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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
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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
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
Note (2): See Appendix A in the main paper for a complete line list.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
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)
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
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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