Helium in double-detonation models of type Ia supernovae

The double-detonation explosion model has been considered a candidate for explaining astrophysical transients with a wide range of luminosities. In this model, a carbon-oxygen white dwarf star explodes following detonation of a surface layer of helium. One potential signature of this explosion mecha...

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Published inAstronomy and astrophysics (Berlin) Vol. 599; p. A46
Main Authors Boyle, Aoife, Sim, Stuart A., Hachinger, Stephan, Kerzendorf, Wolfgang
Format Journal Article
LanguageEnglish
Published EDP Sciences 01.03.2017
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Summary:The double-detonation explosion model has been considered a candidate for explaining astrophysical transients with a wide range of luminosities. In this model, a carbon-oxygen white dwarf star explodes following detonation of a surface layer of helium. One potential signature of this explosion mechanism is the presence of unburned helium in the outer ejecta, left over from the surface helium layer. In this paper we present simple approximations to estimate the optical depths of important He i lines in the ejecta of double-detonation models. We use these approximations to compute synthetic spectra, including the He i lines, for double-detonation models obtained from hydrodynamical explosion simulations. Specifically, we focus on photospheric-phase predictions for the near-infrared 10 830 Å and 2 μm lines of He i. We first consider a double detonation model with a luminosity corresponding roughly to normal SNe Ia. This model has a post-explosion unburned He mass of 0.03 M⊙ and our calculations suggest that the 2 μm feature is expected to be very weak but that the 10 830 Å feature may have modest opacity in the outer ejecta. Consequently, we suggest that a moderate-to-weak He i 10 830 Å feature may be expected to form in double-detonation explosions at epochs around maximum light. However, the high velocities of unburned helium predicted by the model (~ 19 000 km s-1) mean that the He i 10 830 Å feature may be confused or blended with the C i 10 690 Å line forming at lower velocities. We also present calculations for the He i 10 830 Å and 2 μm lines for a lower mass (low luminosity) double detonation model, which has a post-explosion He mass of 0.077 M⊙. In this case, both the He i features we consider are strong and can provide a clear observational signature of the double-detonation mechanism.
Bibliography:ark:/67375/80W-1SHWPMGB-F
bibcode:2017A%26A...599A..46B
dkey:10.1051/0004-6361/201629712
istex:B3E22EFBD5C6836BC3E71B1338F10AD26A7225A9
publisher-ID:aa29712-16
e-mail: aoife@mpa-garching.mpg.de (AB)
ObjectType-Article-1
SourceType-Scholarly Journals-1
ObjectType-Feature-2
content type line 23
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201629712