Volume 635, March 2020
|Number of page(s)||11|
|Published online||17 March 2020|
Chromospheric activity in bright contact binary stars★
Department of Optics and Quantum Electronics, University of Szeged,
Dóm tér 9, Hungary
2 Baja Astronomical Observatory of University of Szeged, 6500 Baja, Szegedi út, Kt. 766, Hungary
3 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, 1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
4 MTA CSFK Lendület Near-Field Cosmology Research Group, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
Accepted: 27 January 2020
Context. Studying chromospheric activity of contact binaries is an effective way of revealing the magnetic activity processes of these systems. One efficient but somewhat neglected method for this purpose is to follow the changes of the Hα line profiles via optical spectroscopy.
Aims. Our goal is to perform a comprehensive preliminary analysis based on the optical spectral signs of chromospheric activity on the largest sample of contact binaries to date.
Methods. We collected optical echelle spectra on 12 bright contact binaries in 17 nights. We derived new radial velocity curves from our observations. For quantifying the apparent chromospheric activity levels of the systems, we subtracted self-constructed synthetic spectra from the observed ones and measured the equivalent widths of the residual Hα-profiles at each observed epoch. Our well-sampled data set allowed us to study the short-term variations of chromospheric activity levels as well as to search for correlations between them and some basic physical parameters of the systems.
Results. Fitting the radial velocity curves, we re-determined the mass ratios and systemic velocities of all observed objects. We found that chromospheric activity levels of the studied systems show various changes during the orbital revolution: we see either flat, one-peaked, or two-peaked distributions of equivalent width vs. the orbital phase. The first case means that the activity level is probably constant, while the latter two cases suggest the presence of one or two active longitudes at the stellar surfaces. Our correlation diagrams show that mean chromospheric activity levels may be related to the orbital periods, B−V color indices, inverse Rossby numbers, and temperature differences of the components. At the same time, no clear trend is visible with respect to the mass ratios, inclinations, or fill-out factors of the systems. A- and W-type contact binaries in our sample show similar distributions on each of the studied correlation diagrams.
Key words: stars: activity / stars: chromospheres / binaries : close / binaries: spectroscopic
© ESO 2020
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