J/A+A/657/A121 Collisional effects in blue wing of Balmer-alpha (Allard+, 2022)
Collisional effects in the blue wing of the Balmer-alpha line.
Allard N.F., Spiegelman F., Kielkopf J.F., Bourdreux S.
<Astron. Astrophys. 657, A121 (2022)>
=2022A&A...657A.121A 2022A&A...657A.121A (SIMBAD/NED BibCode)
ADC_Keywords: Atomic physics
Keywords: line profile - white dwarf
Abstract:
In order to investigate the near wing of the Lyman-α line,
accurate line profile calculations and molecular data are both
required due to the existence of a close line satellite responsible
for its asymmetrical shape. Lyman-α lines observed with the
Cosmic Origin Spectograph (COS) on the Hubble Space Telescope (HST)
show this peculiarity in the spectra of DBA and DA white dwarf stars.
A similar asymmetrical shape in the blue wing can be predicted in the
Balmer-α line of H perturbed by He and H atoms.
In continuation with a very recent work on the Lyman-α line,
where the n = 2 potential energies and transition dipole moments from
the ground state were determined, we present new accurate H-He
potential energies and electronic transition dipole moments involving
the molecular states correlated with H(n=3)+He and their transition
dipole moments with the states correlated with H(n=2)+He. Those new
data and existing molecular data for H(n=2,3)-H are used to provide a
theoretical investigation of the collisional effects in the blue wing
of the Balmer-α line of H perturbed by He and H atoms. We note
the consequences for the Balmer-α line shape in the physical
conditions found in the cool atmosphere of DZA white dwarfs where
helium densities may be as high as 1021cm-3. This study is
undertaken with a unified theory of spectral line broadening valid at
very high helium densities.
Description:
Fig. 6:
Unified profile of the Balmer alpha line broadened by He collisions
with the He density 5x10-20cm-3. The temperature is 8000K.
Fig. 10:
Unified profile of the Balmer alpha line resonance broadened by H-H
collisions with the H density 10-18cm3. The temperature is 5000K.
Here ω is the wavenumber (energy) offset from the line center.
The wavelength is 1/λ=ω0+ω where ω0 is
the line center energy in cm-1.
The relationship between the computed cross section, given here, and
the normalized absorption coefficient is:
I(Δω)=σ(Δω)/πr0f where r0 is the
classical radius of the electron, and f is the oscillator strength of
the entire transition.
The cross-sections are linearly dependent on density for densities
less than 5x10-20cm-3 and can be obtained by linear extrapolation
below that limit.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig6.dat 19 357 Unified profile of the Balmer alpha line
broadened by He collisions with the He density
5x10-20cm-3. The temperature is 8000K.
fig10.dat 17 3999 Unified profile of the Balmer alpha line
resonance broadened by H-H collisions with the
H density 10-18cm3. The temperature is 5000K.
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Byte-by-byte Description of file: fig6.dat
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Bytes Format Units Label Explanations
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1- 5 I5 cm-1 Deltaomega Wavenumber (energy) offset from the
line center
7- 19 F13.10 10-16cm+2 sigma Computed cross section
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Byte-by-byte Description of file: fig10.dat
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Bytes Format Units Label Explanations
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1- 5 I5 cm-1 Deltaomega Wavenumber (energy) offset from the
line center
7- 17 F11.8 10-20cm+2 sigma Computed cross section
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Acknowledgements:
Nicole Allard, nicole.allard(at)obspm.fr
(End) Patricia Vannier [CDS] 30-Dec-2021