J/ApJ/786/14: Resource Record Summary

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He abundances in M30 and NGC 6397

Short name: J/ApJ/786/14 IVOA Identifier: ivo://CDS.VizieR/J/ApJ/786/14 DOI (Digital Object Identifier): 10.26093/cds/vizier.17860014 Publisher: CDS[+]ivo://CDS[Pub. ID] More Info: https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/786/14 VO Compliance: Level 2: This is a VO-compliant resource.	Status: active Registered: 2017 Jul 03 15:05:57Z
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Description

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 {AA} 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 ({sigma}=0.021) for M30 and Y=0.241+/-0.004 ({sigma}=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.

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	This is service that does not comply with any IVOA standard but instead provides access to special capabilities specific to this resource. VO Compliance: Level 2: This is a VO-compliant resource. Available endpoints for this service interface: Interactive web page: http://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/786/14

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