16282( 5) - 30-Sep-2020 15:49:43 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16282 Version: 5 Check-in Time: 30-Sep-2020 15:49:43 STScI Edit Number: 1 Title The IR CMD of the Metal-Rich Bulge Cluster NGC6553: Pushing its Age to Sub-Gyr Precision ------------------------------------------------------------------------------------ Type Cycle GO 28 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Matteo Correnti Space Telescope Science Institute Y CoI: Dr. Mario Gennaro Space Telescope Science Institute N CoI: Dr. Jason Kalirai The Johns Hopkins University Applied N Physics Laboratory CoI: Dr. Roger Cohen Space Telescope Science Institute N CoI: Dr. Thomas M. Brown Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract Globular Clusters (GCs) in the Milky Way are the primary laboratories for establishing the ages of the oldest stellar populations and for measuring the color-magnitude relation of stars. The gold standard for these studies has involved high-precision visible light investigations with the Hubble Space Telescope (HST). However, the shape of the color-magnitude relation in the visible bandpasses offers little leverage to disentangle the effects of distance, reddening, and metallicity, and these uncertainties impact our derived age measurements for GCs. Recently, a new feature has been observed in several HST WFC3-IR color-magnitude diagrams (CMDs) of nearby GCs. At low stellar masses, the stellar main sequence in an infrared (IR) CMD exhibits a sharp "kink" (due to opacity effects in M dwarfs), such that lower mass and cooler dwarfs become bluer in the F110W - F160W color baseline and not redder. As demonstrated by Correnti et al. (2016, 2018), this inversion of the color- magnitude relation offers a new opportunity to fit GC properties in the IR baseline, and to reduce their uncertainties. Here, we propose a 1-orbit HST WFC3-IR program to measure the color-magnitude relation of stars (down to 2.5 mag below the MS "kink") for the metal-rich bulge cluster NGC6553. We will establish the most accurate age for the cluster to date, with sub-Gyr precision. Combining these observations with the sample analyzed by Correnti et al. (2016, 2018), will establish an independent and sensitive test to the age-metallicity relation of clusters. ------------------------------------------------------------------------------------ Observations Description ------------------------ The target cluster NGC6553 is observed with WFC3/IR using the F110W and F160W broad-band filters. In the target cluster, we expect the magnitude of the kink to occur at M_F110W ~ 5.9 mag and M_F160W ~ 5.1 mag which translates to an apparent magnitude of F110W ~ 20.6 mag at the distance of the cluster. To accurately map the shape of the main sequence and the color-magnitude relation below the main sequence kink we need high signal-to-noise photometry ~ 4 magnitudes below this limit. To resample the PSF, mitigate hot pixels, and minimize errors from flat fielding we apply a 4-point dither pattern. We use the STEP100 sample sequence with 9 samples for each filters. Observations are arranged in 1 visit that covers the available orbit. 16282( 5) - 30-Sep-2020 15:49:43 - [ 2] We sligthly offset our pointing from the target center in order to have a complete overlap with the field of view of the existing WFC3/UVIS observations (GO-15232) and to avoid a sampling of only the innermost region of the cluster. We are not imposing any constraints on the observations orient nor any special requirements. ------------------------------------------------------------------------------------ 16282( 5) - 30-Sep-2020 15:49:43 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-6553 STELLAR CLUSTER, BULGE, RA=18H09M19.5832S, J2000 V = 8.06 GLOBULAR CLUSTER DEC=-25D55'9.65" 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 1.8528834973922183E-4 0.00535 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 16282( 5) - 30-Sep-2020 15:49:43 - [ 4] Visit: 01 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-6553 WFC3/IR MULTIAC IR F160W SAMP-SEQ=STEP100, NSAMP=9 1 DEF POS TARG 0.000, 0.000; CUM (299.231 SEQ 1-8 NON-INT S) ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-6553 WFC3/IR MULTIAC IR F110W SAMP-SEQ=STEP100, NSAMP=9 1 DEF SAME POS AS 1 CUM (299.231 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC-6553 WFC3/IR MULTIAC IR F110W SAMP-SEQ=STEP100, NSAMP=9 1 DEF POS TARG +0.542, +0.182 CUM (299.231 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-6553 WFC3/IR MULTIAC IR F160W SAMP-SEQ=STEP100, NSAMP=9 1 DEF SAME POS AS 3 CUM (299.231 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC-6553 WFC3/IR MULTIAC IR F160W SAMP-SEQ=STEP100, NSAMP=9 1 DEF POS TARG +0.339, +0.485 CUM (299.231 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC-6553 WFC3/IR MULTIAC IR F110W SAMP-SEQ=STEP100, NSAMP=9 1 DEF SAME POS AS 5 CUM (299.231 S) ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC-6553 WFC3/IR MULTIAC IR F110W SAMP-SEQ=STEP100, NSAMP=9 1 DEF POS TARG -0.203, +0.303 CUM (299.231 S) ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC-6553 WFC3/IR MULTIAC IR F160W SAMP-SEQ=STEP100, NSAMP=9 1 DEF SAME POS AS 7 CUM (299.231 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-6553 1 WFC3/IR MULTIAC IR F160W none none none none 1 N/A CUM NGC-6553 2 WFC3/IR MULTIAC IR F110W none none none none 1 N/A CUM 16282( 5) - 30-Sep-2020 15:49:43 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-6553 3 WFC3/IR MULTIAC IR F110W none none none none 1 N/A CUM NGC-6553 4 WFC3/IR MULTIAC IR F160W none none none none 1 N/A CUM NGC-6553 5 WFC3/IR MULTIAC IR F160W none none none none 1 N/A CUM NGC-6553 6 WFC3/IR MULTIAC IR F110W none none none none 1 N/A CUM NGC-6553 7 WFC3/IR MULTIAC IR F110W none none none none 1 N/A CUM NGC-6553 8 WFC3/IR MULTIAC IR F160W none none none none 1 N/A CUM 16282( 5) - 30-Sep-2020 15:49:43 - [ 6] Summary Form for Proposal 16282 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=9, SAMP-SEQ=STEP100 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements POS TARG +0.339, +0.485, POS TARG +0.542, +0.182, POS TARG -0.203, +0.303, POS TARG 0.000, 0.000, SAME POS AS 1, SAME POS AS 3, SAME POS AS 5, SAME POS AS 7, SEQ 1-8 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F110W, F160W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC-6553 ------------------------------------------------------------------------------------------------------------------------------------