Nonadiabatic resonant dynamic tides and orbital evolution in close binaries

This investigation is devoted to the effects of nonadiabatic resonant dynamic tides generated in a uniformly rotating stellar component of a close binary. The companion is considered to move in a fixed Keplerian orbit, and the effects of the centrifugal force and the Coriolis force are neglected. Semi-analytical solutions for the linear, nonadiabatic resonant dynamic tides are derived by means of a two-time variable expansion procedure. The solution at the lowest order of approximation consists of the resonantly excited oscillation mode and displays a phase shift with respect to the tide-generating potential. Expressions are established for the secular variations of the semi-major axis, the orbital eccentricity, and the star's angular velocity of rotation caused by the phase shift. The orders of magnitude of these secular variations are considerably larger than those derived earlier by Zahn (1977) for the limiting case of dynamic tides with small frequencies. For a 5 solar mass ZAMS star, an orbital eccentricity e = 0.5, and orbital periods in the range from 2 to 5 days, numerous resonances of dynamic tides with second-degree lower-order gravity modes are seen to induce secular variations of the semi-major axis, the orbital eccentricity, and the star's angular velocity of rotation with time scales shorter than the star's nuclear life time.Comment: accepted for publication in A&A, 13 page

Energy Dissipation through Quasi-Static Tides in White Dwarf Binaries

We study tidal interactions in white dwarf binaries in the limiting case of quasi-static tides. The formalism is valid for arbitrary orbital eccentricities and therefore applicable to white dwarf binaries in the Galactic disk as well as globular clusters. In the quasi-static limit, the total perturbation of the gravitational potential shows a phase shift with respect to the position of the companion, the magnitude of which is determined primarily by the efficiency of energy dissipation through convective damping. We determine rates of secular evolution of the orbital elements and white dwarf rotational angular velocity for a 0.3 solar mass helium white dwarf in binaries with orbital frequencies in the LISA gravitational wave frequency band and companion masses ranging from 0.3 to 10^5 solar masses. The resulting tidal evolution time scales for the orbital semi-major axis are longer than a Hubble time, so that convective damping of quasi-static tides need not be considered in the construction of gravitational wave templates of white dwarf binaries in the LISA band. Spin-up of the white dwarf, on the other hand, can occur on time scales of less than 10Myr, provided that the white dwarf is initially rotating with a frequency much smaller than the orbital frequency. For semi-detached white dwarf binaries spin-up can occur on time scales of less than 1Myr. Nevertheless, the time scales remain longer than the orbital inspiral time scales due to gravitational radiation, so that the degree of asynchronism in these binaries increases. As a consequence, tidal forcing eventually occurs at forcing frequencies beyond the quasi-static tide approximation. For the shortest period binaries, energy dissipation is therefore expected to take place through dynamic tides and resonantly excited g-modes.Comment: Submitted to Ap

Een fotometrische studie van de Orion OB associatie

SIGLEKULeuven Campusbibliotheek Exacte Wetenschappen / UCL - Université Catholique de LouvainBEBelgiu

Royal Observatory of Belgium, Ringlaan 3, B-1180 Brussels, Belgium

Hipparcos has provided a lot of new data about double stars including accurate relative positions, magnitudes of the components and parallaxes. Some 170 visual binaries with relatively well known orbits and accurate parallaxes have been selected in order to determine or improve their component masses by making use of these new data. Additional colour information allowed us to obtain the conversion between Hipparcos and bolometric magnitudes. By combining the newly determined parallaxes and differential magnitudes with available ground-based colours and spectral types, we were able to derive component luminosities for our sample of visual binaries. This increase in stellar mass material allows to re-assess the currently adopted mass-luminosity relation (MLR) in the range 0 ! M bol ! 7 mag. Key words: Hipparcos; binaries; mass-luminosity relation. 1. INTRODUCTION The quality improvement of the Hipparcos parallaxes is extremely valuable for nearby binaries with orbits since these data ca..