White dwarf-red dwarf binaries in the Galaxy

Contains fulltext : 30919.pdf (publisher's version ) (Open Access)This PhD thesis shows several studies on white dwarf - red dwarf binaries. White dwarfs are the end products of most stars and red dwarfs are normal hydrogen burning low-mass stars. White dwarf - red dwarf binaries are both blue (white dwarf) and red (red dwarf). Together with the fact that they are intrinsically equally bright, these binaries stand out in any colour-colour diagram. These studies have mainly used the largest astronomical database available at present, the Sloan Digital Sky Survey. This database contains 287 million objects in 5 optical filters and spectroscopy for about 1% as well. The first study in this thesis describes the discovery of 15 rare white dwarf - red dwarf binaries. The second study involves the bright, eclipsing binary DE Canum Venaticorum for which a large number of photometric and spectroscopic observations are analysed. The last part of this thesis describes the selection and analyzation of a large sample of white dwarf - red dwarf binaries in the Sloan Digital Sky Survey, which are selected on the basis of their colours and apparent motion in the sky. With the use of spectral models the available spectra for these objects are fitted to determine the white dwarf temperature and secondary spectral type. After that, the whole photometric sample of binaries was taken and classified on the basis of their colours alone. With the use of a simulated galactic model the space density for white dwarf - red dwarf binaries is determined. This is the first time that this kind of study has been done.Radboud University Nijmegen, Department of Astrophysics, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), 28 november 2007Promotor : Groot, P.J.IV, 162 p

Proper Motion Selected White Dwarf -- Red Dwarf Binaries

One of the main unknowns in binary evolution is the so-called common-envelope phase: a short lived phase during which the core of a giant and the companion star exist within a single envelope. Products and good tracers of common-envelope evolution are detached close white dwarf + low-mass main-sequence star (red dwarf) binaries. Their combined colours locate them in distinct regions of colour-colour diagrams. We have used a combination of proper motion and SDSS colours to distinguish between our targets and background quasars. We selected a very clean population of white dwarf -- red dwarf binaries. We will investigate the orbital period distribution of these systems together with their characteristics to compare with results from population synthesis codes and set limits on the physics of the common-envelope phase

DE CVn: A Bright, Eclipsing Red Dwarf - White Dwarf Binary

Contains fulltext : 35976.pdf (preprint version ) (Open Access)DE CVn is a relatively unstudied eclipsing binary where one of the components is an M dwarf. Its brightness makes it an ideal system for a detailed study in the context of common-envelope evolution of a detached white dwarf - red dwarf binary with a relatively short orbital period (~8.7 hours). We present a detailed study of the basic parameters (e.g. orbital period, components' masses, spectral type) for this system from photometric and spectroscopic studies. The eclipses observed during several photometric observing runs were used to derive the ephemeris. We have used spectroscopic data to derive the radial velocity variations of the emission lines and these are used to determine the components' masses and the orbital separation. The secondary component in DE CVn is an M3 main-sequence star and the primary star, which is not visible in the spectra, is a cool white dwarf with a temperature of ~8000 K. From the photometry and spectroscopy together, we have set a limit on the binary inclination. This system is a post-common-envelope system where the progenitor of the present day white dwarf was a low-mass star (M<2 Msun). The time before DE CVn becomes a semi-detached system is longer than the Hubble time

Relationship between sunshine duration and temperature trends across Europe since the second half of the twentieth century

Global radiation is a fundamental source of energy in the climate system. A significant impact of global radiation on temperature change is expected due to the widespread dimming/brightening phenomenon observed since the second half of the twentieth century. This work describes the analysis of 312 stations with sunshine duration (SD) series, a proxy for global radiation, and temperature series in the European Climate Assessment & Dataset (ECA&D) with data over the period 1961-2010. The relationship between SD and temperature series is analyzed for four temperature variables: maximum (Tmax), minimum (Tmin), mean temperature (Tmean), and diurnal temperature range (DTR). The analyses are performed on annual and seasonal basis. The results show strong positive correlations between SD and temperatures over Europe, with highest correlation for DTR and Tmax during the summer period. These results confirm the strong relationship between SD and temperature trends over Europe since the second half of the twentieth century. This study supports previous suggestions that dimming (brightening) has partially decreased (increased) temperatures thereby modulating the greenhouse gas induced warming rates over EuropeThe second author was supported by a postdoctoral fellowship from the “Departament d’Innovació, Universitats i Empresa de la Generalitat de Catalunya” (2011 BP-B 00078), the project NUCLIERSOL (CGL2010-18546), and the postdoctoral fellowship JCI-2012-1250