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J/ApJ/786/14        He abundances in M30 and NGC 6397       (Mucciarelli+, 2014)

The helium abundance in the metal-poor globular clusters M30 and NGC 6397. Mucciarelli A., Lovisi L., Lanzoni B., Ferraro F.R. <Astrophys. J., 786, 14 (2014)> =2014ApJ...786...14M (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Effective temperatures ; Abundances Spectroscopy Keywords: globular clusters: individual: M30, NGC 6397 - stars: abundances - techniques: spectroscopic Abstract: We present the helium abundance of the two metal-poor clusters M30 and NGC 6397. Helium estimates have been obtained by using the high-resolution spectrograph FLAMES at the European Southern Observatory Very Large Telescope and by measuring the He I line at 4471 Å in 24 and 35 horizontal branch (HB) stars in M30 and NGC 6397, respectively. This sample represents the largest data set of He abundances collected so far in metal-poor clusters. The He mass fraction turns out to be Y=0.252±0.003 (σ=0.021) for M30 and Y=0.241±0.004 (σ=0.023) for NGC 6397. These values are fully compatible with the cosmological abundance, thus suggesting that the HB stars are not strongly enriched in He. The small spread of the Y distributions are compatible with those expected from the observed main sequence splitting. Finally, we find a hint of a weak anticorrelation between Y and [O/Fe] in NGC 6397 in agreement with the prediction that O-poor stars are formed by (He-enriched) gas polluted by the products of hot proton-capture reactions. Description: In this work we analyzed a set of high-resolution spectra acquired with the multi-object spectrograph FLAMES in the MEDUSA/GIRAFFE mode at the Very Large Telescope of the European Southern Observatory (ESO). The spectra are part of a data set secured within a project aimed at studying the general properties of blue straggler stars (Ferraro et al. 2006ApJ...647L..53F, 2009Natur.462.1028F, 2012Natur.492..393F; Lovisi et al. 2012, J/ApJ/754/91; 2013, J/ApJ/772/148). The employed GIRAFFE grating is HR5A (4340-4587 Å, with a spectral resolution of ∼18000), suitable to sample the He I line at 4471.5 Å. Spectra have been reduced with the standard ESO FLAMES pipeline. Six exposures of 45 minutes each have been secured in each cluster. Objects: ---------------------------------------------------------- RA (ICRS) DE Designation(s) ---------------------------------------------------------- 21 40 22.12 -23 10 47.5 M30 = NGC 7099 17 40 42.09 -53 40 27.6 NGC 6397 = GCl 74 ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 62 59 Stellar parameters and He abundances
See also: J/A+A/490/777 : Abundances of Population II stars in NGC 6397 (Lind+, 2008) J/A+A/505/L13 : Lithium in globular NGC 6397 (Gonzalez Hernandez+, 2009) J/AJ/142/63 : Abundance of five stars in NGC 6397 (Koch+, 2011) J/ApJ/754/91 : Abundances and velocities of NGC 6397 stars (Lovisi+, 2012) J/ApJ/772/148 : Blue straggler and red giant stars in M30 (Lovisi+, 2013) J/A+A/589/A61 : Stellar parameters and abundances for M30 (Gruyters+, 2016) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 7 A7 --- GC Globular cluster identifier (M30, NGC6397) 9- 16 I8 --- ID Source identifier ([LML2012] NNNNNNN for NGC6397 and [LML2013] NNNNNNNNN for M30 in Simbad) (1) 18- 28 F11.7 deg RAdeg Right Ascension in decimal degrees (J2000) (1) 30- 40 F11.7 deg DEdeg Declination in decimal degrees (J2000) (1) 42- 46 I5 K Teff Effective temperature (1) 48- 50 F3.1 [cm/s2] log(g) Log of the surface gravity (1) 52- 56 F5.3 --- Y Helium mass fraction 58- 62 F5.3 --- e_Y The 1σ uncertainty in Y
Note (1): Taken from Lovisi et al. (2012, J/ApJ/754/91; 2013, J/ApJ/772/148).
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 16-Jun-2017
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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