Volume 574, February 2015
|Number of page(s)||14|
|Section||Stellar structure and evolution|
|Published online||20 January 2015|
Long-term variability of high-mass X-ray binaries⋆
IESL, Foundation for Research and Technology-Hellas,
2 Physics Department, University of Crete, 71003 Heraklion, Greece
3 Observatorio Astronómico, Universidad de Valencia, 46100 Burjassot, Spain
Received: 17 September 2014
Accepted: 7 November 2014
We present photometric observations of the field around the optical counterparts of high-mass X-ray binaries. Our aim is to study the long-term photometric variability in correlation with their X-ray activity and derive a set of secondary standard stars that can be used for time series analysis. We find that the donors in Be/X-ray binaries exhibit larger amplitude changes in the magnitudes and colours than those hosting a supergiant companion. The amplitude of variability increases with wavelength in Be/X-ray binaries and remains fairly constant in supergiant systems. When time scales of years are considered, a good correlation between the X-ray and optical variability is observed. The X-rays cease when optical brightness decreases. These results reflect the fact that the circumstellar disk in Be/X-ray binaries is the main source of both optical and X-ray variability. We also derive the colour excess, E(B − V), selecting data at times when the contribution of the circumstellar disk was supposed to be at minimum, and we revisit the distance estimates.
Key words: techniques: photometric / stars: emission-line, Be / stars: neutron / X-rays: binaries
Finding charts with the identification of the secondary standard stars are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A33
© ESO, 2015
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