Astronomy and Astrophysics – Astronomy
Scientific paper
May 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.2709r&link_type=abstract
American Astronomical Society, 180th AAS Meeting, #27.09; Bulletin of the American Astronomical Society, Vol. 24, p.770
Astronomy and Astrophysics
Astronomy
2
Scientific paper
The Algols can be separated into two roughly distinct groups: the long-period Algols with orbital periods {P >} 5 -- 6 days, and the short-period Algols with {P <} 5 days (Peters 1980). In the long-period systems, the gas stream circles the mass gainer to form a well-defined classical accretion disk, but in the short-period group the gas stream makes a direct impact with the star and an asymmetric transient accretion disk results. In the direct-impact systems, the gas stream has a velocity of about 500 {\kmps} at impact which is much greater than the rotational velocity of the mass gainer ({vrot < 150} {\kmps}). A turbulent shock forms in the atmosphere or envelope of the primary, and the circumstellar material consists of the shock region and the regions on or around the mass gainer which result from the dissipation of the shock. The expected properties of the shock, e.g., its temperature, size, location (depth) relative to the photosphere of the primary, and the mass of the gas which eventually forms a ring or disk around the star, were calculated using the analysis described in Olson (1980; ApJ, 241, 257) and Ulrich and Burger (1976; ApJ, 206, 509). Several short-period Algols were chosen for this study including U Cep, RW Tau, and β Per. We found that the depth of the shock region was very sensitive to the rate of mass transfer from the Roche lobe-filling secondary. In the case of the active binary U Cep, the shock formed at a depth of ({10(-4) - 10(-3) }) R_{*} below the photosphere for the expected mass transfer rates of ({10(-6) - 10(-4) }) M_dot yr(-1). For RW Tau, the mass transfer rate is {10(-9) } M_dot yr(-1) and again the shock is expected to form below the photosphere at a depth of {10(-5) } R_{*}. However, for lower rates like ({10(-11) - 10(-10) }) M_dot yr(-1) which are appropriate for β Per, the shock forms at or just above the photosphere of the mass gainer. These predicted properties of the shock regions are consistent with the observed characteristics of the circumstellar material in these systems. This work was partially supported by NSF grants AST 89-01238 and AST 91-114214.
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