Discovery of the first symbiotic star in NGC6822

Details Discovery of the first symbiotic star in NGC6822 Discovery of the first symbiotic star in NGC6822

2009-02-10

arxiv.org/abs/0902.1648v1

Astronomy and Astrophysics

Astrophysics

Galaxy Astrophysics

6 pages, 4 figures, accepted to MNRAS

Scientific paper

10.1111/j.1365-2966.2009.14617.x

We report the discovery of the first symbiotic star (V=21.6, K_S=15.8 mag) in the Local Group dwarf irregular galaxy NGC6822. This star was identified during a spectral survey of Ha emission-line objects using the Southern African Large Telescope (SALT) during its performance-verification phase. The observed strong emission lines of HI and HeII suggest a high electron density and T* < 130 000 K for the hot companion. The infrared colours allow us to classify this object as an S-type symbiotic star, comprising a red giant losing mass to a compact companion. The red giant is an AGB carbon star, and a semi-regular variable, pulsating in the first overtone with a period of 142 days. Its bolometric magnitude is M_bol=-4.4 mag. We review what is known about the luminosities of extragalactic symbiotic stars, showing that most, possibly all, contain AGB stars. We suggest that a much larger fraction of Galactic symbiotic stars may contain AGB stars than was previously realised.

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