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  • Other Sources  (89)
  • 1
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    Short period Miras and Galactic Structure (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Red Giants on the Asymptotic Giant Branch typically are more luminous than M(sub K) = -7 mag. Therefore, a new Two Micron Sky Survey (2MASS) which will go as faint as m(sub K) = 10 mag will be able to observe most of these stars in the Milky Way. Such a complete census will enable us to develop a much better understanding of Galactic Structure. It will be important to separate the luminous red giants into their different subclasses because these subclasses trace different Galactic Populations. For example, Miras with periods less than 300 days can be used to study the 'thick disk', while Miras with periods greater than 300 days belong to the 'thin disk'.
    Keywords: ASTRONOMY
    Type: Astrophysics and Space Science (ISSN 0004-640X); 217; 1-2; p. 101-104
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  • 2
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    The Goddard High Resolution Spectrograph: Instrument, goals, and science results (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The Goddard High Resolution Spectrograph (GHRS), currently in Earth orbit on the Hubble Space Telescope (HST), operates in the wavelength range 1150-3200 A with spectral resolutions (lambda/delta lambda) of approximately 2 x 10(exp 3), 2 x 10(exp 4), and 1 x 10(exp 3). The instrument and its development from inception, its current status, the approach to operations, representative results in the major areas of the scientific goals, and prospects for the future are described.
    Keywords: SPACECRAFT INSTRUMENTATION
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 106; 702; p. 890-908
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  • 3
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    The High Resolution Spectrograph for the Space Telescope (1982)
    In:  CASI
    Details
    Publication Date: 2009-11-16
    Description: The High Resoltuion Spectrograph (HRS) in conjunction with the Space Telescope (ST), extends ultraviolet astronomical spectroscopy to higher spectra, spatial, and time resolutions than previously achieved, as well as to fainter and more distant celestial objects. Other significant advances inherent in the instrument are high photometric accuracy and efficient operation via exposure meter control and real time rejection of bad data. These capabilities are provided to accomplish the scientific programs of the HRS investigation definition team, which concern the interstellar medium, stellar winds, and evolutionary aspects of stellar atmosphere studies; the determination of chemical abundances relevant to stellar evolution; the investigation of quasars and Seyfert galaxy nuclei; and the analysis of the atmospheres of solar system objects, including comets.
    Keywords: ASTRONOMY
    Type: Space Telescope Science Inst. The Space Telescope Obs.; p 76-105
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  • 4
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    High-luminosity single carbon stars in stellar and galactic evolution (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: In the solar neighborhood, approximately half of all intermediate mass main sequence stars with initially between 1 solar mass and about 5 solar masses become carbon stars with luminosities near 10,000 lunar luminosities for typically less than 1 million years. These high luminosity carbon stars lose mass at rates nearly always in excess of 10 to the -7th solar mass/yr and sometimes in excess of 0.00001 solar mass/yr. Locally, close to half of the mass returned into the interstellar medium by intermediate mass stars before they become white dwarfs is during the carbon star phase. A much greater fraction of lower metallicity stars become carbon-rich before they evolve into planetary nebulae, than do higher-metallicity stars; therefore, carbon stars are much more important in the outer than in the inner Galaxy.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics Review (ISSN 0935-4956); 2; 227-247
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  • 5
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    The absence of circumstellar dust debris around G giants (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The IRAS data base has been searched for evidence for circumstellar dust around luminosity class III G giants, stars whose progenitors are mostly main-sequence A stars. While 20 percent of all main-sequence A dwarfs have dust which absorbs at least 5 x 10 to the -6th of the light from the star, less than 3 percent of all G giants have such clouds. One possible explanation for the absence of detectable dust debris around the G giants is that the Poynting-Robertson effect leads to the decay of the dust around the main-sequence A stars, and that the supply of these grains is not renewed indefinitely. In this case, the derived upper limit to the grain radius of about 0.2 cm for the bulk of the grains emitting the far-infrared emission is consistent with data derived from ground-based submillimeter observations. Another possible explanation for the lack of grains around at least some G giants is that the dust around the original A dwarf is mainly composed of relatively volatile material like water ice which thermally evaporates in a relatively short time during the giant phase of higher luminosity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 365; 317-320
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  • 6
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    Cool interstellar matter in early-type galaxies (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: IRAS fluxes of early-type galaxies have been examined. From studying a magnitude-limited sample, it seems that although the statistics are poor, perhaps a third of these objects and possibly even more have an appreciable amount of dust. In general, the infrared emission is strongest at 100 microns, and quite often the far-infrared luminosity of an early-type galaxy can be well in excess of 10 to the 8th solar luminosities. The data are most easily understood if the infrared results from dust reprocessing of starlight. Within 3 kpc of the center of an early-type galaxy, there may be more cold matter than hot gas; recent models that the interstellar media of these objects are composed primarily of hot gas appear to be oversimplifications. The X-ray data do indicate that the thermal pressure in the early-type galaxies often is sufficiently high that in view of the expected low temperatures of their interstellar clouds, it can be speculated that the cold material that is present may be forming low-mass stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 306; 483-489
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  • 7
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    RV Tauri stars as post-asymptotic giant branch objects (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: RV Tau stars are rare, luminous pulsators of spectral types F, G, and K. Analysis of the IRAS data shows that the mass-loss rates from RV Tau stars have apparently significantly decreased during the past 500 yr. It seems likely that these stars have just evolved from the phase of rapid mass loss, characteristic of the last stages of the asymptotic giant branch (AGB). The birthrate of RV Tau stars in the solar neighborhood is about a tenth of the birthrate of all planetary nebulae, and this is consistent with the view that we are witnessing the subset of stars undergoing post-AGB evolution that are low mass and at least in some cases of low metallicity.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 309; 732-736
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  • 8
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    Mass loss from carbon stars (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The present consideration of the circumstellar envelopes around carbon stars on the basis of IRAS data indicates that the grains are composed of amorphous carbon rather than graphite, with an extrapolated outflowing material opacity that is large enough for the radiation pressure on the grains to drive the matter to infinity. At least 10 percent of the carbon stars have a mass loss rate that has changed by a factor of 2 during the past 1000 years. The stars that are losing large amounts of mass are generally long period variables. All these results are consistent with a two-step process of mass loss from most of the stars with substantial mass-outflow rates.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 303; 327-332
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  • 9
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    Supernova nucleosynthesis in low-metallicity populations (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The mass loss rate in low-metallicity stars is discussed, and the consequences of that rate for the fate of such stars are considered. It is shown that, if radiation pressure on dust is important in driving the mass loss from red giants, and if these stars do not dredge up large amounts of processed material during their evolution, then the total amount of mass lost by Population II stars with low metallicity is small. Consequently, the rate of supernovae in populations of low metallicity is much higher than in populations of solar abundances. This conclusion leads to the prediction that the supernova rate should be high in galaxies that have some intermediate mass stars and have metallicity less than about 0.1 of the solar value.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 301; 624-628
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  • 10
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    Carbon star radial velocities and dark matter in the universe (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Optical radial velocities of carbon stars in the Milky Way are compared to center-of-mass velocities derived from CO radio emission produced in their circumstellar envelopes. It seems that there is an intrinsic velocity dispersion in the optically measured radial velocities. If the carbon stars in the dwarf spheroidals behave in a fashion similar to those in the Milky Way, then the use of their optical radial velocities to infer the mass-to-light ratio of dwarf spheroidal galaxies and the nature of the dark matter in the universe is suspect. Measurement of the radial velocities of K giants may possibly avoid these uncertainties associated with atmospheric motions.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 91; 539
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