One year of monitoring of the Type IIb supernova SN 2011dh

Abstract

Optical UBVRI photometry and low-resolution spectroscopy of the Type IIb supernova SN 2011dh in M51 are presented, covering the first year after the explosion. The light curve andspectral evolution are discussed. The early phase light-curve evolution of SN 2011dh is verysimilar to SN 1993J and SN 2008ax. In the late phase, however, SN 2011dh declines faster thanSN 1993J. The late phase decline in the B band is steeper than in the R and I bands, indicatingthe possibility of dust formation. With a peak V-band absolute magnitude of MV =-17.123±0.18 mag, SN 2011dh is a marginally faint type IIb event. The reddening corrected colourcurves of SN 2011dh are found to be redder than other well-studied Type IIb supernovae. Thebolometric light curve indicates ~;0.09Mȯ of 56Ni is synthesized during the explosion. TheHe I lines were detected in the spectra during the rise to maximum. The nebular spectra ofSN 2011dh show a box-shaped emission in the red wing of the [OI] 6300-6363Å feature, that is attributed to Hα emission from a shock-excited circumstellar material. The analysis ofnebular spectra indicates that ~0.2Mȯ of oxygen was ejected during the explosion. Further, the [Ca II]/[O I] line ratio in the nebular phase is ~0.7, indicating a progenitor with a mainsequence mass of 10-15Mȯ. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.