Abstract

Probing the mixing of H and He in White Dwarf Stars atmosphere through Globular Clusters

Fabiola Campos (Universidade Federal do Rio Grande do Sul)

P. Bergeron (Universite de Montreal), A.D. Romero (Universidade Federal do Rio Grande do Sul), S. O. Kepler (Universidade Federal do Rio Grande do Sul), C. J. Bonatto (Universidade Federal do Rio Grande do Sul), D. E. Winget (University of Texas at Austin), M. H. Montgomery (University of Texas at Austin), J. S. Kalirai (Space Telescope Science Institute; Center for Astrophysical Sciences, Johns Hopkins University), H. B. Richer (University of British Columbia), L. R. Bedin (Istituto Nazionale di Astrosica, Osservatorio Astronomico di Padova)

We fitted white dwarf cooling sequences to the archival data of the globular clusters NGC 6397, 47 Tucanae and M 4, obtained with the Hubble Space Telescope (ACS). In order to maintain the consistency between all the evolutionary phases and eliminate the subjectivity in setting white dwarf isochrones, we fixed the reddening and distance modulus to those shown for each cluster in Richer et al. (2013). Our white dwarf isochrones were calculated from full evolutionary models and white dwarf atmosphere models, specifically for this work. When we fit the isochrones computed with pure H atmosphere models, none of the them correctly adjusts the blue turn caused by the collision induced absorption in any of the three clusters. We show that to correctly fit the blue turn, it is necessary to use isochrones computed with atmosphere models including a mixture of H and He for the blue turn to occur in luminosity compatible with the data.

Mode of presentation: poster