J/MNRAS/511/231 Lithium study with GC NGC 6752 (Schiappacasse-Ulloa+, 2022)
Lithium abundances as a tracer of asymptotic giant branch star pollution in
the globular cluster NGC 6752.
Schiappacasse-Ulloa J., Lucatello S., Rain M.J., Pietrinferni A.
<Mon. Not. R. Astron. Soc., 511, 231-240 (2022)>
=2022MNRAS.511..231S 2022MNRAS.511..231S (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Stars, population II ;
Populations, stellar ; Stars, supergiant ; Stars, giant ;
Stars, metal-deficient ; Spectroscopy ; Photometry ; Optical ;
Effective temperatures ; Abundances, [Fe/H]
Keywords: stars: abundances - stars: Population II -
globular clusters: general - globular clusters: individual: NGC 6752
Abstract:
This paper presents a chemical abundance analysis of 217 stars in the
metal-poor globular cluster NGC 6752, distributed from the turn-off to
the lower red giant branch. Al and Li abundances were derived through
spectral synthesis applied to spectra collected with FLAMES, in both
GIRAFFE and UVES modes. The work aims to gain insight into the nature
of the polluter(s) responsible for the abundance variations and the
C-N, Na-O, Al-Mg anticorrelations associated with the
multiple-population phenomenon. We found a plateau at
A(Li) = 2.33 ± 0.06 dex in unevolved stars, with the average Li
content decreasing continuously down to ∼1.25 dex at the bottom of the
red giant branch. As expected in the classic anticorrelation scenario,
we found stars low in Al and high in Li abundance, and stars high in
Al and low in Li. However, in addition, we also found evidence of
Al-rich, second-generation stars with high Li content. This finding
suggests the need for Li production, known to happen in
intermediate-mass (∼4-8 M☉) asymptotic giant branch stars
through the Cameron-Fowler mechanism. It is worth noting that the Li
abundance observed in Al-rich stars never exceeds that in Al- poor
stars.
Description:
NGC 6752 is an ideal candidate for the investigation of potential
systematic differences between both Li-poor and Li-rich stars. We
expect to characterize the different stellar populations of the
cluster in terms of Li. We aim to analyse all the available archival
data homogeneously, from the turn-off to the RGB bump, to paint a
comprehensive picture of Li and Al in the cluster, (i.e see section
Introduction).
We analysed the spectra of 217 stars of NGC 6752, including TO,
subgiant branch (SGB), and red giant branch (RGB) stars. The spectra
of 126 stars, previously analysed by Gruyters et al.
(2014A&A...567A..72G 2014A&A...567A..72G, Cat. J/A+A/567/A72), were kindly provided to us
by the authors. They used spectra observed with the mid-resolution
spectrograph FLAMES/GIRAFFE using the setup HR15N (6470-6790 Å)
under the ESO-VLT programs. The spectra of the remaining 91 stars were
downloaded from the Gaia-ESO collection of the ESO archive. They are a
combination of FLAMES/GIRAFFE (HR15N: 6444-6816 Å) and
FLAMES/UVES (4768-5801 Å and 5822-6830 Å) spectra. The cluster
members were selected based on Gaia EDR3 (Gaia Collaboration et al.
2021A&A...649A...1G 2021A&A...649A...1G, Cat. I/350) data. Only stars within 3σ on
parallax and proper motion values from the cluster mean values were
considered members. The wavelength range covered by the presently
analysed GIRAFFE and UVES spectra allows measurement of both the Li
doublet at 6708 Å and Al lines at 6696 and 6698 Å, (i;e see
section 2 Target selection and observation). Next, as seen in the
section 3 Data analysis, we derived photometric and spectroscopic
stellar parameters as well as the Li and Al abundances. We reported
the results for the 217 stars in the table1.dat with all associated
uncertainties.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 101 217 Stellar parameters of our stars sample in the
metal-poor globular cluster NGC 6752
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See also:
J/A+A/567/A72 : Stellar parameters and abundances in NGC 6752 (Gruyters+, 2014)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- ID Identifier name from NGC 6752 IDs and 2MASS
JHHMMSS.ss+DDMMSS.s designation (IDs)
18- 24 F7.2 K Teff Effective temperature derived as explicited
in sections 3.1 Photometric stellar
parameters and 3.2 Spectroscopic stellar
parameters (Teff)
26- 31 F6.2 K e_Teff Derived uncertainty of Teff as explained
in the section 3.5 Observational
uncertainties (s_Teff)
33- 36 F4.2 [cm/s2] logg Logarithm of the surface gravity derived as
explicited in sections 3.1 Photometric
stellar parameters and 3.2 Spectroscopic
stellar parameters (logg)
38- 41 F4.2 [cm/s2] e_logg Derived uncertainty of logg as explained in
the section 3.5 Observational uncertainties
(s_logg)
43- 47 F5.2 [Sun] [Fe/H] Iron to hydrogen abundance ratio adopted
value -1.56 as explicited in sections 3.1
Photometric stellar parameters and 3.2
Spectroscopic stellar parameters (Fe_H)
49- 52 F4.2 [Sun] e_[Fe/H] Derived uncertainty 0.01 dex of [Fe/H] as
explained in the section 3.5 Observational
uncertainties (s_Fe)
54- 57 F4.2 km/s vt Microturbulence velocity derived as
explicited in sections 3.1 Photometric
stellar parameters and 3.2 Spectroscopic
stellar parameters (vm_2)
59- 62 F4.2 km/s e_vt Derived uncertainty of vt as explained in
the section 3.5 Observational uncertainties
(s_vm)
64- 69 F6.4 [-] A(Li) Lithium abundances as A(Li) =
log(NLi/NH)+12 derived with equivalent
widths measurements from spectroscopic
analysis as explained in the section 3.2
Spectroscopic stellar parameters and 3.4
Measurement of Li and Al (Li1)
71- 74 F4.2 [-] e_A(Li) Derived uncertainty of A(Li) as explained in
the section 3.5 Observational uncertainties
(s_Li)
76- 96 F21.18 [-] [Al/Fe] Aluminium to iron abundance ratio derived
with equivalent widths measurements from
spectroscopic analysis as explained in the
section 3.2 Spectroscopic stellar parameters
and 3.4 Measurement of Li and Al (Al_Fe1)
98- 101 F4.2 [-] e_[Al/Fe] Derived uncertainty of [Al/Fe] as explained
in the section 3.5 Observational
uncertainties (s_Al)
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 16-Jan-2025