J/A+A/640/A25 Metal-poor stars limb-darkening coefficients (Karovicova+, 2020)
Fundamental stellar parameters of benchmark stars from CHARA interferometry.
I. Metal-poor stars.
Karovicova I., White T.R., Nordlander T., Casagrande L., Ireland M.,
Huber D., Jofre P.
<Astron. Astrophys. 640, A25 (2020)>
=2020A&A...640A..25K 2020A&A...640A..25K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, metal-deficient ; Models, atmosphere
Keywords: standards - techniques: interferometric - surveys -
Abstract:
Benchmark stars are crucial as validating standards for current as
well as future large stellar surveys of the Milky Way. However, the
number of suitable metal-poor benchmark stars is currently limited,
owing to the difficulty in determining reliable effective temperatures
(Teff) in this regime. We aim to construct a new set of metal-poor
benchmark stars, based on reliable interferometric effective
temperature determinations and a homogeneous analysis. The aim is to
reach a precision of 1% in Teff, as is crucial for sufficiently
accurate determinations of the full set of fundamental parameters and
abundances for the survey sources. We observed ten late type
metal-poor dwarf and giants: HD 2665, HD 6755, HD 6833, HD 103095,
HD 122563, HD 127243, HD 140283, HD 175305, HD 221170 and HD 224930.
Only three of the ten stars (HD 103095, HD 122563 and HD 140283) have
previously been used as benchmark stars. For the observations, we used
the high angular resolution optical interferometric instrument PAVO at
the CHARA array. We modelled angular diameters using 3D limb darkening
models and determined effective temperatures directly from the
Stefan-Boltzmann relation, with an iterative procedure to interpolate
over tables of bolometric corrections. Surface gravities (log(g)) were
estimated from comparisons to Dartmouth stellar evolution model
tracks. We collected spectroscopic observations from the ELODIE and
FIES spectrographs and estimated metallicities ([Fe/H]) from a 1D
non-LTE abundance analysis of unblended lines of neutral and singly
ionized iron. We inferred Teff to better than 1% for five of the stars
(HD 103095, HD 122563, HD 127243, HD 140283 and HD 224930). The
effective temperatures of the other five stars are reliable to between
2-3%; the higher uncertainty on the Teff for those stars is mainly due
to their having a larger uncertainty in the bolometric fluxes. We also
determined log(g) and [Fe/H] with median uncertainties of 0.03dex and
0.09dex, respectively. This study presents reliable and homogeneous
fundamental stellar parameters for ten metal-poor stars that can be
adopted as a new set of benchmarks. The parameters are based on our
consistent approach of combining interferometric observations, 3D limb
darkening modelling and spectroscopic observations. The next paper in
this series will extend this approach to dwarfs and giants in the
metal-rich regime.
Description:
Limb-darkening coefficients derived for the target stars using the 3D
STAGGER-grid (Magic et al., 2015A&A...573A..90M 2015A&A...573A..90M, Cat. J/A+A/573/A90).
The coefficients a1, a2, a3, and a4 appearing in Eq. 7 of Magic et al.
(2015A&A...573A..90M 2015A&A...573A..90M,) are provided for each star, in 38 observed
channels of the PAVO instrument at the CHARA array (Ireland+, 2008,
Proc. SPIE, 701324). See Sect. 3.1 of the paper for further details.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 33 10 Target stars
tables.dat 55 380 Limb-darkening coefficients a1, a2, a3, a4 in the
38 observed channels for the 10 target stars
(tables 9-18)
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See also:
J/A+A/573/A90 : STAGGER-grid of 3D stellar models. IV. (Magic+, 2015)
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star name
11- 12 I2 h RAh Simbad right ascension (J2000.0)
14- 15 I2 min RAm Simbad right ascension (J2000.0)
17- 21 F5.2 s RAs Simbad right ascension (J2000.0)
23 A1 --- DE- Simbad declination sign (J2000.0)
24- 25 I2 deg DEd Simbad declination (J2000.0)
27- 28 I2 arcmin DEm Simbad declination (J2000.0)
30- 33 F4.1 arcsec DEs Simbad declination (J2000.0)
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Byte-by-byte Description of file: tables.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star Name
11- 12 I2 --- Ch [1/38] Channel number
14- 22 F9.7 --- a1 Limb darkening coefficient a1
24- 33 F10.7 --- a2 Limb darkening coefficient a2
35- 44 F10.7 --- a3 Limb darkening coefficient a3
46- 55 F10.7 --- a4 Limb darkening coefficient a4
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Acknowledgements:
Iva Karovicova, karovicova(at)uni-heidelberg.de
(End) Patricia Vannier [CDS] 10-Jun-2020