J/A+A/650/A194 Titans metal-poor reference stars. I. (Giribaldi+, 2021)
Titans metal-poor reference stars.
I. Accurate effective temperatures and surface gravities for dwarfs and
subgiants from 3D non-LTE Hα profiles and Gaia parallaxes.
Giribaldi R.E., da Silva A.R., Smiljanic R., Cornejo Espinoza D.
<Astron. Astrophys. 650, A194 (2021)>
=2021A&A...650A.194G 2021A&A...650A.194G (SIMBAD/NED BibCode)
ADC_Keywords: Stars, metal-deficient ; Effective temperatures ; Stars, masses ;
Abundances, [Fe/H] ; Stars, diameters ; Stars, ages
Keywords: line: profiles - techniques: spectroscopic - surveys -
stars: atmospheres - stars: fundamental parameters -
stars: Population II
Abstract:
Several large stellar spectroscopic surveys are producing overwhelming
amounts of data that can be used for determining stellar atmospheric
parameters and chemical abundances. Nonetheless, the accuracy achieved
in the derived astrophysical parameters is still insufficient, mainly
because of the paucity of adequate calibrators, particularly in the
metal-poor regime ([Fe/H]≤-1.0).
Our aim is to increase the number of metal-poor stellar calibrators
that have accurate parameters. Here, we introduce the Titans
metal-poor reference stars: a sample of 41 dwarf and subgiant stars
with accurate, but model-dependent, parameters.
Effective temperatures (Teff) were derived by fitting observed
Hα profiles with synthetic lines computed using three
dimensional (3D) hydrodynamic model atmospheres that take into account
departures from the local thermodynamic equilibrium (non-LTE effects).
Surface gravities (logg) were computed using evolutionary tracks and
parallaxes from Gaia early-data release 3.
The same methods recover the Teff values of the Gaia benchmark stars,
which are mostly based on interferometric measurements, with a
1σ dispersion of 50K. We assume this to be the accuracy of the
Hα profiles computed from 3D non-LTE models for metal-poor
dwarfs and subgiants, although this is likely an upper-bound estimate
dominated by the uncertainty of the standard Teff values. We achieved
an internal precision typically between 30-40K, these errors dominated
by instrumental effects. The final total uncertainty for the Teff
values of the Titans are thus estimated to be of the order of 1%. The
typical error for logg is 0.04dex. In addition, we identified a few
members of Gaia-Enceladus, of Sequoia, and of the Helmi stream in our
sample. These stars can pave the way for the accurate chemical
characterization of these Galactic substructures.
Using the Titans as reference, large stellar surveys will be able to
improve the internal calibration of their astrophysical parameters.
Ultimately, this sample will help users of data from Gaia and large
surveys in reaching their goal of redefining our understanding of
stars, stellar systems, and the Milky Way.
Description:
The main source of sample stars was the work of Casagrande et al.
(2010A&A...512A..54C 2010A&A...512A..54C, Cat. J/A+A/512/A54). Additional candidates were
assembled from Ryan et al. (1996ApJ...471..254R 1996ApJ...471..254R); Gehren et al.
(2006A&A...451.1065G 2006A&A...451.1065G); Reddy & Lambert (2008MNRAS.391...95R 2008MNRAS.391...95R); Nissen &
Schuster (2010A&A...511L..10N 2010A&A...511L..10N, Cat. J/A+A/511/L10); Beers et al.
(2017ApJ...835...81B 2017ApJ...835...81B, Cat. J/ApJ/835/81).
Table 2 displays the fundamental parameters, metallicities, V
magnitudes, and reddening of the Titans. Uncertainties accompanying
the temperature values are internal. To compute total uncertainties,
the estimated model accuracy error of ±50K must be included in
the error expansion as discussed in Sec. 3.4 in the paper. The bottom
part of the table incorporates seven Gaia benchmark stars.
Table 4 displays the membership classification of the Titans to the
Galactic substructures. Parallax values are from Gaia EDR3. In the
membership column GE means Gaia-Enceladus, HS Helmi stream, and Sq
Sequoia. The bottom part of the table incorporates seven Gaia
benchmark stars. The symbol (+) means likely membership according to
the criterion of Massari et al. (2019A&A...630L...4M 2019A&A...630L...4M) and (++) means
according to the criterion of Myeong et al. (2019MNRAS.488.1235M 2019MNRAS.488.1235M).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 44 41 *Atmospheric parameters of the Titans in the
literature
table2.dat 93 48 Fundamental parameters and metallicities of
the Titans
table4.dat 58 48 Membership classification of the Titans
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Note on table1.dat: These parameters were used as initial guess values in our
analysis.
