Chromospheric activity in bright contact binary stars

Abstract

Context. Studying chromospheric activity of contact binaries is an important way of revealing the magnetic activity processes of these systems. An efficient but somewhat neglected method for that is to follow the changes of the Hα line profiles via optical spectroscopy. Aims. Our goal was 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 at 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 wellsampled 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, or onepeaked, 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 in connection with 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 mass ratios, inclinations and fill-out factors of the systems. A-and W-type contact binaries in our sample show similar distributions at each of the studied correlation diagrams.

Simultaneous Photometric and Spectroscopic Analysis of V505 Lacertae, a Photospherically and Chromospherically Active Contact Binary Star

“…Chromospheric activity is another stellar activity occurring in LMCBs, which is revealed by excess emissions of certain specific spectral lines (e.g., Mg II λ280 nm, Ca II H and K (λ396.8 and 393.4 nm), Hβ (λ486.1 nm), Na I λ589.7 nm, Hα (λ656.3 nm), Ca II IRT (λ849.8, 854.2, and 866.2 nm), etc.) ranging from the ultraviolet to infrared regions (Barden 1985;Ruciński 1985;Kandulapati et al 2015;Mitnyan et al 2018Mitnyan et al , 2020Cheng et al 2019;Liu et al 2019). Previously, Barden (1985) noted that Hα excess emission is detected only for the more-massive component of a W-subtype system; this finding was recently confirmed for the VW Cep system by Mitnyan et al (2018), who also found a correlation between spottedness and the chromospheric activity of the system.…”

“…In addition, to investigate whether chromospheric activity occurs in the V505 Lac system, a spectral subtraction technique (Barden 1985;Montes et al 2000;Mitnyan et al 2018Mitnyan et al , 2020Şenavcı et al 2018) was applied to the Ca II H and K and Hα absorption lines; these lines are known to be optical diagnostic indicators of chromospheric activity. Before performing this task, we tested the consistency of the spectral synthesis described above by modeling two spectral regions: the Fe I λ495.7 nm region, which was used for temperature determination, and the λ558.0-564.0 nm region, which includes mostly photospheric lines (Şenavcı et al 2018).…”

A Contact Binary Misclassified as an Ellipsoidal Variable: Complications for Detached Black Hole Searches

“…The similar depth minima in the light curve suggest that each star has a similar temperature. In a contact binary, each star typically has a similar effective temperature and in turn likely has a similar spectrum (e.g., Pribulla et al 2003;Mitnyan et al 2020). Assuming a contact binary configuration, we model the system as a contact binary in PHOEBE to constrain system parameters.…”