the Eolian archipelago, located about 25 km from the northeast coast of Sicily. The archipelago comprises seven major volcanic islands, two of which are active volcanoes (Vulcano and Stromboli). Vulcano covers an area of about 50 square km, and is about 10 km long. Explosive volcanic activity has predominated in the geological evolution of Vulcano Island, and there is no evidence that this pattern has ceased. Rather, the current situation is one of unrest, so a strict regimen of continuous geophysical and geochemical monitoring has been undertaken over the last decade. Though the year-round population of Vulcano is small (under 1000), during the summer the island becomes a very popular resort, and has thousands of additional tourists at any time throughout the high season, thus substantially increasing the number of people potentially at risk from an explosive eruption or other hazards such as noxious gas emissions (e.g., CO2, H2S, SO2). During the past ten years, remote sensing data have been repetitively acquired with optical and microwave airborne sensors. The present work shows the preliminary results of a study based on the integration of various remote sensing data sets with field spectroscopy, and other laboratory analyses, for the geological and geomorphological mapping of the island. It is hoped that such work will also usefully contribute to the evaluation of the volcanic hazard potential of the islands as well as to the evaluation of the status of its current activity.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: Summaries of the Fifth Annual JPL Airborne Earth Science Workshop. Volume 2: TIMS Workshop; p 1-4
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...