RSAA Colloquia / Seminars / Feast-of-Facts: Thursday, 12 April 2018, 11:00-12:00; Duffield Lecture Theatre

Carolina Salgado Escalona

"Investigating globular cluster abundance anomalies in different environments (End-of-Thesis Colloquium)"

The origin of the star to star abundance variations for light elements shown in galactic globular clusters (GGCs) is not well understood, which represents a significant problem for stellar astrophysics. While the light element abundance variations are very common in globular clusters, they are comparatively rare in the galactic halo field population. However, very little is known regarding the occurrence of the abundance anomalies in other environments such as dwarf spheroidal galaxies and massive star clusters younger than the ancient globular clusters. Consequently, during my Ph.D. thesis was investigated the anti-correlation and bimodality of CH and CN band strengths through the measurement of CH(lambda ~ 4300), S(3839) and S(4142) indices for 45 red giants stars in Sculptor dwarf spheroidal galaxy. We report the discovery of a third carbon-enhanced metal poor star in Sculptor, which shows evidence of a strong s-process element enhancement. Through the calibration of five GCs (NGC 1851, NGC 288, NGC 6752, M 55 and M 30) we also have studied the correlation CN/Na in the Sculptor red giant sample. Our results indicate that variations analogous to those seen in GGCs are not present in our Sculptor sample. Instead we find a positive correlation between CH and CN, and no correlation between Na and CN. Also, we have found a deficiency of [Na/Fe] in Sculptor relative to GGCs, which is consistent with previous works for dSph galaxies. The outcome reinforces the apparent need for a high stellar density environment to produce the light element abundance variations. In addition, we have investigated CN and CH band strengths along with carbon and nitrogen abundances in massive star clusters of Small Magellanic Cloud. These clusters have metallicity and luminosity comparable to GGCs but shows differences in age. The investigated clusters are Lindsay 1, Kron 3 and NGC 339, which have ages between 6 and 7.5 Gyr. Our results show large spread in nitrogen in these three clusters, which is an indicator of multi population. Due to the possibility of evolutionary mixing on the red giant branch, the existence of CN-CH anti-correlation is not sufficient in itself to indicate the presence of abundance anomalies. Consequently, we have investigated the Na, CN correlation through the measurement of sodium D-lines and Na abundances. At least for NGC339 we can confirm the positive correlation between nitrogen and sodium. Our results are a key factor in gaining understanding on the origin and evolution of stellar systems and also it will provide an accurate context for studying the problem of origin of anomalies constraining the age dependence of them in the unexplored 6-11 Gyr age range.