Kavli Affiliate: Lars Bildsten
| First 5 Authors: Thomas Kupfer, Evan B. Bauer, Jan van Roestel, Eric C. Bellm, Lars Bildsten
| Summary:
We present the discovery of a new double detonation progenitor system
consisting of a hot subdwarf B (sdB) binary with a white dwarf companion with
an P=76.34179(2) min orbital period. Spectroscopic observations are consistent
with an sdB star during helium core burning residing on the extreme horizontal
branch. Chimera light curves are dominated by ellipsoidal deformation of the
sdB star and a weak eclipse of the companion white dwarf. Combining
spectroscopic and light curve fits we find a low mass sdB star, $M_{rm
sdB}=0.383pm0.028$ M$_odot$ with a massive white dwarf companion, $M_{rm
WD}=0.725pm0.026$ M$_odot$. From the eclipses we find a blackbody temperature
for the white dwarf of 26,800 K resulting in a cooling age of $approx$25 Myrs
whereas our MESA model predicts an sdB age of $approx$170 Myrs. We conclude
that the sdB formed first through stable mass transfer followed by a common
envelope which led to the formation of the white dwarf companion $approx$25
Myrs ago.
Using the MESA stellar evolutionary code we find that the sdB star will start
mass transfer in $approx$6 Myrs and in $approx$60 Myrs the white dwarf will
reach a total mass of $0.92$ M$_odot$ with a thick helium layer of $0.17$
M$_odot$. This will lead to a detonation that will likely destroy the white
dwarf in a peculiar thermonuclear supernova. PTF1 2238+7430 is only the second
confirmed candidate for a double detonation thermonuclear supernova. Using both
systems we estimate that at least $approx$1% of white dwarf thermonuclear
supernovae originate from sdB+WD binaries with thick helium layers, consistent
with the small number of observed peculiar thermonuclear explosions.
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