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SkyMapper Protected Science Project

Finding the Galactic Population of Symbiotic Binary Stars

Adrian Lucy, Jeno Sokoloski (Columbia), Juan Luna (IAFE/Conicet)

Symbiotic systems are interacting binary stars in which a compact object (usually a white dwarf) accretes material from a red-giant companion. Some symbiotic stars appear to end their lives as type Ia supernovae. But the Galactic population of symbiotic stars, and the way in which symbiotics can evolve to become type Ia supernovae, are poorly understood. One of the reasons is that standard spectroscopic methods of identifying symbiotic stars lead to strong selection biases. SkyMapper can overcome these biases. We will use the SkyMapper photometric survey to identify new symbiotic stars and to estimate how many of these systems exist in our Galaxy. Symbiotics will stand out because of their distinctive colour signature - red at the red end of the optical spectrum (due to the red giant mass-donor star) and blue at the blue end of the optical spectrum (due to the accreting WD) - and their variability. The broad spectral coverage of the SkyMapper filters are perfect for our project, and we will use optical spectroscopy of early candidates to refine the region of colour-colour space where symbiotic systems reside. This research has implications for the progenitors of type Ia supernovae and binary stellar evolution.