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  • ASTROPHYSICS  (1.748)
  • 2010-2014
  • 1995-1999
  • 1985-1989  (1.748)
  • 1999
  • 1997
  • 1989  (1.039)
  • 1985  (709)
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  • 2010-2014
  • 1995-1999
  • 1985-1989  (1.748)
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  • 1
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    An upper limit on the high-energy gamma-ray emission of Vela X-1 (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The possibility of high-energy gamma-ray emission from the X-ray binary Vela X-1 was investigated by analyzing the COS-B satellite observations, using the COS-B X-ray detector for a phase coherent analysis in the search of rotational periodicity. The rotational upper limit is compared to the X-ray, TeV, and PeV fluxes reported by Chodil et al. (1967), North et al. (1984), and Protheroe et al. (1984), respectively. It was found that, under certain conditions, the upper limit determined here is not inconsistent with the reports of TeV and PeV emission.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 226; 1, De
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  • 2
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    Optical depth of molecular gas in starburst galaxies - Is M82 the prototype? (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: An attempt is made to survey the CO(2-1) emission toward the centers of 17 IR-luminous galaxies which have previously been detected in CO(1-0). These galaxies span a wide range of size and L(FIR)/L(B) ratio, many have multiple-wavelength studies establishing them as starbursts, and some bear a morphological resemblance to M 82. Nine galaxies are detected and useful upper limits are placed on the remaining eight. Using the CO(2-1)/CO(1-0) ratio of antenna temperature as a diagnostic of optical depth, it is found that all of the galaxies contain predominantly optically thick molecular gas. This implies that the phase of starburst during which the molecular gas is optically thin, currently witnessed in M 82, is either uncommon or short-lived.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 225; 1, No
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  • 3
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    Phase transitions as the origin of large scale structure in the universe (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A review of the formation of large scale structure through gravitational growth of primordial perturbations is given. This is followed by a discussion of how symmetry breaking phase transitions in the early universe might have produced the required perturbations, in particular through the formation and evolution of a network of cosmic strings.
    Schlagwort(e): ASTROPHYSICS
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  • 4
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    The search for evidence of particle acceleration at SN 1987A in MeV to PeV gamma rays (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The prospects for obtaining evidence of the particle acceleration by SN 1987A pulsar wind are discussed. It is noted that, of the seven experiments that searched for high-energy signals since the discovery of SN 1987A, operating in both the TeV region (air Cerenkov arrays) and the 100-TeV region (air shower arrays), not one has reported a continuous signal from the supernova. The only signal reported so far that could be interpreted as a signal from the supernova remnant is from an air shower experiment YANZOS (Bond, 1988), in which a transient flux of photons above 3 TeV was observed. It is pointed out however, that, if a TeV signal is seen, the accompanying gamma-ray flux around 100 MeV should be well above threshold for detection by the EGRET detector on Gamma-Ray Observatory.
    Schlagwort(e): ASTROPHYSICS
    Materialart: New York Academy of Sciences, Annals (ISSN 0077-8923); 571; 522-531
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  • 5
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    Interplanetary shock phenomena beyond 1 AU (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Attention is given to spatial dependences exhibited by spacecraft measurements obtained between 1 and 30 AU, together with temporal variations occurring between solar activity cycle maxima and minima. At 1-3 AU radial distances, shocks develop in association with the corotating solar wind streams characterizing solar minimum and accelerate solar wind evolution with distance while heating the solar wind and generating waves and turbulence. At solar maximum, shocks are observed more frequently at 1 AU but still in association with transient solar events; acceleration leading to energetic storm particles is observed both within and beyond 1 AU. The superimposed effect of large numbers of intense shocks may be responsible for the solar cycle modulation of galactic cosmic rays.
    Schlagwort(e): ASTROPHYSICS
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  • 6
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    Nucleus studies of Comet Halley (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Early results from, and research initiatives warranted by, the earth-based observations of Halley's near-nucleus and related phenomena are reviewed. Where appropriate, this information is combined with spacecraft data obtained by the various flight projects. The basic objective is to gain a greater insight into the nature of the comet's nucleus and its environment.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Advances in Space Research (ISSN 0273-1177); 5; 12, 1; 307-316
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  • 7
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    Preliminary results of the Giotto radio science experiment (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Doppler and ranging measurements using the radio signal of the Giotto spacecraft were taken before, during, and after the encounter with Comet Halley on Mar. 13, 14, 1986. The spacecraft velocity was found to decrease by a total of 23.3 cm/s due to impacting gas and (primarily) dust in the cometary atmosphere. A preliminary dust production rate of 1000 kg/s is found to be consistent with this deceleration. Power spectra of the carrier phase fluctuations reveal an increase in level and a flattening of the spectrum just prior to encounter, presumably associated with the enhanced dust impact rate. Finally, simulated Doppler time profiles are computed using the radial dependence of plasma density observed by the Giotto in situ investigations. It is shown that the cometary electron content profile would have been clearly seen if a dual-frequency downlink radio configuration had been available at encounter.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Advances in Space Research (ISSN 0273-1177); 5; 12, 1
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  • 8
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    A preliminary look at the dust in Comet Halley (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Highlights of infrared observations of the dust are discussed and compared with first results from the space probes. An emission feature was detected at 3.4 microns; the 10 and 20 micron silicate features were well-observed; and far-infrared data out to 160 micron were obtained. Organic material seems to be abundant in grains and may explain the 3.4 micron emission. Calculations are presented for one example of organic material. A component of the grains may volatize at temperatures around 300 K.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Advances in Space Research (ISSN 0273-1177); 5; 12, 1; 325-334
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  • 9
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    Cometary kilometric radio waves and plasma waves correlated with ion pick-up effect at Comet Halley (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Bow-shock movements at Comet Halley are inferred from the discrete spectra of the cometary kilometric radiation (30-195 kHz); the observed emissions can be interpreted as being generated and propagating from the moving shock. The shock motion is possibly associated with the time variation of the solar wind and cometary outgassing. It is concluded that these plasma wave phenomena are manifestations of ion pick-up processes, which occur even in a remote region 7 million to 10 million km from the cometary nucleus.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Advances in Space Research (ISSN 0273-1177); 5; 12, 1; 83-88
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  • 10
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    CNO isotopes in red giant stars (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Observational data on CNO abundance ratios in red giants and the interstellar medium (ISM) are analyzed for the implications for the production and distribution of CNO nuclides. The data included isotope abundance measurements for the atmospheres and recent ejecta of cool giants, e.g., carbon stars, S-type stars, red supergiants and oxygen-rich giants beginning an ascent of the giant branch. The contribution of intermediate-mass stars to galactic nuclear evolution is discussed after comparing red giant abundances with ISM abundances, particularly the isotopes O-16, -17 and -18. The O-12/O-18 ratios of red giants are distinctly different from those in interstellar molecular clouds. The CNO values also vary widely from the values found in the solar system.
    Schlagwort(e): ASTROPHYSICS
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  • 11
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    CNO abundances in novae ejecta (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Isotope production, particularly CNO, which are enhanced in novae events and the interstellar medium (ISM) by novae are discussed in terms of emission-line data taken a few weeks after novae events. The emission-line abundances emerge only after the fading of absorption spectrum, and are also detectable in thin shells which sometimes, though rarely, form after novae. CNO abundances in these shells are equivalent to those observed in fading novae, with CNO/H ratios being 100 times solar values. Possible heavy element production pathways in the events and their shrinking are discussed, along with observation techniques for detecting CNO isotopes through absorption data on atomic transitions in novae ejecta and the ISM.
    Schlagwort(e): ASTROPHYSICS
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  • 12
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    An analysis of IRAS' solar system dust bands (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Measurements of longitudinal variations in the brightness and in the latitude of the solar system dust bands recently discovered by IRAS will determine the orbital elements of the particles involved and may discriminate between cometary and asteroidal models of the origin of these bands. The expected variations for bands of dust particles with common orbital elements and small eccentricity and inclination are calculated as functions of semimajor axis.
    Schlagwort(e): ASTROPHYSICS
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  • 13
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    Mass input into and output from the meteoritic complex (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The consequences which arise from the mutual collisions occurring between interplanetary meteoroids, the Poynting-Robertson (PR) effect and the radiation pressure ejection of small meteoroids are examined. The size distribution and flux of micrometeoroids at 1 AU are derived and the dependence of spatial density on distance from the sun is established. The following conclusions are made: (1) the lifetimes of meteoroids with masses approximately greater than 0.00001 g are dominated by catastrophic collisions; (2) after bering crushed by collisions, 70 to 85 percent of this mass will be in the form of zodiacal light particles (with masses in the range of 10 to the -10th g to 10 to the -5th g) which will in part be transported by the PR effect towards the sun where they will evaporate; (3) the 15 to 30 percent of the collisional fragments which have masses approximately less than 10 to the -10th g will, for the most part, be injected into hyperbolic orbits by radiation pressure.
