The H-alpha Emission Line Variations of HR 6819
  The star system HR 6819 was recently proposed by Rivinius et al. as the site
of the nearest example of a stellar mass black hole. Their spectra show
evidence of two components: a B3 III star in a 40 d orbit and a stationary
B-emission line star. Based upon the orbital mass function and the lack of
evidence of a spectral component with reflex orbital motion, Rivinius et al.
suggested that HR 6819 is a triple system consisting of an inner B3 III star
plus black hole binary orbited by a distant Be star. Here we present an
alternative model based upon an examination of the H-alpha emission line in
their spectra. We show that the emission line displays the small reflex motion
expected for the companion in the inner orbit and shows variations in profile
shape related to orbital phase. This indicates that HR 6819 is a binary system
consisting of a massive Be star and a low mass companion that is the stripped
down remnant of a former mass donor star in a mass transfer binary.
