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Paper: Tracing the Early Chemical Evolution of Local Group Dwarf Galaxies Using RR Lyrae Stars
Volume: 529, RR Lyrae/Cepheid 2019: Frontiers of Classical Pulsators
Page: 235
Authors: Martínez-Vázquez, C. E.
Abstract: RR Lyrae stars (RRLs) are powerful tracers of the early evolution of their host stellar system since they provide direct insight into the age and the chemical evolution of the old (>10 Gyr) population they belong to. Their pulsation properties can be used to obtain individual metallicities and derive the metallicity distribution of a purely old population. We have found a large metallicity spread present in the population of RRLs of the Sculptor dSph (536 RRLs, ∼ 2 deg2), consistent with a rapid chemical enrichment that occurred at the early stages of Sculptor's life. When comparing the metallicity distribution of the RRLs (purely old population) with that of the RGB stars (age-degenerate population) we found that i) the star formation in the center of Sculptor lasted substantially longer than in the outer parts, thus constraining the timescales for the outside-in evolution of this galaxy, and ii) the RRL population has an intrinsic metallicity spread and presents a clear spatial metallicity gradient, which therefore was in place at a very early epoch. We have also extended our approach to six M31 dwarf satellites observed with the Hubble Space Telescope (HST). From 111 HST orbits, we have detected ∼ 900 RRLs in these six galaxies, deriving their metallicity distribution function. Finally, we broadened our approach to more Local Group galaxies located in different environments, in order to show the potential of this approach for more distant objects when the JWST and the next generation of ELTs are operative. We have found robust evidence of an early chemical enrichment in the old population of some of them.
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