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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
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SEQUENCE:1
UID:UW-Physics-Event-8173
DTSTART:20230202T213000Z
DTEND:20230202T223000Z
DTSTAMP:20260414T054746Z
LAST-MODIFIED:20230124T203804Z
LOCATION:4421 Sterling Hall
SUMMARY:The discovery and properties of binary-stripped helium stars\,
  Astronomy Colloquium\, Ylva Götberg\, Carnegie Observatories
DESCRIPTION:Massive stars stripped of their H-rich envelopes through m
 ass transfer or common envelope ejection are thought to be the main pr
 ogenitors of H-poor supernovae\, to emit large amounts of hard ionizin
 g radiation\, and to constitute two necessary steps in the binary evol
 ution pathways towards compact objects merging in gravitational wave e
 vents. Despite their importance\, these stripped helium stars have rem
 ained elusive. With new UV photometry combined with optical magnitudes
 \, and follow-up optical spectroscopy\, we identified a first sample o
 f dozens of such stripped star systems in the Magellanic Clouds. We ob
 tain estimates for their stellar parameters by fitting their optical s
 pectra to a newly computed grid of helium star atmosphere models. Alig
 ned with theoretical expectations\, we find that stripped stars are ho
 t (Teff~50-100 kK)\, compact (log g ~ 5)\, He-rich (Y_surf ~0.6-1)\, a
 nd H-poor (X_surf ~0-0.4). Furthermore\, by matching the spectroscopic
  fits with the photometrical data\, we find small radii (~1 Rsun)\, a 
 range of luminosities (L ~ 1\,000-100\,000 Lsun)\, and masses that are
  sufficient to lead to core-collapse (~2-8 Msun). There are strong ind
 ications that the stellar winds are surprisingly weak\, suggesting tha
 t binary-stripped helium stars are the main responsible for both IIb a
 nd Ib supernovae.  Apart from providing an observational anchor for bo
 th binary evolution models and simulations of common envelope ejection
 \, this sample of stars proves that the full mass range of helium star
 s exists\, forming a bridge between subdwarfs and Wolf-Rayet stars.
URL:https://www.physics.wisc.edu/events/?id=8173
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