2011MNRAS.411.2726B

Extensive optical and near-infrared observations of the Type Ib supernova (SNIb) 1999dn are presented, covering the first year after explosion. These new data turn this object, already considered a prototypical SNIb, into one of the best observed objects of its class. The light curve of SN 1999dn is mostly similar in shape to that of other SNeIb but with a moderately faint peak (M_V=-17.2 mag). From the bolometric light curve and ejecta expansion velocities, we estimate that about 0.11 M_☉ of ⁵⁶Ni were produced during the explosion and that the total ejecta mass was 4-6 M_☉with a kinetic energy of at least 5 {x} 10⁵¹ erg. The spectra of SN 1999dn at various epochs are similar to those of other stripped envelope SNe showing clear presence of H at early epochs. The high explosion energy and ejected mass, along with the small flux ratio [Ca II]/[O I] measured in the nebular spectrum, together with the lack of signatures of dust formation and the moderate metallicity environment is not inconsistent with a single massive progenitor (M_ZAMS≥ 23-25 M_☉) for SN 1999dn.

Based on observations collected at the European Organisation for Astronomical Research in the Southern hemisphere, Chile [European Southern Observatory (ESO) programmes 64.H-0604 and 65.H-0292], at the Italian 3.58-m Telescopio Nazionale Galileo and the William Herschel Telescope (WHT; La Palma, Spain), and at the Copernico telescope (Asiago, Italy).