CoBiToM project - I. Contact binaries towards merging

Binary and multiple stellar systems are numerous in our solar neighbourhood with 80per cent of the solar-type stars being members of systems with high order multiplicity. The Contact Binaries Towards Merging (CoBiToM) Project is a programme that focuses on contact binaries and multiple stellar systems, as a key for understanding stellar nature. The goal is to investigate stellar coalescence and merging processes, as the final state of stellar evolution of low-mass contact binary systems. Obtaining observational data of approximately 100 eclipsing binaries and multiple systems and more than 400 archival systems, the programme aspires to give insights for their physical and orbital parameters and their temporal variations, e.g. the orbital period modulation, spot activity etc. Gravitational phenomena in multiple-star environments will be linked with stellar evolution. A comprehensive analysis will be conducted, in order to investigate the possibility of contact binaries to host planets, as well as the link between inflated hot Jupiters and stellar mergers. The innovation of CoBiToM Project is based on a multimethod approach and a detailed investigation, that will shed light for the first time on the origin of stellar mergers and rapidly rotating stars. In this work, we describe the scientific rationale, the observing facilities to be used and the methods that will be followed to achieve the goals of CoBiToM Project and we present the first results as an example of the current research on evolution of contact binary systems

The intermediate polar cataclysmic variable GK Persei 120 years after the nova explosion: a first dynamical mass study

We present a dynamical study of the intermediate polar and dwarf nova cataclysmic variable GK Persei (Nova Persei 1901) based on a multisite optical spectroscopy and R-band photometry campaign. The radial velocity curve of the evolved donor star has a semi-amplitude K-2 = 126.4 +/- 0.9 km s(-1) and an orbital period P = 1.996872 +/- 0.000009 d. We refine the projected rotational velocity of the donor star to v(rot) sin i = 52 +/- 2 km s(-1) that, together with K-2, provides a donor star to white dwarf mass ratio q = M-2/M-1 = 0.38 +/- 0.03. We also determine the orbital inclination of the system by modelling the phase-folded ellipsoidal light curve and obtain i = 67 degrees +/- 5 degrees. The resulting dynamical masses are M-1 = 1.03(-0.11)(+0.16) M-circle dot and M-2 = 0.39(-0.06)(+0.07) M-circle dot at 68 per cent confidence level. The white dwarf dynamical mass is compared with estimates obtained by modelling the decline light curve of the 1901 nova event and X-ray spectroscopy. The best matching mass estimates come from the nova light curve models and an X-ray data analysis that uses the ratio between the Alfven radius in quiescence and during dwarf nova outburst

Interacting binaries and extrasolar planets: Challenges for VLTI

Optical Interferometry can play an important role in modern astronomy. Extrasolar planet and binary star research, are some of the fields, where we will face important discoveries in the future. For the VLTI this will be a real challenge, since it will be the pioneer in angular resolution. In addition, high flux sensitivity will help detecting not only Jupiter-sized planets, but Earth-sized planets too. The ability of the VLTI in detecting new planets, measuring stellar diameters and stellar proper motions, with the use of such techniques, is presented

CCD photometry and modeling of the overcontact binary systems NN Vir and YYCrB

New ground-based BV RI CCD observations of the eclipsing binary systems NN Vir and YY CrB are analyzed and illustrated. New times of minima are given and new ephemerides are proposed. The light curves are analyzed with the Wilson-Devinney light curve synthesis code and new geometric and photometric elements are derived. These elements are used together with the available spectroscopic data to compute absolute elements. The evolutionary status of each system is studied by means of mass-radius diagrams. The systems NN Vir and YY CrB are found to be A-type and W-type W UMa systems, respectively