We present new spectroscopic metal abundances for 74 RR Lyrae stars in omega Cen obtained with FLAMES. The well-known metallicity spread is visible among the RR Lyrae variables. The metal-intermediate (MInt) RR Lyrae stars ([Fe/H] ~ -1.2) are fainter than the bulk of the dominant metal-poor population ([Fe/H] ~ -1.7), in good agreement with the corresponding zero-age horizontal branch models with cosmological helium abundance Y = 0.246. This result conflicts with the hypothesis that the progenitors of the MInt RR Lyrae stars correspond to the anomalous blue main-sequence stars, which share a similar metallicity but whose properties are currently explained by assuming for them a large helium enhancement. Therefore, in this scenario, the coexistence within the cluster of two different populations with similar metallicities ([Fe/H] ~ -1.2) and different helium abundances has to be considered.
New Metallicities of RR Lyrae Stars in omega Centauri: Evidence for a Non He-Enhanced Metal-Intermediate Population / Sollima A.; Borissova J.; Catelan M.; Smith H.A.; Minniti D.; Cacciari C.; Ferraro F.R.. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - STAMPA. - 640:(2006), pp. L43-L46. [10.1086/503099]
New Metallicities of RR Lyrae Stars in omega Centauri: Evidence for a Non He-Enhanced Metal-Intermediate Population
SOLLIMA, ANTONIO;FERRARO, FRANCESCO ROSARIO
2006
Abstract
We present new spectroscopic metal abundances for 74 RR Lyrae stars in omega Cen obtained with FLAMES. The well-known metallicity spread is visible among the RR Lyrae variables. The metal-intermediate (MInt) RR Lyrae stars ([Fe/H] ~ -1.2) are fainter than the bulk of the dominant metal-poor population ([Fe/H] ~ -1.7), in good agreement with the corresponding zero-age horizontal branch models with cosmological helium abundance Y = 0.246. This result conflicts with the hypothesis that the progenitors of the MInt RR Lyrae stars correspond to the anomalous blue main-sequence stars, which share a similar metallicity but whose properties are currently explained by assuming for them a large helium enhancement. Therefore, in this scenario, the coexistence within the cluster of two different populations with similar metallicities ([Fe/H] ~ -1.2) and different helium abundances has to be considered.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.