    Schlagwort(e): ASTROPHYSICS
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  • 14
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    Selection effects against small comets (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Everhart's (1967) formulation is used to determine the correlation between the probability of discovering a comet and the size of its nuclear radius. The analysis is concentrated on comets that are not more than two or three hundred meters in diameter; hence, heliocentric variations in cometary brightness can be neglected. The effect of cometary physical decay is also considered, and a strong observational bias against the detection of small active comets is found. The following three factors are involved: (1) small comets must pass closer to the earth than large comets in order to be detected, (2) the resulting higher angular velocity for nearby comets leads to a decrease in the time available to discover a small comet, and (3) small comets physically decay and vanish faster than do large comets.
    Schlagwort(e): ASTROPHYSICS
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  • 15
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    IRAS observations of the interplanetary dust emission (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The Infrared Astronomical Satellite (IRAS) has completed a sensitive, highly redundant survey of the full sky in four broad photometric bands at 12, 25, 60, and 100 micrometers wavelength. The survey measured interplanetary dust emission over elongation angle ranging from 60 to 120 degrees. Bright emission from the main cloud is consistent with optically thin blackbody emission. The grains are evidently quite black, with an 'apparent albedo' of about 0.07. The data show clear evidence for deviation of the dust symmetry surface from the ecliptic plane. Surprising bands of emission were discovered near the ecliptic plane and about ten degrees on either side of it. The heliocentric distance of this material, suggested to be asteroidal in origin, is inferred to be about 2.5 AU from both color temperature and parallax measurements.
    Schlagwort(e): ASTROPHYSICS
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  • 16
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    Large and small scale structures of molecular clouds in the Taurus Perseus complex (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The gaseous components studied in H I and OH absorption against the extragalactic radiosources 3C123 and 3C111 are found to be the low-density edges of condensations of a few 100 solar masses. The densest part of one of these condensations has a structure similar to that found in other dark clouds: it is fragmented into several cores of a few solar masses, with an orbital velocity dispersion of about 2 km/s. In turn, the extended low-density layer, optically thick in CO (2-1), is not a common feature. It depends on the ambient UV field, but the dust temperature in the core may control its existence. Even more critically; it is found that the lower is the dust temperature, the less massive is the core and the more extended is the envelope around it, for a given total mass in a given external pressure.
    Schlagwort(e): ASTROPHYSICS
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  • 17
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    Cepheid variables as extra-galactic distance indicators (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The role of Cepheid variables in establishing the inner distance scale to nearby galaxies is discussed. Emphasis is placed on the necessity for broad wavelength coverage in attempting to account for metallicity differences and reddening internal to the parent galaxies. In addition linear detectors are essential in minimizing the effects of any unresolved background contribution to the photometry. Recent infrared observations of Cepheids in Local Group galaxies are surveyed and all published data on extra galactic Cepheids are presented for convenient access.
    Schlagwort(e): ASTROPHYSICS
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  • 18
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    The 50 millisecond pulsar in the Large Magellanic Cloud and the X-ray pulse emission mechanism (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Schlagwort(e): ASTROPHYSICS
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  • 19
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    Interstellar clouds - From a dynamical perspective on their chemistry (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The possibility is examined that in the course of its dynamical evolution, a single mass of interstellar gas would exhibit properties of diffuse clouds, dense clouds and finally also of clouds perturbed by shocks or intense UV or X-ray radiation generated by a star of its own creation. This concept provides a common thread through the bewildering diversity of physical and chemical compositional properties shown by interstellar clouds. From this perspective, instead of being static objects, interstellar clouds are possibly incessantly evolving from initially diffuse to later dense state and then to star formation which ultimately restructures or disperses the remaining cloud material to begin the whole evolutionary process once again. Based on a simplified study of interstellar chemistry from a dynamical perspective, the ideas are presented as an heuristic: to encourage thought on the future direction of molecular astrophysics and the need to consider the chemical behavior of interstellar clouds in conjunction with, rather than in isolation from, their dynamical behavior. A physical basis must be sought for the semiempirical temperature formula which has been given a critical role in the collapse of diffuse clouds. Self-shielding effects in the chemistry of CO were neglected and this drawback should be removed; the ability of the model to explain the fractional abundances of more complex molecules, such as cyanopolyynes, should be examined.
    Schlagwort(e): ASTROPHYSICS
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  • 20
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    Cometary comae (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The basis of our knowledge about the structure and composition of a comet nucleus is examined. Such knowledge is inferred from observations of the cometary atmosphere (coma). However, photodissociation, photoionization, and chemistry destroy the mother molecules evaporating from the nucleus. To extract the primary information, the chemical kinetics and the physics of the coma are modeled with a computer and the results are compared with coma observations. The physics and chemistry for a dust free coma are described taking into account energy balance, multi-fluid flow for fast atomic and molecular hydrogen and the bulk fluid, and the transition from a collision dominated inner region to the free molecular flow outer region. Special attention is paid to the molecular data requirements for the current modeld and for extended models which will include solar wind interaction and dust. Such models are an important tool in support of the Giotto mission to Halley's comet, in the analysis and interpretation of coma observations, and in the understanding of the earliest history of the solar system.
    Schlagwort(e): ASTROPHYSICS
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  • 21
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    Assisting extrasolar planetary detection through the determination of stellar space orientations (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Various methods outlined for indirect planetary detection would greatly benefit (in some cases require) the determination of the planetary orbital plane, which is theoretically equivalent to the stellar equatorial plane. Determining the stellar space orientation, therefore, would greatly benefit extrasolar planetary detection. Stellar rotation periods determined from short-term variations in Ca II H and K sunspot emission are utilized together with both stellar radii measurements and Doppler-broadened spectral line profiles to get the stellar inclination to the line of sight. The clocklike on-the-plane-of-the-sky component determination utilizes the concentration of sunspot-associated plage areas at central stellar latitudes when viewed in Ca II H or K emission. One can perform Ca II H and K emission speckle interferometry to measure the clocklike angle of this stellar Ca II H and K emission band, modeling it as an elliptical intensity distribution. Both components should be determinable to within 10 deg for at least the resolvable fifth magnitude stars.
    Schlagwort(e): ASTROPHYSICS
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  • 22
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    Problems with interpreting the radio emission from hot stars (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Problems in hot star radio emission interpretation due to radio flux source and other modeling assumptions are examined. An upper limit constraint on the value of the mass loss rate divided by the constant wind velocity is imposed by assuming that the outflow is due to bremsstrahlung in a spherically symmetric wind with the stationary photosphere visible at 4500 A, and by the need for it to be less than the luminosity divided by c. The constraints are satisfied for the deduced values for OB supergiants, and to some extent for early 0 stars, but not for Wolf-Rayet stars, due to mass loss rates excessive by a factor of 10. It is suggested that the problem can be solved by postulating that part of the radio flux from Wolf-Rayet stars is due to processes in a low-density magnetized plasma.
    Schlagwort(e): ASTROPHYSICS
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  • 23
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    Dynamical evolution of the Oort cloud (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: New studies of the dynamical evolution of cometary orbits in the Oort cloud are made using a revised version of Weissman's (1982) Monte Carlo simulation model, which more accurately mimics the perturbation of comets by the giant planets. It is shown that perturbations by Saturn and Jupiter provide a substantial barrier to the diffusion of cometary perihelia into the inner solar system. Perturbations by Uranus and Neptune are rarely great enough to remove comets from the Oort cloud, but do serve to scatter the comets in the cloud in initial energy. The new model gives a population of 1.8 to 2.1 x 10 to the 12th comets for the present-day Oort cloud, and a mass of 7 to 8 earth masses. Perturbation of the Oort cloud by giant molecular clouds in the galaxy is discussed, as is evidence for a massive 'inner Oort cloud' internal to the observed one. The possibility of an unseen solar companion orbiting in the Oort cloud and causing periodic comet showers is shown to be dynamically plausible but unlikely, based on the observed cratering rate on the earth and moon.
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  • 24
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    A new emission feature in IRAS spectra and the polycyclic aromatic hydrocarbon spectrum (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: IRAS spectra of those sources which show strong 7.7 and 11.3 micron emission features also show a plateau of emission extending from 11.3 to about 13.0 microns. Like the 11.3 micron feature, this new feature is attributed to the CH out-of-plane bending mode in polycyclic aromatic hydrocarbons (PAHs). Its discovery reinforces the identification of the 'unidentified infrared emission features' as emission from PAHs. The wavelength of this new feature suggests that interstellar PAHs are not as partially hydrogenated as hitherto thought. It also constrains their molecular structure.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 299; L93-L97
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  • 25
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    Near-infrared mapping of ARP 299 (IC 694-NGC 3690) - Colliding galaxies unveiled (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Near-infrared maps and multicolor photometry of the interacting galaxies IC 694 and NGC 3690 which form Arp 299 (= Markarian 171) are presented. These data reveal for the first time the distribution of nuclei and old red stars in a cataclysmically interacting system. The nuclei are considerably offset from the visual centroids of the galaxies but not from the mass centroids. The near-infrared colors of the most active regions are strongly affected by extinction, emission form hot dust, and bremsstrahlung. Near-infrared emission is also identified with secondary regions of star formation, probably resulting from the galaxies' interaction.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 299; 896-904
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  • 26
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    Molecular cloud evolution and star formation (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The present state of knowledge of the relationship between molecular clouds and young stars is reviewed. The determination of physical parameters from molecular line observations is summarized, and evidence for fragmentation of molecular clouds is discussed. Hierarchical fragmentation is reviewed, minimum fragment scales are derived, and the stability against fragmentation of both spherically and anisotropically collapsing clouds is discussed. Observational evidence for high-velocity flows in clouds is summarized, and the effects of winds from pre-main sequence stars on molecular gas are discussed. The triggering of cloud collapse by enhanced pressure is addressed, as is the formation of dense shells by spherical outflows and their subsequent breakup. A model for low-mass star formation is presented, and constraints on star formation from the initial mass function are examined. The properties of giant molecular clouds and massive star formation are described. The implications of magnetic fields for cloud evolution and star formation are addressed.
