We present the first study of high-precision internal proper motions (PMs) in a large sample of globular clusters, based on Hubble Space Telescope (HST) data obtained over the past decade with the ACS/WFC, ACS/HRC, and WFC3/UVIS instruments. We determine PMs for over 1.3 million stars in the central regions of 22 clusters, with a median number of ∼60,000 stars per cluster. These PMs have the potential to significantly advance our understanding of the internal kinematics of globular clusters by extending past line-of-sight (LOS) velocity measurements to two-or three-dimensional velocities, lower stellar masses, and larger sample sizes. We describe the reduction pipeline that we developed to derive homogeneous PMs from the very heterogeneous archival data. We demonstrate the quality of the measurements through extensive Monte-Carlo simulations. We also discuss the PM errors introduced by various systematic effects, and the techniques that we have developed to correct or remove them to the extent possible. We provide in electronic form the catalog for NGC 7078 (M 15), which consists of 77,837 stars in the central 2. ′ 4. We validate the catalog by comparison with existing PM measurements and LOS velocities, and use it to study the dependence of the velocity dispersion on radius, stellar magnitude (or mass) along the main sequence, and direction in the plane of the sky (radial/tangential). Subsequent papers in this series will explore a range of applications in globular-cluster science, and will also present the PM catalogs for the other sample clusters.

We present results of an extensive spectroscopic survey of Subgiant stars in the stellar system ω Centauri. Using infrared Ca II triplet lines, we derived metallicities and radial velocities for more than 250 stars belonging to different stellar populations of the system. We find that the most metal rich component, the anomalous Sub Giant Branch (SGB-a), has a metallicity of [Fe/H] ∼ -0.6 fully compatible with that determined along the anomalous Red Giant Branch (RGB-a). Our analysis suggests that the age of this component and of the other metal-intermediate (−1.4 < [F e/H] < − 1.0) stellar populations of the system are all comparable to that of the dominant metal poor population within 2 Gyr, regardless of any choice of helium abundance. These results impose severe constraints on the time-scale of the enrichment process of this stellar system, excluding the possibility of an extended star formation period. The radial velocity analysis of the entire sample demonstrates that only metal-intermediate populations are kinematically cooler than the others.

We present new determinations of bolometric corrections and effective temperature scales as a function of infrared optical colours, using a large data base of photometric observations of about 6500 Population II giants in Galactic globular clusters (GGCs), covering a wide range in metallicity (−2.0 < [Fe/H] < 0.0).  New relations for BCK versus (V − K) , (J − K) and BCV versus (B − V), (V − I), (V − J), and new calibrations for Teff, using both an empirical relation and model atmospheres, are provided.  Moreover, an empirical relation to derive the R parameter of the infrared flux method as a function of the stellar temperature is also presented.

Abstract. We present deep V, I photometry of two 9.4 × 9.4 field in the outer regions of the M 33 galaxy. We obtain a robust detection of the luminosity of the Red Giant Branch Tip (I TRGB = 20.72 ± 0.08) from which we derived a new estimate of Our observations demonstrate that Red Giant Branch and Asymptotic Giant Branch stars have a radial distribution that is much more extended than the young MS stars associated with the star-forming disc.