J/A+A/615/A17 Red giant Aluminium abundances in NGC 2808 (Carretta+, 2018)
Aluminium abundances in five discrete stellar populations of the globular
cluster NGC 2808.
Carretta E., Bragaglia A., Lucatello S., Gratton R.G., D'Orazi V, Sollima A.
<Astron. Astrophys. 615, A17 (2018)>
=2018A&A...615A..17C 2018A&A...615A..17C (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Clusters, globular ; Spectroscopy ; Stars, giant
Keywords: stars: abundances - stars: atmospheres - stars: Population II -
globular clusters: general - globular clusters: individual: NGC 2808
Abstract:
We observed a sample of 90 red giant branch (RGB) stars in NGC 2808
using FLAMES/GIRAFFE and the high resolution grating with the set up
HR21. These stars have previous accurate atmospheric parameters and
abundances of light elements. We derived aluminium abundances for them
from the strong doublet AlI 8772-8773 Angstrom as in previous works
of our group. In addition, we were able to estimate the relative CN
abundances for 89 of the stars from the strength of a large number of
CN features. When adding self consistent abundances from previous UVES
spectra analysed by our team, we gathered [Al/Fe] ratios for a total
of 108 RGB stars in NGC 2808. The full dataset of proton-capture
elements is used to explore in details the five spectroscopically
detected discrete components in this globular cluster. We found that
different classes of polluters are required to reproduce the
(anti)-correlations among all proton-capture elements in the
populations P2, I1, and I2 with intermediate composition. This is in
agreement with the detection of lithium in lower RGB second generation
stars, requiring at least two kind of polluters. To have chemically
homogeneous populations the best subdivision of our sample is into six
components, as derived from statistical cluster analysis. By comparing
different diagrams [element/Fe] vs [element/Fe] we show for the first
time that a simple dilution model is not able to reproduce all the
sub-populations in this cluster. Polluters of different masses are
required. NGC 2808 is confirmed to be a tough challenge to any
scenario for globular cluster formation.
Description:
FLAMES-GIRAFFE HR21 spectra of 90 RGB stars in the GC NGC2808 are
analyzed and Al, (C)N abundances are derived. These abundances are
used in connection with previous data on Fe, Na, and O to study the
multiple populations in this cluster.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 49 90 Names, coordinates, Vmag, RV
table3.dat 40 140 Group classification, [Al/Fe], [N/Fe]
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See also:
J/ApJ/810/148 : Red giant abundances in NGC 2808 (Carretta, 2015)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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3- 7 I5 --- Star Star ID, Cl* NGC 2808 PKD NNNNN in Simbad
9- 18 F10.6 deg RAdeg Right ascension (J2000.0)
20- 29 F10.6 deg DEdeg Declination (J2000.0)
31- 35 F5.1 --- S/N Signal-to-noise ratio
37- 42 F6.2 km/s HRV Heliocentric radial velocity
44- 49 F6.3 mag Vmag V magnitude
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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3- 7 I5 --- Star Star ID, Cl* NGC 2808 PKD NNNNN in Simbad
9 A1 --- Flag [UG] U (UVES) or G (GIRAFFE) spectrum
11 I1 --- Group [0/5] Group classification from Carretta
(2015ApJ...810..148C 2015ApJ...810..148C, Cat. J/ApJ/810/148) (1)
13- 18 F6.3 [-] [Al/Fe] ? Abundance ratio [Al/Fe]
20- 24 F5.3 [-] e_[Al/Fe] ? Error on [Al/Fe]
26- 31 F6.3 [-] [N/Fe] ? Abundance ratio [N/Fe]
33- 37 F5.3 [-] e_[N/Fe] ? Error on [N/Fe]
39- 40 I2 --- NCN Number of CN features used
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Note (1): Group classification as follows:
0 = not classified
1 = P1, with primordial or almost abundance ratio
2 = P2, with primordial or almost primordial abundance ratio
3 = I1, with intermediate composition
4 = I2, with intermediate composition
5 = E, with severely extreme changes from the original composition
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Acknowledgements:
Eugenio Carratta, eugenio.carretta(at)oabo.inaf.it
(End) Patricia Vannier [CDS] 12-Feb-2018