    Schlagwort(e): ASTROPHYSICS
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  • 27
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    Far-infrared and submillimeter photometry of evolved stars (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Broad-band photometric observations at far infrared and submillimeter wavelengths (lambda is greater than 30 microns and less than 1) provide a unique probe of circumstellar shells in evolved objects and of the mass loss processes which produce them. The problems which these observations explore include: dust properties and dust-to-gas ratios in the outflowing material, the mass and structure of the circumstellar shell, and the pumping mechanism for maser emission. This contribution reviews the early work in this still largely unexploited field and reports results in each of the areas listed above. The dramatic advances forthcoming in this area from the IRAS satellite are previewed along with further progress which will come from the next generation of infrared and submillimeter telescopes.
    Schlagwort(e): ASTROPHYSICS
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  • 28
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    Mass loss from red giants - Infrared spectroscopy (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: A discussion is presented of IR spectroscopy, particularly high-resolution spectroscopy in the approximately 1-20 micron band, as it impacts the study of circumstellar envelopes. The molecular bands within this region contain an enormous amount of information, especially when observed with sufficient resolution to obtain kinematic information. In a single spectrum, it is possible to resolve lines from up to 50 different rotational/vibrational levels of a given molecule and to detect several different isotopic variants. When high resolution techniques are combined with mapping techniques and/or time sequence observations of variable stars, the resulting information can paint a very detailed picture of the mass-loss phenomenon. To date, near-IR observations have been made of 20 molecular species. CO is the most widely observed molecule and useful information has been gleaned from the observed rotational excitation, kinematics, time variability and spatial structure of its lines. Examples of different observing techniques are discussed in the following sections.
    Schlagwort(e): ASTROPHYSICS
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    The infrared characteristics of circumstellar silicate grains (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: A theoretical study of the infrared emission from circumstellar shells around late-type giants is made, with the aim of deriving the infrared characteristics of the silicate grains condensing in these shells. A large grid of models has been compared with observations of optically visible Miras, IRC sources and OH/IR stars. From fitting the observed relation between the color temperature and the strength of the 10-micron feature, it is concluded that the ratio of the 3.5 to 10-micron absorption efficiencies of the dust is about 0.25, a factor of 2 less than a previous determination. Detailed modeling of the 2 to 13-micron spectrum of OH 26.5 + 0.6, IRC + 10011 and R Cas yielded a similar ratio. These detailed models also show that the shape of the 10-micron feature, particularly around 8 and 13 microns, varies from source to source. The derived 10-micron feature is narrower for larger dust column densities. These observed differences in the intrinsic shape of the 10-micron feature are not due to differences in size of the condensing particles. Probably they are related to structural or compositional differences in the condensing silicates.
    Schlagwort(e): ASTROPHYSICS
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  • 30
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    Protostellar angular momentum transport by spiral density waves (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The application of rotational stability criteria to a specific model of star formation leads to the conclusion that the growth of stellar angular momentum is limited by its transfer to the disk. Excess accreted angular momentum can be transferred by torques connected with spiral density waves induced by even a slight protostellar triaxiality. In addition, viscous damping of the density waves is likely to cause the excess angular momentum to be deposited within a small region close to the protostar. Thus, it would be appropriate to treat that part of the growing protostellar disk beyond the outer Lindblad resonance as an accretion disk with a torque applied to its inner edge. It is noted that this situation is directly relevant to certain models of the evolution of the protosun and solar nebula.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Icarus (ISSN 0019-1035); 64; 435-447
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    The plasma regime at comet Giacobini-Zinner (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The paper reviews results on the plasma regime at Comet Giacobini-Zinner obtained by the International Cometary Explorer. The observations are consistent with the existence of a weak shock which may be pulsating, but do not exclude the suggestion that the shock, though present around the subsolar point, is an the process of decaying to a wave on the flanks. 'The pick-up' of cometary ions leads to ion cyclotron, mirror, beam, and electrostatic instabilities which cause strong turbulence in the inner coma.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Advances in Space Research (ISSN 0273-1177); 5; 12, 1
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  • 32
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    Ammonia in the hot galactic centre cloud G 1.6-0.025 (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: As part of an extensive southern survey of interstellar NH3 with the Parkes 64-m radio telescope (with a beamwidth of 81 arcsec), the (1,1), (2,2), and (3,3) transitions have been observed towards the galactic centre molecular cloud Gl.6-0.025. The cloud has an overall size of 10 arcmin, and contains several concentrations with differing velocities. It has several features also observed in other galactic centre clouds, e.g. high optical depths and kinetic temperatures above 50 K.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of Australia, Proceedings (ISSN 0066-9997); 6; 2, 19
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    A calculation of the Rosseland mean opacity of dust grains in primordial solar system nebulae (1985)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The Rosseland mean opacity owing to grains was calculated as a function of temperature and density for nebulae having solar elemental abundances. The values of the mean opacity were evaluated with a generalized formulation allowing for anisotropic scattering. The values of the mean opacity do not depend sensitively on the choice of the particle size distribution function, provided that there are few particles having sizes in excess of several tens of microns. The results indicate that thermal convection in primordial nebulae occurs over broader ranges of altitudes at low temperatures than at high temperatures, and for size distributions for which extensive aggregation has not yet occurred.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Icarus (ISSN 0019-1035); 64; 471-492
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    Diagnostics of solar and astrophysical plasmas - Dependent on autoionization phenomena (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The application of autoionization calculations to problems in solar and astrophysical plasma diagnostics is discussed. Attention is given to space plasmas having high spectral resolution, particularly in the wavelength region between about 300 and 1100 A. It is shown that atomic resonance data can be used to calculate many of the spectral line intensities in solar plasmas in order to obtain information concerning the physical properties of the emitting gas, including temperature, density, ionization balance, and atmospheric structure and dynamics. Recent spectral observations of nonsolar plasmas are also discussed. A list of the major high-resolution astrophysical plasma spectrometers and spectrographs is provided.
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  • 35
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    On the identification of formaldehyde in Halley's comet (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The v1 and v5 infrared bands of formaldehyde in Halley's comet have been synthesized, using a line-by-line model for solar infrared fluorescence from low-temperature H2CO. Fully resolved spectra were convolved to spectral resolutions comparable with those used on the IKS spectrometer on the Vega 1 spacecraft. Excellent agreement is obtained between the observed and modeled spectra, permitting a definite identification of H2CO in Halley's comet. The retrieved production rate is 4.5 + or - 0.5 x 10 to the 28th molecules/s, and the rotational temperature is probably less than 150 K, with a best-fit value of about 50 K. Production rates (or upper limits) are also retrieved from ground-based spectra of Comets Halley and Wilson (1986), and it is shown that the production rate of H2CO exhibits significant temporal variability, relative to H2O, in Comet Halley.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 344; 940-948
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    The orbital inclination of Cygnus XR-1 measured polarimetrically (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The X-ray binary Cyg XR-1/HDE 226868 was observed polarimetrically over one orbit at three different optical wavelengths. The standard theory of Brown, et al. (1978) is used to derive an orbital inclination i = 62 deg (+5 deg, -37 deg), where the error is the 90-percent-confidence interval derived by the method of Simmons, et al. (1980). The value of the orbital inclination is significantly lower than values based on polarimetric observations. The difference is a result of the observational protocols used. A bias toward larger values of the inclination caused by the tidal distortion of the primary is still found in the present result. The inclination derived corresponds to a mass of the compact component of 6.3 solar masses, above the maximum mass of any degenerate configuration consistent with general relativity except a black hole.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 344; 830-834
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  • 37
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    The infrared emission bands. II - A spatial and spectral study of the Orion bar (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The 3-13 micron emission of the Orion Bar is spectroscopically and spatially studied. There are three emission components, one from 'classical' dust that accounts for the bulk of the emission longward of 20 microns, a second one from large amorphous carbon grains or polycyclic aromatic hydrocarbon (PAH) clusters accounting for the broad features, and a third from PAH molecules that accounts for the sharp bands. The 3.3 and 11.3 micron features, which are due to C-H modes, are well correlated spatially, while the 7.7 micron band, due to C=C modes, has a different distribution than the 3.3 and 11.1 micron bands. It is concluded that the sharp emission bands arise in the photodissociation transition region between the H II region and the molecular cloud and are not present in the H II region. The broad continuum feature from 11-13 microns is strong in both regions.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 344; 791-798
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    4U1722 + 11 - The discovery of an X-ray selected BL Lac object (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The Uhuru X-ray source 4U1722 + 11 was observed using the microchannel-plate detector (High Resolution Imager) on the Einstein Observatory, and its coordinates measured to a precision of about 5 arcsec. A 16th-magnitude stellar object within the error circle was observed spectroscopically at CTIO, and at the AAT, and found to have a featureless continuum. Subsequent radio observations at the VLA have established that the object is a radio source at the level of 60 mJy, and optical polarization measurements have determined that the source exhibits variable polarization at the level of 10 percent. On the basis of these observations, it is concluded that 4U1722 + 11 is a member of the class of objects known as X-ray selected blazars of BL Lac objects.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 240; 33-39
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  • 39
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    AGB evolution in the Large Magellanic Cloud (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Observations and theoretical studies of the evolution of massive asymptotic giant branch (AGB) stars in the Magellanic Clouds are reviewed. Recent results support the hypothesis that AGB is truncated, probably through mass loss, before these stars can attain the theoretically predicted maximum luminosity. In particular, IRAS observations of the LMC provide little evidence for the presence of highly obscured 'cocoon' stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 156; 1-2,; 73-79
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  • 40
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    The signature of a black hole transit (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: This paper considers the possibility of identifying a black hole on the basis of the detection of some unique effect occurring during the transit of a black hole across the stellar disk of a companion star in a binary system. The results of Monte-Carlo calculations show that the amplitude of the photometric and polarimetric light curves in a typical X-ray binary is too small to be observed with present instrumentation, but that a black hole transit might be detectable in a binary having a large separation of the components. No binary system suggested as containing a stellar-mass-sized black hole is a like candidate to exhibit an observable transit signature, with the possible exception of X Persei/4U0352+30 described by White et al. (1976).
