We present a detailed study of the radial distribution of the multiple populations identified in the Galactic globular cluster omega Cen. We used both space-based images (ACS/WFC and WFPC2) and ground-based images (FORS1@VLT and [email protected] ESO telescop
es) to map the cluster from the inner core to the outskirts (~20 arcmin). These data sets have been used to extract high-accuracy photometry for the construction of color-magnitude diagrams and astrometric positions of ~900 000 stars. We find that in the inner ~2 core radii the blue main sequence (bMS) stars slightly dominate the red main sequence (rMS) in number. At greater distances from the cluster center, the relative numbers of bMS stars with respect to rMS drop steeply, out to ~8 arcmin, and then remain constant out to the limit of our observations. We also find that the dispersion of the Gaussian that best fits the color distribution within the bMS is significantly greater than the dispersion of the Gaussian that best fits the color distribution within the rMS. In addition, the relative number of intermediate-metallicity red-giant-branch stars which includes the progeny of the bMS) with respect to the metal-poor component (the progeny of the rMS) follows a trend similar to that of the main-sequence star-count ratio N_bMS/N_rMS. The most metal-rich component of the red-giant branch follows the same distribution as the intermediate-metallicity component. We briefly discuss the possible implications of the observed radial distribution of the different stellar components in omega Cen.
The solar-age open cluster M67 (C0847+120, NGC2682) is a touchstone in studies of the old Galactic disk. Despite its outstanding role, the census of cluster membership for M67 at fainter magnitudes and their properties are not well-established. Using
the proprietary and archival ESO data, we have obtained astrometric, photometric, and radial velocities of stars in a 34x 33 field centered on the old open cluster M67. The two-epoch archival observations separated by 4 years and acquired with the Wide Field Imager at the 2.2m MPG/ESO telescope have been reduced with our new astrometric techniques, as described in the first paper of this series. The same observations served to derive calibrated BVI photometry in M67. Radial velocities were measured using the archival and new spectroscopic data obtained at VLT. We have determined relative proper motions and membership probabilities for ~2,400 stars. The precision of proper motions for optimally exposed stars is ~2 mas/yr, gradually degrading down to ~5 mas/yr at V= 20. Our relatively precise proper motions at V>16 are first obtained in this magnitude range for M67. Radial velocities are measured for 211 stars in the same field. We also present a detailed comparison with recent theoretical isochrones from several independent groups. For M67 area we provide positions, calibrated BVI photometry, relative proper motions, membership probabilities, and radial velocities. We demonstrate that the ground-based CCD mosaic observations just a few years apart are producing proper motions, allowing a reliable membership determination. We produced a catalogue that is made electronically available to the astronomical community.
Context. Searching for planets in open clusters allows us to study the effects of dynamical environment on planet formation and evolution. Aims. Considering the strong dependence of planet frequency on stellar metallicity, we studied the metal rich
old open cluster NGC 6791 and searched for close-in planets using the transit technique. Methods. A ten-night observational campaign was performed using the Canada-France-Hawaii Telescope (3.6m), the San Pedro Martir telescope (2.1m), and the Loiano telescope (1.5m). To increase the transit detection probability we also made use of the Bruntt et al. (2003) eight-nights observational campaign. Adequate photometric precision for the detection of planetary transits was achieved. Results. Should the frequency and properties of close-in planets in NGC 6791 be similar to those orbiting field stars of similar metallicity, then detailed simulations foresee the presence of 2-3 transiting planets. Instead, we do not confirm the transit candidates proposed by Bruntt et al. (2003). The probability that the null detection is simply due to chance coincidence is estimated to be 3%-10%, depending on the metallicity assumed for the cluster. Conclusions. Possible explanations of the null-detection of transits include: (i) a lower frequency of close-in planets in star clusters; (ii) a smaller planetary radius for planets orbiting super metal rich stars; or (iii) limitations in the basic assumptions. More extensive photometry with 3-4m class telescopes is required to allow conclusive inferences about the frequency of planets in NGC 6791.
