Line Profiles of the Calcium I Resonance Line in Cool Metal-polluted White Dwarfs

Metal-polluted white dwarfs (DZ stars) are characterized by a helium-rich atmosphere contaminated by heavy elements traces originating from accreted rocky planetesimals. As a detailed spectroscopic analysis of those objects can reveal the composition of the accreted debris, there is a great interest...

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Bibliographic Details
Published in:The Astrophysical journal 2019-04, Vol.875 (2), p.137
Main Authors: Blouin, S., Allard, N. F., Leininger, T., Gadéa, F. X., Dufour, P.
Format: Article
Language:English
Subjects:
Absorption spectra
Air pollution
Astrophysics
Atmosphere
Atmospheric models
Calcium
Dipole moments
Heavy elements
Helium
Line spectra
line: profiles
opacity
Planet formation
Resonance
Resonance lines
Sciences of the Universe
Solar and Stellar Astrophysics
Spectral absorption
Spectroscopic analysis
stars: individual (SDSS J080440.63+223948.6, WD J2356-209, WD 2251-070)
Temperature range
White dwarf stars
white dwarfs
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Summary:Metal-polluted white dwarfs (DZ stars) are characterized by a helium-rich atmosphere contaminated by heavy elements traces originating from accreted rocky planetesimals. As a detailed spectroscopic analysis of those objects can reveal the composition of the accreted debris, there is a great interest in developing accurate DZ atmosphere models. However, the coolest DZ white dwarfs are challenging to model due to the fluidlike density of their atmospheres. Under such extreme conditions, spectral absorption lines are heavily broadened by interactions with neutral helium, and it is no longer justified to use the conventional Lorentzian profiles. In this work, we determine the theoretical profiles of the Ca i resonance line (the most prominent spectral line for the coolest DZ white dwarfs) in the dense atmospheres of cool DZ white dwarfs. To do so, we use a unified theory of collisional line profiles and accurate ab initio potential energies and transition dipole moments for the CaHe molecule. We present the resulting profiles for the full range of temperatures and helium densities relevant for the modeling of cool, metal-polluted white dwarfs (from 3000 to 6000 K and from 1021 to 1023 cm−3). We also implement these new profiles in our atmosphere models and show that they lead to improved fits to the Ca i resonance line of the coolest DZ white dwarfs.
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/ab1266