CONSEQUENCES OF THE STAR-STREAM INTERACTION IN ALGOL

We have studied the H-alpha line profile of Algol to determine the nature of the interaction between the gas stream and the primary, and have found evidence of an asymmetric transient accretion disk with an average radius of (1.8 +/- 0.2)R(A), an electron density N(e) greater-than-or-similar-to 10(10) cm-3, and mass greater-than-or-similar-to 10(-12) M .. The trailing side of the disk is wider and denser than the leading side. Algol is the first partially eclipsing short-period Algol-type system in which a transient disk has been found. The emission produced by the disk is weak relative to the continuum of the triple system, so the disk emission was enhanced by subtracting the composite theoretical photospheric absorption-line profile of the three stars from the observed line profile. Our theoretical calculations of the depth of the shock region produced when the gas stream strikes the primary indicate that the shock occurs above the photosphere of the star. This result is based on the best estimates of the rate of mass loss from the secondary which range from 10(-11) to 10(-10) M. yr-1 for Algol. The predicted location of the shock is in agreement with results of a previous paper in which a localized region was found just above the photosphere of the primary. The analyses of H-alpha and ultraviolet resonance lines have shown that the circumstellar material in Algol consists of four components in addition to the gas stream. There is a localized high-density H-alpha-region, a high-temperature region, and a high-rotational-velocity region, which are all part of a low-density transient H II accretion disk. We feel that these transient phenomena are all consequences of the impact of the gas stream on the primary star; known as the star-stream interaction.