J/A+A/555/A12 Foreground Galactic stars properties (Kordopatis+, 2013)
Through thick and thin: Structure of the Galactic thick disc from
extragalactic surveys.
Kordopatis G., Hill V., Irwin M., Gilmore G., Wyse R.F.G., Tolstoy E.,
de Laverny P., Recio-Blanco A., Battaglia G., Starkenburg E.
<Astron. Astrophys. 555, A12 (2013)>
=2013A&A...555A..12K 2013A&A...555A..12K
ADC_Keywords: Milky Way ; Stars, distances ; Effective temperatures ;
Abundances, [Fe/H] ; Radial velocities
Keywords: Galaxy: evolution - Galaxy: structure - Galaxy: disk -
stars: abundances - methods: observational - Galaxy: stellar content
Abstract:
We study the chemical and kinematic properties of roughly a thousand
FLAMES-GIRAFFE LR8 spectra of faint magnitude foreground Galactic
stars observed serendipitously during extra-galactic surveys in four
lines-of-sight: three in the southern Galactic hemisphere (surveys of
the Carina, Fornax and Sculptor dwarf spheroidal galaxies) and one in
the northern Galactic hemisphere (a survey of the Sextans dwarf
spheroidal galaxy). The foreground stars span distances up to ∼3kpc
from the Galactic plane and Galactocentric radii up to 11kpc.
The stellar atmospheric parameters (effective temperature, surface
gravity, metallicity) are obtained by an automated parameterisation
pipeline and the distances of the stars are then derived by a
projection of the atmospheric parameters on a set of theoretical
isochrones using a Bayesian approach. The metallicity gradients are
estimated for each line-of-sight and compared with predictions from
the Besancon model of the Galaxy, in order to test the chemical
structure of the thick disc. Finally, we use the radial velocities in
each line-of-sight to derive a proxy for either the azimuthal or the
vertical component of the orbital velocity of the stars.
Only three lines-of-sight have a sufficient number of foreground stars
for a robust analysis. Towards Sextans in the Northern Galactic
hemisphere and Sculptor in the South, we measure a consistent decrease
in mean metallicity with height from the Galactic plane, suggesting a
chemically symmetric thick disc. This decrease can either be due to an
intrinsic thick disc metallicity gradient, or simply due to a change
in the thin disc/thick disc population ratio and no intrinsic
metallicity gradients for the thick disc. We favour the latter
explanation. In contrast, we find evidence of an unpredicted
metal-poor population in the direction of Carina. This population was
earlier detected by Wyse et al. (2006ApJ...639L..13W 2006ApJ...639L..13W), but our more
detailed analysis provides robust estimates of its location
(|Z|<1kpc), metallicity (-2<[M/H]←1dex) and azimuthal orbital
velocity (Vphi∼120km/s).
Description:
These tables contain all the parameters that have been computed, based
on the LR8 spectra of targets selected as being foreground Galactic
members. The atmospheric parameters were computed using the pipeline
presented in Kordopatis et al. (2011A&A...535A.106K 2011A&A...535A.106K). The
line-of-sight distances and the projected atmospheric parameters were
computed by projecting the pipeline atmospheric parameters on the
Yonsei-Yale isochrones as in Kordopatis et al. (2011A&A...535A.106K 2011A&A...535A.106K).
The calibrated metallicities are obtained by applying the corrections
established in Kordopatis et al. (2013b, in prep.) for the 4th data
release of the RAVE survey.
The radial velocities, the photometric values and the positions are
taken from Battaglia et al. (2008, Cat. J/MNRAS/383/183) and Koch et
al. (2006, Cat. J/AJ/131/895).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 53 679 Atmospheric parameters of the selected faint
foreground stars
table4.dat 57 679 Positions, radial velocities, magnitudes and
distances of the selected faint foreground stars
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See also:
J/AJ/131/895 : Stars in the Carina dwarf spheroidal galaxy (Koch+, 2006)
J/MNRAS/383/183 : CaII triplet of RGB from VLT/FLAMES obs. (Battaglia+, 2008)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- ID Identification of the star according to its
line-of-sight (G1)
9- 12 I4 K Teff1 Effective temperature (2)
14- 17 I4 K Teff2 Effective temperature once projected on the
Yonsei-Yale isochrones
19- 21 I3 K e_Teff2 Error on the effective temperature
23- 26 F4.2 [cm/s2] logg1 Logarithmic surface gravity (2)
28- 31 F4.2 [cm/s2] logg2 Logarithmic surface gravity from isochrones
33- 36 F4.2 [cm/s2] e_logg2 Error on the logarithmic surface gravity
38- 42 F5.2 [Sun] [M/H]1 [-3.4/0.5] Overall metallicity (2)
44- 48 F5.2 [Sun] [M/H]2 [-4.0/0.3] Overall calibrated metallicity
after applying the calibration of
Kordopatis et al. 2013 (in preparation)
50- 53 F4.2 [Sun] e_[M/H]2 Error on metallicity
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Note (2): as derived by the automatic parameterisation pipeline of
Kordopatis et al. 2011A&A...535A.106K 2011A&A...535A.106K
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- ID Identification of the star according to its
line-of-sight (G1)
8- 15 F8.4 deg RAdeg Right Ascension (J2000)
17- 24 F8.4 deg DEdeg Declination (J2000)
26- 30 F5.2 mag Vmag V apparent magnitude
32- 35 F4.2 mag (V-I) V-I colour index
37- 42 F6.2 km/s HRV Heliocentric Radial velocity
44- 47 F4.2 km/s e_HRV Error on the heliocentric radial velocity
49- 52 I4 pc Dist Line-of-sight distance
54- 57 I4 pc e_Dist Error on the line-of-sight distance
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Global notes:
Note (G1): ID composed of line-of-sight code (roman number) and
a sequence number. The line-of-sight code indicates the region:
I = Sculptor
II = Sextans
III = Fornax
IV = Carina
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Acknowledgements:
Georges Kordopatis, gkordo(at)ast.cam.ac.uk
(End) Patricia Vannier [CDS] 24-May-2013