A New Infrared Array Photometric Survey of Galactic Globular Clusters: A Detailed Study of the Red Giant Branch Sequence as a Step toward the Global Testing of Stellar Models

Abstract

We present high quality near infrared Color Magnitude Diagrams of 10 Galactic Globular Clusters (GCs) spanning a wide metallicity range (−2.15 < [F e/H] < −0.2). This homogeneous data-base has been used to perform a detailed analysis of the Red Giant Branch (RGB), adopting a variety of observables to describe its physical and chemical properties.First, a set of metallicity indicators have been measured, namely: (i) the RGB (J-K) and (V-K) colors at different magnitude levels; (ii) the RGB K magnitude at different colors; (iii) the RGB slope. For these parameters we present new calibrations in terms of both spectroscopic iron abundance and global metallicity, including the α-element enhancement. These relations can be used to derive a photometric estimate of the GC metal content from the RGB morphology and location.Second, the location in luminosity of the main RGB features (namely, the Bump and the Tip) and their dependence on metallicity have been studied, yielding quantitative observational relationships.Finally, adopting new transformations between the observational and theoretical quantities, the mean ridge lines for the clusters of our sample have been reported in

DEEPHST/ACS PHOTOMETRY OF THE M81 HALO

“…The degree to which field stars in the M81 halo are enhanced in the α-capture elements is currently not known. We can estimate the effect of such an enhancement on our MDF using the formalism of Ferraro et al (2000): We conclude this section by providing a series of consistency checks on our principle result, which is that the mean metallicity and age of stars in our M81 field are [M/H] = −1.15±0.11 and 9±2 Gyr, respectively. First, the location of the weak RGB bump (described in the previous section) at I ∼ 27.42 ± 0.05 can be used to provide an independent estimate of the age/metallicity of the M81 field stars.…”

Red Giant Branch Stars: The Theoretical Framework

“…Figure 18 shows a comparison between the FPC83, together with the more recent Ferraro et al (2000) data, and the theoretical relationship given above (which is on the same scale as the bolometric magnitude provided by the quoted papers), using the ZAHB distance scale given by the same SC98 models. The solid line represents the theoretical value, while the TRGB M bol dashed lines mark values increased by steps of 0.1 mag, TRGB M bol to show how the observational data are distributed in the various magnitude intervals.…”

The impact of an updated14N(p,γ)15O reaction rate on advanced evolutionary stages of low-mass stellar models

“…They adopted the distance obtained by Thompson et al (2001) from the analysis of one eclipsing binary system belonging to the cluster, and determined the TRGB apparent I-band brightness from a well populated CMD, deriving an absolute magnitude M TRGB I = −4.04 ± 0.12 in the I-Cousins filter. To date, all theoretical calibrations of the TRGB method have been within 1.5σ of Ferraro et al (2000). The two filled circles with error bars correspond to the empirical estimates for ω Cen and 47 Tuc, obtained by Bellazzini et al (2004). this calibration as shown by Cassisi (2010).…”