1. Universidade Federal do Rio Grande do Norte
2. Centro de Ciências Exatas e da Terra
3. DFTE - Departamento de Física Teórica e Experimental
4. CCET - DFTE - Artigos publicados em periódicos

Título:	Constraints on helium enhancement in the globular cluster m4 (NGC 6121): the horizontal branch test
Autor(es):	Valcarce, A. A. R. Catelan, M. Alonso-Garcia, J. Cortés, C. Medeiros, José Renan de
Palavras-chave:	Globular clusters: general;Globular clusters: individual (M4 = NGC 6121);Hertzsprung–Russell and C–M diagrams;Stars: abundances;Stars: evolution;Stars: horizontal-branch
Data do documento:	2014
Editor:	American Astronomical Society
Referência:	MEDEIROS, José Renan de et al. Constraints on helium enhancement in the globular cluster m4 (NGC 6121): the horizontal branch test. The Astrophysical Journal, [s. l.], v. 782, p. 85-93, 2014. ISSN 1538-4357 versão online. DOI https://doi.org/10.1088/0004-637X/782/2/85. Disponível em: http://iopscience.iop.org/article/10.1088/0004-637X/782/2/85/meta. Acesso em: 19 maio 2020.
Resumo:	Recent pieces of evidence have revealed that most, and possibly all, globular star clusters are composed of groups of stars that formed in multiple episodes with different chemical compositions. In this sense, it has also been argued that variations in the initial helium abundance (Y) from one population to the next are also the rule, rather than the exception. In the case of the metal-intermediate globular cluster M4 (NGC 6121), recent high-resolution spectroscopic observations of blue horizontal branch (HB) stars (i.e., HB stars hotter than the RR Lyrae instability strip) suggest that a large fraction of blue HB stars are second-generation stars formed with high helium abundances. In this paper, we test this scenario by using recent photometric and spectroscopic data together with theoretical evolutionary computations for different Y values. Comparing the photometric data with the theoretically derived color-magnitude diagrams, we find that the bulk of the blue HB stars in M4 have ΔY lesssim 0.01 with respect to the cluster's red HB stars (i.e., HB stars cooler than the RR Lyrae strip)—a result which is corroborated by comparison with spectroscopically derived gravities and temperatures, which also favor little He enhancement. However, the possible existence of a minority population on the blue HB of the cluster with a significant He enhancement level is also discussed.
URI:	https://repositorio.ufrn.br/jspui/handle/123456789/29026
ISSN:	0004-637X (print), 1538-4357 (online)
Aparece nas coleções:	CCET - DFTE - Artigos publicados em periódicos

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