Infrared Spectroscopy of GX 1+4/V2116 Ophiuchi: Evidence for a Fast Red Giant Wind?

We present infrared spectroscopy of the low-mass X-ray binary GX 1+4/V2116 Ophiuchi. This symbiotic binary consists of a 2 minute accretion-powered pulsar and an M5 III red giant. A strong He I 1.083 μm emission line with a pronounced P Cygni profile was observed. From the blue edge of this feature, we infer an outflow velocity of 250±50 km s−1. This is an order of magnitude faster than a typical red giant wind, and we suggest that radiation from the accretion disk or the neutron star may contribute to the acceleration of the outflow. We infer a wind mass-loss rate of ~10-6 M☉ yr−1. Accretion from such a strong stellar wind provides a plausible alternative to Roche lobe overflow for supplying the accretion disk that powers the X-ray source. The H I Paβ and He I 1.083 μm emission lines show no evidence for the dramatic variability previously reported in some optical lines and no evidence for pulsations at the 2 minute pulsar period.