Two New Galactic Supersoft X-Ray Binaries: V Sagittae and T Pyxidis

Joseph Patterson, Jonathan Kemp, Anouk Shambrook, John Thorstensen, David Skillman, Jerry Gunn, Lasse Jensen, Tonny Vanmunster, Sergei Shugarov, Janet Mattei, Tariq Shahbaz, and Rudolf Novák

Publications of the Astronomical Society of the Pacific

April 1998, Volume 110, Page 380

We discuss the nature of V Sagittae and T Pyxidis, two enigmatic blue variable stars commonly classed among the cataclysmic variables. These stars have bolometric luminosities in the range (1-50) × 10³⁶ erg/s, far in excess of that realized in any accretion-powered CV. The stars also show extremely blue colors (B-V = -0.3, U-B = -1.3 after dereddening) and orbital light curves which are quite similar yet not seen in any normal CV. But in all these respects, as well as in the rich and highly excited emission-line spectrum, the stars provide a good match for the newly discovered class of "supersoft" X-ray binaries, probably powered by quasi-steady nuclear burning of accreted gas on a white dwarf. Both stars show photometric waves at the orbital period. V Sge also shows a deep minimum, a true eclipse of the accretion disk arising from fairly high binary inclination. T Pyx is nearly face-on (probably i ~ 10 - 20 °), resulting in narrow lines and a low amplitude for the orbital signal. T Pyx shows a very stable photometric wave at P = 0.076227 d, but interpretation of this is hampered by another transient signal at 0.1098 d. This might be construed as evidence for a magnetic white dwarf.

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Copyright © 1998 Astronomical Society of the Pacific.