J/A+A/527/A148 NGC6397 red giants chemical composition (Lind+, 2011)
Tracing the evolution of NGC6397 through the chemical composition of its stellar
populations.
Lind K., Charbonnel C., Decressin T., Primas F., Grundahl F., Asplund M.
<Astron. Astrophys. 527, A148 (2011)>
=2011A&A...527A.148L 2011A&A...527A.148L
ADC_Keywords: Clusters, globular ; Abundances ; Equivalent widths
Keywords: stars: Population II - globular clusters: individual: NGC 6397 -
methods: observational - techniques: spectroscopic - stars: abundances
Abstract:
The chemical compositions of globular clusters provide important
information on the star formation that occurred at very early times in
the Galaxy. In particular the abundance patterns of elements with
atomic number z≤13 may shed light on the properties of stars that
early on enriched parts of the star-forming gas with the rest-products
of hydrogen-burning at high temperatures. We analyse and discuss the
chemical compositions of a large number of elements in 21 red giant
branch stars in the metal-poor globular cluster NGC6397. We compare
the derived abundance patterns with theoretical predictions in the
framework of the "wind of fast rotating massive star"-scenario.
High-resolution spectra were obtained with the FLAMES/UVES
spectrograph on the VLT. We determined non-LTE abundances of Na, and
LTE abundances for the remaining 21 elements, including O (from the
[OI] line at 630nm), Mg, Al, alpha, iron-peak, and neutron-capture
elements, many of which had not been previously analysed for this
cluster. We also considered the influence of possible He enrichment in
the analysis of stellar spectra. We find that the Na abundances of
evolved, as well as unevolved, stars in NGC6397 show a distinct
bimodality, which is indicative of two stellar populations: one
primordial stellar generation of composition similar to field stars,
and a second generation that is polluted with material processed
during hydrogen-burning, i.e., enriched in Na and Al and depleted in O
and Mg. The red giant branch exhibits a similar bimodal distribution
in the Stroemgren colour index cy=c1-(b-y), implying that there
are also large differences in the N abundance. The two populations
have the same composition for all analysed elements heavier than Al,
within the measurement uncertainty of the analysis, with the possible
exception of [Y/Fe]. Using two stars with almost identical stellar
parameters, one from each generation, we estimate the difference in He
content, Delta-Y=0.01±0.06, given the assumption that the mass
fraction of iron is the same for the stars. NGC6397 hosts two stellar
populations that have different chemical compositions of N, O, Na, Mg,
and probably Al. The cluster is dominated (75%) by the second
generation. We show that massive stars of the first generation can be
held responsible for the abundance patterns observed in the second
generation long-lived stars of NGC6397. We estimate that the initial
mass of this globular cluster is at least ten times higher than its
present-day value.
Description:
The tables contain stellar parameters, equivalent widths, and
line-by-line abundances for stars in the metal-poor globular cluster
NGC6397. All abundances are given in logarithmic units relative to
hydrogen, according to A(x)=log(N(x)/N(H))+12, where N(x) is the
number density of element x and N(H) the number density of hydrogen.
For photometric data, Li abundances, and equivalent widths of Fe lines
we refer to Lind et al. (2009, Cat. J/A+A/503/545). Table 2 contains
improved non-LTE Na abundances for the targets presented in Lind et al
(2009,, Cat. J/A+A/503/545).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 47 1478 Equivalent widths and LTE line-by-line
abundances for 19 elements of 21 red giants
table2.dat 97 133 Equivalent widths and non-LTE abundances of Na
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See also:
J/A+A/503/545 : Equivalent widths of Li, Na, Fe, Ca in NGC 6397 (Lind+, 2009)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID Identification number of target,
<[LPC2009] NNNNNNN> in Simbad
9- 11 A3 --- Ion Element and ionisation stage of the line
15- 19 F5.1 nm lambda Approximate central wavelength of line (2)
22- 26 F5.2 pm EW Equivalent width of line
29- 33 F5.2 pm e_EW rms uncertainty on EW
36- 40 F5.2 [---] eps LTE elemental abundance of Ion (G1)
44- 47 F4.2 [---] e_eps rms uncertainty on eps
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Note (2): See Appendix A in the main paper for a complete line list.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID Identification number of target,
<[LPC2009] NNNNNNN> in Simbad
10- 13 I4 K Teff Effective temperature
17- 20 F4.2 [cm/s2] logg Surface gravity
24- 27 F4.2 km/s Vturb Microturbulence velocity
30- 34 F5.2 pm W5682 ? Equivalent width of NaI 568.2nm line
37- 41 F5.2 pm e_W5682 ? Error on W5682
44- 48 F5.2 pm W5688 ? Equivalent width of NaI 568.8nm line
51- 55 F5.2 pm e_W5688 ? Error on W5688
58- 62 F5.2 pm W8183 ? Equivalent width of NaI 818.3nm line
65- 69 F5.2 pm e_W8183 ? Error on W8183
71 A1 --- l_W8194 [<] Limit flag on W8194 (indicates upper limit)
72- 76 F5.2 pm W8194 ? Equivalent width of NaI 819.4nm line
79- 83 F5.2 pm e_W8194 ? Error on W8194
85 A1 --- l_e(Na) [<] Limit flag on e(Na) (indicates upper limit)
87- 90 F4.2 [---] e(Na) ? Non-LTE sodium abundance (G1)
94- 97 F4.2 [---] e_e(Na) ? Error on e(Na) (G1)
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Global Notes:
Note (G1): abundance of ion x is defined as ε(x)=log(N(x)/N(H))+12
where N(x) is the number density of element x and N(H) the number
density of hydrogen (ε(H)=12.0)
Acknowledgements:
Karin Lind, klind(at)mpa-garching.mpg.de
(End) Karin Lind [MPA, Germany], Patricia Vannier [CDS] 11-Jan-2011