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

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.

arXiv comment8 pages, 6 figures, accepted for publication in MNRAS

References in corpus (6)

• Evolutionary Binary Sequences for Low- and Intermediate-Mass X-ray Binaries
• Irradiation Pressure Effects in Close Binary Systems
• X-ray and UV Variability in the Core of M15: the nature of X2127+119/AC211
• Understanding the LMXB X2127+119 in M15 I. X-ray eclipses and dips
• The Discovery of a Second Luminous Low Mass X-ray Binary in the Globular Cluster M15
• Understanding the LMXB X2127+119 in M15

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