13808( 2) - 18-Jul-2014 12:44:06 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13808 Version: 2 Check-in Time: 18-Jul-2014 12:44:06 STScI Edit Number: 1 Title Westerlund 2, top to bottom: how massive star clusters form. ------------------------------------------------------------------------------------ Type Cycle GO 22 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Antonella Nota Space Telescope Science Institute - ESA Y CoI: Dr. Elena Sabbi Space Telescope Science Institute Y CoI: Dr. Alceste Z. Bonanos National Observatory of Athens N CoI: Dr. Carol Christian Space Telescope Science Institute N CoI: Dr. Selma E. de Mink Carnegie Institution of Washington N CoI: Prof. Eva K. Grebel Zentrum fur Astronomie - Universitat N Heidelberg CoI: Dr. Monica Tosi INAF, Osservatorio Astronomico di Bologna N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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 13808( 2) - 18-Jul-2014 12:44:06 - [ 2] baseline possible ------------------------------------------------------------------------------------ 13808( 2) - 18-Jul-2014 12:44:06 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 ESO-127-18 STELLAR CLUSTER, STAR RA=10H24M5.5000S +/- 0.1", J2000 V = 10.5 FORMING REGION DEC=-57D45'49.00" +/- 0.1" Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 13808( 2) - 18-Jul-2014 12:44:06 - [ 4] Visit: 01 Visit Requirements: ORIENT 186.532D TO 186.532 D; AFTER 01-AUG-2015:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ESO-127-18 ACS/WFC ACCUM WFC F814W 1 3 S (3 S) POS TARG -30, -30 ------------------------------------------------------------------------------------------------------------------------------------ 2 ESO-127-18 ACS/WFC ACCUM WFC F814W 1 350 S (350 POS TARG -30, -30 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 ESO-127-18 ACS/WFC ACCUM WFC F814W 1 350 S (350 POS TARG -15, -15 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 ESO-127-18 ACS/WFC ACCUM WFC F814W 1 350 S (350 POS TARG -7, -7 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 ESO-127-18 ACS/WFC ACCUM WFC F814W 1 350 S (350 POS TARG 0, 0 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 ESO-127-18 ACS/WFC ACCUM WFC F814W 1 350 S (350 POS TARG 15, 15 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ ESO-127-18 1 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ESO-127-18 2 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ESO-127-18 3 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ESO-127-18 4 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ESO-127-18 5 ACS/WFC ACCUM WFC F814W none none none none 1 N/A ESO-127-18 6 ACS/WFC ACCUM WFC F814W none none none none 1 N/A 13808( 2) - 18-Jul-2014 12:44:06 - [ 5] Summary Form for Proposal 13808 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01-AUG-2015:00:00:00, ORIENT 186.532D TO 186.532 D, POS TARG -15, -15, POS TARG -30, -30, POS TARG -7, -7, POS TARG 0, 0, POS TARG 15, 15 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ESO-127-18 ------------------------------------------------------------------------------------------------------------------------------------