Circumstellar Na I and Ca II lines of type Ia supernovae in symbiotic scenario

TL;DR

This study models circumstellar Na I and Ca II lines in type Ia supernovae within symbiotic systems, concluding that observed lines in SN 2006X likely originate from distant clouds, not the red giant wind.

Contribution

It provides a detailed model of circumstellar line formation considering ionization and heating effects, and constrains mass loss rates in supernova progenitors.

Findings

Na I lines are too weak to detect in typical red giant winds.

Ca II lines can be detected in the wind at certain densities.

Observed lines in SN 2006X originate from distant clouds, not the wind.

Abstract

Formation of circumstellar lines of Na I and Ca II in type Ia supernovae is studied for the case, when supernova explodes in a binary system with a red giant. The model suggests a spherically-symmetric wind and takes into account ionization and heating of the wind by X-rays from the shock wave and by gamma-quanta of ^{56}Ni radioactive decay. For the wind density typical of the red giant the expected optical depth of the wind in Na I lines turnes out too low (\tau<0.001}) to detect the absorption. For the same wind densities the predicted optical depth of Ca II 3934 \AA is sufficient for the detection (\tau>0.1). I conclude that the absorption lines detected in SN 2006X cannot form in the red giant wind; they are rather related to clouds at distances larger than the dust evaporation radius (r>10^{17} cm). From the absence in SN 2006X of Ca II absorption lines not related with the similar Na I components I derive the upper limit of the mass loss rate by the wind with velocity u: \dot{M}<10^{-8}(u/10 km/s) M_{\odot} yr^{-1}.