On the metallicity distribution of classical Cepheids in the Galactic inner disk

We present homogeneous and accurate iron abundances for almost four dozen (47) of Galactic Cepheids using high-spectral resolution (R$sim$40,000) high signal-to-noise ratio (S/N $ge$ 100) optical spectra collected with UVES at VLT. A significant fraction of the sample (32) is located in the inner disk (RG $le$ 6.9 kpc) and for half of them we provide new iron abundances. Current findings indicate a steady increase in iron abundance when approaching the innermost regions of the thin disk. The metallicity is super-solar and ranges from 0.2 dex for RG $sim$ 6.5 kpc to 0.4 dex for RG $sim$ 5.5 kpc. Moreover, we do not find evidence of correlation between iron abundance and distance from the Galactic plane. We collected similar data available in the literature and ended up with a sample of 420 Cepheids. Current data suggest that the mean metallicity and the metallicity dispersion in the four quadrants of the Galactic disk attain similar values. The first-second quadrants show a more extended metal-poor tail, while the third-fourth quadrants show a more extended metal-rich tail, but the bulk of the sample is at solar iron abundance. Finally, we found a significant difference between the iron abundance of Cepheids located close to the edge of the inner disk ([Fe/H]$sim$0.4) and young stars located either along the Galactic bar or in the nuclear bulge ([Fe/H]$sim$0). Thus suggesting that the above regions have had different chemical enrichment histories. The same outcome applies to the metallicity gradient of the Galactic bulge, since mounting empirical evidence indicates that the mean metallicity increases when moving from the outer to the inner bulge regions.

On the relative distance of Magellanic Clouds using Cepheid NlR and Optical-NIR PW relations

We present new estimates of the relative distance of the Magellanic Clouds (MCs) by using NIR and Optical-NIR Cepheid Period Wesenheit (PW) relations. The relative distances are independent of uncertainties affecting the zero-point of the PW relations, but do depend on the adopted pivot periods. We estimated the pivot periods for fundamental (FU) and first overtone (FO) Cepheids on the basis of their period distributions. We found that log P=0.5 (FU) and log P=0.3 (FO) are solid choices, since they trace a main peak and a shoulder in LMC and SMC period distributions. By using the above pivot periods and ten PW relations, we found MC relative distances of 0.53$pm$0.06 (FU) and 0.53$pm$0.07 (FO) mag. Moreover, we investigated the possibility to use mixed-mode (FU/FO, FO/SO) Cepheids as distance indicators and we found that they follow quite well the PW relations defined by single mode MC Cepheids, with deviations typically smaller than 0.3{sigma}.

Stroemgren photometry of Galactic Globular Clusters. I. New Calibrations of the metallicity index

We present a new calibration of the Stroemgren metallicity index m1 using red giant (RG) stars in 4 globular clusters (GCs:M92,M13,NGC1851,47Tuc) with metallicity ranging from [Fe/H]=-2.2 to -0.7, marginally affected by reddening (E(B-V)<0.04) and with accurate u,v,b,y photometry.The main difference between the new metallicity-index-color (MIC) relations and similar relations available in the literature is that we adopted the u-y/v-y colors instead of the b-y.These colors present a stronger sensitivity to effective temperature, and the MIC relations show a linear slope. The difference between photometric estimates and spectroscopic measurements for RGs in M71,NGC288,NGC362,NGC6397, and NGC6752 is 0.04+/-0.03dex (sigma=0.11dex). We also apply the MIC relations to 85 field RGs with metallicity raning from [Fe/H]=-2.4 to -0.5 and accurate reddening estimates. We find that the difference between photometric estimates and spectroscopic measurements is-0.14+/-0.01dex (sig=0.17dex). We also provide two sets of MIC relations based on evolutionary models that have been transformed into the observational plane by adopting either semi-empirical or theoretical color-temperature relations. We apply the semi-empirical relations to the 9 GCs and find that the difference between photometric and spectroscopic metallicities is 0.04+/-0.03dex (sig=0.10dex).A similar agreement is found for the sample of field RGs, with a difference of -0.09+/-0.03dex (sig=0.19dex).The difference between metallicity estimates based on theoretical relations and spectroscopic measurements is -0.11+/-0.03dex (sig=0.14dex) for the 9 GGCs and -0.24+/-0.03dex (sig=0.15dex) for the field RGs. Current evidence indicates that new MIC relations provide metallicities with an intrinsic accuracy better than 0.2dex.