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysics and Space Science (ISSN 0004-640X); 155; 1, Ma
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  • 41
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    Far-infrared observations of thermal dust emission from supernova 1987A (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Observations of SN1987A in the spectral range 18-35 microns taken on November 16 and 23, 1988, 632 and 639 days after core collapse, are reported. A strong and rather flat continuum underlies weak fine-structure lines from heavy elements and declines slowly between 24 and 30 microns. The spectral shape indicates thermal emission from an almost featureless dust component, probably graphite, with silicates contributing less than 20 percent of the emitting dust mass. Some of the emission may be an 'echo' of supernova light reflected from a preexisting dust cloud, but a better explanation which can account for the entirety of emission from infrared to gamma wavelengths, is that dust is being formed in the supernova ejecta. This also accounts more naturally for the inferred dust composition.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature (ISSN 0028-0836); 340; 697-699
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  • 42
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    X-ray spectroscopy of the ultrasoft transient 4U 1543 - 47 (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The X-ray transient 4U 1543 - 47 was observed in August 1983 by the Exosat observatory near the maximum of an outburst. The X-ray spectrum was measured using a gas scintillation proportional counter (GSPC) and a transmission grating spectrometer (TGS). A broad (FWHM about 2.7 keV) line at 5.9 keV is detected in the GSPC, which is interpreted as a redshifted and broadened iron K-alpha line. The line broadening and redshift may arise from either Compton scattering in a cool plasma with small optical depth and/or from Droppler and relativistic effects in the vicinity of compact object. The spectrum below 2 keV, obtained with the TGS, shows evidence for a broad emission feature at 0.74 keV, which may be an iron L-transition complex. However, such an emission feature could be an artifact caused by an anomalously low interstellar absorption by neutral oxygen. The contimuum emission is extremely soft and is well described by an unsaturated Comptonized spectrum from very cool plasma (kT = 0.84 keV) with large scattering depth.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 344; 320-324
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    Contributions of low-luminosity sources to the X-ray background (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: HEAO 1 A-2 data are used to determine hard X-ray fluxes, or upper limits, for complete optically selected samples of active and normal galaxies, in order to estimate or to constrain their local X-ray luminosity functions. It is found that the luminosity function of Seyfert nuclei must flatten down drastically shortly below the observational limit of Piccinotti et al (1982); little can be added by dwarf active nuclei hidden in otherwise normal galaxies. Also analyzed is the possible contribution to the X-ray background from galaxies with strong star-formation activity, in the light of the possibility of a substantial cosmological evolution suggested by recent radio and IRAS data.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 344; 125-134
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  • 44
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    Three-point correlations of galaxy clusters (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: A relation between two- and three-point correlation functions similar to that of galaxies is presently established by estimating the irreducible angular three-point correlation function of Abell clusters in distance classes 5 and 6, for Galactic latitudes below 40 deg. The shape of the three-point correlation function is fully consistent with the quadratic scaling law found by Groth and Peebles (1977) for galaxies. The three-point correlation function is inconsistent with the expectations from biasing.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 344; 75-88
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  • 45
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    An asymmetric outgassing model for cometary nongravitational accelerations (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The standard nongravitation force model has been modified by allowing the water-vaproization curve to peak a certain number of days (DT) either before or after perihelion, and the modification is shown to often improve the data fit. The best fit to the astrometric data is generally achieved for a value of DT corresponding to the offset in the comet's visual light curve. The asymmetric model, which more accurately mimics the comet's outgassing history, suggests only weakly that the rotation direction of Comet Halley is direct, and it does not provide evidence that the rotation axis of Comet Kopff passed through its orbit plane in the early twentieth century. Approximate lag angles of 4 deg for Comet Halley and 10 deg for Comet d'Arrest are found using the asymmetric model, and it is noted that these values are lower than those obtained with the standard model.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal (ISSN 0004-6256); 98; 1083-109
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    The IRAS Bright Galaxy Sample. IV - Complete IRAS observations (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Total flux densities, peak flux densities, and spatial extents at 12, 25, 60, and 100 microns are presented for the 330 sources in the IRAS Bright Galaxy Sample. The flux density ratios S sub nu (60 microns)/S sub nu (100 microns) and S sub nu (12 microns)/S sub n (25 microns) are found to correlate with both the infrared luminosity and the ratio of IR to visible flux. The relation between these two flux density ratios is shown to follow that found previously, with different slopes appearing for the warmer and colder galaxies in the sample. The results suggest that single photon heating of small grains (often the dominant source of 12 and 25 micron radiation from galaxies) significantly affects the emission of some galaxies at 60 microns, and that optical depth effects may alter the emergent radiation at 12 and 25 microns.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal (ISSN 0004-6256); 98; 766-797
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    Global properties of infrared bright galaxies (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Infrared flux densities of 182 galaxies, including 50 galaxies in the Virgo cluster, were analyzed using IRAS data for 12, 25, 60, and 100 microns, and the results were compared with data listed in the Point Source Catalog (PSC, 1985). In addition, IR luminosities, L(IRs), colors, and warm dust masses were derived for these galaxies and were compared with the interstellar gas masses and optical luminosities of the galaxies. It was found that, for galaxies whose optical diameter measures between 5 and 8 arcmin, the PSC flux densities are underestimated by a factor of 2 at 60 microns, and by a factor of 1.5 at 100 microns. It was also found that, for 49 galaxies, the mass of warm dust correlated well with the H2 mass, and that L(IR) correlated with L(H-alpha), demonstrating that the L(IR) measures the rate of star formation in these galaxies.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series (ISSN 0067-0049); 70; 699-722
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    A CO survey of regions around 34 open clusters (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Results are presented from a systematic search for CO emission from regions around 34 young open clusters in the outer Galaxy. The clusters have well-determined distances ranging from about 1 to 5 kpc and ages not greater than about 100 Myr. It was found that some moderately young clusters have no associated CO emission. All the surveyed clusters younger than about 5 Myr have associated with them at least one molecular cloud more massive than 10,000 solar mass, while the molecular clouds associated with clusters older than about 10 Myr are not more massive than a few thousands solar masses. It was also found that molecular clouds are receding from young clusters at a rate of about 10 km/sec, and that they seem to be destroyed by their interaction with the stars. Sites of ongoing star formation were identified in a number of clouds associated with young clusters.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series (ISSN 0067-0049); 70; 731-812
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    Theories of the origin and evolution of the giant planets (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Following the accretion of solids and gases in the solar nebula, the giant planets contracted to their present sizes over the age of the solar system. It is presently hypothesized that this contraction was rapid, but not hydrodynamic; at a later stage, a nebular disk out of which the regular satellites formed may have been spun out of the outer envelope of the contracting giant planets due to a combination of total angular momentum conservation and the outward transfer of specific angular momentum in the envelope. If these hypotheses are true, the composition of the irregular satellites directly reflects the composition of planetesimals from which the giant planets formed, while the composition of the regular satellites is indicative of the composition of the less volatile components of the outer envelopes of the giant planets.
