J/A+A/594/A79 NGC 6121 turnoff and subgiant stars abundances (Spite+, 2016)
Abundances in a sample of turnoff and subgiant stars in NGC 6121 (M4).
Spite M., Spite F., Gallagher A.J., Monaco L., Bonifacio P., Caffau E.,
Villanova S.
<Astron. Astrophys. 594, A79 (2016)>
=2016A&A...594A..79S 2016A&A...594A..79S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular; Stars, population II ; Abundances
Keywords: stars: abundances - Galaxy: abundances -
globular clusters: individual: M4 - Galaxy: halo
Abstract:
The stellar abundances observed in globular clusters show complex
structures, currently not yet understood.
The aim of this work is to investigate the relations between the
abundances of different elements in the globular cluster M4, selected
for its uniform deficiency of iron, to explore the best models
explaining the pattern of these observed abundances. Moreover, in
turnoff stars, the abundances of the elements are not suspected to be
affected by internal mixing.
In M4, using low and moderate resolution spectra obtained for 91
turnoff (and subgiant) stars with the ESO FLAMESGiraffe spectrograph,
we have extended previous measurements of abundances (of Li, C and Na)
to other elements (C, Si, Ca, Sr and Ba), using model atmosphere
analysis. We have also studied the influence of the choice of the
microturbulent velocity.
Firstly, the peculiar turnoff star found to be very Li-rich in a
previous paper does not show any other abundance anomalies relative to
the other turnoff stars inM4. Secondly, an anti-correlation between C
and Na has been detected, the slope being significative at more than
3σ. This relation between C and Na is in perfect agreement with
the relation found in giant stars selected below the RGB bump.
Thirdly, the strong enrichment of Si and of the neutron-capture
elements Sr and Ba, already observed in the giants in M4, is
confirmed. Finally, the relations between Li, C, Na, Sr and Ba
constrain the enrichment processes of the observed stars.
The abundances of the elements in the turnoff stars appear to be
compatible with production processes by massive AGBs, but are also
compatible with the production of second generation elements (like Na)
and low Li produced by, for example, fast rotating massive stars.
Description:
Observations were conducted at the Very Large Telescope (VLT)
(Paranal, Chile) between April and July 2010 using the LR2 setting
from 400 to 456nm with a resolving power R=6000, the HR12 setting
from 583 to 614nm, and the HR15N setting from 666 to 679nm, both
with a resolving power of about R=20000. The frames were processed
using the FLAMES-GIRAFFE reduction pipeline. More information can be
found in Monaco et al. (2012A&A...539A.157M 2012A&A...539A.157M, Cat. J/A+A/539/A157). The
spectroscopic data are available through the Giraffe archive at Paris
Observatory (http://giraffe-archive.obspm.fr/).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 75 91 Abundances measured in our sample of M4 stars
computed with the model parameters Teff logg and vt
given by Monaco et al. (2012, Cat. J/A+A/539/A157)
table4.dat 75 91 Abundances measured in our sample of M4 stars
computed with the model parameters Teff logg given
by Monaco et al. (2012, Cat. J/A+A/539/A157) but
with vt=1.3km/s
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See also:
J/A+A/539/A157 : Li and Na in globular cluster M4 (Monaco+, 2012)
Byte-by-byte Description of file: table3.dat table4.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID Star identification, [MVB2012] NNNNN in Simbad
8- 12 F5.2 [Sun] [Fe/H] Metallicity (from qdopted model)
15- 19 F5.2 [Sun] [Na/Fe] ?=99.99 non-LTE relative abundance [Na/Fe]
22- 26 F5.2 --- Nacorr ?=99.99 [Na/Fe]nonLTE - [Na/Fe]LTE
28- 32 F5.2 --- A(Li) ?=99.99 Logarithmic abundance of Li
35- 39 F5.2 [Sun] [C/Fe] ?=99.99 Relative abundance [C/Fe]
(3D computations)
42- 46 F5.2 [Sun] [Si/Fe] ?=99.99 Relative abundance [Si/Fe]
49- 53 F5.2 [Sun] [Ca/Fe] ?=99.99 Relative abundance [Ca/Fe]
56- 60 F5.2 [Sun] [Ni/Fe] ?=99.99 Relative abundance [Ni/Fe]
63- 67 F5.2 [Sun] [Sr/Fe] ?=99.99 Relative abundance [Sr/Fe]
70- 74 F5.2 [Sun] [Ba/Fe] ?=99.99 Relative abundance [Ba/Fe]
75 A1 --- f_[Ba/Fe] [*] * when [Ba/Fe] from only the 4554Å line
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Acknowledgements:
Monique Spite, monique.spite(at)obspm.fr
(End) Patricia Vannier [CDS] 22-Aug-2016