12908( 2) - 29-Jun-2012 16:22:53 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 12908 Version: 2 Check-in Time: 29-Jun-2012 16:22:53 STScI Edit Number: 0 Title What Causes Extended Main Sequence Turn-offs in Intermediate-Age Star Clusters? ------------------------------------------------------------------------------------ Type Cycle GO 20 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Paul Goudfrooij Space Telescope Science Institute Y CoI: Dr. Leo Girardi Osservatorio Astronomico di Padova N CoI: Dr. Alessandro Bressan Scuola Internazionale Superiore di Studi N Avanzati CoI: Dr. Rupali Chandar University of Toledo N CoI: Dr. Jason S. Kalirai Space Telescope Science Institute N CoI: Dr. Leandro Kerber Universidade Estadual Santa Cruz N CoI: Dr. Paola Marigo Universita di Padova N CoI: Dr. Thomas H. Puzia Pontificia Universidad Catolica de Chile N CoI: Dr. Stefano Rubele Osservatorio Astronomico di Padova N ------------------------------------------------------------------------------------ Abstract Recently, deep images from the ACS camera aboard HST provided conclusive evidence that several massive intermediate-age star clusters in the Magellanic Clouds present extended main-sequence turn-off regions (eMSTOs), and in some cases also dual red clumps. These observations challenge the notion that star clusters are simple stellar populations, and pose serious questions regarding the mechanisms responsible for star cluster formation. We propose to collect HST imaging that should lead to an understanding of the nature of the eMSTO phenomenon. We will perform deep WFC3 imaging in F438W and F814W for 3 Magellanic Cloud star clusters whose ages and dynamical properties (mass, radius) will allow a critical study of the physical conditions that cause the eMSTO phenomenon. The data will allow us to derive detailed star formation histories via CMD reconstruction methods. The underlying field population will be characterized by means of ACS images of nearby areas obtained in parallel. Without high-quality HST imaging data for these three pivotal clusters, the discussion regarding the onset of multiple stellar populations in star clusters may persist for years. ------------------------------------------------------------------------------------ Observations Description ------------------------ The target star clusters are observed with WFC3 using the F438W and F814W filters. Since the shape and position of the red giant branch (RGB) in the color-magnitude diagram (CMD) is used to determine metallicities, we include exposures in each filter that do not saturate the bright giants. On the other hand, we need color uncertainties less than 0.05 mag down to well beyond the estimated magnitude of the main sequence turnoff to achieve an accurate age determination and to enable a robust identification of multiple turnoff structures if the target cluster in question has multiple stellar populations. Hence, at least one short exposure is used in each filter to avoid saturation of the giants and red clump stars, while at least two longer exposures are used to achieve deep photometry. At least two dither positions are used for each 12908( 2) - 29-Jun-2012 16:22:53 - [ 2] target star cluster to allow a robust elimination of hot pixels and cosmic ray hits during the analysis. ACS is used in parallel to the primary WFC3 exposures, using the filters F435W and F814W. This will allow a robust determination of the field population contribution to the star cluster pointings. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 12908( 2) - 29-Jun-2012 16:22:53 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-2209 STELLAR CLUSTER, RA=06H08M35.9000S +/- 0.1", J2000 V = 13.1 +/- 0.1 GLOBULAR CLUSTER DEC=-73D50'18.00" +/- 0.1" Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-2249 STELLAR CLUSTER, RA=06H25M49.4440S +/- 0.1", J2000 V = 12.23 +/- 0.15 GLOBULAR CLUSTER DEC=-68D55'13.10" +/- 0.1" Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC-152 STELLAR CLUSTER, RA=00H32M54.9220S +/- 0.1", J2000 V = 12.33 +/- 0.05 GLOBULAR CLUSTER DEC=-73D07'2.10" +/- 0.1" Reference Frame: ICRS Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. ------------------------------------------------------------------------------------------------------------------------------------ 12908( 2) - 29-Jun-2012 16:22:53 - [ 4] Visit: 01 Visit Requirements: SCHED 30%; ORIENT 0.0D TO 28.8 D; ORIENT 59D TO 167 D; ORIENT 219D TO 250 D; ORIENT 272D TO 359.9 D On Hold Comments: Additional Comments: Applies to NGC 2209. Visit orientation constraints to avoid bright stars close to the edges of the ACS FOV. