Variable stars in Local Group Galaxies - I. Tracing the early chemical enrichment and radial gradients in the Sculptor dSph with RR Lyrae stars

Martínez-Vázquez, C. E.; Monelli, M.; Bono, G.; Stetson, P. B.; Ferraro, I.; Bernard, E. J.; Gallart, C.; Fiorentino, G.; Iannicola, G.; Udalski, A.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 454, Issue 2, p.1509-1516

Advertised on:
12
2015
Number of authors
10
IAC number of authors
3
Citations
54
Refereed citations
44
Description
We identified and characterized the largest (536) RR Lyrae (RRL) sample in a Milky Way dSph satellite (Sculptor) based on optical photometry data collected over ˜24 years. The RRLs display a spread in V-magnitude (˜0.35 mag) which appears larger than photometric errors and the horizontal branch (HB) luminosity evolution of a mono-metallic population. Using several calibrations of two different reddening free and metal independent period-Wesenheit relations we provide a new distance estimate μ = 19.62 mag (σμ = 0.04 mag) that agrees well with literature estimates. We constrained the metallicity distribution of the old population, using the MI period-luminosity relation, and we found that it ranges from -2.3 to -1.5 dex. The current estimate is narrower than suggested by low and intermediate spectroscopy of RGBs (Δ [Fe/H]≤ 1.5). We also investigated the HB morphology as a function of the galactocentric distance. The HB in the innermost regions is dominated by red HB stars and by RRLs, consistent with a more metal-rich population, while in the outermost regions it is dominated by blue HB stars and RRLs typical of a metal-poor population. Our results suggest that fast chemical evolution occurred in Sculptor, and that the radial gradients were in place at an early epoch.
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Matteo
Monelli