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  • 50
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    Coupled evolution of the atmospheres and interiors of planets and satellites (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The evolution of a planetary atmosphere can be powerfully influenced by the planetary interior's function as both a source and a sink of atmospheric constituents; the interior can in turn be strongly influenced by the atmosphere because the mechanism of interior heat loss depends on a volatile content for which the atmosphere can serve both as sink and source. The dependence of mantle rheology on volatile content could furnish a feedback mechanism tending to keep regassing/degassing in balance, thereby maintaining a relatively constant atmospheric mass. Consideration of the abundances of radiogenic and nonradiogenic noble gases in the earth's atmosphere, and of the fluxes of these gases from the mantle, support a large degassing event early on, followed by a decrease in degassing efficiency with time and relatively inefficient outgassing over most of geologic time.
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    On structural patterns in H II regions (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: High-resolution photographs of H II regions show that a large number of stars embedded in the nebulosities appear to be surrounded by 'emply' spaces. This phenomenon seems to be quite common but has escaped attention up to now. The effect is not a photographic one, nor does it arise in the half-tone reproduction processes employed in publications, but no satisfactory explanation is apparent.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 101; 547-554
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    Meteoritic silicon carbide and its stellar sources - Implications for galactic chemical evolution (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Interstellar silicon carbide grains in meteorites provide a novel means for studying the carbon-star population of about 5 x 10 to the 9th years ago. Their C-12/C-13 ratios differ greatly from the solar value but resemble those of present-day csrbon stars, implying little change in the galactic C-13 inventory. Isotope data on nitrogen and silicon suggest that the silicon carbide grains come mainly from red giants, with small contributions from novae.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature (ISSN 0028-0836); 339; 351-354
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  • 53
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    A CCD portrait of Comet P/Tempel 2 (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: The development of activity in Comet P/Tempel 2 is studied from aphelion (R = 4 AU) to perihelion (R = 1.4 AU) using extensive time-series CCD photometry and CCD spectra. The comet undergoes a profound morphological change at R of about 2-2.5 AU, from a bare nucleus at larger distances to an active comet supporting a coma of gas and dust. Cyclic photometric variations with the period T = 8.95 + or - 0.01 hr. are present at all R, and are attributed to the rotation of the nucleus at this period. The nucleus is prolate (axes a:b:c = 1.9:1:1), a property shared with other nuclei studied using CCD photometry. Novel results include a limit on the bulk density of the nucleus, rho above 300 kg/cu m, and a 20-A-resolution CCD spectrum of the nucleus. Spatially and temporally resolved photometry is used to study the effects of nucleus rotation on the coma. The coma does not share the dramatic photometric variations shown by the nucleus. It possesses a steep surface-brightness distribution, which is attributable to progressive destruction of the coma grains with increasing space exposure.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Journal (ISSN 0004-6256); 97; 1766-179
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    IRAS observations of optically selected galaxies. I - The properties of the UGC redshift sample (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The FIR properties of more than 2400 optically selected galaxies in the Uppsala General Catalog are examined. The galaxies were detected by IRAS at 60 and 100 microns and have measured redshifts. A simple radiative transfer model is presented to study the nature of dust-heating sources. It is shown that for many normal disk galaxies, dust heated by old disk stars competes with dust heated by UV photons from newly formed stars. It is found that the 60-micron/100-micron flux density ratio may be used as an indicator of the dominant dust-heating source. Scaling relations with galaxy size and mass are presented which make it possible to estimate the contributions of any cirrus-like component to the total FIR luminosity.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 341; 129-150
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    Star formation rates and abundance gradients in disk galaxies (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Analytic models for the evolution of disk galaxies are presented, placing special emphasis on the radial properties. These models are straightforward extensions of the original Schmidt (1959, 1963) models, with a dependence of star formation rate on gas density. The models provide successful descriptions of several measures of galactic disk evolution, including solar neighborhood chemical evolution, the presence and amplitude of metallicity and color gradients in disk galaxies, and the global rates of star formation in disk galaxies, and aid in the understanding of the apparent connection between young and old stellar populations in spiral galaxies.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 339; 700-711
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    The Baade-Wesselink method applied to field RR Lyrae stars. III - YZ Capricorni, RV Phoenicis, and V440 Sagittarii (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Application of the Baade-Wesselink method to three field RR Lyrae variables reveals evidence of shock waves in the atmospheres of RV Phe and V440 Sgr (but not YZ Cap) during maximum light. The results yield distance moduli of 24.21 + or - 0.20 for M31, 18.26 + or - 0.20 for the LMC, and 18.85 + or - 0.20 for the SMC. Using the Sandage (1982) age/turn-off luminosity relationship of VandenBerg and Bell (1985), estimated ages of 18.8 Gyr for M92 and of 15.7 Gyr for 47 Tuc are derived.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 209; 1-2,; 154-164
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    The outer R Aquarii nebula - Comparison of 6 centimeter radio continuum and Balmer line emission (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The 6 cm radio continuum structure of the R Aquarii outer nebula is compared with CCD imagery of H-alpha and H-beta line emission. It is shown that the 6 cm VLA imagery is morphologically similar and quantitatively related spatially to Balmer line imagery. There is negligible interstellar or circumstellar absorption along the line of sight to the outer nebula. The 6 cm structure of the outer nebula is consistent with thermal bremsstrahlung emission by a hot, optically thin gas. Spectra of the outer R Aquarii nebula are suggestive of shock-wave heating. The approximate equality of mass loss and radiative cooling suggests that the system's wind is probably enough to power the outer nebula and may account for its long-term persistence.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 337; 795-802
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    Slow expansion of the shell of the recurrent nova T Pyxidis and detection of a faint extended envelope (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: New H-alpha narrow-based CCD imaging of the recurrent nova T Pyxidis and the detection of a very faint, extended H-alpha halo surrounding the already known shell are reported. A forbidden O III image containing an emitting shell with a morphology different from that of the H-alpha shell is presented, and measurements of the H-alpha shell expansion are reported which rule out the 1966 eruption date for the shell origin, assuming uniform expansion. It is proposed that the observed shell consists of slowly moving, solar abundance ejecta which are photoionized.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 337; 720-729
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    Radar observations of Comet Halley (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Five nights of Arecibo radar observations of Comet Halley are reported which reveal a feature in the overall average spectrum which, though weak, seems consistent with being an echo from the comet. The large radar cross section and large bandwidth of the feature suggest that the echo is predominantly from large grains which have been ejected from the nucleus. Extrapolation of the dust particle size distribution to large grain sizes gives a sufficient number of grains to account for the echo. The lack of a detectable echo from the nucleus, combined with estimates of its size and rotation rate from spacecraft encounters and other data, indicate that the nucleus has a surface of relatively high porosity.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 338; 1094-110
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    Pre-main-sequence disk accretion in Z Canis Majoris (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: It is suggested that the pre-main-sequence object Z CMa is a luminous accretion disk, similar in many respects to the FU Orionis variables. Z CMa shows the broad, doubled optical absorption lines expected from a rapidly rotating accretion disk. The first overtone CO absorption detected in Z CMa is blue-shifted, suggesting line formation in a disk wind. Accretion at rates about 0.001 solar mass/yr over 100 yr is required to explain the luminosity of Z CMa. The large amount of material accreted (0.1 solar mass/yr) indicates that Z CMa is in a very early stage of stellar evolution, possibly in an initial phase of massive disk accretion.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 338; 1001-101
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    The optical/infrared counterpart(s) of IRAS 18333-2357 (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Observations of the potential optical counterparts of the unusual source IRAS 18333-2357 are reported. There are three distinct optical objects located within roughly 2 arcsec of the IR source: a red star, a very blue star, and an extended emission line nebulosity. IRAS 18333-2357 indeed appears to be physically associated with the Galactic globular cluster M22, and while it probably should be considered a PN, its very small nebular mass and extreme abundance anomalies are very unusual among known PNe. IRAS 18333-2357 does not appear to be at an early stage of PN evolution, but instead may be in a late stage. The lack of an associated radio or H-alpha source is the result of abundance anomalies in the source.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 338; 862-874
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    RX Puppis - Detection of asymmetrical radio structure (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Subarcsecond observations of the RX Puppis symbiotic system with the VLA have resolved 2 cm continuum emission which deviates from a previously reported circularly symmetric radio distribution. The radio structure is comprised of at least three nearly colinear components. Under the assumption that the strongest feature is coincident with the hot star, the other two features lie 230 and 590 AU distant. These radio features are reminiscent of small-scale radio structure detected toward R Aquarii, another symbiotic star system, and probably represents material ejected from the RX Puppis system at an earlier epoch.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 337; 514-519
