Pinpointing the Onset of Multiple Populations in Globular Clusters

0 Assigned ID: 246 ----- Attempting Submission 1 (Thu Mar 05 16:50:50 GMT 2020) ----- HST Phase I Proposal 246 successfully submitted. Receipt: # 246-1 FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser Removed time constraints and reduced POS TARGs shifts as suggested. -699757235 ----- Attempting Submission 1 (Mon Jun 29 09:48:34 GMT 2020) ----- ----- Attempting Submission 2 (Thu Oct 08 08:02:42 GMT 2020) ----- An higher level (>12e-/pixel) has been reccomended by the CS to account for the increasing CTE losses Pinpointing the Onset of Multiple Populations in Globular Clusters Studies of massive stellar clusters in the Large and Small Magellanic Clouds, spanning a wide range of ages from 100 Myr to 11 Gyr, have potentially pinpointed the onset of the multiple populations (MPs) phenomenon. Focusing on clusters with similar mass (~10^5 Msun), all systems with ages above 2 Gyr were found to host MPs while clusters below this limit do not. Such a relation with age is not expected in any scenario for the origin of MPs, and constitutes one of the most important findings in the field in recent years. One potential explanation for the observations is that MPs do exist within the young clusters, but only below a certain stellar mass limit. We propose to obtain deeper imaging of NGC 1783, a 1.7 Gyr cluster that does not show MPs on its RGB (~1.6 Msun), in order to search for splitting along main sequence stars (~1 Msun and below) caused by the chemical anomalies. Based on stellar isochrones with MPs abundance variations, we expect to observe main sequence splitting with an additional 10 orbits of exposure using our unique optical-UV filter combination. Determining if a stellar mass limit exists for MPs would consistute a major step forward in the search for the origin of the multiple populations phenomenon. Deep WFC3/UVIS observations to identify multiple populations along the Main Sequence of the intermediate-age stellar cluster NGC1783 in the Large Magellanic Cloud and to study their properties. 8 orbits will be dedicated to observations with the F343N filter (1 image per orbit), and two orbits to obtain 6 images with F438W. Observations are split in 4 Visits. Visit 03 and Visit 04 include 3 orbits to get F343N images. Visit 05 and Visit 06 inlcude 2 orbits: one to get an F343N image and 1 for 3 F438W images. A pre-defined UVIS DITHER 3PT is adopted both for the F343N and F438W images. Small offsets among visits are applied. The requested images will be combined with archival ACS/WFC images (GO-10595). To maximize the overlap with these observations without the need to put stringent constraints on the ORIENT angles, which might be strongly dependent on the gyros performances, the UVIS-CENTER aperture is adopted. Our team has extensive experience in working with high precision photometry with the Hubble Space Telescope on stellar clusters in the Magellanic Clouds. Dr. Dalessandro (PI) has extensive experience with PSF photometry (using HST and ground-based adaptive optics) in crowded fields and in the study of multiple population photometric, structural and kinematical properties. Prof. Bastian has led four proposals to use HST to study multiple populations in the Large and Small Magellanic Clouds, resulting in 11 refereed publications to date by the team (and a further 3 by other groups), with another two in preparation. Dr. Cabrera-Ziri and Ms. Martocchia have carried out a number of projects that requried precise photometry with HST and/or other facilities. Prof. Salaris is an expert in stellar models and has published numerous papers on the multiple populations phenomenon, making explicit predictions for how the colours of stars affected by multiple population change in the different HST filters. A selection of papers written by the co-Is of this proposal in the last few years, using HST to study multiple populations in Magellanic Cloud and Galactic stellar clusters are given below. 11) "Searching for globular cluster chemical anomalies on the main sequence of a young massive cluster", Cabrera-Ziri et al. 2020, MNRAS, submitted 10) "Photometric characterization of multiple populations in star clusters: the impact of the first dredge-up", Salaris et al. 2020, MNRAS, 492, 3459 9) "A Family Picture: The Long Term Evolution of Multiple Populations Structures", Dalessandro et al. 2019, ApJ, 884, 24 8) "The search for multiple populations in Magellanic Clouds clusters - V. A correlation between cluster age and abundance spreads", Martocchia, S. et al. 2019, MNRAS, 487, 5324 7) "Multiple Stellar Populations in Globular Clusters" Bastian & Lardo 2018, ARA&A, 56,83 6) "The Peculiar Radial Distribution of Multiple Populations in the Massive Globular Cluster M80", Dalessandro et al. 2018, ApJ, 859, 15 5) "IC 4499 revised: Spectro-photometric evidence of small light-element variations", Dalessandro et al. 2018, A&A, 618, 131 4) "The search for multiple populations in Magellanic Cloud Clusters IV: Coeval multiple stellar populations in the young star cluster NGC 1978", Martocchia et al. 2018, MNRAS, 477, 4696 3) "Age As a Major Factor in the Onset of Multiple Populations in Stellar Clusters", Martocchia et al. 2018, MNRAS, 473, 2688 2) "The Search for Multiple Populations in Magellanic Cloud Clusters III: No evidence for Multiple Populations in the SMC cluster NGC 419", Martocchia, S, et al. 2017, MNRAS, 468, 3150 1) "Multiple Populations in the Old and Massive Small Magellanic Cloud Globular Cluster NGC 121" Dalessandro et al. 2016, ApJ 829, 2 Stellar Populations and the Interstellar Medium 6 false false true false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER 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 F438W POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1

false

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