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-2209 WFC3/UVI ACCUM UVIS1 F814W CR-SPLIT=NO 1 60 S POS TARG -0.1, -0.1 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-2209 WFC3/UVI ACCUM UVIS1 F814W CR-SPLIT=NO 1 485 S PAR 3 WITH 2 S ------------------------------------------------------------------------------------------------------------------------------------ 3 ANY ACS/WFC ACCUM WFC F814W 1 450 S see below ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-2209 WFC3/UVI ACCUM UVIS1 F438W CR-SPLIT=NO 1 850 S PAR 5 WITH 4 S ------------------------------------------------------------------------------------------------------------------------------------ 5 ANY ACS/WFC ACCUM WFC F435W 1 500 S see below ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC-2209 WFC3/UVI ACCUM UVIS1 F438W CR-SPLIT=NO 1 850 S POS TARG 0.18, 2.414; S PAR 7 WITH 6 ------------------------------------------------------------------------------------------------------------------------------------ 7 ANY ACS/WFC ACCUM WFC F435W 1 500 S see below ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC-2209 WFC3/UVI ACCUM UVIS1 F814W CR-SPLIT=NO 1 485 S SAME POS AS 6; PAR 9 S WITH 8 ------------------------------------------------------------------------------------------------------------------------------------ 9 ANY ACS/WFC ACCUM WFC F814W 1 480 S see below ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-2209 1 WFC3/UVI ACCUM UVIS1 F814W none none none none 1 N/A S NGC-2209 2 WFC3/UVI ACCUM UVIS1 F814W none none none none 1 N/A S ANY 3 ACS/WFC ACCUM WFC F814W none none none none 1 383.0 S NGC-2209 4 WFC3/UVI ACCUM UVIS1 F438W none none none none 1 N/A S 12908( 2) - 29-Jun-2012 16:22:53 - [ 5] 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 | ------------------------------------------------------------------------------------------------------------------------------------ ANY 5 ACS/WFC ACCUM WFC F435W none none none none 1 820.0 S NGC-2209 6 WFC3/UVI ACCUM UVIS1 F438W none none none none 1 N/A S ANY 7 ACS/WFC ACCUM WFC F435W none none none none 1 840.0 S NGC-2209 8 WFC3/UVI ACCUM UVIS1 F814W none none none none 1 N/A S ANY 9 ACS/WFC ACCUM WFC F814W none none none none 1 361.0 S 12908( 2) - 29-Jun-2012 16:22:53 - [ 6] Visit: 02 Visit Requirements: SCHED 30%; ORIENT 0.0D TO 35 D; ORIENT 49D TO 57 D; ORIENT 76D TO 114 D; ORIENT 120D TO 171 D; ORIENT 183D TO 198.5 D; ORIENT 220D TO 246 D; ORIENT 253D TO 274 D; ORIENT 292.5D TO 359.9 D On Hold Comments: Additional Comments: Applies to NGC 2249. Visit orientation constraints to avoid bright stars close to the edges of the ACS FOV. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-2249 WFC3/UVI ACCUM UVIS1 F814W CR-SPLIT=NO 1 60 S POS TARG -0.1, -0.1 S ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-2249 WFC3/UVI ACCUM UVIS1 F814W CR-SPLIT=NO 1 425 S PAR 3 WITH 2 S ------------------------------------------------------------------------------------------------------------------------------------ 3 ANY ACS/WFC ACCUM WFC F814W 1 450 S see below ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-2249 WFC3/UVI ACCUM UVIS1 F438W CR-SPLIT=NO 1 825 S PAR 5 WITH 4 S ------------------------------------------------------------------------------------------------------------------------------------ 5 ANY ACS/WFC ACCUM WFC F435W 1 500 S see below ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC-2249 WFC3/UVI ACCUM UVIS1 F438W CR-SPLIT=NO 1 825 S POS TARG 0.18, 2.414; S PAR 7 WITH 6 ------------------------------------------------------------------------------------------------------------------------------------ 7 ANY ACS/WFC ACCUM WFC F435W 1 500 S see below ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC-2249 WFC3/UVI ACCUM UVIS1 F814W CR-SPLIT=NO 1 425 S SAME POS AS 6; PAR 