Institute of Astronomy

Extragalactic Symbiotic Stars: an Important Test for Binary Evolution Models

SpeakerTalk DateTalk Series
Joanna Mikolajewska29 July 2016Binary Stars Talks


Symbiotic stars (SySt) are amongst the longest orbital period interacting binaries. The components are an evolved cool giant and an accreting, hot, luminous (usually a WD) companion, embedded in rich and complex surroundings, including both ionized and neutral regions, accretion/excretion discs, interacting winds and jest. surrounded by a dense ionized nebula.  SySt are are important tracers of late evolutionary phases of low- and medium-mass stars, and excellent laboratories to explore interactions and evolution in binary stars. In addition, the composition of SySt makes some of them a promising öfactoryö of SN Ia, independently of the scenario leading to their eruption.   While about 300 Galactic symbiotics are known, and a few dozen are relatively well studied, their distances (and hence their component luminosities and other distance-related parameters) are poorly determined. This makes comparison with the theoretical models for their interaction and evolution very challenging.  Fortunately, SySt are detectable throughout the Milky Way as tracers of luminous binary stars.  Here we will present some preliminary results of our ongoing systematic search for SySt in M33 and M31. Our goal is to obtain large, complete, luminosity-limited samples of extragalactic SySt to derive their total numbers and their spatial distribution in different type galaxies. Large SySt samples, all at the same distances, also enable us to determine the values and distribution of their luminosity-related parameters.  These will provide strong constraints on binary stellar evolution and the progenitor masses.