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PRODID:https://murmitoyen.com/events/vanille/udem/
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UID:69db60277e3fc
DTSTAMP:20260412T050439
DTSTART:20171102T113000
SEQUENCE:0
TRANSP:OPAQUE
DTEND:20171102T123000
URL:https://murmitoyen.com/events/vanille/udem/detail/788118-sirius-astroph
 ysical-puzzles-from-astrometry-of-white-dwarfs-in-nearby-visual-binaries-h
 oward-bond-penn-state-university-stsci
LOCATION:Pavillon Roger-Gaudry \, 2900\, boul. Édouard-Montpetit\, Local M
 -415\, Montréal\, QC\, Canada
SUMMARY:Sirius Astrophysical Puzzles from Astrometry of White Dwarfs in Nea
 rby Visual Binaries  - Howard Bond - Penn State University\, STScI
DESCRIPTION:Résumé:
I will discuss Sirius and three other nearby visual b
 inaries in which one component is a white dwarf (WD). Our Hubble Space Tel
 escope astrometry of Sirius and Procyon obtained over the past 2 decades\,
  combined with ground-based data going back to the 19th century\, provides
  precise dynamical masses for the components. A recent analysis of histori
 cal and new ground-based data (and one HST point) for the 40 Eridani BC sy
 stem has also updated the mass of the iconic WD 40 Eri B\, the first one t
 o be discovered. For Stein 2051B\, we determined its mass through HST astr
 ometry of a background star\, relativistically deflected as the WD passed 
 closely in front. Theoretical WD mass-radius relations agree very well wit
 h the new data for all 4 WDs. The derived age (cooling time plus main-sequ
 ence evolution) of Sirius B agrees well with that of the primary Sirius A.
  However\, several astrophysical puzzles remain\, including the high orbit
 al eccentricities of the binaries\, the lack of direct evidence for the ex
 pected past interactions between the stars\, and the evidence that many WD
 s have very thin outer hydrogen layers compared to theoretical expectation
 .
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