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We introduce a new parameter ??-the difference in magnitude between the red giant branch (RGB) bump and the point on the main sequence (MS) at the same color as the bump (which we call the "benchmark")-to estimate the helium content in old stellar systems. The ?? parameter is a helium indicator, since an increase in helium makes, at fixed age and iron abundance, the RGB bump brighter and the MS benchmark fainter. Moreover, its sensitivity to helium is linear over the entire metallicity range. ?? is also minimally affected by changes of a few gigayears in cluster age, by uncertainties in the photometric zero point, by the amount of reddening, or by the effects of evolution on the horizontal branch. The two main drawbacks of the ?? parameter include the need for precise and large photometric data sets and a strong dependence of the ?Y/?? slope on metallicity. We selected almost two dozen relatively bright Galactic globular clusters (GGCs) with low foreground reddening and a broad range of iron abundance (-2.45 ? [Fe/H] ? -0.70 dex), together with precise and homogeneous multiband (BVI) photometry. The observed ?? parameters and those predicted from ?-enhanced evolutionary models agree reasonably well if we assume a primordial helium content of Y= 0.20 (abundance by mass). The discrepancy becomes ?4? (?B= 0.20 mag) only in the metal-poor regime. Comparison with prescriptions based on a canonical primordial helium content (Y= 0.245 indicates that the observed ?? values are smaller than predicted. These findings support previous results suggesting that current evolutionary models overestimate the luminosity of the RGB bump. The inclusion of envelope overshooting can eliminate the discrepancy. The ?? parameter of GGCs provides an independent detection of prestellar helium, at least at the 5? level.

We present new and accurate radial velocity (RV) measurements of luminous stars of all ages (old horizontal branch, intermediate-age red clump, and young blue plume, as well as red giants of a range of ages: 20.6 ? V? 22) in the Carina dwarf spheroidal galaxy, based on low-resolution spectra collected with the FORS2 multiobject slit spectrograph at the VLT. This data set was complemented by RV measurements based on medium- and high-resolution archive spectra of brighter (V? 20.6) Carina targets collected with the GIRAFFE multiobject fiber spectrograph at the VLT. The combined sample includes more than 21,340 individual spectra of ?2000 stars covering the entire body of the galaxy. The mean (?RV? = 220.4 ± 0.1 km s-1) and the dispersion (? = 11.7 ± 0.1 km s-1) of the RV distribution of candidate Carina stars (?1210 objects, 180 ? RV ? 260 km s-1, 4?) agree quite well with similar measurements available in the literature. To further improve the statistics, the accurate RV measurements recently provided by Walker et al. were also added to the current data set. We ended up with a sample of ?1370 RV measurements of candidate Carina stars that is ?75% larger than any previous Carina RV sample. We found that the hypothesis that the Carina RV distribution is Gaussian can be discarded at 99% confidence level. The mean RV across the body of the galaxy varies from ?220 km s-1at a distance of 7' (?200 pc) from the center to ?223 km s-1at 13' (?400 pc, 6? level) and flattens out to a constant value of ?221 km s-1at larger distances (600 pc, 4? level). Moreover, and even more importantly, we found that in the Carina regions where the mean RV is smaller, the dispersion is also smaller, and the RV distribution is more centrally peaked (i.e., the kurtosis attains larger values). The difference in mean RV is more than 4 km s-1(9? level) when moving from east to west and more than 3 km s-1(?7? level) when moving from north to south. The RV gradient appears to be in the direction of the Carina proper motion. However, this parameter is affected by large uncertainties to reach a firm conclusion. There is evidence of a secondary maximum in RV across the Carina center (|D| ? 200 pc). The occurrence of a secondary feature across the Carina center is also supported by the flat-topped radial distribution based on the photometric catalog. These findings are reminiscent of a substructure with transition properties that are already detected in dwarf ellipticals, and they call for confirmation by independent investigations.

We present precise and deep optical photometry of the globular M92. Data were collected in three different photometric systems: Sloan Digital Sky Survey (g', r', i', and z'; MegaCam at CFHT), Johnson-Kron-Cousins (B, V, and I; various ground-based telescopes), and Advanced Camera for Surveys (ACS) Vegamag (F475W, F555W, and F814W; Hubble Space Telescope). Special attention was given to the photometric calibration, and the precision of the ground-based data is generally better than 0.01 mag. We computed a new set of ?-enhanced evolutionary models accounting for the gravitational settling of heavy elements at fixed chemical composition ([?/Fe] = +0.3, [Fe/H] = -2.32 dex, and Y= 0.248). The isochrones-assuming the same true distance modulus (? = 14.74 mag), the same reddening [E(B- V) = 0.025 ± 0.010 mag], and the same reddening law-account for the stellar distribution along the main sequence and the red giant branch in different color-magnitude diagrams (i', g'- i'; i', and g'- r'; i', g'- z'; I, and B- I; and F814W and F475W-F814W). The same outcome applies to the comparison between the predicted zero-age horizontal-branch (ZAHB) and the HB stars. We also found a cluster age of 11 ± 1.5 Gyr, in good agreement with previous estimates. The error budget accounts for uncertainties in the input physics and the photometry. To test the possible occurrence of CNO-enhanced stars, we also computed two sets of ?- and CNO-enhanced (by a factor of 3) models, both at fixed total metallicity ([M/H] = -2.10 dex) and at fixed iron abundance. We found that the isochrones based on the former set give the same cluster age (11 ± 1.5 Gyr) as the canonical ?-enhanced isochrones. The isochrones based on the latter set also give a similar cluster age (10 ± 1.5 Gyr). These findings support previous results concerning the weak sensitivity of cluster isochrones to CNO-enhanced chemical mixtures.