0 Assigned ID: 97 ----- Attempting Submission 1 (Tue Apr 04 12:07:58 GMT 2017) ----- Submitted again after recomendations by CS Anaalisa Calamida. -196725747 ----- Attempting Submission 1 (Tue Jul 18 16:31:24 GMT 2017) ----- ----- Attempting Submission 2 (Wed Sep 06 19:22:56 GMT 2017) ----- ----- Attempting Submission 3 (Fri Sep 08 17:56:34 GMT 2017) ----- Extending the Search for Multiple Populations in Massive Intermediate Age Clusters We propose to obtain imaging of 4 massive clusters in the LMC/SMC, spanning an age range of 2-6.5 Gyr, in order to search for chemical abundance spreads (i.e. multiple populations - MPs) within them. This proposal is meant to compliment our Cycle 23 proposal, which had the unexpected result where we found MPs in all clusters older than 6 Gyr (4 clusters) and did not find MPs in any clusters younger than 2 Gyr (8 clusters). Here we will explore this age gap to pinpoint the exact age where MPs begin to occur on the red giant branch (RGB), which will in turn show the stellar mass where MPs can develop. Additionally, we will study one 6.5 Gyr cluster that is a factor of ~3 less massive than previously studied to look for the influence of cluster mass on whether MPs can develop. The proposed sample occupies a critical region of parameter space (age/mass) where there are no Milky Way counterparts. We propose to obtain imaging of 4 massive star clusters one within the LMC/SMC, spanning a wide range of ages (0.1 - 10 Gyr), in order to search for elemental abundance spreads and multiple populations. The clusters will be observed in the F343N, F336W and F438W WFC3/UVIS filters, which will provide accurate color-magnitude diagrams (CMD) for studies of these phenomena. A CMD for such a large range of stellar ages covers everything from red and very bright giants down to the main sequence stars of various brightness and colors. To reach our science goals, it is crucial not to saturate the bright giants by using a short exposure and to reach a sufficient depth beyond the main-sequence turn-off using long exposures. Therefore, for each cluster, a short exposure and long exposures with CR-split in each filter are required. To cover the gap between the two WFC3/UVIS CCD chips, we use two dithered pointings. In order to maximize the overlap, we also require a specific orientation to match the orientation of those target clusters which have archival observations with the WFC3/UVIS. This orientation is specified in the Visit Orientation Requirement for these clusters/visits as follows: Visit1 - ngc419, Min=307, Max=307; Visit2 - ngc104 (47Tuc), Min=0, Min=1 Stellar Populations 6 false false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/UVIS Imaging No No F343N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F343N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F343N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F343N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W /Users/verap/WFC3/Cycle25/go15062/OP-cache/Untitled-v01.xml The scheduling data was generated by CASM 25.2. CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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CASM was run in Phase II mode. 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