SN 2015as: a low-luminosity Type IIb supernova without an early light-curve peak
Abstract
We present results of the photometric (from 3 to 509 d post-explosion) and spectroscopic (up to 230 d post-explosion) monitoring campaign of the He-rich Type IIb supernova (SN) 2015as. The (B - V) colour evolution of SN 2015as closely resemble those of SN 2008ax, suggesting that SN 2015as belongs to the SN IIb subgroup that does not show the early, short-duration photometric peak. The light curve of SN 2015as reaches the B-band maximum about 22 d after the explosion, at an absolute magnitude of -16.82 ± 0.18 mag. At ∼75 d after the explosion, its spectrum transitions from that of a SN II to a SN Ib. P Cygni features due to He i lines appear at around 30 d after explosion, indicating that the progenitor of SN 2015as was partially stripped. For SN 2015as, we estimate a 56Ni mass of ∼0.08 M⊙ and ejecta mass of 1.1-2.2 M⊙, which are similar to the values inferred for SN 2008ax. The quasi-bolometric analytical light-curve modelling suggests that the progenitor of SN 2015as has a modest mass (∼0.1 M⊙), a nearly compact (∼0.05 × 1013 cm) H envelope on top of a dense, compact (∼2 × 1011 cm) and a more massive (∼1.2 M⊙) He core. The analysis of the nebular phase spectra indicates that ∼0.44 M⊙ of O is ejected in the explosion. The intensity ratio of the [Ca ii]/[O i] nebular lines favours either a main-sequence progenitor mass of ∼15 M⊙ or a Wolf-Rayet star of 20 M⊙.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- February 2018
- DOI:
- 10.1093/mnras/sty478
- arXiv:
- arXiv:1802.06731
- Bibcode:
- 2018MNRAS.476.3611G
- Keywords:
-
- techniques: photometric;
- techniques: spectroscopic;
- supernovae: general;
- supernovae: individual: SN 2015as;
- galaxies: individual: UGC 5460;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 23 pages, 18 figures, 10 tables, Accepted for publication in MNRAS, 16 February, 2018