J/MNRAS/496/1881 Abundances in cool metal-polluted white dwarfs (Blouin, 2020)
Magnesium abundances in cool metal-polluted white dwarfs.
Blouin S.
<Mon. Not. R. Astron. Soc., 496, 1881-1890 (2020)>
=2020MNRAS.496.1881B 2020MNRAS.496.1881B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, white dwarf ; Abundances, peculiar ;
Effective temperatures ; Stars, masses ; Stars, distances ;
Stars, distances ; Photometry, ugriz
Keywords: planets and satellites: composition - stars: abundances -
stars: atmospheres - white dwarfs
Abstract:
The accretion of rocky material is responsible for the presence of
heavy elements in the atmospheres of a large fraction of white dwarf
stars. Those objects represent a unique opportunity to infer the bulk
composition of exoplanetesimals. This chemical characterization
requires the use of detailed atmosphere models to determine the
elemental abundances at the photospheres of white dwarfs. In this
work, we use a state-of-the-art model atmosphere code to reanalyse the
first large survey of metal-polluted white dwarfs for which abundances
are found for multiple elements. We show that the improved
constitutive physics of our models lead to systematically higher Mg
abundances than previous analyses. We find an average logMg/Ca number
abundance ratio of 1.5. This value is significantly above the
reference abundance for chondrites, which is expected as current
diffusion models predict that for the cool helium-atmosphere white
dwarfs of our sample, Mg should remain in the atmosphere longer than
Ca. This helps resolve a recently identified Mg depletion problem,
where the planetesimals accreted by white dwarfs were reported to be
Mg-deficient compared to the expected composition of their planetary
systems.
Description:
Our sample is identical to the Sloan Digital Sky Survey (SDSS) sample
analysed in Hollands et al. (2017MNRAS.467.4970H 2017MNRAS.467.4970H, Cat.
J/MNRAS/467/4970), but we excluded the 27 known magnetic objects. We
decided to exclude magnetic DZs as a description of line broadening
under strong magnetic fields (B>1MG) and high helium densities is not
yet available. From the results of Hollands et al.
(2017MNRAS.467.4970H 2017MNRAS.467.4970H, Cat. J/MNRAS/467/4970), we are confident that
excluding magnetic objects will not induce a bias in the average
abundances of our sample. We also excluded SDSS J122656.39+293643.9
since its SDSS spectrum is so noisy that we are unable to extract any
meaningful abundances from it, as well as SDSS J051212.78-050503.4 and
SDSS J082303.82+054656.1, for which no SDSS spectrum is available. In
total, the sample analysed here contains 201 objects. Their
observational properties (ugriz photometry and Gaia DR2 distances) are
listed in Table 1.
The model atmosphere code used in this paper is described at length in
Blouin et al. (2018ApJ...863..184B 2018ApJ...863..184B, 2018ApJ...867..161B 2018ApJ...867..161B). Of
particular importance for this work are the unified line profiles that
are used to retrieve the photospheric abundances of Ca and Mg. We
computed a six-dimensional grid of model atmospheres with Teff
varying from 4000 to 9000K in steps of 500K, logg from 7.0 to 9.0 in
steps of 0.5dex, logH/He from -5 to -2 in steps of 1dex, logCa/He from
-11 to -7 in steps of 0.5dex, logMg/Ca from 0.24 to 2.24 in steps of
0.5dex, and logFe/Ca from 0.16 to 2.16 in steps of 0.5dex. The
atmospheric parameters found with the fitting procedure are listed in
Table 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 98 201 Observational data
table2.dat 88 201 Atmospheric parameters
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See also:
I/347 : Distances to 1.33 billion stars in Gaia DR2
(Bailer-Jones+, 2018)
J/MNRAS/467/4970 : Cool DZ white dwarfs. I. (Hollands+, 2017)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16)
(Ahumada+, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Name SDSS identifier (JHHMMSS.ss+DDMMSS.s)
21- 45 A25 --- OName Montreal White Dwarf Database identifier
47- 51 F5.2 mag umag SDSS u-band magnitude
53- 57 F5.2 mag gmag SDSS g-band magnitude
59- 63 F5.2 mag rmag SDSS r-band magnitude
65- 69 F5.2 mag imag SDSS i-band magnitude
71- 76 F6.3 mag zmag SDSS z-band magnitude
78- 83 F6.2 pc Dist ? Estimated distance from Bailer-Jones
(2018AJ....156...58B 2018AJ....156...58B, Cat. I/347)
85- 90 F6.2 pc b_Dist []? Lower bound on Dist
(68 per cent confidence interval)
92- 98 F7.2 pc B_Dist ? Upper bound on Dist
(68 per cent confidence interval)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Name SDSS identifier (JHHMMSS.ss+DDMMSS.s)
21- 24 I4 K Teff Effective temperature
26- 29 I4 K e_Teff Error on Teff
31- 35 F5.3 [cm/s2] logg Surface gravity (1)
37- 41 F5.3 [cm/s2] e_logg ? Error on logg
43- 47 F5.3 Msun Mass ? Star mass
49- 53 F5.3 Msun e_Mass ? Error on Mass
55- 59 F5.1 [-] logCa/He Logarithm of the Ca/He abundance ratio (2)
61- 63 F3.1 [-] e_logCa/He Error on logCa/He
65- 68 F4.1 [-] logMg/He Logarithm of the Mg/He abundance ratio (2)
70- 72 F3.1 [-] e_logMg/He Error on logMg/He
74- 77 F4.1 [-] logFe/He Logarithm of the Fe/He abundance ratio (2)
79- 81 F3.1 [-] e_logFe/He Error on logFe/He
83 A1 --- l_logH/He Limit flag on logH/He
85- 88 F4.1 [-] logH/He Logarithm of the H/He abundance ratio (2)
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Note (1): logg=8 is assumed when no trigonometric parallax is available or when
it is too uncertain
Note (2): All abundances are number abundances
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 29-Jun-2023