Please let us know if there is any problem. Regards LRBedin ----- Submission 1 (Mon May 15 14:57:35 GMT 2006) ----- Phase II Proposal 10922 (dms) successfully submitted. ----- Attempting Submission 2 (Fri May 04 15:17:09 GMT 2007) ----- This is a WFPC2 back-up of the original WFC/ACS proposal 10922 Assigned ID: 109 ----- Submission 1 (Thu Jan 26 15:41:03 GMT 2006) ----- Searching for Signs of a Double Generation of Stars in Galactic Globular Clusters This proposal has been stimulated by new findings of ours that may have a strong impact on the interpretation of globular cluster (GC) stellar populations. In 2004, based on HST data, we have found that the main sequence of the Galactic globular cluster Omega Centauri is split into two sequences; spectroscopic analysis has shown that the only isochrones which are able to fit the combination of color and metallicity of the bluest of the two sequences were younger and greatly enriched in helium. A number of observational facts, and theoretical evidence suggest that our results on Omega Centauri might represent an extreme case of a phenomenon which has also been at work in other GCs. We have selected the most promising GCs to find out whether this hypothesis is correct, and make a strong case for its likelihood and the value of pursuing it.
We intend to measure the main sequence (MS) of these two clusters with the highest possible photometric and astrometric precision, pushing HST to its photometric and astrometric limits (imaging-wise). High-precision photometry is needed to investigate any possible split in the MS due to multiple populations. High-precision astrometry is needed to measure proper motions (using archival data as a first epoch) with the aim of cleaning the CMDs from field stars. Following Anderson and King (ACS/ISR-2006-01), in order minimize photometric errors (due to imperfect modeling of the PSF and the detector's charge-diffusion variations, CTE, etc...), we plan to take the observations with as many large dithers and different orientations as possible. RESOLVED STELLAR POPULATIONS 12 false 0.0 false false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the NED database. J2000 18 55 3.3000 -30 28 43.00 J2000 STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the NED database. 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