J/A+A/538/A36 Lithium abundances of bulge RGB stars (Lebzelter+, 2012)
Lithium abundances along the RGB: FLAMES-GIRAFFE spectra of a large sample of
low-mass bulge stars.
Lebzelter T., Uttenthaler S., Busso M., Schultheis M., Aringer B.
<Astron. Astrophys. 538, A36 (2012)>
=2012A&A...538A..36L 2012A&A...538A..36L
ADC_Keywords: Stars, late-type ; Abundances ; Photometry, infrared ;
Radial velocities
Keywords: stars: late-type - stars: evolution - stars: abundances
Abstract:
A small number of K-type giants on the red giant branch (RGB) is known
to be very rich in lithium (Li). This fact is not accounted for by
standard stellar evolution theory. The exact phase and mechanism of Li
enrichment is still a matter of debate.
Our goal is to probe the abundance of Li along the RGB, from its base
to the tip, to confine Li-rich phases that are supposed to occur on
the RGB.
For this end, we obtained medium-resolution spectra with the FLAMES
spectrograph at the VLT in GIRAFFE mode for a large sample of 401
low-mass RGB stars located in the Galactic bulge. The Li abundance was
measured in the stars with a detectable Li 670.8 nm line by means of
spectral synthesis with COMARCS model atmospheres. A new 2MASS
J-K-Teff calibration from COMARCS models is presented in the Appendix.
Thirty-one stars with a detectable Li line were identified, three of
which are Li-rich according to the usual criterion
(logεLi>1.5). The stars are distributed all along the RGB,
not concentrated in any particular phase of the red giant evolution
(e.g. the luminosity bump or the red clump). The three Li-rich stars
are clearly brighter than the luminosity bump and red clump, and do
not show any signs of enhanced mass loss.
We conclude that the Li enrichment mechanism cannot be restricted to a
clearly defined phase of the RGB evolution of low-mass stars
(M∼1M☉), contrary to earlier suggestions from disk field stars.
Description:
The table presents the coordinates (J2000) and J-, H-, and K-band
magnitudes from the 2MASS catalogue, the radial velocities measured
from the spectra, their estimated temperature and surface gravity log
g, general metal and lithium abundances for the Li-detected stars, as
well as a flag for foreground star candidates. The foreground star
candidates were selected by their proper motion in the SPM4 catalogue.
All stars are located in a 25 arcmin diameter field centred on the
Galactic coordinates (l,b)=(0,-10).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 77 401 Data for 401 bulge RGB stars
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Byte-by-byte Description of file:tablea1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq Number of the star in the original target list
5- 14 F10.6 deg RAdeg Right ascension (J2000), from 2MASS
16- 25 F10.6 deg DEdeg Declination (J2000), from 2MASS
27- 32 F6.3 mag Jmag 2MASS J-band magnitude
34- 39 F6.3 mag Hmag 2MASS H-band magnitude
41- 46 F6.3 mag Kmag 2MASS Ks-band magnitude
48- 55 F8.3 km/s RV Radial velocity
57- 60 I4 K Teff Effective surface temperature, from (J-K)
62- 64 F3.1 [cm/s2] logg ? Logarithm of surface gravity
66- 70 F5.2 [-] [M/H] ? General metal abundance [M/H]
72- 75 F4.1 [-] eps(Li) ? Lithium abundance, on log ε scale
(H=12)
77 A1 --- FG [*] Flag (*) for foreground star candidates
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Acknowledgements:
Stefan Uttenhaler, Dep. of Astronomy, Vienna,
stefan.uttenthaler(at)univie.ac.at
(End) Lebzelter & Uttenthaler [Viennna] , Patricia Vannier [CDS] 24-Nov-2011