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    On the generation of flux tube waves in stellar convection zones. I - Longitudinal tube waves driven by external turbulence (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The source functions and the energy fluxes for wave generation in magnetic flux tubes embedded in an otherwise magnetic field-free, turbulent, and compressible fluid are derived. The calculations presented here assume that the tube interior is not itself turbulent, e.g., that motions within the flux tube are due simply to external excitation. Specific results for the generation of longitudinal tube waves are presented.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 337; 470-484
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    Test particle simulation study of whistler wave packets observed near Comet Giacobini-Zinner (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Nonlinear interactions of water group ions with large-amplitude whistler wave packets detected at the leading edge of steepened magnetosonic waves observed near Comet Giacobini-Zinner (GZ) are studied using test particle simulations of water-ion interactions with a model wave based on GZ data. Some of the water ions are found to be decelerated in the steepened portion of the magnetosonic wave to the resonance velocity with the whistler wave packets. Through resonance and related nonlinear interaction with the large-amplitude whistler waves, the water ions become trapped by the packet. An energy balance calculation demonstrates that the trapped ions lose their kinetic energy during the trapped motion in the packet. Thus, the nonlinear trapping motion in the wave structure leads to effective energy transfer from the water group ions to the whistler wave packets in the leading edge of the steepened MHD waves.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Geophysical Research Letters (ISSN 0094-8276); 16; 25-28
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    A second supernova inside Puppis A? (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Narrow-band images of an unusual swirl structure located near the center of the Puppis A supernova remnant are presented which reveal three overlapping filamentary systems of highly diverse composition. One is dominated by emission lines of nitrogen, one by oxygen, and one by sulfur. Spectra indicate that these small rings have high velocities and a corresponding kinematic age of less than 800 yr. Heavy-element abundances are extremely high and different in each system, some reminiscent of knots in Cas A, and others of circumstellar matter observed surrounding supernova 1987A. The youth and unusual chemistry lead to the suggestion that a second supernova has exploded within the shell of Puppis A, giving rise to the swirl structure.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature (ISSN 0028-0836); 337; 48-50
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    Formation of large-scale structure from cosmic strings and massive neutrinos (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Numerical simulations of large-scale structure formation from cosmic strings and massive neutrinos are described. The linear power spectrum in this model resembles the cold-dark-matter power spectrum. Galaxy formation begins early, and the final distribution consists of isolated density peaks embedded in a smooth background, leading to a natural bias in the distribution of luminous matter. The distribution of clustered matter has a filamentary appearance with large voids.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Physical Review Letters (ISSN 0031-9007); 62; 379-382
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    Molecule formation in fast neutral winds from protostars (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: A time-dependent chemical model is used to analyze the processes generating and destroying molecules in very high velocity winds from low-mass protostars. CO and SiO are found to be generated in significant quantities despite the persistence of H in atomic form, consistently with recent protostellar wind detections of CO and H I at velocities in excess of 100 km/sec. A moderate mass-loss rate, in conjunction with a temperature distribution that decreases rather rapidly with distance from the protostar, are the conditions for substantial molecule formation.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 336; L29-L31
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    The orbital inclination of A0620 - 00 measured polarimetrically (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The mass of the degenerate primary in A0620 - 00 is inferred from its spectroscopic mass function to be not less than 3.2 solar masses, making it an excellent candidate for a black hole. The exact value of the mass depends on the orbital inclination. The inclination of a binary system can be determined from the shape of its Stokes parameter light curves if the linear polarization of the system varies as a function of orbital phase. A0620 - 00 over one 8-hour binary period was observed with the 4.5-m equivalent MMT. Its polarization in the visible is variable with orbital phase. The standard theory of Brown et al. (1978) was used to derive an orbital inclination of i = 57 deg (+20 deg, -50 deg), where the error is the 90-percent confidence interval. An inclination of i = 57 deg corresponds to a mass of the compact primary of 6.6 solar masses, but the large uncertainty in the measured value of the inclination allows the derived mass of A0620 - 00 to be as low as 3.8 solar masses. If this is taken to be the maximum mass of any degenerate configuration consistent with general relativity except a black hole, then the mass of A0620 - 00 is still not well enough determined to conclude that it must be a black hole.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 101; 1135-113
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    Does mass accretion lead to field decay in neutron stars? (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Adopting the hypothesis of accretion-induced magnetic field decay in neutron stars, the consequent evolution of a neutron star's spin and magnetic field are calculated. The results are consistent with observations of binary and millisecond radio pulsars. Thermomagnetic effects could provide a possible physical mechanism for such accretion-induced field decay.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature (ISSN 0028-0836); 342; 656-658
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    Interstellar polycyclic aromatic hydrocarbons - The infrared emission bands, the excitation/emission mechanism, and the astrophysical implications (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A comprehensive study of the PAH hypothesis is presented, including the interstellar, IR spectral features which have been attributed to emission from highly vibrationally excited PAHs. Spectroscopic and IR emission features are discussed in detail. A method for calculating the IR fluorescence spectrum from a vibrationally excited molecule is described. Analysis of interstellar spectrum suggests that the PAHs which dominate the IR spectra contain between 20 and 40 C atoms. The results are compared with results from a thermal approximation. It is found that, for high levels of vibrational excitation and emission from low-frequency modes, the two methods produce similar results. Also, consideration is given to the relationship between PAH molecules and amorphous C particles, the most likely interstellar PAH molecular structures, the spectroscopic structure produced by PAHs and PAH-related materials in the UV portion of the interstellar extinction curve, and the influence of PAH charge on the UV, visible, and IR regions.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series (ISSN 0067-0049); 71; 733-775
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    Processes affecting the composition and structure of silicate grains in cometary nuclei (1989)
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    Publikationsdatum: 2011-08-19
    Beschreibung: Characteristics which might be observed in silicate grains from a cometary nucleus are examined on the basis of theoretical studies of the life cycle of refractory grains and laboratory experiments using simple analogs to the complex natural system. The life-cycle of a typical silicate grain is reviewed from condensation in a circumstellar outflow to incorporation into a cometary parent body. The possibility for grain metamorphism in the cometary environment is discussed and results are presented from experiments on the properties of interstellar grains. Also, consideration is given to the information about presolar refractory grains that might be gained from studying samples returned from a cometary nucleus.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Earth, Moon, and Planets (ISSN 0167-9295); 47; 33-50
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    The Exosat spectral survey of AGN (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Results are presented from Exosat observations of 48 hard X-ray selected Seyfert-type active galactic nuclei (AGN). These include all 30 of the emission line AGN in the Piccinotti (1981) sample. Combining Exosat LE and ME data has yielded X-ray spectra over the broad energy range 0.1-10 keV. Spectra in the about 2-10 keV range are found to be well described by a simple power law, with a narrow distribution of spectral indices across the sample about a mean energy index alpha = 0.70. Exosat has also revealed a substantial number of sources with complex soft X-ray spectra. Evidence that soft emission components occur in many Seyferts, together with detection of rapid variability in the soft component, provides a quantitative support for an accretion disk model for AGN. Approximately half of the present sample of AGN show low-energy absorption attributable to substantial cold matter within the host galaxy. A few cases show evidence for column variability and reduced low-energy opacity (by photo-ionization). These results and the observed rarity of intrinsic absorption in the higher luminosity sources suggest the absorbing matter lies close to the central continuum source.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 240; 833-880
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    Large-scale cosmic microwave background anisotropies in isocurvature baryon open universe models (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The large-angular-scale cosmic microwave background anisotropy is calculated in a low-density baryon-dominated universe with isocurvature primordial inhomogeneities. In models in which the initial power spectra of perturbations are steeper than white noise, predictions for the quadrupole moment of the anisotropy are found to be in conflict with existing observational limits, if the universe remained fully ionized and Compton drag inhibited growth of inhomogeneities until z = about 100. In order to lower the amplitude of the anisotropy, it is necessary to substantially prolong the duration of the growth phase of density perturbations, while smearing out fine-scale anisotropies, thereby requiring reionization to occur at a redshift smaller than 100, but larger than the redshift of the last scattering surface (in a reionized model).
