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DTSTAMP:20260414T163826
DTSTART:20150423T113000
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URL:https://murmitoyen.com/events/vanille/udem/detail/599523-creating-and-m
 easuring-white-dwarf-photospheres-in-the-laboratory
LOCATION:Université de Montréal - Pavillon Roger-Gaudry\, 2900\, chemin d
 e la Tour\, Montréal\, QC\, Canada\, H3T 1J6
SUMMARY:Creating and Measuring White Dwarf Photospheres in the Laboratory
DESCRIPTION:Ross Falcon\, Sandia National LaboratoriesWhite dwarf (WD) atmo
 spheric parameters (i.e.\, effective temperature\, T_eff\, and surface gr
 avity\, log(g) ) are a foundation for many research threads in astrophysi
 cs\, including: constraining the age of our Galaxy through cosmochronology
 \, probing stellar interiors with asteroseismology\, and determining inte
 rgalactic distances using type 1a supernovae.  Astronomers infer WD atmos
 pheric parameters using atmosphere models\, of which theoretical line pro
 files are critical ingredients.  The standard in the WD-astronomy communi
 ty for theoretical hydrogen line profiles came from the University of Mon
 treal in the work by Tremblay & Bergeron (2009)\, whose improved profiles
  resulted in a systematic increase in the inferred T_eff and log(g) (and 
 hence\, mass) of observed WDs.  Falcon et al. (2010) used an observationa
 l mass-determination method mostly independent from line profiles that in
 corporates gravitational redshifts to also infer an increased WD mean mas
 s.  The significance of these works motivates our laboratory experiments 
 to create plasmas at white dwarf photospheric conditions (electron tempera
 ture\, T_e ~ 1 eV or 12\,000 K\; electron density\, n_e ~ 10^17 cm^-3) to
  test the theoretical profiles used in WD atmosphere models.  We use x-ra
 y radiation produced at the Sandia National Laboratories Z Pulsed Power F
 acility to initiate plasma formation in a large (120x120x10-mm) gas cell 
 and spectroscopically measure multiple hydrogen Balmer lines.  I summariz
 e the plasma formation\, present measured profiles of H Balmer lines\, an
 d discuss plasma-condition diagnosis.  I point out intriguing results sug
 gesting that WD atmospheric parameters inferred from H-beta may be more a
 ccurate than those inferred from higher-order lines.  The consequence of t
 his follows that of Tremblay & Bergeron by trending spectroscopically inf
 erred surface gravities (and masses) to higher values.Présentée par le 
 Groupe Astronomie et astrophysique du Département de physique de l'Univer
 sité de Montréal. Cette conférence est destinée à des spécialistes 
 dans le domaine de l'astrophysique et sera donnée en anglais.
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