Initial conditions of multiple populations in the dynamically most pristine globular cluster, NGC 2419

0 Assigned ID: 872 ----- Attempting Submission 1 (Fri Apr 07 21:01:23 GMT 2017) ----- HST Phase I Proposal 872 (n2419apt) successfully submitted. Receipt: # 872-1 ----- Attempting Submission 2 (Fri Apr 07 21:39:33 GMT 2017) ----- HST Phase I Proposal 872 (n2419apt) successfully submitted. Receipt: # 872-2 I am hereby submitting the Phase II proposal for our program to image the globular cluster NGC 2419 in F343N and F336W. -1979391459 ----- Attempting Submission 1 (Wed Jul 19 13:23:20 GMT 2017) ----- Initial conditions of multiple populations in the dynamically most pristine globular cluster, NGC 2419 The remote globular cluster (GC) NGC 2419 is unique in the Milky Way by having a half-mass relaxation time that exceeds the age of the Universe. This makes it an ideal target for studying the initial spatial distributions of sub-populations within the cluster. Most scenarios for the origin of multiple populations in GCs predict that enriched ("2nd-generation") stars should have a more centrally concentrated radial distribution than the pristine stars. This has indeed been found by a number of studies for the outer regions of GCs, although these (mostly ground-based) studies generally did not probe the center. We have recently found the opposite trend from HST observations of the central regions of the GC M15, where the enriched stars are the least centrally concentrated. This suggests a more complex situation than implied by most formation scenarios. Here we propose to determine the radial distributions of subpopulations in the central regions of NGC 2419 and determine whether it formed with a more centrally concentrated pristine population. This unique, dynamically pristine environment is free of the dynamical effects (such as orbital mixing and mass segregation) that may have modified the spatial distributions in other clusters, and will thus directly reflect the initial conditions. We will use F336W and F343N data to unambiguously separate pristine and enriched stars, based on their N abundances (that are enhanced by about 2 dex in enriched stars). By combining these data with archival observations at longer wavelengths, we will also determine the He abundances of the different populations. Images of NGC 2419 will be obtained with WFC3-UVIS in F343N (6 orbits) and F336W (3 orbits). The exposures will be grouped into visits of three orbits each, with two such visits for F343N and one visit for F336W. In each visit, the exposures will be dithered according to the 3x2 "C6" dither pattern in ISR WFC3-2010-09, i.e., a 3 point line dither (one dither point per orbit) with 2 point sub-dithers. Stellar Populations 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 WFC3/UVIS Imaging No No F343N WFC3/UVIS Imaging No No F336W POS-TARG DITHER DITHER 2 0.135 WFC3-UVIS-MOS-DITH-LINE false true 0.109 3 46.84 POS-TARG WFC3-UVIS-MOS-DITH-LINE 25.07 1

true

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