THE TYPE IIb SUPERNOVA 2011dh FROM A SUPERGIANT PROGENITOR

A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh.Our modeling suggests that a large progenitor star-with R ∼ 200 R -is needed to reproduce the early light curve (LC) of SN 2011dh.This is consistent with the suggestion that the yellow super-giant star detected at the location of the supernova (SN) in deep pre-explosion images is the progenitor star.From the main peak of the bolometric LC and expansion velocities, we constrain the mass of the ejecta to be ≈2 M , the explosion energy to be E = (6-10) × 10 50 erg, and the 56 Ni mass to be approximately 0.06 M .The progenitor star was composed of a helium core of 3-4 M and a thin hydrogen-rich envelope of ≈0.1M with a main-sequence mass estimated to be in the range of 12-15 M .Our models rule out progenitors with helium-core masses larger than 8 M , which correspond to M ZAMS 25M .This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.