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The X-Ray Binary X2127+119 in M15: Evidence for a Very-Low-Mass, Stripped-Giant Companion

L. van Zyl·P. A. Charles·S. Arribas·T. Naylor·E. Mediavilla·C. Hellier
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Abstract

We present integral field spectroscopy of X2127+119, the luminous X-ray binary in the globular cluster M15, obtained with INTEGRAL/WYFFOS on the William Herschel Telescope. We find that tomograms of HeII 4686 line profiles appear to be incompatible with the previously-assumed view of X2127+119, in which the binary consists of a 1.4-solar-mass neutron star and a 0.8-solar-mass sub-giant companion near the main-sequence turn-off for M15. Our data imply a much smaller mass ratio M_2/M_x of 0.1. We find that models of X2127+119 with black-hole compact objects give a poor fit to our data, while a neutron-star compact object is consistent with the data, implying that X2127+119's companion may have a much lower mass (~0.1 solar masses) than previously assumed. As an 0.1-solar-mass main-sequence star would be unable to fill its Roche lobe in a binary with X2127+119's orbital period (17.1 hours), the companion is likely to be the remnant of a significantly more massive star which has had most of its envelope stripped away.

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L. van Zyl, P. A. Charles, S. Arribas, T. Naylor, E. Mediavilla, C. Hellier. 2004-01-27. The X-Ray Binary X2127+119 in M15: Evidence for a Very-Low-Mass, Stripped-Giant Companion. https://doi.org/10.1111/j.1365-2966.2004.07676.x

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