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Envelope-Stripping in Binaries
Envelope-Stripping in Binaries
My research focuses on understanding the evolution and impact of massive interacting binaries. I have focused specifically on massive stars stripped of their hydrogen-rich envelopes through mass transfer or common envelope ejection. The existence of these stripped stars was predicted over half a century ago, but only recently the first sample has been identified observationally.
Below, I highlight a few recent efforts done within my team and collaborations.
Huge increase in stripped star candidates
Huge increase in stripped star candidates
Bethany Ludwig (postdoctoral researcher at KU Leuven) submitted an extensive study that systematically and carefully collects all sources in the Swift data of the Magellanic Clouds that agree with our expectations for envelope-stripped stars. Bethany has increased the sample size from dozens to hundreds.
The entire UV photometry catalog that will be made available contains over 700,000 sources.
Metallicity affect stripped star masses
Metallicity affect stripped star masses
Beryl Hovis-Afflerbach (now graduate student at U Northwestern) published an article about how the mass distribution of stripped stars is affected by metallicity. We demonstrated that the number of massive stripped stars (>7 Msun) is predicted to be strongly quenched at low metallicities because of intermediate convection zones that cause the many binaries to not interact on time. However, we also note how important the massive stripped stars could be for the hard, helium ionizing emission that is radiated in stellar populations.
First BLOeM binary results
First BLOeM binary results
The Binarity at LOw Metallicity (BLOeM) collaboration publishes the first results for the large spectroscopic ESO program in the SMC. These include:
Binary fraction of Oe/Be stars by Bodensteiner et al. (2025)
Binary fraction of cool supergiants by Patrick et al. (2025)
Binary fraction of blue supergiants by Britavskiy et al. (2025)
Binary fraction of early B-type main sequence stars by Villaseñor et al. (2025)
Observed properties of stripped stars
Observed properties of stripped stars
We measure the stellar properties of stripped stars by fitting observed optical spectra with a new spectral model grid computed with CMFGEN. We find that the stars agree well with our expectations for core-helium burning stripped stars: they are extremely hot (Teff~50-100 kK), compact (log g ~ 5), and helium-rich (X(He, surface) ~ 0.5-1).
The work was published in the Astrophysical Journal (Götberg et al. 2023).
Missing population discovered!
Missing population discovered!
We use ultraviolet excess to identify hot candidate stripped stars in the Magellanic Clouds. We present follow-up optical spectroscopy that shows a clear agreement with our expectations from both binary evolution models and spectral model predictions.
The work was published in Science (Drout & Götberg et al. 2023).
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