2003AJ....125.2163C

Spectroscopy and concurrent optical photometry of the low-mass X-ray binary 2A 1822-371 (V691 CrA) are analyzed. Knowledge of the orbit, based on previously derived parameters for the pulsar, allows us to use our resolved double He I absorption velocities to further constrain the mass of the donor star at ∼0.40-0.43 M_☉. This star must be somewhat evolved, since a main-sequence star of this mass would not fill its Roche lobe. The accretion flow within the system is found to be very stratified, with higher ionization lines showing the greatest velocities. The negative systemic velocity suggests the system may belong to the halo population.