SN 2015bh: NGC 2770's 4th supernova or a luminous blue variable on its way to a Wolf-Rayet star?

Journal
Date Issued
2017
Author(s)
Thöne, C. C.
•
de Ugarte Postigo, A.
•
Leloudas, G.
•
Gall, C.
•
Cano, Z.
•
Maeda, K.
•
Schulze, S.
•
•
Wiersema, K.
•
Groh, J.
•
de la Rosa, J.
•
Bauer, F. E.
•
Malesani, D.
•
Maund, J.
•
Morrell, N.
•
Beletsky, Y.
DOI
Abstract
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.
Volume
599
Start page
A129
Uri
Url
Issn Identifier
0004-6361
Ads BibCode
2017A&A...599A.129T
Rights
open.access
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