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Discovery of the first symbiotic star in NGC 6822

Authors

  • Alexei Y. Kniazev,

    Corresponding author
    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
    2. Southern African Large Telescope Foundation, PO Box 9, Observatory, 7935 Cape Town, South Africa
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  • Petri Väisänen,

    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
    2. Southern African Large Telescope Foundation, PO Box 9, Observatory, 7935 Cape Town, South Africa
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  • Patricia A. Whitelock,

    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
    2. Astronomy Department, University of Cape Town, 7701 Rondebosch, South Africa
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  • John W. Menzies,

    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
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  • Michael W. Feast,

    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
    2. Astronomy Department, University of Cape Town, 7701 Rondebosch, South Africa
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  • Eva K. Grebel,

    1. Astronomisches Rechen-Institut, Zentrum für Astronomie Heidelberg, Mönchhofstr. 12–14, D-69120 Heidelberg, Germany
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  • David A. H. Buckley,

    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
    2. Southern African Large Telescope Foundation, PO Box 9, Observatory, 7935 Cape Town, South Africa
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  • Yas Hashimoto,

    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
    2. Southern African Large Telescope Foundation, PO Box 9, Observatory, 7935 Cape Town, South Africa
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  • Nicola Loaring,

    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
    2. Southern African Large Telescope Foundation, PO Box 9, Observatory, 7935 Cape Town, South Africa
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  • Encarni Romero-Colmenero,

    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
    2. Southern African Large Telescope Foundation, PO Box 9, Observatory, 7935 Cape Town, South Africa
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  • Ramotholo Sefako,

    1. South African Astronomical Observatory, PO Box 9, Observatory, 7935 Cape Town, South Africa
    2. Southern African Large Telescope Foundation, PO Box 9, Observatory, 7935 Cape Town, South Africa
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  • Eric B. Burgh,

    1. Space Astronomy Laboratory, University of Wisconsin, Madison, WI 53706, USA
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  • Kenneth Nordsieck

    1. Space Astronomy Laboratory, University of Wisconsin, Madison, WI 53706, USA
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  • Based on observations made with the Southern African Large Telescope (SALT) and the Infrared Survey Facility (IRSF).

E-mail: akniazev@saao.ac.za

ABSTRACT

We report the discovery of the first symbiotic star (V= 21.6, KS= 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.

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