Discovery of the first symbiotic star in NGC 6822

Alexei Y. Kniazev, Petri Väisänen, Patricia A. Whitelock, John W. Menzies, Michael W. Feast, Eva K. Grebel, David A.H. Buckley, Yas Hashimoto, Nicola Loaring, Encarni Romero-Colmenero, Ramotholo Sefako, Eric B. Burgh, Kenneth Nordsieck

    Research output: Contribution to journalArticlepeer-review

    23 Citations (Scopus)

    Abstract

    We report the discovery of the first symbiotic star (V = 21.6, K S = 15.8 mag) in the Local Group dwarf irregular galaxy NGC 6822. This star was identified during a spectral survey of Hα emission-line objects using the Southern African Large Telescope during its performance-verification phase. The observed strong emission lines of H i and He ii 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 asymptotic giant branch (AGB) carbon star, and a semiregular variable, pulsating in the first overtone with a period of 142 d. Its bolometric magnitude is Mbol = -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 realized.

    Original languageEnglish
    Pages (from-to)1121-1126
    Number of pages6
    JournalMonthly Notices of the Royal Astronomical Society
    Volume395
    Issue number2
    DOIs
    Publication statusPublished - 2009 May

    Keywords

    • Binaries: symbiotic
    • Galaxies: individual: NGC 6822
    • Stars: mass-loss

    ASJC Scopus subject areas

    • Astronomy and Astrophysics
    • Space and Planetary Science

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