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 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 2006ApJ...647L..53F, 2009Natur.462.1028F 2009Natur.462.1028F,
2012Natur.492..393F 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:
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RA (ICRS) DE Designation(s)
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21 40 22.12 -23 10 47.5 M30 = NGC 7099
17 40 42.09 -53 40 27.6 NGC 6397 = GCl 74
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 62 59 Stellar parameters and He abundances
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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
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Bytes Format Units Label Explanations
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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
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Note (1): Taken from Lovisi et al. (2012, J/ApJ/754/91; 2013, J/ApJ/772/148).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 16-Jun-2017