Fluorine variations in the globular cluster NGC 6656 (m22): Implications for internal enrichment timescales

Valentina D'Orazi*, Sara Lucatello, Maria Lugaro, Raffaele G. Gratton, George Angelou, Angela Bragaglia, Eugenio Carretta, Alan Alves-Brito, Inese I. Ivans, Thomas Masseron, Alessio Mucciarelli

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

26 Citations (Scopus)
22 Downloads (Pure)

Abstract

Observed chemical (anti)correlations in proton-capture elements among globular cluster stars are presently recognized as the signature of self-enrichment from now extinct, previous generations of stars. This defines the multiple population scenario. Since fluorine is also affected by proton captures, determining its abundance in globular clusters provides new and complementary clues regarding the nature of these previous generations and supplies strong observational constraints to the chemical enrichment timescales. In this paper, we present our results on near-infrared CRIRES spectroscopic observations of six cool giant stars in NGC 6656 (M22): the main objective is to derive the F content and its internal variation in this peculiar cluster, which exhibits significant changes in both light- and heavy-element abundances. Across our sample, we detected F variations beyond the measurement uncertainties and found that the F abundances are positively correlated with O and anticorrelated with Na, as expected according to the multiple population framework. Furthermore, our observations reveal an increase in the F content between the two different sub-groups, s-process rich and s-process poor, hosted within M22. The comparison with theoretical models suggests that asymptotic giant stars with masses between 4 and 5 M are responsible for the observed chemical pattern, confirming evidence from previous works: the difference in age between the two sub-components in M22 must be not larger than a few hundred Myr.

Original languageEnglish
Article number22
Pages (from-to)1-9
Number of pages9
JournalAstrophysical Journal
Volume763
Issue number1
DOIs
Publication statusPublished - 20 Jan 2013

Bibliographical note

Copyright 2013 the American Astronomical Society. First published in the Astrophysical journal, 763(1), 22, 2013, published by IOP Publishing. The original publication is available at http://www.doi.org/10.1088/0004-637X/763/1/22. Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

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