Modeling R Coronae Borealis Stars: Effects of He-Burning Shell Temperature and Metallicity. (arXiv:2007.03076v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Crawford_C/0/1/0/all/0/1">Courtney L. Crawford</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clayton_G/0/1/0/all/0/1">Geoffrey C. Clayton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Munson_B/0/1/0/all/0/1">Bradley Munson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Chatzopoulos_E/0/1/0/all/0/1">Emmanouil Chatzopoulos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Frank_J/0/1/0/all/0/1">Juhan Frank</a>
The R Coronae Borealis (RCB) stars are extremely hydrogen-deficient carbon
stars which produce large amounts of dust, causing sudden deep declines in
brightness. They are believed to be formed primarily through white dwarf
mergers. In this paper, we use MESA to investigate how post-merger objects with
a range of He-burning shell temperatures from 2.1 – 5.4 x 10^8 K with solar and
subsolar metallicities evolve into RCB stars. The most successful model of
these has subsolar metallicity and a temperature near 3 x 10^8 K. We find a
strong dependence on He-burning shell temperature for surface abundances of
elements involved in the CNO cycle, as well as differences in effective
temperature and radius of RCBs. We find around 1 dex diminished surface
abundances for the models with 10% subsolar metallicity, which is expected.
Models with subsolar metallicities also exhibit longer lifetimes than their
solar counterparts. Additionally, we find that convective mixing of the burned
material occurs only in the first few years of post-merger evolution, after
which the surface abundances are constant during and after the RCB phase,
providing evidence for why these stars show a strong enhancement of partial
He-burning products.
The R Coronae Borealis (RCB) stars are extremely hydrogen-deficient carbon
stars which produce large amounts of dust, causing sudden deep declines in
brightness. They are believed to be formed primarily through white dwarf
mergers. In this paper, we use MESA to investigate how post-merger objects with
a range of He-burning shell temperatures from 2.1 – 5.4 x 10^8 K with solar and
subsolar metallicities evolve into RCB stars. The most successful model of
these has subsolar metallicity and a temperature near 3 x 10^8 K. We find a
strong dependence on He-burning shell temperature for surface abundances of
elements involved in the CNO cycle, as well as differences in effective
temperature and radius of RCBs. We find around 1 dex diminished surface
abundances for the models with 10% subsolar metallicity, which is expected.
Models with subsolar metallicities also exhibit longer lifetimes than their
solar counterparts. Additionally, we find that convective mixing of the burned
material occurs only in the first few years of post-merger evolution, after
which the surface abundances are constant during and after the RCB phase,
providing evidence for why these stars show a strong enhancement of partial
He-burning products.
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