Defense
Student: Vinicius Branco Silva
Program: Astronomia
Título: “Extragalactic globular clusters: from a new family of stellar population models to its
application"
Advisor: Profa. Dra. Paula Rodrigues T. Coelho - IAG/USP
Judging Comitee:
- Profa. Dra. Paula Rodrigues Teixeira Coelho – Presidente e Orientadora – IAG/USP
- Prof. Dr. Jorge Luis Melendez Moreno – IAG/USP
- Profa. Dra. Lucimara Pires Martins – UNICID
- Profa. Dra. Ana Leonor Chies Santiago Santos – UFRGS (por videoconferência)
- Prof. Dr. Bruno Moreira de Souza Dias – UNAB, Chile (por videoconferência)
- Dra. Simone Daflon dos Santos – ON/MCTI (por videoconferência)
Other Members:
- Profa. Dra. Ariane Lançon - University of Strasbourg, França
- Profa. Dra. Beatriz Leonor Silveira Barbuy - IAG/USP
- Prof. Dr. Marcos Perez Diaz - IAG/USP
- Prof. Dr. Charles José Bonatto – UFRGS
- Prof. Dr. Ricardo Piorno Schiavon – LJMU, Reino Unido
- Prof. Dr. João Francisco Coelho Santos Jr. – UFMG
Abstract:
Globular clusters (GCs) are invaluable for advancing our knowledge in Galactic and
extragalactic astronomy. In the Milky Way, nearly all massive and ancient GCs
harbour multiple populations (MPs) of stars, presenting multiple sequences in all
stellar evolutionary phases in the colour-magnitude diagram, and affecting
spectrophotometric indices. The main evidence of subpopulations in GCs is chemical
anticorrelations in light elements. Thus, GC presents a ``first population'' (1P) with
Galactic field-star-like chemical abundances and a ``second population'' (2P)
enriched in N and Na and depleted in C and O. If the extragalactic GCs are
counterparts to the Galactic ones, the effects of MPs must also be seen in the
integrated light. In this context, we provide spectrophotometric insights to
disentangle 1P and 2P in the synthetic integrated light of GCs at various metallicity
regimes based on stellar population synthesis techniques. To that end, we
computed model atmospheres and synthetic stellar spectra to model the integrated
light of the sub-populations, employing two methods: 1) based on resolved colour-
magnitude diagrams of Galactic GCs, and 2) isochrones based on the fast rotating
massive stars formation scenario of MPs. We measured spectrophotometric indices
on the computed integrated spectra, accounting for stochastic fluctuations. We
validated results from the literature on the sensitivity of optical spectral indices to
the effects of MPs, and expanded the results to other metallicity regimes. We
proposed new spectral indices sensitive to the MP effects in the near-UV and optical
wavelength ranges, which demonstrate robustness in the 1P/2P subpopulation split.
We suggested a photometric pseudo-diagram combining HST filters, which
effectively separates 1P from 2P. We are advancing the characterisation of MPs in
extragalactic environments in GCs, with the identification of sensitive
spectrophotometric indices. In the future, up-to-date stellar physics, accounting for
non-standard mixing, may enhance our interpretation of MP formation scenario
candidates.
Keywords: atlases, globular clusters: general, stars: atmospheres, stars: abundances, stars:
evolution, stars: low-mass, stars: Population II