Annalisa Calamida 5 Maggio 2009 Metallicity distribution of red-giants in ω Cen.

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Transcript of Annalisa Calamida 5 Maggio 2009 Metallicity distribution of red-giants in ω Cen.

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Annalisa Calamida 5 Maggio 2009 Metallicity distribution of red-giants in Cen Slide 2 This work has been made in collaboration with: G. Bono, R. Buonanno (Universita' di Roma Tor Vergata) C. E. Corsi, G. Iannicola, L. Pulone, I. Ferraro, M. Monelli + others (INAF-OAR) P. B. Stetson (DAO, Victoria, Canada) L. M. Freyhammer (, UK) F. Grundahl (Department of Physics and Astronomy, Denmark) S. Cassisi, A. Pietrinferni, M. Del Principe, A. Piersimoni (INAF-OAC) S. DeglInnocenti, P. Prada Moroni (Universita di Pisa) Slide 3 Summary Why Omega Centauri? Omega Centauri red giants metallicity distributions Conclusions Slide 4 Why Cen? Most luminous (M V ~ -10) and most massive (M ~ 510 6 M ) galactic globular cluster Retrograde orbit (z max = 1 Kpc; R a = 6 Kpc) Metallicity dispersion : -2.2 < [Fe/H] < -0.5 Overabundance -elements (O, Mg, Si, Ca) Overabundance s -elements (Ba, Mo, La, Zi) Evidence of primordial chemical self-enrichment in short time scales (1-3 Gyr) Relic of a dwarf galaxy accreted on the Milky Way Merging of two stellar systems 0.2-1.4~1~1< 0.1Metallicity spread, [Fe/H] (dex) 10 6 -10 8 ~10 6 ~ 10 5 Mass (M ) -8/-13-10< -9Magnitude (M V ) dSphs CenGCsProperties Slide 5 Many different RGBs: Metal-poor (1) Metal-intermediate (2) Metal-rich (3) U, V photometry from [email protected] Main peak at [Fe/H] ~ -1.7 Secondary peak at [Fe/H] ~ -1.2 Tail up to [Fe/H] ~ -0.5 Gratton et al. (2005) Pancino et al. (2000) Slide 6 Literature: questions RGB-a (3): [Fe/H] ~ - 0.8 SGB-a: best-fit with old (~ 17 Gyr), low-metallicity isochrones SGB-a Split MS at V ~ 20mag, blue MS (Bedin et al. 2004) Best-fit with [Fe/H] ~ -1.0, d = 1.6 Kpc Hypothesis: Super-metal-poor population ([Fe/H]it seems that v-y is more sensitive to CN abundance variations than u-y Hilker & Richtler (2000) Slide 13 We provided new empirical, theoretical and semi-empirical metallicity calibrations of the Strmgren m 1 index The new calibrations gives reliable metallicity estimates ( 0.25 dex) for GCs and field red giants Preliminary evidence that at least ~1/3 of Cen RG stars show CN-abundance peculiarities Metallicity distribution of Cen RGs: evidence of a sharp cut-off at low metallicities (very few metal-poor stars), two main metallicity peaks at [Fe/H] ~ -1.8,-1.3 dex and a metal-rich shoulder at [Fe/H]~ -0.4 dex Conclusions II Slide 14 Slide 15 We can define the reddening-free indices (Stetson 1991) : [c] = c 1 - 0.2 (b-y) [m] = m 1 +0.33 (b-y) Using Cardelli et al. (1989) extinctions curves we derived values for the Danish Stroemgren filters: E (u-y)/E(B-V) = 1.84 (1.825*) E(c 1 )/E(b-y) = 0.2 E (v-y)/ E(B-V) = 1.328 (1.236) E(m 1 )/E(b-y) = -0.33 E(b-y)/E(B-V) = 0.70 (0.74) * Crawford values (1976) Slide 16 Z = abundance by mass of metals X = abundance by mass of hydrogen (Z/X) = 0.0245 for the sun