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  • Weitere Quellen  (321)
  • NASA Technical Reports  (321)
  • ASTROPHYSICS  (122)
  • GEOPHYSICS  (67)
  • ASTRONOMY  (56)
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  • NASA Technical Reports  (321)
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  • 1
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    Comparison of SAGE II ozone measurements and ozone soundings at Uccle (Belgium) during the period February 1985 to January 1986 (1990)
    In:  Other Sources
    Details
    Publikationsdatum: 2011-08-19
    Beschreibung: The ozone profiles obtained from 24 balloon soundings at Uccle (50 deg 48 min N, 4 deg 21 min E) made with electrochemical ozonesondes were used as correlative data for SAGE II ozone profiles retrieved within a distance of at most 600 km from Uccle. The agreement between the two data sets is in general quite good, especially for profiles nearly coincident in time and space, and during periods of little dynamic activity over the area considered. The percent difference between the ozone column density of the mean balloon and SAGE profile is 4.4 percent (-3.3) percent in the altitude region between 10 and 26 km. From a statistical analysis it appears that there is a small but meaningful difference between the mean profiles at the level of the ozone maximum and around the 30-km level. An error analysis of both data sets give similar results, leading to the conclusion that these differences are instrumentally induced. However, differences between the mean profiles in the lower stratosphere are probably real and due to the high ozone variability in time and space in that altitude region.
    Schlagwort(e): GEOPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 95; 11903-11
    Format: text
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  • 2
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    The Orion OB1 association. 1: Stellar content (1994)
    In:  Other Sources
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    Publikationsdatum: 2019-07-13
    Beschreibung: Walfraven photometry of established and probable members of the Orion OB1 association is presented. Effective temperature, surface gravity, luminosity and mass are derived for all stars, using atmosphere model by Kurucz (1979). Absolute magnitudes are calculated using the Straizys and Kuriliene (1981) tables. Distance moduli and visual extinctions are determined. A comparison of the visual extinctions to IRAS 100 micrometers data shows that the near edge of the Orion A and B clouds lies at a distance of approximately 320 pc, while the far edge is at approximately 500 pc. A method for deriving the ages of the subgroups by comparing theoretical isochrones to the observations in the log g, log T(sub eff) plane is presented. The derived ages suggest, contrary to earlier studies, that subgroup 1b is younger than 1c, which can possibly be explained by past geometries of the system of stars and gas. The initial mass function for Orion OB1 is derived with the aid of the Kolmogorov-Smirnoff test. Through extensive simulations, we show that it is very difficult to derive accurately the Initial Mass Function (IMF) from the available data. To within somewhat weak limits the IMF is found to be of the form xi(log M) = AM(exp -1.7 +/- 0.2) for all subgroups. The energy output of the subgroups in the form of stellar winds and supernovae is calculated and compared to the observed size and expansion velocity of the Orion-Eridanus bubble. It is shown that the energy output of the association can account for the morphology and kinematics of the interstellar medium (ISM).
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 289; 1; p. 101-120
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  • 3
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    Walraven photometry of nearby southern OB associations (1990)
    In:  Other Sources
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    Publikationsdatum: 2019-07-12
    Beschreibung: Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars in the regions of five nearby southern OB associations: Scorpio Centaurus (Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2. Derived V and (B - V) in the Johnson system are included.
    Schlagwort(e): ASTRONOMY
    Materialart: Astronomy and Astrophysics Supplement Series (ISSN 0365-0138); 85; 2 c; 915-970
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  • 4
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    Towards Calibrating the Vestan Regolith: Correlating the Petrology, Chemistry and Spectroscopy of Howardites (2013)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-19
    Beschreibung: The Dawn spacecraft carries a visible and infrared mapping spectrometer (VIR) [1] that has acquired spectra for the wavelength range 0.25-5.0 m at various spatial resolutions covering much of the vestan surface [2]. Through comparison of VIR spectra with laboratory spectra of howardite, eucrite and diogenite meteorites, the distribution of more diogenite-rich and more eucrite-rich terranes on Vesta have been mapped [3], but these maps are qualitative in nature. The available laboratory spectra are not well-integrated with detailed sample petrology or composition limiting their utility for lithologic mapping. Importantly, howardites are now recognized to come in two subtypes, regolithic and fragmental [4]. The former are breccias assembled in part from true regolith, while the latter have had much less exposure to the space environment. We are attempting to develop a more quantitative basis for mapping the distribution of lithologic types on Vesta through acquiring laboratory spectra on splits of howardites that have been petrologically and chemically characterized [5]. Noble gas analyses have been done on some allowing identification of those howardites that have been exposed in the true regolith of Vesta [6].
