J/A+A/546/A57 Spectroscopy of 400 red giants in the Bulge (Uttenthaler+, 2012)
Constraining the structure and formation of the Galactic bulge from a field in
its outskirts. FLAMES-GIRAFFE spectra of about 400 red giants around
(l, b)=(0°, -10°).
Uttenthaler S., Schultheis M., Nataf D.M., Robin A.C., Lebzelter T.,
Chen B.
<Astron. Astrophys. 546, A57 (2012)>
=2012A&A...546A..57U 2012A&A...546A..57U
ADC_Keywords: Stars, late-type ; Spectroscopy ; Radial velocities ; Abundances
Keywords: Galaxy: bulge - Galaxy: formation - Galaxy: kinematics and dynamics -
stars: abundances - stars: late-type
Abstract:
The presence of two stellar populations in the Milky Way bulge has
been reported recently, based on observations of giant and dwarf stars
in the inner an intermediate bulge.
We aim at studying the abundances and kinematics of stars in the outer
Galactic bulge, thereby providing additional constraints on formation
models of the bulge.
Spectra of 401 red giant stars in a field at (l,b)=(0,-10) were
obtained with the FLAMES-GIRAFFE spectrograph at the VLT. Stars of
luminosities down to below the two bulge red clumps are included in
the data set. From these spectra we measure general metallicities,
abundances of iron and the alpha-elements, and radial velocities of
the stars. The abundances are derived from an interpolation and
fitting procedure within a grid of COMARCS model atmospheres and
spectra. These measurements as well as photometric data are compared
to simulations with the Besancon and TRILEGAL models of the Galaxy.
We confirm the presence of two populations among our sample stars: i)
a metal-rich one at [M/H]~+0.3, comprising about 30% of the sample,
with low velocity dispersion and low alpha-abundance, and ii) a
metal-poor population at [M/H]~-0.6 with high velocity dispersion and
high alpha-abundance. The metallicity difference between the two
populations, a systematically and statistically robust figure, is
Delta[M/H]=0.87±0.03. The metal-rich population could be connected to
the Galactic bar. We identify this population as the carrier of the
double red clump feature. We do not find a significant difference in
metallicity or radial velocity between the two red clumps, a small
difference in metallicity being probably due to a selection effect and
contamination by the metal-poor population. The velocity dispersion
agrees well with predictions of the Besancon Galaxy model, but the
metallicity of the "thick bulge" model component should be shifted to
lower metallicity by 0.2 to 0.3dex to well reproduce the observations.
We present evidence that the metallicity distribution function depends
on the evolutionary state of the sample stars, suggesting that
enhanced mass loss preferentially removes metal-rich stars. We also
confirm the decrease of alpha-element over-abundance with increasing
metallicity. Conclusions: Our sample is consistent with the existence
of two populations, one being a metal-rich bar, the second one being
more like a metal-poor classical bulge with larger velocity
dispersion.
Description:
Table 3 of the paper summarises the ID of the programme stars, their
coordinates from the 2MASS catalogue as well as their 2MASS
photometry, temperature estimates (based on J-K), radial velocities,
general metallicities, iron abundance, and [alpha/Fe] abundance of the
stars as measured from the spectra.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 91 401 Data for 401 sample stars
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See also:
II/213 : OGLE Galactic Bulge periodic variables (Udalski+ 1996)
J/AJ/110/2788 : JHK photometry for Galactic bulge stars (Tiede+ 1995)
J/A+A/486/177 : Bulge field stars from FLAMES-GIRAFFE spectra (Zoccali+, 2008)
J/A+A/517/A44 : Spitzer sources in the Galactic bulge (Uttenthaler+, 2010)
J/A+A/530/A54 : Abundances of 650 bulge red giants (Gonzalez+, 2011)
J/ApJS/194/18 : The Galactic Bulge Survey: X-ray observations (Jonker+, 2011)
J/A+A/538/A36 : Lithium abundances of bulge RGB stars (Lebzelter+, 2012)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [1/514] Programme star ID
6- 15 F10.6 deg RAdeg Right ascension (J2000.0)
18- 27 F10.6 deg DEdeg Declination (J2000.0)
30- 35 F6.3 mag Kmag 2MASS Ks magnitude
38- 43 F6.3 mag Hmag 2MASS H magnitude
46- 51 F6.3 mag Jmag 2MASS J magnitude
54- 57 I4 K Teff Effective surface temperature
60- 67 F8.3 km/s HRV Heliocentric radial velocity
70- 74 F5.2 [Sun] [M/H] ? General metallicity
77- 81 F5.2 [Sun] [Fe/H] ? Iron abundance
84- 88 F5.2 [Sun] [alpha/Fe] ? α-elements abundance
91 A1 --- fg [*] Flag for foreground star candidates
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Acknowledgements:
Stefan Uttenthaler, stefan.uttenthaler(at)univie.ac.at
(End) S. Uttenthaler (Vienna Univ., Austria), P. Vannier [CDS] 13-Aug-2012