Astronomy and Astrophysics – Astronomy
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aj....107..662a&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 107, no. 2, p. 662-672
Astronomy and Astrophysics
Astronomy
96
B Stars, Binary Stars, Blue Stars, Magellanic Clouds, O Stars, Optical Properties, Spectral Energy Distribution, Stellar Evolution, Stellar Models, Stellar Spectra, Supergiant Stars, Supernovae, Ubv Spectra, Astronomical Photography, Astronomical Photometry, Charge Coupled Devices, Hertzsprung-Russell Diagram, Light Curve, Stellar Mass
Scientific paper
We present a homogeneous set of UBVRc IC photometry of the progenitor of supernova (SN) 1993J in M81. The photometry is inconsistent with the spectral energy distribution of a single star for any reasonable extinction (AV less than 3 mag). Models of the spectral energy distribution which include the spectra of a red and a blue star, or of a red star plus the net spectrum of an OB association, give excellent agreement with our photometry. The progenitor image is embedded in weak extended emission, which further supports a composite model, and an OB association contamination model in particular. Stellar evolution theory, along with the plausibility of the OB association contamination model, favors the choice of the red star as the progenitor of SN 1993J. The best fitting models for the red star indicate that it is a KOI with Mbol approximately -7.8. The allowed range (95% confidence) of the optical parameters for representative extinction values is: spectral type G8I - K51; Mbol = -6.8 - -7.9, for AV = 0.5 mag, and spectral type G2I - K5I; Mbol = -7.4 - -8.2, for AV = 1.0 mag. The properties of the red star do not support the canonical stellar evolution scenario in which M supergiants are the progenitors of Type II supernovae. Rather, some evolution to the blue, presumably following the M supergiant phase, is required in order to match our observations. Two factors which are likely to be important in explaining the red star's unexpected location in the Hertzsprung-Russell (H-R) diagram are that it may be in a mass-transfer binary and that it is probably metal rich. Our estimate for the mass of the red star (approximately 17 solar mass) indicates that it had an initial mass very similar to (the much bluer) SN 1987A. We note that the LMC and inner region M81 exhibit an approximately = 0.7 dex difference in metallicity. The assumption that this metallicity difference applies to SN 1987A and SN 1993J suggests that metallicity may play an important role in determining the extent of blueward post-red supergiant (RSG) evolution. The secondary maximum and lack of a plateau in the light curve of SN 1993J have led several authors to conclude that the progenitor of SN 1993J had a very low mass hydrogen envelope. It has been suggested that removal of the hydrogen envelope by mass transfer in a binary system could result in post-RSG evolution toward the blue.
Aldering Greg
Humphreys Roberta M.
Richmond Michael
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