A new look at the pulsating DB white dwarf GD 358: Line-of-sight velocity measurements and constraints on model atmospheres
(2003) In Astronomy & Astrophysics 397. p.1043-1055- Abstract
- We report on our findings of the bright, pulsating, helium atmospherewhite dwarf GD 358, based on time-resolved optical spectrophotometry. Weidentify 5 real pulsation modes and at least 6 combination modes atfrequencies consistent with those found in previous observations. Themeasured Doppler shifts from our spectra show variations with amplitudesof up to 5.5 km s<SUP>-1</SUP> at the frequencies inferred from the fluxvariations. We conclude that these are variations in the line-of-sightvelocities associated with the pulsational motion. We use the observedflux and velocity amplitudes and phases to test theoretical predictionswithin the convective driving framework, and compare these with similarobservations of the hydrogen... (More)
- We report on our findings of the bright, pulsating, helium atmospherewhite dwarf GD 358, based on time-resolved optical spectrophotometry. Weidentify 5 real pulsation modes and at least 6 combination modes atfrequencies consistent with those found in previous observations. Themeasured Doppler shifts from our spectra show variations with amplitudesof up to 5.5 km s<SUP>-1</SUP> at the frequencies inferred from the fluxvariations. We conclude that these are variations in the line-of-sightvelocities associated with the pulsational motion. We use the observedflux and velocity amplitudes and phases to test theoretical predictionswithin the convective driving framework, and compare these with similarobservations of the hydrogen atmosphere white dwarf pulsators (DAVs).The wavelength dependence of the fractional pulsation amplitudes(chromatic amplitudes) allows us to conclude that all five real modesshare the same spherical degree, most likely, l=1. This is consistentwith previous identifications based solely on photometry. We find that ahigh signal-to-noise mean spectrum on its own is not enough to determinethe atmospheric parameters and that there are small but significantdiscrepancies between the observations and model atmospheres. The sourceof these remains to be identified. While we infer T<SUB>eff</SUB> =24 kKand log g ~ 8.0 from the mean spectrum, the chromatic amplitudes, whichare a measure of the derivative of the flux with respect to thetemperature, unambiguously favour a higher effective temperature, 27 kK,which is more in line with independent determinations from ultra-violetspectra.The data presented herein were obtained at the W.M. Keck Observatory,which is operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W.M. Keck Foundation. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/130623
- author
- Kotak, Rubina LU ; van Kerkwijk, M. H. ; Clemens, J. C. and Koester, D.
- organization
- publishing date
- 2003
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- stars: atmospheres, convection, stars: individual: GD 358, stars: white dwarfs, stars: oscillations
- in
- Astronomy & Astrophysics
- volume
- 397
- pages
- 1043 - 1055
- publisher
- EDP Sciences
- external identifiers
-
- wos:000180249800032
- scopus:0037252804
- ISSN
- 0004-6361
- DOI
- 10.1051/0004-6361:20021580
- language
- English
- LU publication?
- yes
- id
- e14eb0ec-654e-4913-9d95-e25d34cad35f (old id 130623)
- date added to LUP
- 2016-04-01 16:33:56
- date last changed
- 2022-12-12 19:46:07
@article{e14eb0ec-654e-4913-9d95-e25d34cad35f,
abstract = {{We report on our findings of the bright, pulsating, helium atmospherewhite dwarf GD 358, based on time-resolved optical spectrophotometry. Weidentify 5 real pulsation modes and at least 6 combination modes atfrequencies consistent with those found in previous observations. Themeasured Doppler shifts from our spectra show variations with amplitudesof up to 5.5 km s<SUP>-1</SUP> at the frequencies inferred from the fluxvariations. We conclude that these are variations in the line-of-sightvelocities associated with the pulsational motion. We use the observedflux and velocity amplitudes and phases to test theoretical predictionswithin the convective driving framework, and compare these with similarobservations of the hydrogen atmosphere white dwarf pulsators (DAVs).The wavelength dependence of the fractional pulsation amplitudes(chromatic amplitudes) allows us to conclude that all five real modesshare the same spherical degree, most likely, l=1. This is consistentwith previous identifications based solely on photometry. We find that ahigh signal-to-noise mean spectrum on its own is not enough to determinethe atmospheric parameters and that there are small but significantdiscrepancies between the observations and model atmospheres. The sourceof these remains to be identified. While we infer T<SUB>eff</SUB> =24 kKand log g ~ 8.0 from the mean spectrum, the chromatic amplitudes, whichare a measure of the derivative of the flux with respect to thetemperature, unambiguously favour a higher effective temperature, 27 kK,which is more in line with independent determinations from ultra-violetspectra.The data presented herein were obtained at the W.M. Keck Observatory,which is operated as a scientific partnership among the CaliforniaInstitute of Technology, the University of California and the NationalAeronautics and Space Administration. The Observatory was made possibleby the generous financial support of the W.M. Keck Foundation.}},
author = {{Kotak, Rubina and van Kerkwijk, M. H. and Clemens, J. C. and Koester, D.}},
issn = {{0004-6361}},
keywords = {{stars: atmospheres; convection; stars: individual: GD 358; stars: white dwarfs; stars: oscillations}},
language = {{eng}},
pages = {{1043--1055}},
publisher = {{EDP Sciences}},
series = {{Astronomy & Astrophysics}},
title = {{A new look at the pulsating DB white dwarf GD 358: Line-of-sight velocity measurements and constraints on model atmospheres}},
url = {{https://lup.lub.lu.se/search/files/4710369/624165.pdf}},
doi = {{10.1051/0004-6361:20021580}},
volume = {{397}},
year = {{2003}},
}