0 Assigned ID: 5972 ----- Attempting Submission 1 (Thu Nov 07 12:23:50 GMT 2024) ----- HST Phase I Proposal 5972 successfully submitted. Receipt: # 5972-1 0 ----- Attempting Submission 1 (Thu Jan 30 07:20:22 GMT 2025) ----- Of the ~150 old globular clusters in the Milky Way, there are 3 outstanding systems that defy the globular cluster classification and show the presence of multi-age and multi-iron populations: Omega Centauri in the Galactic halo, Terzan 5 and Liller 1 in the bulge, which may be fossil witnesses to the past evolution and assembly of the Milky Way. The discovery of such systems provides a unique opportunity to gain deeper insights into the assembly history of the Milky Way. Analysis of archival HST observations of the Glimpse-C01 cluster suggests that it may be the fourth member of this emerging class of exotic clusters hosting multi-age, multi-iron stellar populations, and the first to be located in the Milky Way disk. To confirm this scenario, we require a second epoch of ACS and WFC3 observations to measure the proper motions of the stars in the direction of the cluster, which are the fundamental ingredient for distinguishing cluster members from field interlopers. Given the extreme crowding conditions and the severe reddening in the direction of the cluster, the proposed goal can be achieved by exploiting the high-resolution and stable astrometric optical/near-IR capabilities of the ACS/WFC and WFC3/IR cameras, while JWST observations would quickly saturate due to the target's relatively small distance from the Sun. The observations will be used to analyse and directly measure the age(s) of the stellar population(s) for the first time, and to reconstruct the cluster orbit in the Milky Way potential field, thus shedding light on its origin, the possible formation mechanism of its multi-age populations, and the role of the cluster in the Milky Way assembly history. The goal of the proposal is to sample the stellar population of the cluster Glimpse-C01 using a combination of ACS/WFC and WFC3/IR observations. Specifically, we plan to organize the observations into a single visit of three HST orbits. The first orbit will be dedicated to WFC3/IR observations. It consists of a combination of images taken in the F110W and F160W filters with SAMP-SEQ=STEP25 and NSAMP=9-14. We use the IR-FIX aperture and apply small shifts among different exposures using POS_TARG. The second and third orbits will be dedicated to ACS/WFC observations. We plan to obtain 3 exposures of 693-712 s in each orbit, using the ACS-WFC-DITHER-LINE pattern and the WFC-FIX aperture. Our team has extensive experience in working with both space and ground-based observations of star clusters located in the Galactic bulge. The proposing team has led several HST and JWST observing campaigns with more than 300 orbits awarded over the last ten Cycles and also 5 hours awarded with the JWST during Cycle 1 and 19 h during Cycle 3. Dr. Cadelano (PI) is an expert on stellar populations in star clusters and in the study of multiple population photometric, structural and kinematical properties. He has a large experience in high-precision stellar photometry in crowded environments, in all photometric bands from the ultraviolet to the near-infrared using both space telescope (JWST, HST, Galex, UVIT) and ground-based telescopes (e.g. ESO-VLT). Prof. Ferraro, Prof. Lanzoni, Dr. Dalessandro, Dr. Origlia, Dr. Massari and Dr. Pallanca have carried out an outstanding number of projects on stellar clusters located in different environmentes (e.g. Galactic bulge, Magellanic Clouds) both through spectroscopy and photometry. They authored the vast majority of papers reporting the discovery and characterization of the stellar populations in Terzan 5 and Liller 1. Dr. Pallanca is an expert in the analysis of stellar populations affected by differential reddening and developed a tool to investigate and correct this effect in crowded stellar fields. Prof. Vesperini is one of the main experts in stellar dynamics of