Speaker
Description
Post-asymptotic giant branch (post-AGB) stars have recently lost their envelopes and are contracting to higher effective temperatures, while maintaining constant luminosity, to become white dwarfs. About half of the optically bright post-AGB stars are found to exhibit near-infrared excesses in their spectral energy distributions, interpreted as hot dusty discs around the objects, and are observed to be in binaries with orbital periods ranging from 100 to 3000 days. Some post-AGB stars have been found to have luminosities below the luminosity at the tip of the red giant branch (RGB; about 2500 solar luminosities) and are interpreted as post-RGB stars. Post-RGB stars can only form through binary interactions because, unlike AGB stars, RGB stars lack the mass-loss rates required to shed their entire envelopes.
Observed Galactic post-AGB and post-RGB binaries have orbital periods that are at odds with binary population synthesis models. Their orbital periods require the systems to have undergone mass transfer via Roche-lobe overflow, which is thought to be unstable for giant star donors and would result in a common envelope that shortens the orbital period to less than 100 days. However, recent detailed binary evolution models have shown that mass transfer is indeed stable for RGB donors over a substantial binary parameter space.
We therefore compare the Galactic post-RGB binaries with stable mass transfer models containing RGB donors. We determine post-RGB luminosity-orbital period relations for different metallicities and find that they appear to be consistent with the Galactic post-RGB binaries. We use these relations to estimate the orbital periods of Galactic post-RGB stars without known orbital periods, as well as for candidates in the Large Magellanic Cloud and the Small Magellanic Cloud. These predictions can be verified by long-term radial velocity monitoring of these objects, which will help to test our proposed stable mass transfer formation channel for post-RGB binaries.
| Talk category | NOVA Network 3 |
|---|---|
| Preference for a talk or poster | Talk |
| Talk preference for PhD students | 3rd year |
