J/ApJ/791/39 NGC 6218 and NGC 5904 lithium abundances (D'Orazi+, 2014)
Lithium abundances in globular cluster giants: NGC 6218 (M12) and NGC 5904 (M5).
D'Orazi V., Angelou G.C., Gratton R.G., Lattanzio J.C., Bragaglia A.,
Carretta E., Lucatello S., Momany Y.
<Astrophys. J., 791, 39 (2014)>
=2014ApJ...791...39D 2014ApJ...791...39D (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Abundances ; Stars, giant ;
Stars, population II
Keywords: globular clusters: individual: NGC 6218, NGC 5904 -
stars: abundances - stars: Population II
Abstract:
Convergent lines of evidence suggest that globular clusters host
multiple stellar populations. It appears that they experience at least
two episodes of star formation whereby a fraction of first-generation
stars contribute astrated ejecta to form the second generation(s). To
identify the polluting progenitors, we require distinguishing chemical
signatures such as that provided by lithium. Theoretical models
predict that lithium can be synthesized in AGB stars, whereas no net
Li production is expected from other candidates. It has been shown
that in order to reproduce the abundance pattern found in M4, Li
production must occur within the polluters, favoring the AGB scenario.
Here, we present Li and Al abundances for a large sample of RGB stars
in M12 and M5. These clusters have a very similar metallicity, while
demonstrating differences in several cluster properties. Our results
indicate that the first-generation and second-generation stars share
the same Li content in M12; we recover an abundance pattern similar to
that observed in M4. In M5, we find a higher degree of complexity, and
a simple dilution model fails in reproducing the majority of the
stellar population. In both clusters, we require Li production across
the different stellar generations, but production seems to have
occurred to different extents. We suggest that such a difference might
be related to the cluster mass with the Li production being more
efficient in less-massive clusters. This is the first time a
statistically significant correlation between the Li spread within a
GC and its luminosity has been demonstrated. Finally, although
Li-producing polluters are required to account for the observed
pattern, other mechanisms, such as MS depletion, might have played a
role in contributing to the Li internal variation, though at a
relatively low level.
Description:
We utilized the multi-object FLAMES@VLT facility (Pasquini et al.
2002Msngr.110....1P 2002Msngr.110....1P) to collect intermediate-resolution spectra of RGB
stars, both below and above the bump luminosity, in our target
clusters (Program: 087.2-0276(A), PI: Valentina D'Orazi). Employing
the HR15N setup (6470-6790 Å), our wavelength coverage included the
Li I doublet at 6707.78 Å with a nominal resolution of R = 17,000.
We observed a total of 72 stars in NGC 6218 and 113 stars in NGC 5904
using this configuration. The sample was selected from the photometric
catalogs provided by Y. Momany et al. (2011, private communication).
Objects:
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RA (ICRS) DE Designation(s)
----------------------------------------------------------
16 47 14.18 -01 56 54.7 NGC 6218 = M 12
15 18 33.22 +02 04 51.7 NGC 5904 = M 5
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 43 63 Stellar parameters, Li and Al abundances for
targets in NGC 6218 (M12)
table3.dat 43 101 Stellar parameters, Li and Al abundances for
targets in NGC 5904 (M5)
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See also:
J/A+A/464/939 : Abundances of red giants in NGC 6218 (Carretta+, 2007)
J/AJ/141/62 : M5 chemical abundances for evolved stars (Lai+, 2011)
J/MNRAS/449/4038 : Li abundance of giants in 3 globular clusters
(D'Orazi+, 2015)
J/ApJ/819/135 : Lithium-rich giants in globular clusters (Kirby+, 2016)
Byte-by-byte Description of file: table2.dat table3.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID Star identifier (NNNNN)
7- 11 F5.2 mag Vmag The V band magnitude
13- 15 I3 --- S/N Signal-to-Noise ratio
17- 20 I4 K Teff Effective temperature
22- 25 F4.2 [cm/s2] log(g) Log surface gravity
27- 30 F4.2 km/s VTurb Microturbulence velocity
32 A1 --- l_A(Li) Upper limit flag on A(Li)
33- 36 F4.2 [-] A(Li) ? Log lithum abundance
38 A1 --- l_[Al/Fe] Upper limit flag on [Al/Fe]
39- 43 F5.2 [-] [Al/Fe] ? Log of the Al/Fe abundance ratio
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 27-Mar-2017