The Be/X-ray binary LS 992/RX J0812.4-3114: Physical parameters and long-term variability^*

¹ Foundation for Research and Technology-Hellas, 711 10 Heraklion, Crete, Greece
² Physics Department, University of Crete, 710 03 Heraklion, Crete, Greece
³ SAX SDC, Agenzia Spaziale Italiana, c/o Telespazio, via Corcolle 19, 00131 Roma, Italy
⁴ South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape Town, South Africa
⁵ Physics & Astronomy Department, Southampton University, SO17 1BJ, UK
⁶ Astronomy & Astrophysics Department. University of Valencia, 46100 Burjassot-Valencia, Spain

Corresponding author: P. Reig, pablo@physics.uoc.gr

Received: 2 August 2000
Accepted: 9 November 2000

Abstract

We present the first long-term optical and infrared study of the optical counterpart to the source RX J0812.4-3114, an X-ray pulsar with a Be type companion. During the period covered by the observations the profile of some Balmer lines changed from absorption to emission and back again to absorption. Contemporaneously, the infrared magnitudes varied by more than 0.8 mag. This long-term variability is interpreted as the formation and subsequent dissipation of the Be star's disc. The building up of the disc ended up in an active X-ray state characterised by regular outbursts occurring at 80 day intervals. The overall duration of the formation/dissipation of the disc is found to be years. Optical spectroscopic and infrared photometric observations were used to refine the spectral type of the primary (B0.2IV) and to monitor the circumstellar envelope around the Be star. UBVRI and photometric observations allowed the determination of the astrophysical parameters of the optical companion.