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  • 1
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    Survey incompleteness and the evolution of the QSO luminosity function (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: We concentrate on a type of QSO survey which depends on selecting QSO candidates based on combinations of colors. Since QSO's have emission lines and power-law continua, they are expected to yield broadband colors unlike those of stellar photospheres. Previously, the fraction of QSO's expected to be hiding (unselected) within the locus of stellar (U-J, J-F) colors was estimated at about 15 percent. We have now verified that the KK88 survey is at least 11 percent incomplete, but have determined that it may be as much as 34 percent incomplete. The 'missing' QSO's are expected to be predominantly at z less than or = 2.2. We have studied the proper motion and variability properties of all stellar objects with J less than or = 22.5 or F less than or = 21.5 in the SA 57 field which has previously been surveyed with a multicolor QSO search by KK88.
    Keywords: ASTROPHYSICS
    Type: NASA. Ames Research Center, The Evolution of Galaxies and Their Environment; p 7-8
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  • 2
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    Cometary activity in 2060 Chiron (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Results of a 2-yr (1988-90) investigation of cometary activity in 2060 Chiron based on CCD photometry and spectroscopy are reported. The photometry observations include a new rotational light curve of Chiron, a newly refined rotation period, recent developments of its long-term photometric behavior and surface brightness profiles, a deep image of the coma of Chiron, and narrowband images at wavelengths ranging from 3200 to 6840 A. The spectroscopic data include moderate resolution CCD spectra (10-20 A FWHM). Major results include the detection of impulsive brightening on a time scale of hours, evidence for a secular change in the blue portion of the reflectivity spectrum of the nucleus, no evidence for Rayleigh scattering in the near ultraviolet, and an upper limit of the column density of CO(+) ions in the coma.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 100; 913-932
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  • 3
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    Multicolor photometry of field galaxies to B = 24 (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The redshifts and colors of nearly 10,000 galaxies at galactic latitudes SA57 and SA68 were determined by photometric scans which included UV and near-IR bands, covering 0.5 sq deg of sky. Slopes were calculated for UV, IR, red and blue counts of galaxies with respect to the brightness detected. It was found that galaxies of magnitudes over 20 show increasingly greater UV excess, which may be indicative of star formation regions. Future applications of the data generated for examining galaxy clustering patterns and evolutionary scenarios are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 311; 651-679
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  • 4
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    Numerical studies of collapsing interstellar clouds (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Numerical simulation of the structure and evolution of interstellar clouds was conducted. Steps were taken toward an integrated treatment of the dynamical, thermal, and chemical processes entering model calculations, and a detailed study was made of radiative transfer in molecular lines to allow model predictions to be tested against empirical data. It is shown that the shapes of molecular lines are sensitive to details of the cloud structure and evolutionary state and are thus useful in inferring the cloud density, temperature, chemical composition, age, and initial conditions. The calculations have successfully reproduced and explained several observed cloud properties, including abundances of complex molecular species and the apparent depletion of CO in dense cores.
    Keywords: ASTROPHYSICS
    Type: NASA-CR-180933 , NAS 1.26:180933
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  • 5
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    Wolf-Rayet stars (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The properties and evolutionary status of WR stars are examined, reviewing the results of recent observational and theoretical investigations. Topics discussed include spectral types and line strengths, magnitudes and colors, intrinsic variability, IR and radio observations, X-ray observations, the Galactic distribution of WR stars, WR stars in other galaxies, and WR binaries. Consideration is given to the inferred masses, composition, and stellar winds of WR stars; model atmospheres; WR stars and the Galactic environment; and WR stars as a phase of stellar evolution. Diagrams, graphs, and tables of numerical data are provided.
    Keywords: ASTROPHYSICS
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  • 6
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    Photospheres of hot stars. III - Luminosity effects at spectral type 09.5 (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Hydrogen and helium line profiles with high signal-to-noise ratios were obtained for four stars of spectral type 09.5 (Alpha Cam, Xi Ori A, Delta Ori A,AE Aur) that form a sequence in luminosity: Ia, Ib, II, V. The basic stellar parameters of these stars are determined by fitting the observed line profiles of weak photospheric absorption lines with profiles from models which include the effect of radiation scattered back onto the photosphere from their stellar winds, an effect referred to as wind blanketing. For these stars, the inclusion of wind blanketing is significant only for the most luminous star, Alpha Cam, for which the effective temperature was shifted about -2000 K relative to an unblanketed model.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 340; 1073-109
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  • 7
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    Thermal instabilities in diffuse molecular clouds - Formation of molecular cloud cores (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-08-13
    Description: The stability of diffuse clouds to thermal instabilities is examined using the semiempirical cooling function derived by Tarafdar et al. (1985) for these clouds. It is found that diffuse clouds which obey such a cooling function are susceptible to thermal instability at densities n of less than about 70-80/cu cm. The growth rate for instability is large and the mass contained in unstable regions ranges from about 0.001 to 1 solar mass. It is suggested that such instabilities may trigger formation of molecular cloud cores of the type found in low-mass molecular clouds (e.g., TMC-2). Criteria for thermal instability in self-gravitating systems are also derived.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Letters (ISSN 0004-6388); 25; 4 19; 235-245
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  • 8
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    Submillimeter constraints on dust near Lindroos' post T Tauri stars (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: Young stars from the dynamical sample identified by Lindroos (A&A, 156,223 (1986)) have been observed at 800 micrometers wavelength using the James Clerk Maxwell Telescope on Mauna Kea. The new data are used to constrain the mass of circumstellar dust around these stars. The Lindroos sample is dominated by low-mass stars of age (3-150) x 10(exp 6) yr, intermediate in age between the T Tauri and main-sequence stars. When combined with previous measurements, the present observations are compatible with the depletion of circumstellar dust on a time scale tau approximately 10(exp 7.0) yr. If this dust is present in circumstellar disks, then tau represents the lifetime of these disks.
    Keywords: ASTROPHYSICS
    Type: The Astronomical Journal (ISSN 0004-6256); 108; 2; p. 661-665
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  • 9
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    The solar system beyond Neptune (1995)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We present the results of a deep optical survey for distant solar system objects. An area of 1.2 sq deg of the ecliptic has been imaged to apparent red magnitude 25, resulting in the detection of seven trans-Neptunian objects. These are the first detected members of a trans-Neptunian disk that compries about 35 000 objects larger than 100 km in the 30-50 AU heliocentric distance range. We interpret the new measurements using a set of Monte Carlo models in which the effects of observational bias in the data are taken into account.
    Keywords: ASTROPHYSICS
    Type: The Astronomical Journal (ISSN 0004-6256); 109; 4; p. 1867-1876
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  • 10
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    The ensemble variability properties of faint QSOs (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A refined sample of 64 variable objects with stellar image structure has been identified in SA 57 to B approximately = 22.5, over a time baseline of 15 yr, sampled at 11 distinct epochs. The photometric data typically have a root-mean-square (rms) error at B = 22 of only 0.05 mag. Thirty-five quasars in this field have already been spectroscopically confirmed, 34 of which are among the sample of variables. Of the other variables, six are known spectroscopically to be stars, 10 additional objects are stars based on reliable detection of proper motion, and one is spectroscopically a narrow emission line galaxy. Of the 13 remaining variables, it is argued that they are a mixture of distant halo subdwarfs and quasars with starlike colors. We compute the ensemble average structure function and autocorrelation function from the light curves in the respective quasar rest frames, which are used to investigate the general dependences on apparent magnitude, absolute magnitude, and redshift.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 433; 2; p. 494-509
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