Contact Binary Variables as X-ray Sources

We present cross-identification of archived X-ray point sources with W UMa variable stars found in the All-Sky Automated Survey (ASAS). In a surveyed sky area of 300 square degrees of ASAS, 36 W UMa stars have been found associated with X-ray emission. We compute the distances of these W UMa systems and hence their X-ray luminosities. Our data support the "supersaturation" phenomenon seen in these fast rotators, namely that the faster a W UMa star rotates, the weaker its X-ray luminosity.Comment: 10 pages, 2 figures, 1 table; submitted to A

The Effective Temperatures of Hot Stars II. The Early-O Types

We derive the stellar parameters of a sample of Galactic early-O type stars by analysing their UV and Far-UV spectra from FUSE (905-1187A), IUE, HST-STIS and ORFEUS (1200-2000A). The data have been modeled with spherical, hydrodynamic, line-blanketed, non-LTE synthetic spectra computed with the WM-basic code. We obtain effective temperatures ranging from Teff = 41,000 K to 39,000 K for the O3-O4 dwarf stars, and Teff = 37,500 K for the only supergiant of the sample (O4 If+). Our values are lower than those from previous empirical calibrations for early-O types by up to 20%. The derived luminosities of the dwarf stars are also lower by 6 to 12%; however, the luminosity of the supergiant is in agreement with previous calibrations within the error bars. Our results extend the trend found for later-O types in a previous work by Bianchi & Garcia.Comment: Accepted for publication in The Astrophysical Journal. 38 pages (including 9 figures and 4 tables