The Algol-like Binary TT Hydrae: The Stars, Circumstellar Matter, and Superionized Plasma

Abstract

The characteristics of the eclipsing binary system TT Hydrae are now determined with a reliability surpassing many other Algol-like binaries. The primary component is a B9.5 V main-sequence star with a mass of 2.25 m_sun;, radius 1.9 R_sun;, effective temperature 9800K, and surface gravity log g = 4.23. The secondary star has a mass of 0.41 m_sun; and fills its critical Roche lobe. The conclusion that this is a normal semidetached system is supported by evidence of mass interaction. TT Hydrae is at a distance of about 193 pc and is virtually unreddened. Circumstellar matter shows its presence in deep, sharp absorption lines of Fe II and other singly ionized metals, observed in wide segments of the ultraviolet spectrum. That these lines originate in a circumstellar shell is demonstrated by their reversal into emission during the total eclipse of the primary component.