J/A+A/619/A152 Variation of MgHe line profile with temperature (Allard+, 2018)
Line shapes of the magnesium resonance lines in cool DZ white dwarf atmospheres.
Allard N.F., Kielkopf J.F., Blouin S., Dufour P., Gadea F.X., Leininger T.,
Guillon G.
<Astron. Astrophys. 619, A152 (2018)>
=2018A&A...619A.152A 2018A&A...619A.152A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, white dwarf ; Atomic physics ; Line Profiles
Keywords: line: profiles - white dwarfs - line: formation - atomic processes -
stars: individual: L 119-34
Abstract:
Line shapes of the magnesium resonance lines in white dwarf spectra
are determined by the properties of magnesium atoms and the structure
of the white dwarf atmosphere. Through their blanketing effect, these
lines have a dominant influence on the model structure and thus on the
determination from the spectra of other physical parameters that
describe the stellar atmosphere and elemental abundances.
In continuation of previous work on Mg+He lines in the UV, we present
theoretical profiles of the resonance line of neutral Mg perturbed by
He at the extreme density conditions found in the cool largely
transparent atmosphere of DZ white dwarfs.
We accurately determined the broadening of Mg by He in a unified
theory of collisional line profiles using ab initio calculations of
MgHe potential energies and transition matrix elements among the
singlet electronic states that are involved for the observable
spectral lines.
We computed the shapes and line parameters of the Mg lines and studied
their dependence on helium densities and temperatures. We present
results over the full range of temperatures from 4000 to 12000K needed
for input to stellar spectra models. Atmosphere models were
constructed for a range of effective temperatures and surface
gravities typical for cool DZ white dwarfs. We present synthetic
spectra tracing the behavior of the Mg resonance line profiles under
the low temperatures and high gas pressures prevalent in these
atmospheres.
The determination of accurate opacity data of magnesium resonance
lines together with an improved atmosphere model code lead to a good
fit of cool DZ white dwarf stars. The broadening of spectral lines by
helium needs to be understood to accurately determine the H/He and
Mg/He abundance ratio in DZ white dwarf atmospheres. We emphasize that
no free potential parameters or ad hoc adjustments were used to
calculate the line profiles.
Description:
Fig.5 shows the variation of the absorption cross-section
σ(cm2) of the MgIHe resonance line with temperature.
The relationship between the computed cross section and the normalized
absorption coefficient is:
I(Δω)=σ(Δω)/πr0*f where r0 is the
classical radius of the electron, and f is the oscillator strength of
the transition.
The far red wing is linearly dependent on He density for lower
densities than 1021cm-3 and can be obtained from the tables given
in fig5.dat for T=4000, 6000, 8000 and 12000K (nHe=1021cm-3).
For a more complete profile, opacity tables are available on request
from nicole.allard(at)obspm.fr
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig5.dat 34 435 Cross section of the red wing of the MgIHe
resonance line perturbed by He
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Byte-by-byte Description of file: fig5.dat
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Bytes Format Units Label Explanations
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1- 5 I5 K T Temperature (4000, 6000, 8000 and 12000K)
7- 19 E13.8 0.1nm lambda Wavelength
22- 34 E13.8 cm+2 sigma Absorption cross-section
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Acknowledgements:
Nicole Allard, nicole.allard(at)obspm.fr
(End) Patricia Vannier [CDS] 26-Nov-2018