Francisco Foster: Evidence for Asymmetric Distribution of Circumstellar Material around Type Ia Supernovae


 “Evidence for Asymmetric Distribution of Circumstellar Material around Type Ia Supernovae”

 Francisco Foster Buron

Universidad de Chile   

We have studied the properties of low-velocity material in the line of sight toward nearby Type
Ia supernovae(SNe Ia) that have measuredlate phase nebular velocity shifts (v_neb), thought to be an
environment-independent observable. We found that the distribution of equivalent widths of narrow
blended Na I D1 and D2 and Ca II H and K absorption lines differs significantly between those SNe Ia with
negative and positive v_neb, with generally stronger absorption forSNe Ia with v_neb >= 0. A similar
result had been found previously for the distribution of colors of SNe Ia, which was interpreted as a
dependence of the temperature of the ejecta with viewing angle. Our work suggests that (1) a significant
part of these differences in color should be attributed to extinction, (2) this extinction is
caused by an asymmetric distribution of circumstellar material (CSM),and (3) the CSM absorption
is generally stronger on the side of the ejecta opposite to where the ignition occurs. Since it is difficult to
explain (3) via any known physical processes that occur before explosion, we argue that the asymmetry
of the CSM is originated after explosion by a stronger ionizing flux on the side of the ejecta where
ignition occurs, probably due to a stronger shock breakout and/or more exposed radioactive
material on one side of the ejecta. This result has important implications for both progenitor
and explosion models.


Sala  de Seminario Inst. Astronomia


Viernes 5 de Octubre de 2012


16:00 horas