The distance to eight X-ray sources derived from HIPPARCOS observations

Abstract

The parallaxes of eight galactic X-ray sources measured by Hipparcos are consistent with zero in all but two cases, 4U1145-619 (= Cen X-5) and HZ43. The parallax and proper motion measured for each of the others, including the Be/neutron star binaries X Per and A0535+26 and the massive X-ray binaries 4U0900-40, 4U1700-37, and Cyg XR-1, are consistent with their spectroscopic parallaxes. These results provide no evidence that visible stars in X-ray binaries have a luminosity that is abnormal for their spectral type.