Rubin-152 - A massive star on the Galactic fringe

Rubin-152 is spectroscopically identical with a type O4-5 main-sequence star, and the standard luminosity calibration places it at the unexpected distance of 50 kpc from the Galactic center. Although its radial velocity is inconsistent with a circular orbit, a highly eccentric one cannot be excluded. On the other hand, the data reported here are also consistent with the hypothesis that R-152 is in an advanced stage of evolution, and that it is a nearby, low-mass, low-luminosity object which by perverse coincidence exhibits the effective temperature and surface gravity of a very massive star.