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Published September 10, 2012 | Published
Journal Article Open

The Red Supergiant Progenitor of Supernova 2012aw (PTF12bvh) in Messier 95

Abstract

We report on the direct detection and characterization of the probable red supergiant (RSG) progenitor of the intermediate-luminosity Type II-Plateau (II-P) supernova (SN) 2012aw in the nearby (10.0 Mpc) spiral galaxy Messier 95 (M95; NGC 3351). We have identified the star in both Hubble Space Telescope images of the host galaxy, obtained 17-18 yr prior to the explosion, and near-infrared ground-based images, obtained 6-12 yr prior to the SN. The luminous supergiant showed evidence for substantial circumstellar dust, manifested as excess line-of-sight extinction. The effective total-to-selective ratio of extinction to the star was R'_V ≈ 4.35, which is significantly different from that of diffuse interstellar dust (i.e., R_V = 3.1), and the total extinction to the star was therefore, on average, A_V ≈ 3.1 mag. We find that the observed spectral energy distribution for the progenitor star is consistent with an effective temperature of 3600 K (spectral type M3), and that the star therefore had a bolometric magnitude of –8.29. Through comparison with recent theoretical massive-star evolutionary tracks we can infer that the RSG progenitor had an initial mass 15 ≲ M_(ini)(M_☉) < 20. Interpolating by eye between the available tracks, we surmise that the star had initial mass ~17-18 M_☉. The circumstellar dust around the progenitor must have been destroyed in the explosion, as the visual extinction to the SN is found to be low (AV = 0.24 mag with R_V = 3.1).

Additional Information

© 2012 American Astronomical Society. Received 2012 May 27; accepted 2012 July 11; published 2012 August 22. We thank the referee for useful comments that helped improve this manuscript. This work is based in part on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by AURA, Inc., under NASA contract NAS5-26555. We thank Nancy Elias-Rosa for initial analysis of the HST and CFHT images, and Mark Sullivan for information about the upper limit to the SN 2012aw/PTF12bvh detection by PTF. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA; the observatory was made possible by the generous financial support of the W. M. Keck Foundation. A.G. is supported by grants from the ISF, BSF, and GIF foundations, a Weizmann Minerva grant, and the Lord Sieff of Brimpton Fund. The research of A.V.F. and his group at UC Berkeley is funded by Gary and Cynthia Bengier, the Richard and Rhoda Goldman Fund, NSF grant AST-0908886, the TABASGO Foundation, and NASA/HST grant AR-12623 from STScI. This work was supported in part by the NSF grant PHY-1066293 and the hospitality of the Aspen Center for Physics. We dedicate this paper to the memory of our dear friend and colleague, Weidong Li, with whom two of us (A.V.F. and S.D.V.) spent many fun years identifying the progenitor stars of SNe; his tragic passing deeply saddened those who knew him.

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August 22, 2023
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