Ryan J. Foley, Robert P. Kirshner
Two "twin" Type Ia supernovae (SNe Ia), SNe 2011by and 2011fe, despite having extremely similar optical light curves and spectra, have different ultraviolet (UV) continua as measured in Hubble Space Telescope spectra. The difference in UV continua is inferred to be the result of significantly different progenitor metallicities. This is the first robust detection of different metallicities for SN Ia progenitors. SNe Ia with higher progenitor metallicities are expected to have lower 56Ni yields, and thus lower luminosities, for the same light-curve shape. As a result, progenitor metallicity is a potential systematic bias for measuring SN Ia distances. SNe 2011by and 2011fe have slightly different peak luminosities, which correspond to different 56Ni yields: M_11fe(56Ni)/M_11by(56Ni) = 1.7^+0.7_-0.5. From theoretical models, the differences in 56Ni yields for SNe 2011by and 2011fe imply that their progenitor stars had supersolar and subsolar metallicity, respectively. We also examine the UV spectrum of SN 2011iv, a low-luminosity SN Ia hosted by an elliptical galaxy. SNe Ia in elliptical galaxies are expected to have long delay times, and thus low-metallicity progenitors. SNe 2011fe and 2011iv have similar far-UV spectra, giving additional confidence that the progenitor of SN 2011fe had subsolar metallicity. Although we can qualitatively distinguish different progenitor metallicities, the quantitative interpretation in terms of abundances is limited by the present state of theoretical models.
View original:
http://arxiv.org/abs/1302.4479
No comments:
Post a Comment