Constraints on the Radial Velocity Curve of HDE 245770 = A0535+26

Abstract

We present new radial velocity measurements from IUE high-dispersion spectra of HDE 245770, the Be companion of the X-ray transient binary system, A0535+26. We formally derive the semiamplitude of the star's binary motion by fitting the UV and published radial velocity measurements with the other orbital parameters fixed according to the neutron star orbit from CGRO/BATSE results. The observational errors are still too large to claim detection of the Be star orbital motion, but we use limits on the semiamplitude (K_1<10.6 km s^-1), a classification based on UV criteria (O9.5 III-Ve), and the derived projected rotational velocity (Vsini=250+/-15 km s^-1) to reassess the system masses.