The eccentric short-period orbit of the supergiant fast X-ray transient HD 74194 (=LM Vel)^⋆

¹ Instituto de Astrofísica de La Plata, CCT La Plata-CONICET, Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, ( 1900 ) La Plata, Argentina
e-mail: rgamen@fcaglp.unlp.edu.ar
² Departamento de Física, Universidad de La Serena, Av. Juan Cisternas 1200 Norte, La Serena, Chile
³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA ^⋆⋆
4 Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile
⁵ Centro de Astrobiología, CSIC-INTA, campus ESAC, apartado postal 78, 28 691 Villanueva de la Cañada, Madrid, Spain
⁶ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain

Received: 7 August 2015
Accepted: 12 October 2015

Abstract

Aims. We present the first orbital solution for the O-type supergiant star HD 74194, which is the optical counterpart of the supergiant fast X-ray transient IGR J08408-4503.

Methods. We measured the radial velocities in the optical spectrum of HD 74194, and we determined the orbital solution for the first time. We also analysed the complex Hα profile.

Results. HD 74194 is a binary system composed of an O-type supergiant and a compact object in a short-period (P = 9.5436 ± 0.0002 d) and high-eccentricity (e = 0.63 ± 0.03) orbit. The equivalent width of the Hα line is not modulated entirely with the orbital period, but seems to vary in a superorbital period (P = 285 ± 10 d) nearly 30 times longer than the orbital one.