The orbital and physical properties of five southern Be+sdO binary systems

Abstract

Close binary interactions may play a critical role in the formation of the rapidly rotating Be stars. Mass transfer can result in a mass gainer star spun up by the accretion of mass and angular momentum, while the mass donor is stripped of its envelope to form a hot and faint helium star. FUV spectroscopy has led to the detection of about 20 such binary Be+sdO systems. Here we report on a three-year program of high quality spectroscopy designed to determine the orbital periods and physical properties of five Be binary systems. These binaries are long orbital period systems with $P=$ 95 to 237 days and with small semi-amplitude $K_1<11$ km s${}^{-1}$. We combined the Be star velocities with prior sdO measurements to obtain mass ratios. A Doppler tomography algorithm shows the presence of the He II $\lambda 4686$ line in the faint spectrum of the hot companion in four of the targets. We discuss the observed line variability and show evidence of phased-locked variations in the emission profiles of HD 157832, suggesting a possible disk spiral density wave due to the presence of the companion star. The stripped companions in HD 113120 and HD 137387 may have a mass larger than the 1.4 $M_{\odot }$ indicating that they could be progenitors of Type Ib and Ic supernovae.

50 pages, 23 figures, 16 tables

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• A search for Be stars in multiple systems within the solar neighborhood