IR spectra of the microquasar GRS 1915+105 during a low state

¹ Institute of Astronomy and Astrophysics, National Observatory of Athens, PO Box 20048, Athens 118 10, Greece
² Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
³ Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 03004, 18080 Granada, Spain
⁴ Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF-INTA), PO Box 50727, 28080 Madrid, Spain

Corresponding author: E. T. Harlaftis, ehh@astro.noa.gr

Received: 29 December 2000
Accepted: 12 January 2001

Abstract

There is controversy regarding the nature of the suspected donor star to the microquasar GRS 1915+105, and hence whether GRS 1915+105 is a high mass X-ray binary (HMXB) or a low-mass X-ray binary (LMXB). In order to clarify this issue, we obtained an infrared (J, H and K) spectrum of GRS 1915+105 in its low state which shows a steeper continuum than the prototype X-ray binary Sco X-1. We did not detect any HeII emission at 2.189 μm from GRS 1915+105 in our quiescent spectrum, indicating that the line is transient and is only observed during episodes of high X-ray activity. For our instrument configuration, there is no detection of the ¹²CO lines which are characteristic of late-type stars either in GRS 1915+105 or Sco X-1.