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Published September 11, 2008 | Published
Journal Article Open

The Type IIb SN 2008ax: spectral and light curve evolution


We present spectroscopy and photometry of the He-rich supernova (SN) 2008ax. The early-time spectra show prominent P-Cygni H lines, which decrease with time and disappear completely about 2 months after the explosion. In the same period He I lines become the most prominent spectral features. SN 2008ax displays the ordinary spectral evolution of a Type IIb supernova. A stringent pre-discovery limit constrains the time of the shock breakout of SN 2008ax to within only a few hours. Its light curve, which peaks in the B band about 20 d after the explosion, strongly resembles that of other He-rich core-collapse supernovae. The observed evolution of SN 2008ax is consistent with the explosion of a young Wolf-Rayet (of WNL type) star, which had retained a thin, low-mass shell of its original H envelope. The overall characteristics of SN 2008ax are reminiscent of those of SN 1993J, except for a likely smaller H mass. This may account for the findings that the progenitor of SN 2008ax was a WNL star and not a K supergiant as in the case of SN 1993J, that a prominent early-time peak is missing in the light curve of SN 2008ax, and that H alpha is observed at higher velocities in SN 2008ax than in SN 1993J.

Additional Information

©2008 The Authors. Journal compilation ©2008 RAS. Accepted 2008 June 19. Received June 19; in original form 2008 May 13. This manuscript is partly based on observations collected at the Hale Telescope, Palomar Observatory, as part of a collaborative agreement between the California Institute of Technology, its divisions Caltech Optical Observatories and the Jet Propulsion Laboratory (operated for NASA), and Cornell University. The paper is also based on observations obtained at the 60-inch Telescope of the Palomar Observatory and 2-m Liverpool Telescope. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. We thank John Dann of the Wise Observatory staff for his expert assistance with the observations. This work, conducted as part of the award 'Understanding the lives of massive stars from birth to supernovae' (SJS) made under the European Heads of Research Councils and European Science Foundation EURYI (European Young Investigator) Awards scheme, was supported by funds from the Participating Organisations of EURYI and the EC Sixth Framework Programme. SJS also thanks the Leverhulme Trust for funding through the Philip Leverhulme Prize scheme. The work of DS was carried out at Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. AG acknowledges the Benoziyo Center for Astrophysics and the William Z. and Eda Bess Novick New Scientists Fund at the Weizmann Institute of Science. We acknowledge the usage of the HyperLeda data base (http://leda.univ-lyon1.fr).

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