Identification of the optical counterparts of high-mass X-ray binaries through optical photometry and spectroscopy

¹ IESL, Foundation for Research and Technology, 711 10 Heraklion, Crete, Greece e-mail: pau@physics.uoc.gr
² University of Crete, Physics Department, PO Box 2208, 710 03 Heraklion, Crete, Greece
³ Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal, Universidad de Alicante, 03080 Alicante, Spain

Received: 12 January 2005
Accepted: 8 May 2005

Abstract

We present the results of our search for optical counterparts to high-mass X-ray transient sources discovered by various X-ray missions. We obtained CCD images of the X-ray fields through BVR and Hα filters to identify early-type stars in the versus colour–colour diagram. We also obtained medium-resolution spectroscopy of the candidates in order to confirm the presence of Hα emission and perform spectral classification. We report on the discovery of the optical counterparts to two X-ray sources: XTE J1858+034 and IGR J01363+6610, and the follow-up observations of another two, newly identified by our group: SAX J2103.5+4545 and GRO J2058+42. For another source, IGR J00370+6122, we present the first detailed optical spectral analysis. The optical photometry and spectroscopy reveal B-type companions in all five sources; GRO J2058+42, SAX J2103.5+4545 and IGR J01363+6610 are positively identified with Be/X-ray binaries, IGR J00370+6122 with a supergiant X-ray binary, while the nature of the XTE J1858+034 is uncertain. We also study the relationship between the optical and X-ray emission during quiescent states.