clusters and development of N-body simulations specifically tailored for the study of stellar populations formation and evolution. Dr. Crociati, Dr. Leanza, Dr. Loriga and Dr. Chiappino are young researcher expert on the photometric and spectroscopic analysis of resolved stellar populations. In particular, they have carried out a number of projects aimed at investigating stellar kinematic via proper motions and radial velocity measurements and at the characterization of multiple populations through high-resolution spectroscopy. A selection of papers written by the PI and co-Is of this proposal in the last few years, using also JWST and HST to study resolved stellar populations in are given below. - "A pulsar in a binary with a compact object in the mass gap between neutron stars and black holes", Barr et al. 2024, Science, 383, 275 - "JWST uncovers helium and water abundance variations in the bulge globular cluster NGC 6440", Cadelano et al. 2023, A&A, 679, 13 - "First Evidence of Multi-iron Subpopulations in the Bulge Fossil Fragment Candidate Liller 1", Crociati et al. 2023, ApJ, 951, 17 - "The ESO-VLT MIKiS Survey Reloaded: Exploring the Internal Kinematics of NGC 6440", Leanza et al. 2023, ApJ, 944, 162 - "Clues to the Formation of Liller 1 from Modeling Its Complex Star Formation History", Dalessandro et al. 2022, ApJ, 940, 170 - "Discovery of a Double Sequence of Blue Straggler Stars in the Core-collapsed Globular Cluster NGC 6256", Cadelano et al. 2022, ApJ, 941, 69 - "Expanding the Time Domain of Multiple Populations: Evidence of Nitrogen Variations in the ~1.5 Gyr Old Star Cluster NGC 1783", Cadelano et al. 2022, ApJL, 924, 25, 1247 - "A new class of fossil fragments from the hierarchical assembly of the Galactic bulge", Ferraro et al. 2021, Nature Astronomy, 5, 311 - "A relic from a past merger event in the Large Magellanic Cloud", Mucciarelli et al. 2021, Nature Astronomy, - "3D core kinematics of NGC 6362: central rotation in a dynamically evolved globular cluster", Dalessandro et al. 2021, MNRAS, 506, 8131 - "High-resolution Extinction Map in the Direction of the Strongly Obscured Bulge Fossil Fragment Liller 1", Pallanca et al. 2021, ApJ, 917, 92 - "A New Identity Card for the Bulge Globular Cluster NGC 6440 from Resolved Star Counts", Pallanca et al. 2021, ApJ, 913, 137 - "Photometric characterization of multiple populations in star clusters: the impact of the first dredge-up", Salaris et al. 2020, MNRAS, 492, 3459 - "A Family Picture: The Long Term Evolution of Multiple Populations Structures", Dalessandro et al. 2019, ApJ, 884, 24 - "Detection of multiple stellar populations in extragalactic massive clusters with JWST", Salaris et al. 2019, A&A, 629, A40 - "Size diversity of old Large Magellanic Cloud clusters as determined by internal dynamical evolution", Ferraro et al. 2019, Nature Astronomy, 3, 1149 - "Star-density Profiles of Six Old Star Clusters in the Large Magellanic Cloud", Lanzoni et al. 2019, ApJ, 887, 176 - "The Peculiar Radial Distribution of Multiple Populations in the Massive Globular Cluster M80", Dalessandro et al. 2018, ApJ, 859, 15 - "The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XV. The Dynamical Clock: Reading Cluster Dynamical Evolution from the Segregation Level of Blue Straggler Stars" Ferraro et al. 2018, ApJ, 860, 36 - "IC 4499 revised: Spectro-photometric evidence of small light-element variations", Dalessandro et al. 2018, A&A, 618, 131 - "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 false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 ACS/WFC Imaging No No F814W The scheduling data was generated by CASM 33.0. CASM was run in Phase I mode. WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W POS-TARG DITHER 3.034 LINE false false 3 85.29 ACS-WFC-DITHER-LINE 1 false 1738221564300 /private/var/folders/gf/xth3y_156jl6spmm2jc086gh0000gn/T/OPVisit1740480915553028332.xml The scheduling data was generated by CASM 33.0. CASM was run in Phase II mode. 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