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See also:
J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010)
J/A+A/512/A54 : Teff and Fbol from Infrared Flux Method (Casagrande+, 2010)
J/A+A/598/A54 : Line list (Hansen+, 2017)
J/ApJ/835/81 : Bright metal-poor stars from HES Survey. II. (Beers+, 2017)
J/A+A/623/A72 : Hipparcos stars binarity from Gaia pm anomaly (Kervella+, 2019)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Star Star name
16 A1 --- n_Star [*] Note on Star (1)
18- 21 I4 K Teff Effective temperature
23- 25 I3 K e_Teff ? Effective temperature error
27- 30 F4.2 [cm/s2] logg Surface gravity
32- 36 F5.2 [-] [Fe/H] Metallicity
38- 42 A5 --- Source Source of the parameters used to select
the stars (2)
44 I1 --- NSpectra Number of spectra used in the Hα
line fitting
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Note (1): *: for star HD 160617, indicates that it had HARPS spectra analyzed
instead of UVES.
Note (2): Reference codes as follows:
Ca10 = Casagrande et al., 2010A&A...512A..54C 2010A&A...512A..54C, Cat. J/A+A/512/A54
R+L08 = Reddy & Lambert, 2008MNRAS.391...95R 2008MNRAS.391...95R
Be17 = Beers et al., 2017ApJ...835...81B 2017ApJ...835...81B, Cat. J/ApJ/835/81
N+S10 = Nissen & Schuster, 2010A&A...511L..10N 2010A&A...511L..10N, Cat. J/A+A/511/L10
Ry96 = Ryan et al., 1996ApJ...471..254R 1996ApJ...471..254R
Ge06 = Gehren et al., 2006A&A...451.1065G 2006A&A...451.1065G
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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 A1 --- Flag [G] G for metal-poor Gaia benchmark stars (1)
3- 17 A15 --- Star Star name
18 A1 --- n_Star [*] Note on Star (G1)
21- 24 I4 K Teff Effective temperature
26- 27 I2 K e_Teff Effective temperature error (3)
28 A1 --- u_Teff Uncertainty flag on Teff (4)
30- 33 F4.2 [cm/s2] logg Surface gravity
35- 38 F4.2 [cm/s2] e_logg Surface gravity error
40- 43 F4.2 Msun M Mass
45- 48 F4.2 Msun e_M Mass error
50- 53 F4.2 Rsun R Radius
55- 58 F4.2 Rsun e_R Radius error
60- 64 F5.2 Gyr Age Age
66- 69 F4.2 Gyr e_Age Age error
71- 75 F5.2 [-] [FeI/H] Abundance [FeI/H]
77- 81 F5.2 [-] [FeII/H] Abundance [FeII/H]
83- 87 F5.2 mag Vmag Apparent V magnitude
89- 93 F5.3 mag E(B-V) Colour excess
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Note (1): The new parameters determined here for these stars are likely more
accurate than previously available estimates.
Note (3): Uncertainties accompanying the Teff values are internal. For the total
uncertainties, one has to further include the estimated model accuracy error
of ± 50K (as discussed in Sec. 3.4).
Note (4): uncertain value according to the analysis in Sec. 4.3.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1 A1 --- Flag [G] G for metal-poor Gaia benchmark stars
3- 17 A15 --- Star Star name
18 A1 --- n_Star [*] Note on Star (G1)
20- 25 F6.3 mas plx Gaia EDR3 parallax
27- 31 F5.3 mas e_plx Gaia EDR3 parallax error
33- 39 F7.2 km/s HV Heliocentric velocity
41- 44 F4.2 km/s e_HV Heliocentric velocity error
47- 58 A12 --- Memb Membership (2)
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Note (2): In the membership column, GE means Gaia-Enceladus, HS Helmi-Streams,
and Sq Sequoia.
(+) means likely membership according to the criterion of Massari et al.
(2019A&A...630L...4M 2019A&A...630L...4M) and
(++) means according to the criterion of Myeong et al. (2019MNRAS.488.1235M 2019MNRAS.488.1235M).
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Global notes:
Note (G1): * indicates a binary system identified in Krevella et al.
(2019A&A...623A..72K 2019A&A...623A..72K, Cat. J/A+A/623/A72) or Hansen et al.
(2017A&A...598A..54H 2017A&A...598A..54H, Cat. J/A+A/598/A54).
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Acknowledgements:
Riano Giribaldi, riano(at)camk.edu.pl
History:
29-Jun-2021: Original tables
06-Jan-2023: in table4, for HD 126681,
HV corrected into -45.40 intead of 45.40
(End) Patricia Vannier [CDS] 03-May-2021