0 Assigned ID: 897 ----- Attempting Submission 1 (Fri Apr 08 22:06:21 GMT 2016) ----- This pattern is not used in this proposal. This pattern is not used in this proposal. Change of main filter set approved by PC. Addition of short exposures requested, and PC advised to submit pending approval. -459134667 ----- Attempting Submission 1 (Thu Jul 21 23:33:22 GMT 2016) ----- Unused patterns kept for reference. A close-up view of the star formation history of a young ultracompact dwarf We have recently discovered a young ultracompact dwarf (UCD) in the dwarf spiral galaxy NGC 247. This is by far the nearest known UCD (3.6 Mpc), providing a unique opportunity to study the stellar populations of a UCD in detail. There are indications that this object originated as the nucleus of a smaller dwarf, stripped in a recent merger, and that it harbors multiple stellar populations. We propose to use WFC3-UVIS imaging to map out the internal color gradient of the UCD and to construct a color-magnitude diagram of its stars. We will be able to detect age spreads down to 100 Myr, which would provide an important point of reference for the mystery of multiple stellar populations in star clusters. The technical goals of the observations are: (1) to obtain high spatial resolution imaging of the UCD integrated light, to measure a radial color profile on scales of ~0.05-0.4 arcsec; (2) to construct a color-magnitude diagram (CMD) of individual stars (magnitude range ~24.5-28.5) at the periphery of the UCD, at radii of ~0.4-3.5 arcsec (trying in particular to measure magnitude spreads of post-main-sequence blue loop stars); (3) to construct a CMD of surrounding stream stars, out to radii of ~20 arcsec. We will observe the UCD with three orbits for each of two filters (WFC3/UVIS F475W and F606W, similar to g and V). The same orientation is used for both filters. We will use a three-point subpixel dither pattern (one point per orbit) with a two-point line sub-pattern (each orbit split into two exposures), equivalent to the pattern WFC3-UVIS-MOS-DITH-LINE. We will place the target close to a read-out amplifier (~30 arcsec) in order to reduce CTE loss, using the UVIS2-C1K1C-CTE aperture. Our total exposure times per filter are 2 hours, split into 6 exposures each. The CMD photometry will be done on individual rather than combined frames. Additional short exposures (1-5 min) are obtained in 6 filters (F225W, F275W, F390W, F475W, F606W, F814W) for increased wavelength coverage on the UCD imaging. Stellar Populations 12 false false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER J2000 J2000 WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F555W POS-TARG MOSAIC DITHER 2 2.4 WFC3-UVIS-MOS-DITH-LINE false true 0.119 3 85.754 POS-TARG WFC3-UVIS-MOS-DITH-LINE 33.606 1 true POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 2 false /Users/romanow/Dropbox/work/active/NGC247/OP-cache/NGC247-UCD1-HST-PhaseII-v01.xml The scheduling data was generated by CASM 24.2. CASM was run in Phase II mode. Long exposures in F475W + short exposures in F475W, F225W, F275W. (Tic-Visit :proposal-id 14748 :visit-id "01" :proposal-version -1 :trans-version "20160601" :date "21-Jul-2016 16:31:32.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 3464944 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14748 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14748 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2888 :al-overhead-at-end 116 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14748 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3000 :al-overhead-at-end 116 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14748 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2999 :al-overhead-at-end 116 :internal-dur-at-end 352 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) true 3 0 /Users/romanow/Dropbox/work/active/NGC247/OP-cache/NGC247-UCD1-HST-PhaseII-v02.xml The scheduling data was generated by CASM 24.2. CASM was run in Phase II mode. Long exposures in F606W + short exposures in F606W, F390W, F814W, using the same Orient as the F475W visit. 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