    Schlagwort(e): Geophysics
    Materialart: JSC-CN-28848 , Annual Meeting of the Meteoritical Society; Jul 29, 2013 - Aug 02, 2013; Edmonton, Alberta; Canada
    Format: application/pdf
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  • 5
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    Detection of the overtone of the 3.3 micron emission feature in IRAS 21282+5050 (1994)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The 1.6-1.8 micron spectrum of the planetary nebula, IRAS 21282+5050, a strong emitter of the unidentified interstellar bands, contains a 0.02 micron wide eimission feature centered at 1.680 micron, which is well matched by laboratory spectra of the 0-2 CH stretching mode in polycyclic aromatic hydrocarbons (PAHs). We identify the new feature as the overtone of the well-known 3.3 micron band. In view of the high excitation required for emission in this band, the identification indicates that the emission is by free molecules rather than molecular moieties in solid dust grains. Modeling of the intensity ratio of the 2-0 to 1-0 band implied that the PAHs emitting in these bands contain about 60 carbon atoms. It is inferred that the nu = 2-1 hot band of the CH stretching mode occurs at about 3.43 micron and contributes to the long-wavelength shoulder of the 3.40 micron feature. The main 3.40 micron feature probably is due to aliphatic sidegroups on PAH molecules.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 434; 1; p. L15-L18
    Format: text
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  • 6
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    On the modulated light in the intermediate polar FO Aquarii/H 2215-086 (1994)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The modulated light in the Intermediate Polar FO Aqr at the three periods P(sub spin) = 20.9 min, P(sub orb) = 4.85 hr and P(sub beat) = 22.5 min is studied in different spectral ranges to derive information on their nature. In this system the accretion geometry, with or without an accretion disk, is still a matter of debate (Hellier 1991; Norton et al. 1992). The different orbital behavior of phase coherence between the spin and beat pulses in the X-rays (Norton et al. 1992) and in the optical/IR regions cannot be easily accounted for by only a diskless dominated geometry where the accretion flow is switching from one pole to the other each half of the beat period. We therefore propose an accretion scenario where a non-axisymmetric disk is present. In such a non-standard accretion disk an azimuthal structure provides not only the source of variable mass transfer to the white dwarf, but also a reprocessing site which is mainly viewing the X-ray emission from the lower pole. Our spectral analysis shows that reprocessing is also occurring at the surface of the secondary star. The spin pulsation in the optical and IR continua can be explained by the so-called 'accretion curtain' model (Rosen et al. 1988) though an additional reprocessing component at the spin period cannot be excluded. In contrast to the X-rays, the beat optical/IR modulation is not intrinsic. Reprocessing at the surface of the secondary star and at the thickened part of the disk can also account for the orbital modulation in the UV, optical and IR regions.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 284; 1; p. 125-137
    Format: text
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  • 7
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    Periodic variation in the geomagnetic activity - A study based on the Ap index (1993)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The monthly and daily samples of the Ap index for the interval from 1932 through 1982 were studied using the power spectrum technique. Results obtained for Bartel's period (about 27 days), the semiannual period, the dual-peak solar cycle distribution of geomagnetic storms, and certain other medium-scale periodicities are examined in detail. In addition, results on the cumulative occurrence number of storms per decade as a function of the Ap and Dst indices for the storm are presented.
    Schlagwort(e): GEOPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 98; A6; p. 9215-9231.
    Format: text
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  • 8
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    A study of the optical and ultraviolet spectral characteristics and of the circumstellar material around the new luminous blue variable WRA 751 (1992)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The LBV characteristics of the new LBV candidate WRA 751 suggested by Hu et al. (1990) are studied in greater detail. A comparison is made with observational characteristics of the well-known LBVs Ag Car and HR Car using photometric and spectroscopic data of Hu et al. supplemented with an IUE spectrum and direct CCD images in H-alpha, blue, and red. It is found that the spectra of WRA 751 and HR Car discussed in this paper are similar to the minimum-phase spectrum of AG Car and therefore resemble the Of/WN 9 spectral type. The characteristics of the optical, near- and far-UV (IUE) spectra of the Fe II spectrum in these wavelength regions is due to continuum fluorescence. The H, He I, Fe II and forbidden Fe II emission lines are formed in different parts of the stars' envelopes, corresponding to their expanding velocities. It is concluded that WRA 751 has properties which fit well the LBV properties at minimum-brightness phase, and possesses circumstellar material with observational properties similar to those of the known LBVs AG Car and HR Car.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 257; 2; p. 632-640.
    Format: text
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  • 9
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    A new method for determining the Hubble constant from sub-TeV gamma-ray observations (1994)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: The present uncertainty in the Hubble constant leaves unresolved questions regarding the age of the universe and related matters involving the amount and nature of the dark matter in the universe, consistency with the inflationary model of the universe, and the need for a cosmological constant. It is clear that a significantly precise determination of the Hubble constant by as many different methods as possible is crucial to our knowledge and understanding of the character of the universe. We propose here an entirely new method for determining the Hubble constant, based on measuring the extinction of high-energy gamma-rays emitted by detectable gamma-ray emitting blazars at various redshifts.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 423; 1; p. L1-L4
    Format: text
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  • 10
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    Four micron high-resolution spectra of Jupiter in the North Equatorial Belt: H3(+) emissions and the C-12/C-13 ratio (1994)
    In:  Other Sources
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    Publikationsdatum: 2011-08-24
    Beschreibung: Spectra of the North Equatorial Belt of Jupiter were obtained in March 1992 at an unapodized resolution of 0.1/cm between 2450 and 2600/cm with the Fourier Transform Spectrometer at the 3.6 m Canada-France-Hawaii Telescope (CFHT) on Mauna Kea. Several emissions from the nu(sub 2) band of H3(+) were detected. The excitation temperature derived from the relative intensities of these emissions averaged over a wide range of longitudes is 800 +/- 100 K, and the H3(+) column density is 1.56(sup +1.0)(sub -0.5) x 10(exp 11)/sq. cm. In addition, several strong absorption features due to (13)CH4 were observed. A comparison between (12)CH4 and (13)CH4 absorptions allowed us to obtain a new measurement of the C-12/C-13 ratio. We found that this ratio, estimated for the first time in this spectral range, is 89 (+/- 25), in agreement with the terrestrial value.
    Schlagwort(e): ASTRONOMY
    Materialart: Planetary and Space Science (ISSN 0032-0633); 42; 5; p. 391-399
    Format: text
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