View Full Version : No Trace Of Single Degenerate Companions in Type 1a Spectra

2015-Feb-03, 06:19 PM
A topic of continuing interest. The two main thoughts on type 1a supernovae is that they may originate in predominantly one of two ways:
#1. A white dwarf, situated at a preferred distance, siphons off ablated gas from a red giant or main sequence companion, until the dwarf's mass exceeds the Chandrasekhar Limit, and it detonates.

#2. A white dwarf merges with a second white dwarf, and the resulting merge exceeds the Chandra Limit, and it detontes.

The first is known as the Single Degenerate (SD) scenario. The second is known as the Double Degenerate scenario (DD). Determining the exact nature is pretty critical to limiting models, and using type 1a's as standard candles in astrophysics. So far it's still a task in the works. This paper by Lundqvist, Garnavich, etc...gives a recent update.
The authors assume that the SD scenario should show late-time spectral evidence of the non-degenerate companion as lines from light elements, including some H-alpha. They futher assume the limits on these light element spectral lines from a DD scenario.They choose spectra of SN 2011fe @ 294 days after explosion, and SN 2014J @ 315 days after explosion. Although not excluding some uncertainty, they conclude the spectral evidence suggests the most likely scenario is that both were DD explosions......no single degenerate companion around.


2015-Feb-03, 11:31 PM
Just to be clear, the thread title is ambiguous. The paper looks at two recent nearby SN 1a. This does not mean that there is never a single degenrate SN 1a, merely that these two were probably both double degenerate.

2015-Feb-10, 03:55 AM
On this topic - so far it seems to have shown up only in conference presentations and a white paper (http://keplerscience.arc.nasa.gov/K2/docs/Campaigns/C1/GO1074_Olling.pdf), but Kepler caught a couple of SN Ia on their initial rise during its primary mission and there was no evidence of the light-curve feature expected early on when a shock would be produced from the SN fireball encountering a main-sequence companion. Obviously they'll want to get a better sample if K2 ever scheduling allows, but it's a complementary approach to the spectral modeling.

2015-Feb-12, 02:55 PM
.. and now I hear a talk showing features from a couple of Ia explosions which do show evidence for the shock formed on encountering a main-sequence or larger companion star. Some days you can just hear the Universe laughing, not even behind our backs.

Ken G
2015-Feb-12, 04:16 PM
It certainly seems like nature is determined to not be pinned down by the either one way, or the other way, of making type Ias (and don't forget Craig Wheeler's third way, the white widows!). Against all that, bear in mind that our understanding of the number of close binaries with white dwarfs suggests we should see more type Ia than we actually do, so we are not really looking for more ways to get them-- a more restricted class of possible mechanisms would be more pleasing!