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J/A+A/599/A97   Chemical composition of globular cluster NGC 6426 (Hanke+, 2017)

Insights into the chemical composition of the metal-poor Milky Way halo globular cluster NGC 6426. Hanke M., Koch A., Hansen C.J., McWilliam A. <Astron. Astrophys. 599, A97 (2017)> =2017A&A...599A..97H (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Stars, giant ; Stars, metal-deficient ; Abundances ; Equivalent widths Keywords: stars: abundances - Galaxy: abundances - Galaxy: evolution - Galaxy: halo - globular clusters: individual: NGC 6426 Abstract: We present our detailed spectroscopic analysis of the chemical composition of four red giant stars in the halo globular cluster NGC 6426. We obtained high-resolution spectra using the Magellan2/MIKE spectrograph, from which we derived equivalent widths and subsequently computed abundances of 24 species of 22 chemical elements. For the purpose of measuring equivalent widths, we developed a new semi-automated tool, called EWCODE. We report a mean Fe content of [Fe/H]=-2.34±0.05dex (stat.) in accordance with previous studies. At a mean α-abundance of [(Mg,Si,Ca)/3Fe]=0.39±0.03dex, NGC 6426 falls on the trend drawn by the Milky Way halo and other globular clusters at comparably low metallicities. The distribution of the lighter α-elements as well as the enhanced ratio [Zn/Fe]=0.39dex could originate from hypernova enrichment of the pre-cluster medium. We find tentative evidence for a spread in the elements Mg, Si, and Zn, indicating an enrichment scenario, where ejecta of evolved massive stars of a slightly older population polluted a newly born younger one. The heavy element abundances in this cluster fit well into the picture of metal-poor globular clusters, which in that respect appear to be remarkably homogeneous. The pattern of the neutron-capture elements heavier than Zn point towards an enrichment history governed by the r-process with only little - if any - sign of s-process contributions. This finding is supported by the striking similarity of our program stars to the metal-poor field star HD 108317. Description: Our spectra were gathered with the Magellan Inamori Kyocera Echelle (MIKE) spectrograph, which is mounted at the 6.5-m Magellan2 Telescope located at Las Campanas Observatory, Chile. Throughout this work, in order to compute chemical abundances we have computed equivalent widths using the newly developed semi-automated tool EWCODE. Objects: --------------------------------------------------- RA (2000) DE Designation(s) --------------------------------------------------- 17 44 54.71 +03 10 12.5 NGC 6426 = NGC 6426 --------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file stars.dat 52 4 List of studied red giants table2.dat 86 272 Line list including equivalent widths
See also: J/AJ/112/1054 : VI photometry of NGC 6426 (Zinn+ 1996) J/A+A/573/A13 : Metal abundances in 6 globular cluster (Dias+, 2015) Byte-by-byte Description of file: stars.dat
Bytes Format Units Label Explanations
1- 5 I5 --- Star Star number 7- 8 I2 h RAh Right ascension (J2000) 10- 11 I2 min RAm Right ascension (J2000) 13- 16 F4.1 s RAs Right ascension (J2000) 18 A1 --- DE- Declination sign (J2000) 19- 20 I2 deg DEd Declination (J2000) 22- 23 I2 arcmin DEm Declination (J2000) 25- 28 F4.1 arcsec DEs Declination (J2000) 30- 52 A23 --- Name 2MASS name
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 2 A2 --- El Element 4- 5 A2 --- Ion Ionization stage 10- 16 F7.2 0.1nm lambda Wavelength 21- 24 F4.2 eV chiex Excitation potential 29- 34 F6.3 [-] loggf Oscillator strength 39- 41 I3 0.1pm EW14853 ? Equivalent width for star 14853 45- 47 I3 0.1pm e_EW14853 ? Equivalent width error for star 14853 (1) 52- 54 I3 0.1pm EW5659 ? Equivalent width for star 5659 58- 60 I3 0.1pm e_EW5659 ? Equivalent width error for star 5659 (1) 65- 67 I3 0.1pm EW736 ? Equivalent width for star 736 71- 73 I3 0.1pm e_EW736 ? Equivalent width error for star 736 (1) 78- 80 I3 0.1pm EW2314 ? Equivalent width for star 2314 84- 86 I3 0.1pm e_EW2314 ? Equivalent width error for star 2314 (1)
Note (1): Equivalent width uncertainties provided by EWCODE.
Acknowledgements: Michael Hanke, mhanke(at)ari.uni-heidelberg.de
(End) Michael Hanke [ARI, Germany], Patricia Vannier [CDS] 08-Dec-2016
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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