Field RR Lyrae as Gal. probes. III. Abundances

The current measurements were complemented with similar abundances available in the literature for 46 field RRLs brought to our metallicity scale. We ended up with a sample of old (t>=10Gyr), low-mass stellar tracers (208 RRLs: 169 fundamental, 38 first overtone, and 1 mixed mode) covering 3dex in iron abundance (-3.00<=[Fe/H]<=0.24).

We found that field RRLs are ~0.3dex more {alpha} poor than typical halo tracers in the metal-rich regime ([Fe/H]>=-1.2), while in the metal-poor regime ([Fe/H]<=-2.2) they seem to be on average ~0.1dex more {alpha} enhanced. This is the first time that the depletion in {alpha} elements for solar iron abundances is detected on the basis of a large, homogeneous, and coeval sample of old stellar tracers. Interestingly, we also detected a close similarity in the [{alpha}/Fe] trend between {alpha}-poor, metal-rich RRLs and red giants (RGs) in the Sagittarius dwarf galaxy as well as between {alpha}-enhanced, metal-poor RRLs and RGs in ultrafaint dwarf galaxies.