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  • 1
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    Photometric light curves for seven rapidly-rotating K dwarfs in the Pleiades and Alpha Persei clusters (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Light curves and period estimates were obtained for several Pleiades and Alpha Persei cluster K dwarfs which were identified as rapid rotators in earlier spectroscopic studies. A few of the stars have previously-published light curves, making it possible to study the long-term variability of the light-curve shapes. The general cause of the photometric variability observed for these stars is an asymmetric distribution of photospheric inhomogeneities (starspots). The presence of these inhomogeneities combined with the rotation of the star lead to the light curves observed. The photometric periods derived are thus identified with the rotation period of the star, making it possible to estimate equatorial rotational velocities for these K dwarfs. These data are of particular importance because the clusters are sufficiently young that stars of this mass should have just arrived on the main sequence. These data could be used to estimate the temperatures and sizes of the spot groups necessary to produce the observed light curves for these stars.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 99; 471-481
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  • 2
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    Are the virial masses of clusters smaller than we think? (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The constraints that the available X-ray spectral and imaging data place on the mass distribution and mass to light ratio of rich clusters are considered. It was found for the best determined cases that the mass to light ratio is less than 125 h sub 50 at radii exceeding 1 h sub 50 Mpc. The mass to light ratio is approximately constant at radii exceeding 1 h sub 50 Mpc but may rise to values of roughly 200 h sub 50 in the central regions. The fraction of the total mass that is in baryons, primarily the hot X-ray emitting gas, is roughly 30 percent thus setting the mass to light ratio of the dark material to roughly 70. The model that fits the X-ray data for Coma is in good agreement with the observed optical velocity dispersion vs. radius data.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 317; 593-600
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  • 3
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    Physical processes and infrared emission from the Cassiopeia A supernova remnant (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: IRAS 12-100 micron data on the Cas A remnant are presented, and various physical mechanisms and astrophysical sites that may contribute to the observed infrared emission are analyzed. The contributions of various sources of infrared emission to the IRAS fluxes are found to be small. The residual infrared emission is attributed to thermal emission from dust which is swept up by the expanding supernova blast wave and collisionally heated by the postshock X-ray emitting gas. The calculations are consistent with a shock velocity of 1800 km/s and a preshock gas density of about 2/cu cm. The mass of the swept-up gas is about 0.6 solar mass. An excess of 12 micron thermal emission in the spectrum of Cas A suggests the presence of very small particles in the preshocked gas.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 315; 571-579
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  • 4
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    Ground-based infrared observations of comet Halley (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Ground-based 2-23 micron photometry and 10.3 micron imaging of comet Halley taken within hours of the Giotto spacecraft encounter are presented. The photometry shows a color temperature of 360 K and silicate emission features at 10 and 20 microns, and the image shows jet activity similar to that observed by Giotto, but on a scale of thousands of km. The expected 10 micron surface brightness, based on the particle mass distribution measured by Giotto and assuming solid, spherical grains, is a factor of six lower than the observed value. It is suggested that fluffy particles could remove this discrepancy.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); 326; 55-57
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  • 5
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    Gamma-ray burster counterparts - Infrared (1987)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The discovery of an IR counterpart to a gamma-ray burster (GRB) would be a big step forward in understanding this enigmatic phenomenon. A program of searching for IR emission from the smallest GRB source regions has been initiated. Seven boxes have been searched with ground-based telescopes at a wavelength of 2.2 microns and 23 with the IRAS data base at wavelengths of 12, 25, 60, and 100 microns. No convincing candidates were identified. The most constraining result are for two error boxes where the K-band magnitude are found to be fainter than 19.03. This observation is compared with the flux predicted from either a companion star or an accretion disk. The new IR observations pose serious difficulties for several GRB models.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 313; 226-230
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  • 6
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    SPAN: Astronomy and astrophysics (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The Space Physics Analysis Network (SPAN) is a multi-mission, correlative data comparison network which links science research and data analysis computers in the U.S., Canada, and Europe. The purpose of this document is to provide Astronomy and Astrophysics scientists, currently reachable on SPAN, with basic information and contacts for access to correlative data bases, star catalogs, and other astrophysic facilities accessible over SPAN.
    Keywords: ASTROPHYSICS
    Type: NASA-TM-107940 , NAS 1.15:107940 , NSSDC/WDC-A-R/S-87-06
    Format: application/pdf
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  • 7
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    A search for gravitational lenses - Search strategies and a preliminary upper limit on the density of lenses (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Keywords: ASTROPHYSICS
    Type: Texas Symposium on Relativistic Astrophysics; Dec 14, 1986 - Dec 19, 1986; Chicago, IL; United States
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  • 8
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    A VLA gravitational lens survey (1987)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: A VLA survey designed to detect gravitational lensing on sub-arc second and arc second scales is described, and preliminary results of radio data are presented. In particular, it is found that the density of matter in the form of a uniform comoving number density of 10 to the 11th - 10 to the 12th solar mass compact objects, luminous or dark, must be substantially less than the critical density. Data obtained for the radio source 1042+178 are briefly examined.
    Keywords: ASTROPHYSICS
    Type: Observational cosmology; Aug 25, 1986 - Aug 30, 1986; Beijing; China
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  • 9
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    Constraints for models of Be stars derived from UV and IRAS observations (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The effect of different geometrical models (disk and circumstellar shell) on the mass loss determinations of Be stars is investigated. The characteristics of the disk and circumstellar shell models are described. The models are applied to the analysis of the column density derived from the UV lines and emission measurements derived from IRAS observations of 10 Be stars, and the mass loss rate for these stars are calculated. It is observed that the mass loss rates obtained from the circumstellar shell model are a factor of 0.01 smaller than those of the disk model; the mass of the IR emitting region is three times larger in the shell model than that in the disk model; and the radial outflow velocity of the IR emitting region for the shell model is of the order of 0.01 km/sec and for the disk model of the order of 10 km/sec. It is noted that the UV and IRAS observations can be analyzed using the two models if the proper geometry is considered.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 182; 1 Au; 80-90
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  • 10
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    Long-period dynamic spectrograms of low-frequency interplanetary radio emissions (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Dynamic spectrograms of the low-frequency interplanetary radio emissions as observed by Voyagers 1 and 2 from 1983 through mid-1986 are reported. The radio emissions were observed to be most intense in the latter portion of 1983 at 3 kHz but have also been detected at 2 kHz. The emission has been present almost continuously at either 2 or 3 kHz since late 1983. The spectrograms presented herein show that the phenomenon appears almost identically as observed by the two spacecraft separated by more than 10 AU, at least at the higher frequency. One feature revealed by the dynamic spectrograms which had not been noticed previously is a gradual rise in frequency of the 3-kHz component following the onset of the late 1983 event. These new observations reinforce the conclusion that the low-frequency emissions are freely propagating radio waves, but the two-component spectral structure implies that the previous model of emission at twice the plasma frequency at the inner heliosphere shock is inadequate to fully account for the observations. Either an additional source region or an additional source mechanism is suggested.
    Keywords: ASTROPHYSICS
    Type: AD-A179102 , Geophysical Research Letters (ISSN 0094-8276); 14; 49-52
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