12219( 2) - 09-Jul-2010 17:28:02 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12219 Version: 2 Check-in Time: 09-Jul-2010 17:28:02 STScI Edit Number: 0 Title Multiple stellar generations in the Large Magellanic Cloud Star Cluster NGC 1846 ------------------------------------------------------------------------------------ Type Cycle GO 18 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Antonino P. Milone Universita di Padova CoI: Prof. Giampaolo Piotto Universita di Padova N CoI: Dr. Luigi R. Bedin Space Telescope Science Institute N CoI: Dr. Jay Anderson Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract The recent discovery of multiple stellar populations in massive Galactic globular clusters poses a serious challenge for models of star cluster formation and evolution. The finding of multiple main sequences in the massive clusters NGC 2808 and omega Centauri, and multiple sub-giant-branch in NGC 1851 and many other globulars have demonstrated that star clusters are not as simple as we have imagined for decades. Surprisingly the only way to explain the main sequence splitting appears to be Helium enrichment, up to an astonishingly high Y~0.40.An unique angle on this problem can be provided by intermediate-age clusters in the Magellanic Clouds with peculiar main-sequence turn-off morphologies. Recent discoveries, based on ACS data of unparalleled photometric accuracy, have demonstrated that the CMDs of a large fraction of these clusters (~70 %) are not consistent with the simple, single stellar population hypothesis. Explanations for what conditions could give rise to multiple populations in Galactic Globular Clusters remain controversial; this is even more the case for LMC clusters To properly constraint the multipopulation phenomenon in Magellanic Cloud star clusters, we propose deep UV/IR imaging of NGC 1846, a star cluster where multiple populations have already been identified. The proposed observation will allow us to accurately measure the age difference between the stellar populations providing fundamental clues on the formation mechanism. Our simulations of WFC3 performance suggest that we will be able to detect even the main sequence splitting caused by small He differences (Delta Y ~0.02). ------------------------------------------------------------------------------------ Observations Description ------------------------ UVIS and NIR WFC3, and ACS WFC observations of the Large Magellanic Cloud stellar cluster NGC1846 Real Time Justification ----------------------- Calibration Justification ------------------------- 12219( 2) - 09-Jul-2010 17:28:02 - [ 2] Additional Comments ------------------- ------------------------------------------------------------------------------------ 12219( 2) - 09-Jul-2010 17:28:02 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1846-OUT STELLAR CLUSTER, RA=05H07M40.8000S +/- 0.1", J2000 V = 11.31 GLOBULAR CLUSTER DEC=-67D26'56.70" +/- 0.1" Reference Frame: ICRS Comments: ------------------------------------------------------------------------------------------------------------------------------------ 12219( 2) - 09-Jul-2010 17:28:02 - [ 4] Visit: 01 Visit Requirements: ORIENT 124D TO 130 D 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC1846-OUT WFC3/UVI ACCUM UVIS-CENT F336W CR-SPLIT=NO 1 900 S POS TARG -5.6, -4.2; PAR S ER 2 WITH 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC1846-OUT ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=2 1 680 S ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC1846-OUT WFC3/UVI ACCUM UVIS-CENT F336W CR-SPLIT=NO 1 1032 S POS TARG -4.2, -2.8; PAR S ER 4 WITH 3 ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC1846-OUT ACS/WFC ACCUM WFCENTER F475W CR-SPLIT=NO 1 900 S ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC1846-OUT WFC3/UVI ACCUM UVIS-CENT F336W CR-SPLIT=NO 