THE RED SUPERGIANT PROGENITOR OF SUPERNOVA 2012aw (PTF12bvh) IN MESSIER 95

This is the authors' abstract. We don't add key points for this paper.

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 ( A V = 0.24 mag with R V = 3.1).