Volume 599, March 2017
|Number of page(s)||29|
|Section||Stellar structure and evolution|
|Published online||14 March 2017|
SN 2015bh: NGC 2770’s 4th supernova or a luminous blue variable on its way to a Wolf-Rayet star?
1 Instituto de Astrofísica de Andalucía – CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
2 Dark Cosmology Centre, Niels Bohr Institute, Juliane Maries Vej 30, Copenhagen Ø, 2100, Denmark
3 Department of Particle Physics & Astrophysics, Weizmann Institute of Science, 76100 Rehovot, Israel
4 Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
5 Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
6 Department of Astronomy, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, 606-8502 Kyoto, Japan
7 Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8583 Chiba, Japan
8 Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
9 Millennium Institute of Astrophysics, Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
10 INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
11 Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
12 School of Physics, Trinity College Dublin, Dublin 2, Ireland
13 Space Science & Engineering Division, Southwest Research Institute, PO Drawer 28510, San Antonio, TX 78228-0510, USA
14 Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA
15 DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, 2800 Lyngby, Denmark
16 Department of Physics and Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK
17 Las Campanas Observatory, Carnegie Observatories, Casilla 601, La Serena, Chile
Received: 27 October 2016
Accepted: 6 December 2016
Very massive stars in the final phases of their lives often show unpredictable outbursts that can mimic supernovae, so-called, “SN impostors”, but the distinction is not always straightforward. Here we present observations of a luminous blue variable (LBV) in NGC 2770 in outburst over more than 20 yr that experienced a possible terminal explosion as type IIn SN in 2015, named SN 2015bh. This possible SN (or “main event”) had a precursor peaking ~40 days before maximum. The total energy release of the main event is ~1.8 × 1049 erg, consistent with a <0.5 M⊙ shell plunging into a dense CSM. The emission lines show a single narrow P Cygni profile during the LBV phase and a double P Cygni profile post maximum suggesting an association of the second component with the possible SN. Since 1994 the star has been redder than an LBV in an S-Dor-like outburst. SN 2015bh lies within a spiral arm of NGC 2770 next to several small star-forming regions with a metallicity of ~0.5 solar and a stellar population age of 7–10 Myr. SN 2015bh shares many similarities with SN 2009ip and may form a new class of objects that exhibit outbursts a few decades prior to a “hyper eruption” or final core-collapse. If the star survives this event it is undoubtedly altered, and we suggest that these “zombie stars” may evolve from an LBV to a Wolf-Rayet star over the timescale of only a few years. The final fate of these stars can only be determined with observations a decade or more after the SN-like event.
Key words: supernovae: individual: SN 2015bh, SN 2009ip / stars: massive
© ESO, 2017
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