J/MNRAS/444/1812 M54 red giants abundances (Mucciarelli+, 2014)
The cosmological lithium problem outside the Galaxy:
the Sagittarius globular cluster M54.
Mucciarelli A., Salaris M., Bonifacio P., Monaco L., Villanova S.
<Mon. Not. R. Astron. Soc., 444, 1812-1820 (2014)>
=2014MNRAS.444.1812M 2014MNRAS.444.1812M
ADC_Keywords: Clusters, globular ; Abundances ; Stars, giant
Keywords: stars: abundances - stars: atmospheres - stars: Population II -
globular clusters: individual: M54
Abstract:
The cosmological Li problem is the observed discrepancy between Li
abundance (A(Li)) measured in Galactic dwarf, old and metal-poor stars
(traditionally assumed to be equal to the initial value A(Li)0), and
that predicted by standard big bang nucleosynthesis (BBN) calculations
(A(Li)BBN). Here, we attack the Li problem by considering an
alternative diagnostic, namely the surface Li abundance of red giant
branch stars that in a colour-magnitude diagram populate the region
between the completion of the first dredge-up and the red giant branch
bump. We obtained high-resolution spectra with the FLAMES facility at
the Very Large Telescope for a sample of red giants in the globular
cluster M54, belonging to the Sagittarius dwarf galaxy. We obtain
A(Li)=0.93±0.11dex, translating - after taking into account the
dilution due to the dredge-up - to initial abundances (A(Li)0) in
the range 2.35-2.29 dex, depending on whether or not atomic diffusion
is considered. This is the first measurement of Li in the Sagittarius
galaxy and the more distant estimate of A(Li)0 in old stars obtained
so far. The A(Li)0 estimated in M54 is lower by ∼0.35dex than
A(Li)BBN, hence incompatible at a level of ∼3σ. Our result
shows that this discrepancy is a universal problem concerning both the
Milky Way and extragalactic systems. Either modifications of BBN
calculations, or a combination of atomic diffusion plus a suitably
tuned additional mixing during the main sequence, need to be invoked
to solve the discrepancy.
Description:
High-resolution spectra of lower RGB stars in M54 have been secured
with the multi-object spectrograph FLAMES at the ESO Very Large
Telescope, in the GIRAFFE/MEDUSA mode. The observations have been
performed with the setups HR12 (to sample the Na D lines, with a
resolution of 18700) and HR15N (to sample the Li doublet at 6707Å,
with a resolution of 17000). The same target configuration has been
used for both gratings and each target has been observed for a total
time of 26 and 4h, for HR15N and HR12, respectively.
Objects:
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RA (2000) DE Designation(s)
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18 55 03.33 -30 28 47.5 M 54 = NGC 6715
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 63 101 Identification numbers, coordinates, effective
temperature, surface gravity, radial velocity,
[Fe/H] and [Na/Fe] abundances
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See also:
J/AJ/109/1086 : VI Photometry in M54 and Sgr Dwarf Galaxy (Sarajedini+ 1995)
J/AJ/118/1245 : Elemental abundances in five stars in M54 (Brown+, 1999)
J/AJ/119/1760 : M54 and Sgr dSph VI photometry (Layden+, 2000)
J/AJ/140/1500 : RR Lyrae variables in central region of M54 (Montiel+, 2010)
J/MNRAS/406/329 : Variable stars in M54 (Sollima+, 2010)
J/A+A/520/A95 : Abundances of red giants in M54 and Sgr dSph (Carretta+ 2010)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- ID [6750/1043447] ID number
9- 19 F11.7 deg RAdeg Right ascension (J2000)
21- 31 F11.7 deg DEdeg Declination (J2000)
33- 36 I4 K Teff [4627/5090] Effective temperature
38- 41 F4.2 [cm/s2] logg [2.32/2.56] Surface gravity
43- 47 F5.1 km/s RV [102/178] Radial velocity
49- 53 F5.2 [Sun] [Fe/H] [-2/0.52]?=- Metallicity
55- 59 F5.2 [Sun] [Na/Fe] [-1/0.77]? [Na/Fe] abundance
61- 63 A3 --- Mmb [M54 Sgr] indicates the membership to
M54 or to Sgr dSph
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 28-Apr-2015