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 346; L1-L4
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    Why DA and DB white dwarfs do not show coronal activity and p-mode oscillations (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The problems of nonradiative heating of outer atmospheric layers and p-mode oscillations in white dwarfs caused by acoustic waves generated in convective zones are discussed. These effects have been studied by calculating the cutoff periods for adiabatic and isothermal waves propagating in atmospheres of DA and DB stars with Teff greater than or equal 20,000 K and log g = 6-9. The obtained cutoff periods are approximately bounded by 0.01 and 40 sec for high- and low-gravity white dwarfs, respectively. Expected amplitudes of p-mode oscillations corresponding to trapped acoustic waves with small angular wave numbers are estimated, indicating that the amplitudes could be observed as Doppler shifts of spectral lines which might be detectable if adequate spectral resolution were available. The luminosity variations corresponding to these amplitudes are unlikely to be observable when all damping processes are accounted for. Results also indicate that the present theory of convection predicts some irregularities in the behavior of physical parameters.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 346; 435-443
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    A search for methylene in the Orion nebula (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A deep search for the J = 4-3 and 5-4 fine-structure components of the N(KK) = 4(04)-3(13) rotational transition of methylene toward the hot core of the Orion KL nebula is conducted. An approximate 4-sigma emission feature which is frequency-coincident with a hyperfine blend of the J = 4-3 component is detected, and weak features (about 2-3 sigma) frequency-coincident with the resolved F = 6-5 and 5-4 hyperfine components of the J = 5-4 component are observed. The relative intensities of these spectral features and their observational repeatability suggest that assignment to interstellar CH2 is likely correct, although the result must be confirmed.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 346; 794-798
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    Interstellar matter in early-type galaxies - Optical observations (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Results of optical observations of 26 bright elliptical galaxies selected on the basis of IRAS data are discussed. Optical broadband imaging (using B and R filters) and narrow-band imaging (using H-alpha interference filters) have been performed to study dust patches and ionized gas. Long-split spectroscopy has also been made to determine gas kinematics and relative line ratios. The spectroscopic data confirm the presence and distribution of interstellar matter (dust lanes and ionized gas) seen in the direct imaging. Decoupled kinematics of interstellar gas and stars favors an external origin of the interstellar matter. However, for one isolated galaxy, an internal origin is not excluded. The rotation curves determined by optical emission lines are symmetric around the center in most galaxies observed. Galaxy masses and mass-to-light ratios are estimated using the rotation curves of the ionized gas.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 346; 653-674
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    A search for X-ray emission associated with the great attractor (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A search is reported for X-ray emission associated with the object, dubbed the 'great attractor', which has been postulated as the cause of the coherent deviations from the Hubble flow which are observed in nearby parts of the universe. The hypothesis that a substantial fraction of the dynamical mass of the great attractor exists in the form of rich clusters of galaxies is ruled out. The possibility is considered that a substantial fraction of the mass of the great attractor could exist in a form which would increase the apparently diffuse X-ray surface brightness. The observational upper limit to the diffuse X-ray sky surface brightness enhancement in the general direction of the great attractor allows interesting limits to be set on the fraction of the dynamical mass of the great attractor which can exist in the form of X-ray-luminous material.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 346; 638-647
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    A study of several F and G supergiant-like stars with infrared excesses as candidates for proto-planetary nebulae (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Ground-based observations have been obtained for eight F and G supergiant-like stars showing large IR excesses. The combination of ground-based and IRAS data shows that these objects have dual-peak energy distributions, with comparable amounts of energy emitted in the visible and the IR. The IR-emitting cool dust shells are likely to represent the remnants of ejecta from an earlier phase of evolution. It is suggested that these eight objects are similar to IRAS 18095 + 2704 and are intermediate-mass stars in a post-AGB phase of evolution. Model fittings to the 0.4-100 micron energy distribution of these objects suggest that they left the AGB within the last 1000 yr.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 346; 265-276
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    A Bayesian classification of the IRAS LRS Atlas (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The availability of a reclassification of the IRAS LRS Atlas of spectra using a new Bayesian classification procedure (AutoClass) is announced. The classes of objects which result from the application of the AutoClass algorithm include many of the previously known LRS classes. New classes which have interesting astronomical and astrophysical interpretations were also found. Techniques, such as the AutoClass algorithm, have a bright future in the arena of astronomical classification problems.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astronomy and Astrophysics (ISSN 0004-6361); 222; 1-2,
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    The discovery of a new infrared emission feature at 1905 wavenumbers (5.25 microns) in the spectrum of BD + 30 deg 3639 and its relation to the polycyclic aromatic hydrocarbon model (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A new IR emission feature at 1905/cm (5.25 microns) has been discovered in the spectrum of BD + 30 deg 3639. This feature joins the family of well-known IR emission features at 3040, 2940, 1750, 1610, '1310', 1160, and 890/cm. The origin of this new feature is discussed and it is assigned to an overtone or combination band involving C-H bending modes of polycyclic aromatic hydrocarbons (PAHs). Laboratory work suggests that spectral studies of the 2000-1650/cm region may be very useful in elucidating the molecular structure of interstellar PAHs. The new feature, in conjunction with other recently discovered spectral structures, suggests that the narrow IR emission features originate in PAH molecules rather than large carbon grains.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 345; L59-L62
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  • 81
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    A 21 micron emission feature in four proto-planetary nebulae (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The discovery of an unidentified emission feature at 21 microns in the LRS spectra of four IRAS sources is reported. These objects all show large FIR excesses due to a circumstellar dust envelope surrounding a carbon-rich central star and are likely to be in the evolutionary phase between the asymptotic giant branch and planetary nebula stages. The strength of the feature and the carbon richness of the objects suggest that this feature is due to the bending mode of a transient carbon-bearing molecule.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 345; L51-L54
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  • 82
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    Influence of multiple ion species on low-frequency electromagnetic wave instabilities (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The effect of multiple (singly ionized) coexisting newborn ion species on the stability of low-frequency electromagnetic waves was investigated using a plasma model in which solar wind magnetoplasma is made up of isotropic Maxwellian electron and proton populations with a common number density of 4.95/cu cm and temperatures equal to 17.2 eV and 6.9 eV, respectively. It is shown that the effect of multiple ions on wave growth, for given background magnetoplasma conditions and relative densities, depends not only on their mass but also on the physical nature of the wave modes. If the ion masses are disparate, each one of the coexisting ion beams tends to stimulate instabilities without undue influence from the other species. If the masses of newborn ions are similar, they can strongly catalyze wave growth of fluidlike nonresonant modes, but bring about weak growth enhancements in cyclotron resonant instabilities.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Journal of Geophysical Research (ISSN 0148-0227); 94; 13565-13
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  • 83
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    On the black hole lens and its foci (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Methods developed for radio occultation studies of planetary atmospheres are used to predict the electromagnetic focusing properties of a refracting lens representation of a Schwarzschild black hole. The infinity of foci are of three distinct types: a principal forward axial focus which is by far the strongest; higher-order forward axial foci; and backward conical foci with axial nulls.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Advances in Space Research (ISSN 0273-1177); 9; 9, 19
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  • 84
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    The optically thick O III spectrum. I - Diagnostic ratios involving the intercombination lines (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: An escape-probability calculation of the optically thick O III spectrum is carried out to obtain the optical depth dependence of the intercombination doublet at 1663 A and of resonance lines between the 2p2, 2s2p3, and 2p4 configurations. The effect of optical depth on diagnostic ratios involving the intercombination lines is quantitatively established. The general question raised is whether such effects may occur in actual sources.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal Supplement Series (ISSN 0067-0049); 71; 665-675
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  • 85
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    WHT observations of cataclysmic variables in globular clusters. I - V101 in M5 during quiescence and outburst (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: WHT spectroscopy and photometry are used to investigate the structure of the cataclysmic vaiable V101, in the globular cluster M5. An encouraging consistency is found between the properties derived from the color, magnitude, radial-velocity variations and outburst light curve. All these indicate that V101's orbital period lies above the period gap, is at the distance of M5, and is probably a dwarf nova.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 241; 25P-30P
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  • 86
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    Possible test at Jupiter of the nonsymmetric gravitational theory (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Radiometric data generated during spacecraft flybys of Jupiter have the capability to provide an interesting constraint on the coupling of cosmions in the nonsymmetric gravitational theory (NGT) of Moffat. It is shown that the close flyby of Jupiter by Pioneer 11 could imply a possible limit on the NGT l parameter of the sun of solar l less than 2800 km, a limit which could affect the ability of the NGT to account for the precession of the perihelion of Mercury with a large solar quadrupole moment.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Physical Review D - Particles and Fields, 3rd Series (ISSN 0556-2821); 40; 1372
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  • 87
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    Astrophysical contributions of the International Ultraviolet Explorer (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Findings that have been made by the IUE in a variety of astrophysical areas are reviewed. Results on stellar chromospheres and transition regions, evolutionary processes in interacting binaries, winds from early-type stars, the ISM, SN 1987A, active galactic nuclei, and solar system objects are addressed.