1 1032 S POS TARG -2.8, -1.4; PAR S ER 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC1846-OUT ACS/WFC ACCUM WFCENTER F475W CR-SPLIT=NO 1 900 S ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC1846-OUT WFC3/UVI ACCUM UVIS-CENT F336W CR-SPLIT=NO 1 1032 S POS TARG -1.4, 0.0; PAR S ER 8 WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC1846-OUT ACS/WFC ACCUM WFCENTER F475W CR-SPLIT=NO 1 900 S ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC1846-OUT WFC3/UVI ACCUM UVIS-CENT F336W CR-SPLIT=NO 1 1032 S POS TARG 0.0, 1.4; PAR S ER 10 WITH 9 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC1846-OUT ACS/WFC ACCUM WFCENTER F475W CR-SPLIT=NO 1 900 S ------------------------------------------------------------------------------------------------------------------------------------ 11 NGC1846-OUT WFC3/UVI ACCUM UVIS-CENT F336W CR-SPLIT=NO 1 1032 S POS TARG 1.4, 2.8; PAR S ER 12 WITH 11 ------------------------------------------------------------------------------------------------------------------------------------ 12 NGC1846-OUT ACS/WFC ACCUM WFCENTER F475W CR-SPLIT=NO 1 900 S ------------------------------------------------------------------------------------------------------------------------------------ 13 NGC1846-OUT WFC3/UVI ACCUM UVIS-CENT F336W CR-SPLIT=NO 1 1032 S POS TARG 2.8, 4.2; PAR S ER 14 WITH 13 ------------------------------------------------------------------------------------------------------------------------------------ 14 NGC1846-OUT ACS/WFC ACCUM WFCENTER F475W CR-SPLIT=NO 1 900 S ------------------------------------------------------------------------------------------------------------------------------------ 15 NGC1846-OUT WFC3/UVI ACCUM UVIS-CENT F336W CR-SPLIT=NO 1 1032 S POS TARG 4.2, 5.6; PAR S ER 16 WITH 15 ------------------------------------------------------------------------------------------------------------------------------------ 16 NGC1846-OUT ACS/WFC ACCUM WFCENTER F475W CR-SPLIT=NO 1 900 S ------------------------------------------------------------------------------------------------------------------------------------ 17 NGC1846-OUT WFC3/UVI ACCUM UVIS-CENT F336W CR-SPLIT=NO 1 1032 S POS TARG 5.6, 7; PAR 18 S ER WITH 17 12219( 2) - 09-Jul-2010 17:28:02 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------------------------------------------------------ 18 NGC1846-OUT ACS/WFC ACCUM WFCENTER F814W CR-SPLIT=2 1 680 S ------------------------------------------------------------------------------------------------------------------------------------ 19 NGC1846-OUT WFC3/IR MULTIAC IR-FIX F160W NSAMP=12, SAMP-SEQ=STEP50 1 DEF POS TARG -5.6, -4.2 CUM ------------------------------------------------------------------------------------------------------------------------------------ 20 NGC1846-OUT WFC3/IR MULTIAC IR-FIX F160W NSAMP=12, SAMP-SEQ=STEP50 1 DEF POS TARG -4.2, -2.8 CUM ------------------------------------------------------------------------------------------------------------------------------------ 21 NGC1846-OUT WFC3/IR MULTIAC IR-FIX F160W NSAMP=12, SAMP-SEQ=STEP50 1 DEF POS TARG -2.8, -1.4 CUM ------------------------------------------------------------------------------------------------------------------------------------ 22 NGC1846-OUT WFC3/IR MULTIAC IR-FIX F160W NSAMP=12, SAMP-SEQ=STEP50 1 DEF POS TARG -1.4, 0 CUM ------------------------------------------------------------------------------------------------------------------------------------ 23 NGC1846-OUT WFC3/IR MULTIAC IR-FIX F160W NSAMP=12, SAMP-SEQ=STEP50 1 DEF POS TARG 0, 1.4 CUM ------------------------------------------------------------------------------------------------------------------------------------ 24 NGC1846-OUT WFC3/IR MULTIAC IR-FIX F160W NSAMP=12, SAMP-SEQ=STEP50 1 DEF POS TARG 1.4, 2.8 CUM ------------------------------------------------------------------------------------------------------------------------------------ 25 NGC1846-OUT WFC3/IR MULTIAC IR-FIX F160W NSAMP=12, SAMP-SEQ=STEP50 1 DEF POS TARG 2.8, 4.2 CUM ------------------------------------------------------------------------------------------------------------------------------------ 26 NGC1846-OUT WFC3/IR MULTIAC IR-FIX F160W NSAMP=13, SAMP-SEQ=STEP50 1 DEF POS TARG 4.2, 5.6; PAR CUM 27 WITH 26 ------------------------------------------------------------------------------------------------------------------------------------ 27 NGC1846-OUT ACS/WFC ACCUM WFC F814W 1 326 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC1846-OUT 1 WFC3/UVI ACCUM UVIS-CEN F336W none none none none 1 N/A S TER NGC1846-OUT 2 ACS/WFC ACCUM WFCENTER F814W none none none 1 1 N/A NGC1846-OUT 2 ACS/WFC ACCUM WFCENTER F814W none none none 2 1 N/A NGC1846-OUT 3 WFC3/UVI ACCUM UVIS-CEN F336W none none none none 1 N/A S TER NGC1846-OUT 4 ACS/WFC ACCUM WFCENTER F475W none none none none 1 N/A NGC1846-OUT 5 WFC3/UVI ACCUM UVIS-CEN F336W none none none none 1 N/A S TER NGC1846-OUT 6 ACS/WFC ACCUM WFCENTER F475W none none none none 1 N/A NGC1846-OUT 7 WFC3/UVI ACCUM UVIS-CEN F336W none none none none 2 N/A S TER 12219( 2) - 09-Jul-2010 17:28:02 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC1846-OUT 8 ACS/WFC ACCUM WFCENTER F475W none none none none 2 N/A NGC1846-OUT 9 WFC3/UVI ACCUM UVIS-CEN F336W none none none none 2 N/A S TER NGC1846-OUT 10 ACS/WFC ACCUM WFCENTER F475W none none none none 2 N/A NGC1846-OUT 11 WFC3/UVI ACCUM UVIS-CEN F336W none none none none 2 N/A S TER NGC1846-OUT 12 ACS/WFC ACCUM WFCENTER F475W none none none none 2 N/A NGC1846-OUT 13 WFC3/UVI ACCUM UVIS-CEN F336W none none none none 3 N/A S TER NGC1846-OUT 14 ACS/WFC ACCUM WFCENTER F475W none none none none 3 N/A NGC1846-OUT 15 WFC3/UVI ACCUM UVIS-CEN F336W none none none none 3 N/A S TER NGC1846-OUT 16 ACS/WFC ACCUM WFCENTER F475W none none none none 3 N/A NGC1846-OUT 17 WFC3/UVI ACCUM UVIS-CEN F336W none none none none 3 N/A S TER NGC1846-OUT 18 ACS/WFC ACCUM WFCENTER F814W none none none 1 3 N/A NGC1846-OUT 18 ACS/WFC ACCUM WFCENTER F814W none none none 2 3 N/A NGC1846-OUT 19 WFC3/IR MULTIAC IR-FIX F160W none none none none 4 N/A CUM NGC1846-OUT 20 WFC3/IR MULTIAC IR-FIX F160W none none none none 4 N/A CUM NGC1846-OUT 21 WFC3/IR MULTIAC IR-FIX F160W none none none none 4 N/A CUM NGC1846-OUT 22 WFC3/IR MULTIAC IR-FIX F160W none none none none 4 N/A CUM NGC1846-OUT 23 WFC3/IR MULTIAC IR-FIX F160W none none none none 4 N/A CUM NGC1846-OUT 24 WFC3/IR MULTIAC IR-FIX F160W none none none none 4 N/A CUM NGC1846-OUT 25 WFC3/IR MULTIAC IR-FIX F160W none none none none 4 N/A CUM NGC1846-OUT 26 WFC3/IR MULTIAC IR-FIX F160W none none none none 4 N/A CUM NGC1846-OUT 27 ACS/WFC ACCUM WFC F814W none none none none 4 N/A 12219( 2) - 09-Jul-2010 17:28:02 - [ 7] Summary Form for Proposal 12219 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR-FIX, UVIS-CENTER, WFC, WFCENTER ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/IR, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2, CR-SPLIT=NO, NSAMP=12, NSAMP=13, SAMP-SEQ=STEP50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 124D TO 130 D, PAR 10 WITH 9, PAR 12 WITH 11, PAR 14 WITH 13, PAR 16 WITH 15, PAR 18 WITH 17, PAR 2 WITH 1, PAR 27 WITH 26, PAR 4 WITH 3, PAR 6 WITH 5, PAR 8 WITH 7, POS TARG -1.4, 0, POS TARG -1.4, 0.0, POS TARG -2.8, -1.4, POS TARG -4.2, -2.8, POS TARG -5.6, -4.2, POS TARG 0, 1.4, POS TARG 0.0, 1.4, POS TARG 1.4, 2.8, POS TARG 2.8, 4.2, POS TARG 4.2, 5.6, POS TARG 5.6, 7 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W, F336W, F475W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC1846-OUT ------------------------------------------------------------------------------------------------------------------------------------