The spectroscopic orbit of HD 128220.

Abstract

HD 128220 is a double-lined binary containing a subdwarf O star. A new orbital solution is presented, based principally on IUE spectroscopy. The implications of the solution for the physical parameters of the subdwarf are discussed, with the results that M_Osin³i = 1.6±0.7 M_sun;; R_Osin^3/2i = 1.2±0.4 R_sun;; and log(L_Osin³i/L_sun;) = 3.6±0.3.