    Schlagwort(e): ASTROPHYSICS
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  • 88
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    Cosmic impacts, cosmic catastrophes. I (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The discovery of cosmic impacts and their effects on the earth's surface are discussed. The manner in which the object impacts with the earth is described. The formation of crytovolcanic structures by craters is examined. Examples of cosmic debris collisions with earth, in particular the Tunguska explosion of 1908 and the Meteor Crater in Arizona, are provided.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Mercury (ISSN 0047-6773); 18; 185-192
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  • 89
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    Far-infrared spectrophotometry of SN 1987A - Days 265 and 267 (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The paper presents 16-66-micron spectra of SN 1987A taken on days 266 and 268 after core collapse. The spectrum consists of a nearly flat continuum, strong emission lines of hydrogen, and fine-structure lines of Fe II, Fe III, Co II, S I, and possibly Fe I, Ni II, and S III. From the relative strength of three lines which arise from transitions within the ground and excited states of Fe II, the temperature and a lower limit on the density of the line-emitting region are derived. From the line strengths, the abundances of Fe and S I, the end products of explosive nucleosynthesis in the supernova are estimated. An upper limit is also set to the amount of Co II remaining in the mantle. The low measured mass of Fe suggests that the ejecta are clumpy. The flat continuum is most likely free-free emission from the expanding supernova ejecta. About 35 percent of this emission arises from the ionized metals in the mantle; the rest arises from ionized hydrogen. At the time of these observations, there is no evidence for any emission from dust that may have formed in the supernova ejecta or from preexisting dust in the surrounding medium.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 347; 1119-112
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  • 90
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    Terminal velocity of wind, mass loss, and absorption lines of the central star of the planetary nebula 75 + 35.1 deg (1989)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The high-galactic latitude planetary nebula 75 + 35.1 deg was observed in the high-dispersion mode of the International Ultraviolet Explorer (IUE) satellite in the wavelength range 1150-1950 A. The N V resonance doublet at 1240 A and O V subordinate line at 1371 A exhibit strong stellar P Cygni profiles with absorption extending to -2150 km/s and -1000 km/s, respectively. Application of the first moment method implies a mass-loss rate of M = (1-3) x 10 to the -8th solar mass/yr. The high ionization of the wind lines and the presence of strong Fe VI and Fe V lines in the stellar photosphere support that this object is quite hot. A Teff of 75,000 + or - 10,000 K was adopted, although Tc = 94,000 K was found previously from low-resolution IUE data.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 347; 901-909
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  • 91
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    Anatomy of a cosmic-ray neutrino source and the Cygnus X-3 system (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The effects of an intense beam of ultra-high energy cosmic rays from a compact object in the Cygnus X-3 binary system hitting the companion star, and of the subsequent production of secondary neutrinos, are examined. A maximum allowable beam luminosity of about 10 to the 42nd erg/s is found for a system containing a 1-10 solar mass main sequence target star. The proton beam must heat a relatively small area of the target star to satisfy observational constraints on the resulting stellar wind. With such a model, the neutrino to gamma-ray flux ratio of about 1000 can result from a combination of gamma-ray absorption and a large neutrino to gamma-ray duty cycle ratio. It is found that the high density of the atmosphere resulting from compression by the beam leads to pion cascading and a neutrino spectrum peaking at 1-10 GeV energies.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Nature (ISSN 0028-0836); 316; 418-420
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  • 92
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    The physical implications of an isothermal model for the hot intracluster medium (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: HEAO-1 A-2 and Einstein Observatory IPC observations of 15 clusters of galaxies have been used to measure the isothermal beta-model parameters, and the parameters are compared with those derived from model fits to the X-ray images. The physical constraints imposed on this model by existing optical data, the implied gas mass, and the gas contribution to the binding cluster mass are addressed. Values of beta less than unity are obtained, consistent with results from X-ray imaging data. This is interpreted to imply that the gas extends out to 8-10 core radii, about 2-3 Mpc. The isothermal gas mass can be as large as 60 percent of the virial mass for some clusters. This contradicts the fundamental assumption that the cluster potential is determined by an unseen mass which is given by the King approximation to an isothermal sphere, and it is concluded that the isothermal model is a nonphysical model.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 292; 441-446
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  • 93
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    High-energy X-ray observations of the Galactic center region (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The region within five degrees of the Galactic center was observed in high-energy X-rays on November 12, 1977, and it is concluded that the emission definitely comes from more than one source. At least five 2-10 keV sources are important: the transient A1743 - 322, the binary GX 1 + 4, the bulge sources GX 3 + 1 and GX 5 - 1, and A1742 - 294. The composite spectrum of all the sources agrees with the continuum measured 12 days earlier by Leventhal, MacCallum, and Stang (1978) in the 70-250 keV range but, if extrapolated to higher energies, would be softer than and weaker than the HEAO 1 continuum observed in September 1977 or HEAO 3 continuum observed in the fall of 1979.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 290; 557-567
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  • 94
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    On fast X-ray rotators with long-term periodicities (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The support of previous SAS 3 spacecraft observations by new data gathered by the Monitor Proportional Counter aboard the HEAO 2 spacecraft indicates that the pulse period history of the 13.5 sec-pulsing X-ray source LMC X-4 is consistent with standard accretion and torque models only if LMC X-4 is a fast rotator for which the accretion torques nearly cancel. This result leads to a neutron star magnetic field strength estimate of about 1.2 x 10 to the 13th G. Strong evidence is noted for Her X-1's status as a fast rotator, while SMC X-1 is probably an intermediate-to-fast rotator. In the context of slaved disk models for these objects, it is noted that the precession periods expected for the companion stars are significantly longer than the observed 1-2 month time scales; slaved disk models are thereby undermined.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 290; 487-495
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  • 95
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    Electrosphere of an aligned magnetized neutron star (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A fundamentally new self-consistent solution for the electrosphere of an aligned magnetized neutron star is presented. Unlike previous models the electrospheres are finite in extent. This avoids the light cylinder problem. The results may provide a basis for pulsar models.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 213; 43P-49P
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  • 96
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    MgS grain component in circumstellar shells (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: In this letter, far-infrared spectrophotometry (30-55 microns) and photometry (53-200 microns) are presented which define, for the first time, the long wavelength limit of the previously unidentified 30 micron emission feature found in certain extreme carbon star spectra. The spectral similarities are sufficiently similar to those of solid MgS that MgS is proposed to be the band carrier. This is interpreted as the first direct evidence that chemical surface reactions occur on dust grains in circumstellar environments. The presence of MgS indicates that either the oxygen abundance is relatively low and/or the sulfur abundance is high in extreme carbon stars.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 290; L35-L39
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  • 97
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    Laboratory infrared spectra of predicted condensates in carbon-rich stars (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: Laboratory spectra and mass absorption coefficients of MgS, CaS, FeS, SiS2, FeS2, Fe3C, and a commercial iron carbide are presented over the wavelength range 125-15 microns. These spectra confirm that MgS is the most likely source of the unidentified 30-micron emission in carbon-rich sources and that FeS, Fe3C, and 'iron carbide' cannot be responsible for this feature although they could contribute to the continuum in this region. CaS and FeS2 may contribute to the 30-micron feature; however, both higher resolution and higher precision astronomical observations are needed before their presence can be established. SiS2 has a peak near 22 microns and therefore cannot be a significant component of the dust in such regions.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 290; L41-L43
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  • 98
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    Polycyclic aromatic hydrocarbons and the unidentified infrared emission bands - Auto exhaust along the Milky Way (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: The unidentified infrared emission features (UIR bands) are attributed to a collection of partially hydrogenated, positively charged polycyclic aromatic hydrocarbons (PAHs). This assignment is based on a spectroscopic analysis of the UIR bands. Comparison of the observed interstellar 6.2 and 7.7-micron bands with the laboratory measured Raman spectrum of a collection of carbon-based particulates (auto exhaust) shows a very good agreement, supporting this identification. The infrared emission is due to relaxation from highly vibrationally and electronically excited states. The excitation is probably caused by UV photon absorption. The infrared fluorescence of one particular, highly vibrationally excited PAH (chrysene) is modeled. In this analysis the species is treated as a molecule rather than bulk material and the non-thermodynamic equilibrium nature of the emission is fully taken into account. From a comparison of the observed ratio of the 3.3 to 11.3-micron UIR bands with the model calculations, the average number of carbon atoms per molecule is estimated to be about 20. The abundance of interstellar PAHs is calculated to be about 2 x 10 to the -7th with respect to hydrogen.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 2 - Letters to the Editor (ISSN 0004-637X); 290; L25-L28
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  • 99
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    The R Aquarii system at optical and radio wavelengths (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: New continuum observations of all radio components of the R Aquarii system at 2, 6, and 20 cm are reported which allow determination of polarization properties, integrated flux levels, spectral indices, and hence the emission mechanisms of the individual components. Complementary wide-band optical observations are also reported to help determine the nature and structure of the compact double radio source (CDRS) and the R Aquarii radio jet. The results of these observations are discussed in detail with regard to models currently or previously proposed for the R Aquarii system. It is concluded that the compact H II region spectral index is about +0.6, indicative of a thermal and optically thick expanding wind from the long-period variable. The radio jet emission is shown to be optically thin, thermal, cospatial with optical emission, and stable over the last few years. The CDRS is shown to be an extragalactic background object.
    Schlagwort(e): ASTROPHYSICS
    Materialart: Astrophysical Journal, Part 1 (ISSN 0004-637X); 289; 765-767
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  • 100
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    High-angular resolution observations of stellar binary systems (1985)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: A long-term program designed to investigate the spatial structure of centimetric radio emission from close binary systems using multistation VLBI array is discussed. Eleven binaries, including eight RS CVn systems, Algol, LSI 61 deg 303, and Cyg X-1, have been detected. The measured brightness temperatures vary from T(B) about 10 exp 8.5 K during periods of low activity to T(B) about 10 exp 10.5 K during flares. Extensive observation of a few sources has shown that the spatial structure is 'core-halo' with linear dimensions of about a stellar radius and the binary system, respectively. The observations are consistent with gyrosynchrotron emission of mildly relativistic electrons in magnetic fields of about 10 exp 1.5 + or - 0.5 gauss. The core sources appear to be optically thick, while the halo component is optically thin.
    Schlagwort(e): ASTROPHYSICS
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