9 S WITH 8 ------------------------------------------------------------------------------------------------------------------------------------ 9 ANY ACS/WFC ACCUM WFC F814W 1 480 S see below ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-2249 1 WFC3/UVI ACCUM UVIS1 F814W none none none none 1 N/A S NGC-2249 2 WFC3/UVI ACCUM UVIS1 F814W none none none none 1 N/A S ANY 3 ACS/WFC ACCUM WFC F814W none none none none 1 333.0 S 12908( 2) - 29-Jun-2012 16:22:53 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-2249 4 WFC3/UVI ACCUM UVIS1 F438W none none none none 1 N/A S ANY 5 ACS/WFC ACCUM WFC F435W none none none none 1 795.0 S NGC-2249 6 WFC3/UVI ACCUM UVIS1 F438W none none none none 1 N/A S ANY 7 ACS/WFC ACCUM WFC F435W none none none none 1 815.0 S NGC-2249 8 WFC3/UVI ACCUM UVIS1 F814W none none none none 1 N/A S ANY 9 ACS/WFC ACCUM WFC F814W none none none none 1 413.0 S 12908( 2) - 29-Jun-2012 16:22:53 - [ 8] Visit: 03 Visit Requirements: SCHED 100%; ORIENT 0.0D TO 20 D; ORIENT 27D TO 235 D; ORIENT 241D TO 250 D; ORIENT 257D TO 336 D; ORIENT 341D TO 359.9 D On Hold Comments: Additional Comments: Applies to NGC 152. Visit orientation constraints to avoid bright stars close to the edges of the ACS FOV. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-152 WFC3/UVI ACCUM UVIS1 F814W CR-SPLIT=NO 1 200 S PAR 2 WITH 1 S ------------------------------------------------------------------------------------------------------------------------------------ 2 ANY ACS/WFC ACCUM WFC F814W 1 300 S see below ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC-152 WFC3/UVI ACCUM UVIS1 F438W CR-SPLIT=NO 1 750 S PAR 4 WITH 3 S ------------------------------------------------------------------------------------------------------------------------------------ 4 ANY ACS/WFC ACCUM WFC F435W 1 500 S see below ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC-152 WFC3/UVI ACCUM UVIS1 F438W CR-SPLIT=NO 1 750 S POS TARG 0.18, 2.414; S PAR 6 WITH 5 ------------------------------------------------------------------------------------------------------------------------------------ 6 ANY ACS/WFC ACCUM WFC F435W 1 500 S see below ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC-152 WFC3/UVI ACCUM UVIS1 F814W CR-SPLIT=NO 1 500 S SAME POS AS 5; PAR 8 S WITH 7 ------------------------------------------------------------------------------------------------------------------------------------ 8 ANY ACS/WFC ACCUM WFC F814W 1 480 S see below ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-152 1 WFC3/UVI ACCUM UVIS1 F814W none none none none 1 N/A S ANY 2 ACS/WFC ACCUM WFC F814W none none none none 1 136.0 S NGC-152 3 WFC3/UVI ACCUM UVIS1 F438W none none none none 1 N/A S ANY 4 ACS/WFC ACCUM WFC F435W none none none none 1 720.0 S NGC-152 5 WFC3/UVI ACCUM UVIS1 F438W none none none none 1 N/A S ANY 6 ACS/WFC ACCUM WFC F435W none none none none 1 740.0 S 12908( 2) - 29-Jun-2012 16:22:53 - [ 9] 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-152 7 WFC3/UVI ACCUM UVIS1 F814W none none none none 1 N/A S ANY 8 ACS/WFC ACCUM WFC F814W none none none none 1 438.0 S 12908( 2) - 29-Jun-2012 16:22:53 - [ 10] Summary Form for Proposal 12908 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS1, WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC, WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 0.0D TO 20 D, ORIENT 0.0D TO 28.8 D, ORIENT 0.0D TO 35 D, ORIENT 120D TO 171 D, ORIENT 183D TO 198.5 D, ORIENT 219D TO 250 D, ORIENT 220D TO 246 D, ORIENT 241D TO 250 D, ORIENT 253D TO 274 D, ORIENT 257D TO 336 D, ORIENT 272D TO 359.9 D, ORIENT 27D TO 235 D, ORIENT 292.5D TO 359.9 D, ORIENT 341D TO 359.9 D, ORIENT 49D TO 57 D, ORIENT 59D TO 167 D, ORIENT 76D TO 114 D, PAR 2 WITH 1, PAR 3 WITH 2, PAR 4 WITH 3, PAR 5 WITH 4, PAR 6 WITH 5, PAR 7 WITH 6, PAR 8 WITH 7, PAR 9 WITH 8, POS TARG -0.1, -0.1, POS TARG 0.18, 2.414, SAME POS AS 5, SAME POS AS 6, SCHED 100%, SCHED 30% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F435W, F438W, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names ANY, NGC-152, NGC-2209, NGC-2249 ------------------------------------------------------------------------------------------------------------------------------------