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A puzzling periodicity in the pulsating DA white dwarf G 117-B15A

Kotak, Rubina LU ; van Kerkwijk, M H and Clemens, J C (2004) In Astronomy & Astrophysics 413. p.301-308
Abstract
We present time-resolved optical spectrophotometry of the pulsatinghydrogen atmosphere (DA) white dwarf G 117-B15A. We find threeperiodicities in the pulsation spectrum (215 s, 272 s, and 304 s) all ofwhich have been found in earlier studies. By comparing the fractionalwavelength dependence of the pulsation amplitudes (chromatic amplitudes)with models, we confirm a previous report that the strongest mode, at215 s, has ℓ=1. The chromatic amplitude for the 272 s mode is verypuzzling, showing an increase in fractional amplitude with wavelengththat cannot be reproduced by the models for any ℓ at opticalwavelengths. Based on archival HST data, we show that while thebehaviour of the 215 s mode at ultra-violet wavelengths is as expectedfrom... (More)
We present time-resolved optical spectrophotometry of the pulsatinghydrogen atmosphere (DA) white dwarf G 117-B15A. We find threeperiodicities in the pulsation spectrum (215 s, 272 s, and 304 s) all ofwhich have been found in earlier studies. By comparing the fractionalwavelength dependence of the pulsation amplitudes (chromatic amplitudes)with models, we confirm a previous report that the strongest mode, at215 s, has ℓ=1. The chromatic amplitude for the 272 s mode is verypuzzling, showing an increase in fractional amplitude with wavelengththat cannot be reproduced by the models for any ℓ at opticalwavelengths. Based on archival HST data, we show that while thebehaviour of the 215 s mode at ultra-violet wavelengths is as expectedfrom models, the weird behaviour of the 272 s periodicity is notrestricted to optical wavelengths in that it fails to show the expectedincrease in fractional amplitude towards shorter wavelengths. We discusspossible causes for the discrepancies found for the 272 s variation, butfind that all are lacking, and conclude that the nature of thisperiodicity remains unclear.Based in part on data obtained at the W.M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California and the National Aeronauticsand Space Administration. The Observatory was made possible by thegenerous financial support of the W.M. Keck Foundation. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
stars: white dwarfs, stars: oscillations, stars: individual: G 117-B15A
in
Astronomy & Astrophysics
volume
413
pages
301 - 308
publisher
EDP Sciences
external identifiers
  • wos:000187356300033
  • scopus:0348170674
ISSN
0004-6361
DOI
10.1051/0004-6361:20031516
language
English
LU publication?
yes
id
5d1e50c1-9191-4e15-a907-4eab9de75a12 (old id 129649)
date added to LUP
2007-07-13 13:41:21
date last changed
2017-01-01 07:22:01
@article{5d1e50c1-9191-4e15-a907-4eab9de75a12,
  abstract     = {We present time-resolved optical spectrophotometry of the pulsatinghydrogen atmosphere (DA) white dwarf G 117-B15A. We find threeperiodicities in the pulsation spectrum (215 s, 272 s, and 304 s) all ofwhich have been found in earlier studies. By comparing the fractionalwavelength dependence of the pulsation amplitudes (chromatic amplitudes)with models, we confirm a previous report that the strongest mode, at215 s, has ℓ=1. The chromatic amplitude for the 272 s mode is verypuzzling, showing an increase in fractional amplitude with wavelengththat cannot be reproduced by the models for any ℓ at opticalwavelengths. Based on archival HST data, we show that while thebehaviour of the 215 s mode at ultra-violet wavelengths is as expectedfrom models, the weird behaviour of the 272 s periodicity is notrestricted to optical wavelengths in that it fails to show the expectedincrease in fractional amplitude towards shorter wavelengths. We discusspossible causes for the discrepancies found for the 272 s variation, butfind that all are lacking, and conclude that the nature of thisperiodicity remains unclear.Based in part on data obtained at the W.M. Keck Observatory, which isoperated as a scientific partnership among the California Institute ofTechnology, the University of California and the National Aeronauticsand Space Administration. The Observatory was made possible by thegenerous financial support of the W.M. Keck Foundation.},
  author       = {Kotak, Rubina and van Kerkwijk, M H and Clemens, J C},
  issn         = {0004-6361},
  keyword      = {stars: white dwarfs,stars: oscillations,stars: individual: G 117-B15A},
  language     = {eng},
  pages        = {301--308},
  publisher    = {EDP Sciences},
  series       = {Astronomy & Astrophysics},
  title        = {A puzzling periodicity in the pulsating DA white dwarf G 117-B15A},
  url          = {http://dx.doi.org/10.1051/0004-6361:20031516},
  volume       = {413},
  year         = {2004},
}