Contemporaneous spectroscopic and photometric B V observations of the RS CVn type eclipsing binary RT Lacertae were performed in summer 2000. The photometric observations were obtained at the Ege University Observatory, while the...
moreContemporaneous spectroscopic and photometric B V observations of the RS CVn type eclipsing binary RT Lacertae were performed in summer 2000. The photometric observations were obtained at the Ege University Observatory, while the spectroscopic ones were carried out at Catania Astrophysical Observatory in the spectral range 5860-6700 Å. We obtained a high quality radial velocity curve of the system that allowed us to give more accurate values of the orbital parameters. A steady decrease of the barycentric velocity from 1920 to 2000 has been pointed out and has been discussed in the context of a third body hypothesis. Through the subtraction of a ``synthetic'' spectrum, built up with spectra of inactive standard stars, we detected Halpha excess emission which fills in the photospheric absorption profiles of both components. With the exception of a few spectra, taken close to the eclipses, in which some extra absorption or a faint double-peaked broad emission appears, there is no further evidence of circumstellar matter in this system, as suggested in previous works. The hotter and more massive star appears also as the more active at a chromospheric level, since it has a Halpha flux about ten times greater than the companion, on average. Rotational modulation of the Halpha emission has been detected in both stars. The hemisphere of the more massive star facing the observer at phase 0fp75 appears brighter (in Halpha ) than that seen at phase 0fp25 , while for the less massive G9 IV star the maximum Halpha emission is seen around phase 0fp0-0fp1 . From the analysis of the contemporaneous light curve (Lanza et al. \cite{Lanza2001}), the more massive G5 IV star results to be more active than the companion at a photospheric level, in agreement with the chromospheric behaviour observed in Halpha . In addition, the starspots of the G5 IV star are mainly located in the Halpha brighter hemisphere, suggesting a close spatial association of spots and plages in this star. The G9 IV star displays instead the maximum Halpha emission at the phase of maximum visibility of the smaller spotted area found from the light-curve analysis. The minimum Halpha emission occurs when the more heavily spotted region is visible. Based on observations collected at Catania Astrophysical Observatory, Italy, and at Ege University Observatory, Turkey. Table 1 only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/298
