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DTSTAMP:20260417T002229
DTSTART:20130117T113000
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URL:https://murmitoyen.com/events/vanille/udem/detail/172899
LOCATION:Université de Montréal - Pavillon Roger-Gaudry\, 2900\, chemin d
 e la Tour\, Montréal\, QC\, Canada\, H3T 1J6
SUMMARY:Glimpses into the Secret Life of Hot Subdwarf Stars 
DESCRIPTION:Elizabeth Green\, Steward Observatory\, University of ArizonaR
 ésumé/abstract:Subdwarf O and B stars are evolved stars that hold the ke
 ys to several incompletely understood areas of stellar evolution\, for exa
 mple\, binary evolution\, mass transfer and common envelopes.  Hot subdwa
 rf stars are believed to be the helium-burning cores of normal\, low mass\
 , red giant stars that have lost nearly all of their hydrogen envelopes ex
 cept for a tiny wisp of hydrogen floating on top of their helium cores.  
 Interestingly\, many hot subdwarf stars have turned out to be multi-mode p
 ulsators\, which have proved incredibly valuable for stellar pulsation stu
 dies and the rapidly expanding field of asteroseismology\, allowing us to 
 test a number of predictions from standard stellar evolutionary theory.  
 During the last two decades\, binary modeling and asteroseismology have be
 en responsible for considerable progress in understanding the current evol
 utionary status of subdwarf B (sdB) stars and the evolutionary channels th
 at produce them.  It is clear that many (most?) sdB stars are the result 
 of various interrelated\, and fairly well understood\, binary evolution sc
 enarios.  In contrast\, the hotter subdwarf O (sdO) stars are much less w
 ell understood\, partly because none of the handful of known sdO pulsators
  are suitable candidates for asteroseismology investigations and partly be
 cause there appear to be very few\, if any\, sdO counterparts to the short
 -period binary systems that are so common among sdB stars.  A number of d
 ifferent theories have been advanced to explain the existence of sdO stars
  and account for their observed properties.Last year we conducted a survey
  of about 25 bright sdO field stars in an effort to identify rapid pulsato
 rs analogous to the recently discovered sdO pulsators in the Omega Cen glo
 bular cluster.  Somewhat surprisingly\, we didn't find a single sdO pulsa
 tor among our field sample.  Instead\, most unexpectedly\, our precision 
 light curves turned up two sdO stars\, and subsequently an sdB star\, whos
 e luminosities were occasionally observed to drop significantly and then f
 licker irregularly in a manner similar to the light from accretion disks i
 n cataclysmic variables.  In particular\, we suggest that these three hot
  subdwarfs are related to the VY Scl class of cataclysmic variables. We wi
 ll discuss further evidence in favor of the hypothesis that many sdO stars
 \, and at least a few sdB stars\, are members of binary systemscontaining 
 a cool component and\, very possibly\, an accretion disk.Ce séminaire est
  présenté par le groupe astronomie et astrophysique du Département de 
 physique de l'Université de Montréal.
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