High-dispersion spectroscopic observations of HD 77581, a candidate for Vela XR-1 (2U 0900-40).

Using high-dispersion spectra obtained at the Mauna Kea and Cerro Tololo Observatories radial velocity curves have been derived for the 8.95-day binary HD 77581. Consistent orbital elements cannot be derived, and several possible solutions are suggested. The range of possible mass functions is from 0.010 to 0.082. Combining these with a reasonable range of masses for the B0.5 Ib primary of yields a range of masses for the X-ray source from 1.07 to 4.6 . Subject headings: binaries - black holes - neutron stars - stars, individual - X-ray sources