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Stripped-envelope supernovae discovered by the Palomar Transient Factory
  Astronomy and astrophysics

Friday 05 May 2017
from 10:30 to 11:30
at FC61
Speaker : Christoffer Fremling (Stockholm University)
Abstract : This thesis talk is based on research made by the intermediate Palomar Transient Factory [(i)PTF]. The focus is on stripped-envelope (SE) supernovae (SNe) discovered by (i)PTF, and it is particularly closely tied to the still ongoing research on the SE SN, iPTF13bvn (Type Ib), that occurred in the nearby galaxy NGC 5806. This SN was initially thought to have been the explosion of a very massive Wolf-Rayet star, but we have shown that this is very likely not the case. We suggest instead that the most likely scenario is that iPTF13bvn originated from a binary system where the envelope was stripped off from the SN progenitor by tidal forces from a companion star. PTF12os (Type IIb) occurred in the same galaxy as iPTF13bvn, and our analysis shows that PTF12os and iPTF13bvn were very similar amongst themselves, and that both of them were also remarkably similar to the Type IIb SN 2011dh, in terms of all of the available observations (light-curves, spectra). We constrain the Zero-Age Main-Sequence (ZAMS) mass to ∼12M⊙ for iPTF13bvn and ≲15M⊙ for PTF12os. In current stellar evolution models, stars with these masses on the ZAMS cannot lose their hydrogen envelopes and become SE SNe without binary interactions. We also investigate a peculiar SE SN, iPTF15dtg (Type Ic), that shows a double-peaked LC with a narrow initial peak followed by a broad main LC peak. Using hydrodynamical modeling of the main peak of the bolometric LC we show that iPTF15dtg had a very large ejecta mass (∼ 10 M⊙), resulting from an explosion of a very massive star (∼ 35 M⊙). Finally, we have also performed a statistical study of the spectra of all SE SNe (Type IIb, Ib and Ic) discovered by (i)PTF. We find that the spectra of Type Ic SNe show O absorption features that are both stronger and broader compared to Type IIb and Type Ib SNe. As a by-product of the research that will be presented in my thesis, a fully automatic reference image subtraction photometry pipeline for the Palomar 60-inch telescope (P60) was also developed. The imaging data collected within the iPTF by the P60 was reduced on-the-fly by this pipeline and the resulting photometry was automatically uploaded to the web-based iPTF SN follow-up database interface hosted at CalTech.

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