0 Assigned ID: 866 ----- Attempting Submission 1 (Fri Apr 08 21:33:31 GMT 2016) ----- HST Phase I Proposal 866 (gc_variable.apt) successfully submitted. Receipt: # 866-1 ----- Attempting Submission 2 (Fri Apr 08 22:55:14 GMT 2016) ----- HST Phase I Proposal 866 (gc_variable.apt) successfully submitted. Receipt: # 866-2 ----- Attempting Submission 3 (Fri Apr 08 23:39:37 GMT 2016) ----- HST Phase I Proposal 866 (gc_variable.apt) successfully submitted. Receipt: # 866-3 ----- Attempting Submission 4 (Fri Apr 08 23:52:54 GMT 2016) ----- Nuclear clusters are the most massive and densest stellar systems in the local Universe. They can be found in >70% of all galaxies. The nuclear cluster at the centre of the Milky Way appears to be a typical representative of these objects and is the only one which we can actually resolve observationally. However, crowding and extreme extinction pose serious obstacles on our knowledge of its stellar population, especially the old one. Variable stars can provide crucial information on the latter. Existing variability studies of the nuclear cluster suffer from a lack of sensitivity and angular resolution and/or are limited to the central parsec. We propose a groundbreaking variability study of the nuclear star cluster by taking advantage of the large number of archived HST/WFC3 observations at F153M band with a baseline of 4 years. This study will also capitalize on the high sensitivity (50% completeness limit, 21 mag at F153M) and angular resolution (0.2''), as well as the large field coverage (4.8 pc x 4.8 pc) of the data. Our primary goal is to detect RR Lyrae stars, tracing the old, low-metallicity population and providing an important test of the formation scenario of the nuclear cluster through globular cluster infall. Stellar Populations Stellar Physics 0 Regular false false false SUPPORTED