Observed binary populations reflect the Galactic history. Explaining the orbital period-mass ratio relation in wide hot subdwarf binaries. (arXiv:2003.05665v3 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Vos_J/0/1/0/all/0/1">Joris Vos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bobrick_A/0/1/0/all/0/1">Alexey Bobrick</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vuckovic_M/0/1/0/all/0/1">Maja Vuckovic</a>
Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes
of stable mass transfer from evolved red giants. The orbits of these binaries
show a strong correlation between their orbital periods and mass ratios. The
origins of this correlation have, so far, been lacking a conclusive
explanation. We aim to find a binary evolution model which can explain the
observed correlation. Radii of evolved red giants, and hence the resulting
orbital periods, strongly depend on their metallicity. We have performed a
small but statistically significant binary population synthesis study with the
binary stellar evolution code MESA. We have used a standard model for binary
mass loss and a standard Galactic metallicity history. The resulting sdBs were
selected based on the same criteria as used in observations and then compared
with the observed population. We have achieved an excellent match to the
observed period – mass ratio correlation without explicitly fine-tuning any
parameters. Furthermore, our models produce a good match to the observed period
– metallicity correlation. We predict several new correlations which link the
observed sdB binaries to their progenitors, and a correlation between the
period, metallicity and core mass for subdwarfs and young low-mass He white
dwarfs. We also predict that sdB binaries have distinct orbital properties
depending on whether they formed in the bulge, thin or thick disc, or the halo.
We demonstrate, for the first time, how the metallicity history of the Milky
Way is imprinted in the properties of the observed post-mass transfer binaries.
We show that Galactic chemical evolution is an important factor in binary
population studies of interacting systems containing at least one evolved
low-mass (Mi < 1.6 Msol) component. Finally, we provide an observationally
supported model of mass transfer from low-mass red giants onto main-sequence
stars.
Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes
of stable mass transfer from evolved red giants. The orbits of these binaries
show a strong correlation between their orbital periods and mass ratios. The
origins of this correlation have, so far, been lacking a conclusive
explanation. We aim to find a binary evolution model which can explain the
observed correlation. Radii of evolved red giants, and hence the resulting
orbital periods, strongly depend on their metallicity. We have performed a
small but statistically significant binary population synthesis study with the
binary stellar evolution code MESA. We have used a standard model for binary
mass loss and a standard Galactic metallicity history. The resulting sdBs were
selected based on the same criteria as used in observations and then compared
with the observed population. We have achieved an excellent match to the
observed period – mass ratio correlation without explicitly fine-tuning any
parameters. Furthermore, our models produce a good match to the observed period
– metallicity correlation. We predict several new correlations which link the
observed sdB binaries to their progenitors, and a correlation between the
period, metallicity and core mass for subdwarfs and young low-mass He white
dwarfs. We also predict that sdB binaries have distinct orbital properties
depending on whether they formed in the bulge, thin or thick disc, or the halo.
We demonstrate, for the first time, how the metallicity history of the Milky
Way is imprinted in the properties of the observed post-mass transfer binaries.
We show that Galactic chemical evolution is an important factor in binary
population studies of interacting systems containing at least one evolved
low-mass (Mi < 1.6 Msol) component. Finally, we provide an observationally
supported model of mass transfer from low-mass red giants onto main-sequence
stars.
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