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  • ASTROPHYSICS  (8)
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  • 1
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    Simultaneous Exosat and VLA observations of the W UMa binaries, VW Cep and XY Leo - A flare on VW Cep (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Two UMa-type contact binaries, XY Leo and VW Cep, have been observed simultaneously with Exosat, the VLA, and, in the case of XY Leo, optically. The temporal coverage of each star was sufficient to monitor them throughout two orbital revolutions (P about 0.25 days), however, no orbital modulation of either the X-ray or 6-cm data was seen for either star. A large flare from VW Cep was detected, the first such simultaneous flare ever seen on a star other than the sun. Its behavior before, during, and after the flare is remarkably similar to that found in solar flares. For both stars, it is demonstrated that the 6-cm emission cannot be the result of bremsstrahlung radiation of the X-ray emitting plasma.
    Keywords: ASTROPHYSICS
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  • 2
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    A search for pre-main sequence stars in the high-latitude molecular clouds. II - A survey of the Einstein database (1990)
    In:  Other Sources
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    Publication Date: 2019-07-27
    Description: The preliminary results are reported of a survey of every EINSTEIN image which overlaps any high-latitude molecular cloud in a search for X-ray emitting pre-main sequence stars. This survey, together with complementary KPNO and IRAS data, will allow the determination of how prevalent low mass star formation is in these clouds in general and, particularly, in the translucent molecular clouds.
    Keywords: ASTROPHYSICS
    Type: Cambridge Workshop; Sept. 18-21, 1989; Seattle, WA; United States
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  • 3
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    An Einstein survey of the 1 keV soft X-ray background in the Galactic plane (1994)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: We have analyzed 56 Einstein Observatory Imaging Proportional Counter (IPC) observations within +/- 3 deg of the Galactic plane in order to determine the low-latitude soft X-ray background flux in the 0.56-1.73 keV band. Any detected X-ray point source which fell within our regions of study was removed from the image, enabling us to present maps of the background flux as a function of Galactic latitude along 18 meridians. These maps reveal considerable structure to the background in the Galactic plane on an angular scale of approximately 1 deg. Our results are compared with those of an earlier study of the 1 keV X-ray background along l = 25 deg by Kahn & Caillault. The double-peaked structure they found is not discernible in our results, possibly because of the presence of solar backscattered flux in their data. A model which takes into account contributions to the background by extragalactic and stellar sources, the distribution of both atomic and molecular absorbing material with the Galaxy, the energy dependence of the cross section for absorption of X-rays, and the energy dependence of the detector has been constructed and fitted to these new data to derive constraints on the scale height, temperature, and volume emissivity of the unaccounted-for X-ray-emitting material. The results of this model along l = 25 deg are roughly similar to those of the model of Kahn & Caillault along the same meridian.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 424; 2; p. 671-687
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  • 4
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    IUE observations of solar-type stars in the Pleiades and the Hyades (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: An extensive set of IUE observations of solar-type stars (spectral types F5-G5) in the Pleiades is presented. Spectra were obtained in January and August 1988 for both the transition region and chromospheric emission wavelength regions, respectively. Mg II fluxes were detected for two out of three Pleiades stars and C IV upper limits for two of these stars. Long-wavelength high-resolution spectra were also obtained for previously unobserved solar-type stars in the Hyades. With the inclusion of spectra of additional Hyades stars obtained from the IUE archives, surface fluxes and fractional luminosities for both clusters' solar-type stars are calculated; these values provide a better estimate for the Mg II saturation line for single stars.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 383; 594-601
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  • 5
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    Detection of a dozen X-ray-emitting main-sequence B6-A3 stars in Orion (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: The detection of 12 X-ray-emitting main-sequence B6-A3 stars in the Orion Nebula is reported. The luminosity of these stars in the 0.2-3.5 keV band is considerably in excess of field stars of the same spectral type. Consideration is given to the possibilities that these stars may not actually be the source of the X-rays, but that the emission may be attributable to T Tauri or 'naked' T Tauri star companions, or that these hot stars are indeed the sources of emission and that current theories of X-ray emission from early-type stars must be amended.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 338; L57-L60
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  • 6
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    Radio light curves of V471 Tauri (1993)
    In:  Other Sources
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    Publication Date: 2019-08-27
    Description: We have acquired light curves at a wavelength of 6 cm of the eclipsing binary V471 Tauri around the orbit, in order to determine the geometrical location of the radio emission in the binary. Each light curve shows a broad minimum near the time of optical eclipse, suggesting that the radio luminosity originates between the two stars. Other observations at X-ray, UV, and visual wavelengths are also supportive of the idea of a gas cloud more or less permanently located between the stars. This could be explained if the radio emission arises from the interaction of the magnetic fields of the secondary and the white dwarf near the line of centers.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 105; 690; p. 848-852.
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  • 7
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    A VLA survey of BY Draconis variables (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Observations of seven rapidly rotating BY Dra variables, obtained at 6 cm with the D-to-A hybrid array of the VLA on three consecutive days in February, 1986, are reported. The results are presented in tables and graphs (along with data from simple VLA detection observations in 1985 and published optical and X-ray data) and characterized in detail. No strong correlation is found between the radio and optical emission in the one star (BY Dra) detected at more than one session, and the observable microwave emission of the stars is tentatively attributed to flares alone. A weak correlation between the X-ray luminosity and the maximum 6-cm luminosity of dMe stars is inferred, but the evidence is considered insufficient to establish a relationship between surface signs of magnetic activity and nonthermal radio emission.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 95; 887-893
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  • 8
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    Simultaneous Exosat and VLA observations of the contact binaries VW Cephei and XY Leonis - Quiescent emission and a flare on VW Cephei (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Two W UMa-type contact binaries, XY Leo and VW Cep, were observed simultaneously with Exosat, the VLA, and, in the case of XY Leo, optically. The temporal coverage of each star was sufficient to monitor them throughout two orbital revolutions (P about 0.27 days); however, no orbital modulation of either the X-ray or 6 cm data was seen for either star, indicating large emitting regions. A large flare from VW Cep was detected, the best such simultaneous flare data ever obtained from a star other than the sun. Its behavior before, during, and after the flare was remarkably similar to that found in solar flares, although at 6 cm this flare on VW Cep was about 10,000 times more luminous than typical strong solar flares. For both stars, it is demonstrated that the 6 cm emission cannot be the result of bremsstrahlung radiation of the X-ray emitting plasma; in fact, it is shown, in the case of the VW Cep flare, that the 6 cm emission is consistent with gyrosynchrotron radiation from a source region of order of the system separation.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 330; 922-927
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