Astronomy and Astrophysics – Astronomy
Scientific paper
May 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996mnras.280..627m&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Vol. Vol. 280, No. 2, p. 627 - 637
Astronomy and Astrophysics
Astronomy
38
Surveys -- Stars: Activity -- Binaries: Close -- Stars: Coronae -- X-Rays: Stars, W Uma Stars: X-Ray Spectra, W Uma Stars: Stellar Activity
Scientific paper
A spectral survey of X-ray-bright W UMa-type contact binary systems has been undertaken with the ROSAT Position Sensitive Proportional Counter (PSPC). For the longer observations, timing studies are also possible. ROSAT PSPC observations were obtained on seven W UMa systems: VW Cep, XY Leo, BV/BW Dra, SW Lac, W UMa, V839 Oph and AK Her. Data for an eighth target, 44i Boo, were retrieved from the archive. In addition, the authors have used the ROSAT High Resolution Imager (HRI) to resolve the common proper motion pair BV/BW Dra (separation ≍ 16 arcsec). Two-temperature models, for an optically thin plasma, adequately describe the PSPC spectra, with the cooler component at Tcool ≍ 2.3×106K and the hotter component at Thot ≍ 1.0×107K. The total luminosities, in the ROSAT band (0.1-2.4 keV), range from 4.4×1029 to 3.3×1030erg s-1. The results are compared with published PSPC spectral surveys of two other classes of active binary, namely RS CVn and BY Dra systems. In general, the PSPC light-curves were constant to within ≡20% over the course of each observation. VW Cep was observed in both quiescent and active states. During a flare-like event the X-ray flux increased by a factor of two. The temperature of the hotter component rose by a factor of ≍1.5, whilst the volume emission measure increased five-fold.
Hodgkin Simon T.
McGale P. A.
Pye John P.
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