0 ----- Attempting Submission 1 (Thu Jul 17 21:48:09 GMT 2014) ----- Massive stellar clusters are the main indicators of star formation activity in the distant universe, still their origin and evolution is only partially understood. We have demonstrated that combining deep high resolution optical and IR photometry is a powerful method to investigate the initial phases of massive stellar clusters. We are now proposing to obtain deep, high resolution ACS and WFC3 observations designed to individually resolve and measure stars in Westerlund 2 (Wd2), one of the youngest and most massive clusters in the Milky Way, from the upper mass cut-off down to the hydrogen-burning limit. Wd2 is quite unique, because it is close (8kpc), young (<2Myr), massive (>10^4 Mo) and not well studied. Yet, it is perfectly suitable to investigate how it formed, since neither stellar evolution nor cluster dynamics have had enough time to significantly affect its initial conditions. We propose to determine its mass function, which will well approximate its IMF, establish whether primordial mass segregation is present, characterise the population of pre-Main Sequence stars that have been found by Spitzer, and - as a added bonus - take a high resolution view of the surroundings of WR20a, a very massive eclipsing WR binary that might have been ejected from the cluster center. Second epoch observations in two years will allow us to accurately identify the Wd2 cluster members, and will establish the presence of additional walkaway stars, in addition possibly to WR20a. Because high resolution, high dynamic range, and PSF stability - necessary for the astrometric part - are absolute requirements to complete this project, this study can only be done with HST. This is the secon epoch of a proper motion proposal. We are planning to repeat the observations acquried in CY 20 in the filter F814W. The goal is to remove the contamination from the galactic field. We ask to repeat the observations with exactly the same orientation used for the first epoch to reduce the uncertainties on the geometric distorion. We ask to execute the observations after Agugust 2015, to ensure the longest baseline possible RESOLVED STELLAR POPULATIONS 12 false false 0.0 0.0 false false false SUPPORTED STELLAR CLUSTER STAR FORMING REGION This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F658N WFC3/IR Imaging No No F125W WFC3/IR Imaging No No F128N WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F814W 1405633666404 The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. /private/var/folders/0r/cglcw15s7bd4xwgwp14n89dw0003j0/T/OPVisit6606461886576470071.xml (Tic-Visit :proposal-id 13808 :visit-id "01" :proposal-version -1 :trans-version "20140605" :date "17-Jul-2014 17:47:45.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 1705344 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13808 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13808 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2841 :al-overhead-at-end 0 :internal-dur-at-end 347 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3470 :pcs-gap 0 ) true 1 0