MSc Thesis: Progenitor Metallicities of 1987A-like Supernovae - Indirect Measurements at Explosion Sites
Astronomy and astrophysics
Tuesday 27 May 2014
to 14:00 at
Context: The case of Supernova (SN) 1987A has represented a singular stellar explosion since the
origin from an uncommon progenitor star, a blue supergiant (BSG), was identified. A metal-poor
environment has been predicted, by stellar evolutionary models, to play a fundamental role to
trigger the explosion during the BSG phase in the single-star scenario. To date, more SN 1987A-
like events have been discovered that enable a systematic study of the progenitor metallicities
in order to address the question whether exists a favoured progenitor star channel between the
binary and the single-star.
Aims: We present an indirect method to constrain the metallicity of the 1987A-like SN progenitor
stars, through the study of a sample of 12 SNe and their host galaxies. The differences between
the local metallicity distributions of our sample with those of the other core-collapse supernova
(CCSN) sub-types were also investigated.
Methods: For each host galaxy, we computed the metallicity at the explosion site through three
separate steps. Firstly, the SN galactocentric distance distribution was determined from the host
galaxy physical parameters. Secondly, the central oxygen abundance of each galaxy was esti-
mated by means of the luminosity-metallicity relationship. Finally, an extrapolation at the SN
positions was obtained by combining the radial distance distributions with a constant metallicity
gradient estimated from a sample of late-type galaxies. Two volume-limited samples of CCSNe
were accurately selected from respectively the Asiago Supernova Catalogue (ASC, 558 SNe) and
the Sloan Digital Sky Survey (SDSS, 346 SNe), to compare the local metallicity distributions of
the other SN sub-types with that of the 1987A-like SNe.
Results: 1987A-like SNe exploded either close to the centre of their faint hosts or at large galactocentric distances from brighter galaxies, presenting both a distribution at higher distances and
a lower environmental metallicities compared with those of the other CCSN sub-types.
Conclusions: The result of moderately low progenitor metallicities for the 1987A-like SNe, ranging from 8.05 dex (Z = 0.004) to 8.48 dex (Z = 0.012), appears to reproduce the dependence on
low metallicity of the single-star scenario for the explosion of BSG stars.