The Carina Project. VII. Toward the Breaking of the Age-Metallicity Degeneracy of Red Giant Branch Stars Using the C U, B, I Index

Monelli, M.; Milone, A. P.; Fabrizio, M.; Bono, G.; Stetson, P. B.; Walker, A. R.; Cassisi, S.; Gallart, C.; Nonino, M.; Aparicio, A.; Buonanno, R.; Dall'Ora, M.; Ferraro, I.; Iannicola, G.; Pulone, L.; Thévenin, F.
Bibliographical reference

The Astrophysical Journal, Volume 796, Issue 2, article id. 90, 10 pp. (2014).

Advertised on:
12
2014
Number of authors
16
IAC number of authors
4
Citations
14
Refereed citations
13
Description
We present an analysis of photometric and spectroscopic data of the Carina dSph galaxy, testing a new approach similar to that used to disentangle multiple populations in Galactic globular clusters (GCs). We show that a proper color combination is able to separate a significant fraction of the red giant branch (RGB) of the two main Carina populations (the old one, ~12 Gyr, and the intermediate-age one, 4-8 Gyr). In particular, the c U, B, I = (U – B) – (B – I) pseudo-color allows us to follow the RGB of both populations along a relevant portion of the RGB. We find that the oldest stars have a more negative c U, B, I pseudo-color than intermediate-age ones. We correlate the pseudo-color of RGB stars with their chemical properties, finding a significant trend between the iron content and the c U, B, I. Stars belonging to the old population are systematically more metal-poor ([Fe/H] =–2.32 ± 0.08 dex) than the intermediate-age ones ([Fe/H] =–1.82 ± 0.03 dex). This gives solid evidence of the chemical evolution history of this galaxy, and we have a new diagnostic that can allow us to break the age-metallicity degeneracy of H-burning advanced evolutionary phases. We compared the distribution of stars in the c U, B, I plane with theoretical isochrones, finding that no satisfactory agreement can be reached with models developed in a theoretical framework based on standard heavy element distributions. Finally, we discuss possible systematic differences when compared with multiple populations in GCs.
Related projects
NGC 2808 Globular Cluster
Milky Way and Nearby Galaxies
The general aim of the project is to research the structure, evolutionary history and formation of galaxies through the study of their resolved stellar populations, both from photometry and spectroscopy. The group research concentrates in the most nearby objects, namely the Local Group galaxies including the Milky Way and M33 under the hypothesis
Martín
López Corredoira
A view of our Milky Way galaxy with its close neighbors the Magellanic Clouds
Galaxy Evolution in the Local Group
Galaxy formation and evolution is a fundamental Astrophysical problem. Its study requires “travelling back in time”, for which there are two complementary approaches. One is to analyse galaxy properties as a function of red-shift. Our team focuses on the other approach, called “Galactic Archaeology”. It is based on the determination of galaxy
Matteo
Monelli