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Paper: Spectroscopic Orbital Elements for Helium Rich Subdwarf Binary PG1544+488
Volume: 481, 6th Meeting on Hot Subdwarf Stars and Related Objects
Page: 273
Authors: Şener, H.; Jeffery, C.
Abstract: Our research aims to explore a number of binary systems containing at least one unusual hot subdwarf. Such systems demonstrate some of the most extreme outcomes of common-envelope ejection in a close binary. We aim to measure precise orbital parameters and stellar dimensions in an effort to identify the progenitors of these systems. PG1544+488 is a short-period spectroscopic binary containing two subdwarf B stars (Ahmad et al. 2004); it is exceptional because the surfaces of both components are extremely helium-rich. We present a new analysis of spectroscopy of PG1544+488 obtained with the William Herschel Telescope. We refine the orbital parameters, including the period (P=0.502±0.001 d) and mass ratio (q=1.05±0.004), and the atmospheric parameters of each component. Ahmad et al. (2004) argue that PG1544+488 must have been formed as a result of close-binary evolution followed by the ejection of a common-envelope. Since precise tuning is necessary to yield two helium cores of similar masses at the same epoch (Justham et al. 2011), the mass ratio places a very tight constraint on the progenitor system.
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