Single-degenerate type Ia supernovae without hydrogen contamination

TL;DR

This paper proposes that in single-degenerate type Ia supernovae, donor stars can exhaust their hydrogen envelopes before explosion, explaining the lack of hydrogen in observed spectra and aligning with circumstellar observations.

Contribution

It introduces a model where donor stars in single-degenerate SN Ia progenitors rapidly lose their hydrogen envelopes before explosion, accounting for hydrogen absence in spectra.

Findings

Hydrogen in progenitor systems can be below detection limits.

Donor stars become much smaller than their Roche lobes before explosion.

The model explains circumstellar structures observed in SN 2006X.

Abstract

The lack of hydrogen in spectra of type Ia supernovae (SN Ia) is often seen as troublesome for single-degenerate (SD) progenitor models. We argue that, since continued accretion of angular momentum can prevent explosion of the white dwarf, it may be natural for the donor stars in SD progenitors of SN Ia to exhaust their envelopes and shrink rapidly before the explosion. This outcome seems most likely for SD SN Ia progenitors where mass-transfer begins from a giant donor star, and might extend to other SD systems. Not only is the amount of hydrogen left in such a system below the current detection limit, but the donor star is typically orders of magnitude smaller than its Roche lobe by the point when a SD SN Ia occurs, in which case attempts to observe collisions between SN shocks and giant donor stars seem unlikely to succeed. We consider the constraints on this model from the circumstellar structures seen in spectra of SN 2006X and suggest a novel explanation for the origin of this material.