Optical spectroscopy of the Be/X-ray binary V850 Centauri/GX 304-1 during faint X-ray periodical activity
Abstract
Context. Be/X-ray binaries (BeXRBs) are the most populous class of high-mass X-ray binaries. Their X-ray duty cycle is tightly related to the optical companion wind activity, which in turn can be studied through dedicated optical spectroscopic observations.
Aims: We study optical spectral features of the Be circumstellar disk to test their long-term variability and their relation with the X-ray activity. Special attention has been given to the Hα emission line, one of the best tracers of the disk conditions.
Methods: We obtained optical broadband medium resolution spectra from a dedicated campaign with the Anglo-Australian Telescope and the Southern African Large Telescope in 2014-2015. Data span over one entire binary orbit, and cover both X-ray quiescent and moderately active periods. We used Balmer emission lines to follow the evolution of the circumstellar disk.
Results: We observe prominent spectral features, like double-peaked Hα and Hβ emission lines. The HαV/R ratio significantly changes over a timescale of about one year. Our observations are consistent with a system observed at a large inclination angle (I ≳ 60°). The derived circumstellar disk size shows that the disk evolves from a configuration that prevents accretion onto the neutron star, to one that allows only moderate accretion. This is in agreement with the contemporary observed X-ray activity. Our results are interpreted within the context of inefficient tidal truncation of the circumstellar disk, as expected for this source's binary configuration. We derived the Hβ-emitting region size, which is equal to about half of the corresponding Hα-emitting disk, and constrain the luminosity class of V850 Cen as III-V, consistent with the previously proposed class.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- July 2017
- DOI:
- 10.1051/0004-6361/201730538
- arXiv:
- arXiv:1704.08487
- Bibcode:
- 2017A&A...603A..24M
- Keywords:
-
- stars: individual: V850 Cen;
- stars: individual: GX 304-1;
- stars: emission-line;
- Be;
- stars: neutron;
- X-rays: binaries;
- Astrophysics - Solar and Stellar Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 7 pages, 5 figures, Accepted for publication on A&