NGC 6397: The metallicity trend along the isochrone revisited

Autor(es)

Jain, Rashi ^[1] ; Prugniel, Philippe ^[2] ; Martins, Lucimara ^{[2, 3]} ; Lancon, Ariane ^[1]

Afiliação do(s) autor(es)

^[1] Univ Strasbourg, CNRS, Observ Astron Strasbourg, UMR7550, F-67000 Strasbourg - France

^[2] Univ Lyon1, Ctr Rech Astrophys Lyon, Univ Lyon, ENS Lyon, CNRS, UMR5574, F-69230 St Genis Laval - France

^[3] Univ Cidade Sao Paulo, Univ Cruzeiro Sul, NAT, Rua Galvao Bueno 868, BR-01506000 Sao Paulo - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Astronomy & Astrophysics; v. 635, MAR 27 2020.
• Citações Web of Science: 1

Resumo

Context. Recent work has used spectra of similar to 5000 stars in NGC 6397 that were extracted from a MUSE mosaic to determine the atmospheric parameters for these stars by fitting the spectra against the Gottingen Spectral Library. A significant change in metallicity between the turn off and the red giant branch was found and was discussed as a possible manifestation of predicted effects of atomic diffusion. However, the small amplitude of the effect and inconsistency with earlier measurements call for more attention before this result is interpreted. Systematic effects due to the interpolation or to the synthetic spectra cannot be ruled out at this level of precision.Aims. We reanalyze the data with : the ELODIE and MILES reference libraries in order to assess the robustness of the result. These empirical libraries have a finer metallicity coverage down to approximately the cluster metalicity turn-off.Methods. We used the ULySS full-spectrum fitting package, together with the library interpolators to remeasure the three atmospheric parameters effective temperature, surface gravity, and {[}Fe/H] metallicity.Results. We find a very low {[}Fe/H] dispersion along the isochrone (0.07 dex), consistent with our error estimate (0.05 dex). However, the {[}Fe/H] trend is not reproducible. This shows that the data have the potential to reveal patterns of the magnitude of the expected physical effects, but the analysis methods need to be refined to cull systematic effects that currently dominate the patterns. (AU)

• Processo FAPESP: 18/26381-4 - Aperfeiçoando Bibliotecas Estelares Sintéticas com as Estrelas de Referência do Gaia
• Beneficiário: Lucimara Pires Martins
• Modalidade de apoio: Bolsas no Exterior - Pesquisa