16255( 3) - 08-Oct-2020 19:09:54 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16255 Version: 3 Check-in Time: 08-Oct-2020 19:09:54 STScI Edit Number: 0 Title Pinpointing the Onset of Multiple Populations in Globular Clusters ------------------------------------------------------------------------------------ Type Cycle GO 28 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Emanuele Dalessandro INAF, Osservatorio di Astrofisica e Y Scienza dello Spazio CoI: Dr. Nate Bastian Liverpool John Moores University N CoI: Dr. Maurizio Salaris Liverpool John Moores University N CoI: Dr. Ivan Cabrera-Ziri Harvard University N CoI: Ms. Silvia Martocchia Liverpool John Moores University N ------------------------------------------------------------------------------------ Abstract Studies of massive stellar clusters in the Large and Small Magellanic Clouds, spanning a wide range of ages from 100 Myr to 11 Gyr, have potentially pinpointed the onset of the multiple populations (MPs) phenomenon. Focusing on clusters with similar mass (~10^5 Msun), all systems with ages above 2 Gyr were found to host MPs while clusters below this limit do not. Such a relation with age is not expected in any scenario for the origin of MPs, and constitutes one of the most important findings in the field in recent years. One potential explanation for the observations is that MPs do exist within the young clusters, but only below a certain stellar mass limit. We propose to obtain deeper imaging of NGC 1783, a 1.7 Gyr cluster that does not show MPs on its RGB (~1.6 Msun), in order to search for splitting along main sequence stars (~1 Msun and below) caused by the chemical anomalies. Based on stellar isochrones with MPs abundance variations, we expect to observe main sequence splitting with an additional 10 orbits of exposure using our unique optical-UV filter combination. Determining if a stellar mass limit exists for MPs would consistute a major step forward in the search for the origin of the multiple populations phenomenon. ------------------------------------------------------------------------------------ Observations Description ------------------------ Deep WFC3/UVIS observations to identify multiple populations along the Main Sequence of the intermediate-age stellar cluster NGC1783 in the Large Magellanic Cloud and to study their properties. 8 orbits will be dedicated to observations with the F343N filter (1 image per orbit), and two orbits to obtain 6 images with F438W. Observations are split in 4 Visits. Visit 03 and Visit 04 include 3 orbits to get F343N images. Visit 05 and Visit 06 inlcude 2 orbits: one to get an F343N image and 1 for 3 F438W images. A pre-defined UVIS DITHER 3PT is adopted both for the F343N and F438W images. Small offsets among visits are applied. The requested images will be combined with archival ACS/WFC images (GO-10595). To maximize the overlap with these observations without the need to put stringent constraints on the ORIENT angles, which might be strongly dependent 16255( 3) - 08-Oct-2020 19:09:54 - [ 2] on the gyros performances, the UVIS-CENTER aperture is adopted. ------------------------------------------------------------------------------------ 16255( 3) - 08-Oct-2020 19:09:54 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-1783 STELLAR CLUSTER, RA=04H59M8.5900S, J2000 V = 10.93 GLOBULAR CLUSTER DEC=-65D59'15.84" Reference Frame: Other: SIMBAD Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2015.5 0.0 0.0 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 16255( 3) - 08-Oct-2020 19:09:54 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE-3PT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.135 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 16255( 3) - 08-Oct-2020 19:09:54 - [ 5] Visit: 03 Visit Requirements: 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 NGC-1783 WFC3/UVI ACCUM UVIS-CENT F343N FLASH=12 1 3086 S PATTERN 1 1 S ER (9258 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-1783 1 WFC3/UVI ACCUM UVIS-CEN F343N 1 none none none 1 N/A S TER NGC-1783 1 WFC3/UVI ACCUM UVIS-CEN F343N 2 none none none 2 N/A S TER NGC-1783 1 WFC3/UVI ACCUM UVIS-CEN F343N 3 none none none 3 N/A S TER 16255( 3) - 08-Oct-2020 19:09:54 - [ 6] Visit: 04 Visit Requirements: SAME ORIENT AS 03 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 NGC-1783 WFC3/UVI ACCUM UVIS-CENT F343N FLASH=12 1 3086 S POS TARG 0.125, 0.125; S ER (9258 S) PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 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-1783 1 WFC3/UVI ACCUM UVIS-CEN F343N 1 none none none 1 N/A S TER NGC-1783 1 WFC3/UVI ACCUM UVIS-CEN F343N 2 none none none 2 N/A S TER NGC-1783 1 WFC3/UVI ACCUM UVIS-CEN F343N 3 none none none 3 N/A S TER 16255( 3) - 08-Oct-2020 19:09:54 - [ 7] Visit: 05 Visit Requirements: SAME ORIENT AS 03 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 NGC-1783 WFC3/UVI ACCUM UVIS-CENT F343N FLASH=12 1 3095 S POS TARG 0.25, 0.25 S ER (3095 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-1783 WFC3/UVI ACCUM UVIS-CENT F438W FLASH=12 1 938 S POS TARG 0.25, 0.25; S ER (2814 S) PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ 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-1783 1 WFC3/UVI ACCUM UVIS-CEN F343N none none none none 1 N/A S TER NGC-1783 2 WFC3/UVI ACCUM UVIS-CEN F438W 1 none none none 2 N/A S TER NGC-1783 2 WFC3/UVI ACCUM UVIS-CEN F438W 2 none none none 2 N/A S TER NGC-1783 2 WFC3/UVI ACCUM UVIS-CEN F438W 3 none none none 2 N/A S TER 16255( 3) - 08-Oct-2020 19:09:54 - [ 8] Visit: 06 Visit Requirements: SAME ORIENT AS 03 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 NGC-1783 WFC3/UVI ACCUM UVIS-CENT F343N FLASH=12 1 3095 S POS TARG 0.375, 0.375 S ER (3095 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-1783 WFC3/UVI ACCUM UVIS-CENT F438W FLASH=12 1 938 S POS TARG 0.375, 0.375; S ER (2814 S) PATTERN 1 2 ------------------------------------------------------------------------------------------------------------------------------------ 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-1783 1 WFC3/UVI ACCUM UVIS-CEN F343N none none none none 1 N/A S TER NGC-1783 2 WFC3/UVI ACCUM UVIS-CEN F438W 1 none none none 2 N/A S TER NGC-1783 2 WFC3/UVI ACCUM UVIS-CEN F438W 2 none none none 2 N/A S TER NGC-1783 2 WFC3/UVI ACCUM UVIS-CEN F438W 3 none none none 2 N/A S TER 16255( 3) - 08-Oct-2020 19:09:54 - [ 9] Summary Form for Proposal 16255 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS-CENTER ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=12 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 1 2, POS TARG 0.125, 0.125, POS TARG 0.25, 0.25, POS TARG 0.375, 0.375, SAME ORIENT AS 03 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F343N, F438W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC-1783 ------------------------------------------------------------------------------------------------------------------------------------