Hα Spectroscopy of RW Monocerotis

Abstract

Five years of sparse full-orbit Hα spectroscopy are presented for the short-period Algol RW Monocerotis. A spectroscopic mass ratio is derived that confirms the published photometric mass ratio. Of the two published rotation rates of the primary star, 66 and 260 km s-1, the slower best fits our observations. Hα emission was not seen during any of five eclipses, indicating that the secondary is notstrongly chromospherically active. At every epoch an emission feature between the two stars was found, confirming that there is continuous mass transfer. However, an accompanying accretion disk was seen in only two of six observing runs, using out-of-eclipse spectroscopy. Comparing with models, we show how a single out-of-eclipse Hα observation can provide information on the mass transfer presence at that epoch. Finally, we see redshifted absorption just before and after primary eclipse, consistent with the location and velocity of a mass transfer stream. However, the Hα absorption equivalent width (with respect to the out-of-eclipse continuum) falls proportionally with the primary's visibility between first and second contact. This indicates that the stream is projected against the entire face of the primary, a much larger area than predicted by theory.