Gangopadhyay, AnjashaAnjashaGangopadhyayMisra, KuntalKuntalMisraPASTORELLO, AndreaAndreaPASTORELLOSahu, D. K.D. K.SahuTOMASELLA, LinaLinaTOMASELLATARTAGLIA, LeonardoLeonardoTARTAGLIASingh, MridweekaMridweekaSinghDastidar, RayaRayaDastidarSrivastav, S.S.SrivastavOchner, P.P.OchnerBrown, Peter J.Peter J.BrownAnupama, G. C.G. C.AnupamaBENETTI, StefanoStefanoBENETTICAPPELLARO, EnricoEnricoCAPPELLAROKumar, BrajeshBrajeshKumarKumar, BrijeshBrijeshKumarPandey, S. B.S. B.Pandey2020-10-022020-10-0220180035-8711http://hdl.handle.net/20.500.12386/27541We 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 <SUP>56</SUP>Ni mass of ∼0.08 M<SUB>☉</SUB> and ejecta mass of 1.1-2.2 M<SUB>☉</SUB>, 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<SUB>☉</SUB>), a nearly compact (∼0.05 × 10<SUP>13</SUP> cm) H envelope on top of a dense, compact (∼2 × 10<SUP>11</SUP> cm) and a more massive (∼1.2 M<SUB>☉</SUB>) He core. The analysis of the nebular phase spectra indicates that ∼0.44 M<SUB>☉</SUB> 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<SUB>☉</SUB> or a Wolf-Rayet star of 20 M<SUB>☉</SUB>.STAMPAenArticle10.1093/mnras/sty4782-s2.0-85070080271000430944100053https://academic.oup.com/mnras/article-abstract/476/3/3611/4898084?redirectedFrom=fulltext2018MNRAS.476.3611GFIS/05 - ASTRONOMIA E ASTROFISICA