0 Assigned ID: 1246 ----- Attempting Submission 1 (Wed Sep 30 22:31:25 GMT 2020) ----- ----- Attempting Submission 2 (Wed Oct 07 14:18:55 GMT 2020) ----- FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser FLASH level may be too high for this exposure or a long subexposure. See extended explanation in the diagnostic browser This is a resubmission, following the recommendation by the CS to use the dither patterns in ISR WFC3 2020-07 and increase the FLASH for the F300X exposures. We have also changed the POS-TARG offsets from (40, 0) to (-40, 0) which should put the target close to amplifier C (instead of D). -961163573 ----- Attempting Submission 1 (Thu Nov 19 09:42:04 GMT 2020) ----- HST Phase II Proposal 16459 successfully submitted. Receipt: # 16459-1 ----- Attempting Submission 2 (Thu Nov 26 10:19:31 GMT 2020) ----- We are following the recommendation in ISR 2020-08 and using a higher FLASH setting to increase the background level in the F300X exposures to about 20 e-/pixel. The color-magnitude diagram of an extremely metal-poor globular cluster We propose to obtain a color-magnitude diagram (CMD) of the globular cluster (GC) EXT8 in M31. With a metallicity of [Fe/H]=-2.9, EXT8 is by far the most metal-poor GC yet identified, and as such it provides us with unique information on CMD morphology at this low metallicity. At the same time, it challenges theories for the formation of GCs in the context of hierarchical galaxy formation. We will image the cluster with WFC3 in the F300X, F606W, and F814W filters and obtain a CMD that reaches below the horizontal branch. The observations will thus provide the first empirical insight into horizontal branch morphology in a GC near [Fe/H]=-3. Photometry of stars on the red giant branch will provide an independent verification of the spectroscopic metallicity determination and will constrain any metallicity spread present in the cluster (that might be suggestive of an origin as a stripped nucleus). The extremely metal-poor globular cluster EXT8 in M31 will be imaged with WFC3 for two orbits in F606W, three orbits in F814W, and two orbits in F300X in order to produce a color-magnitude diagram that reaches below the horizontal branch. Each orbit will be split into two dithered sub-exposures. The cluster will be positioned on the UVIS2 detector (which is more sensitive in the UV) at a POS-TARG offset of (-40, 0) arcsec in order to place the cluster closer to the read-out amplifier C and minimize CTE losses. The observations are divided into three visits, one for each filter. The two-orbit visits (F606W and F300X) will use a four-point dither pattern and the three-orbit visit (F814W) will use a six-point dither patterns. We are using the offsets in ISR WFC 2020-07 and specifying the dither points via POS-TARG offsets (in addition to the (-40, 0) offset mentioned above), rather than predefined dither patterns. The WFC3 ETC predicts a background level of 10 e- (sky + dark), to which we add FLASH=10 to get to a total of 20. We note that the WFC3 ETC predicts a slightly higher background level than the value computed by APT. Impact of reduced-gyro operations: As each visit consists of WFC3 imaging for 2-3 orbits in a single filter, the slight increase in target acquisition time is expected to have a negligible impact on the S/N of our observations. The observations are not time critical and our program requires no specific orientation (apart from all three visits having the same orientation). We therefore expect that the impact of reduced-gyro operations would be small. The team has decades of experience in the planning, analysis, and interpretation of HST observations of extragalactic globular clusters. This proposal is to follow up on our HIRES observations of EXT8, which have been submitted to Science and will probably have appeared in press by the time the proposal reaches the reviewers. The P.I. (S. Larsen) has led several previous HST programs, including a photometric study of the Fornax globular clusters (Larsen et al. 2014), using the same analysis techniques that will be applied here. The Co-Is (Brodie, Romanowsky) have published numerous papers on observations of extragalactic globular clusters, using data from HST, Keck, and many other space- and ground-based facilities. Publication in a timely fashion is a high priority by our team. Stellar Populations and the Interstellar Medium Galaxies 3 false false true false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER J2000 J2000 WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F300X /private/var/folders/fk/_2w_pz3x0935nsl0qk_7_byr0000gn/T/OPVisit703327984174236409.xml Hst Same orient constraint links visits (01 02 03) The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16459 :visit-id "01" :proposal-version -1 :trans-version "20200619" :date "26-Nov-2020 11:14:57.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1154976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16459 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16459 :visit-id "01" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2854 :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 3238 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16459 :visit-id "01" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2846 :al-overhead-at-end 116 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3238 :pcs-gap 0 ) true 2 0 /private/var/folders/fk/_2w_pz3x0935nsl0qk_7_byr0000gn/T/OPVisit5047674895749655125.xml Hst Same orient constraint links visits (01 02 03) The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16459 :visit-id "02" :proposal-version -1 :trans-version "20200619" :date "26-Nov-2020 11:08:40.0" :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 1732464 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16459 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16459 :visit-id "02" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2854 :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 3238 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16459 :visit-id "02" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2846 :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 3238 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16459 :visit-id "02" :orbit-number 3 :pcs-time 392 :si-vis-utilization 2836 :al-overhead-at-end 116 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3238 :pcs-gap 0 ) true 3 0 /private/var/folders/fk/_2w_pz3x0935nsl0qk_7_byr0000gn/T/OPVisit14160975148072868001.xml Hst Same orient constraint links visits (01 02 03) The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16459 :visit-id "03" :proposal-version -1 :trans-version "20200619" :date "26-Nov-2020 11:14:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1154976 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16459 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16459 :visit-id "03" :orbit-number 1 :pcs-time 383 :si-vis-utilization 2855 :al-overhead-at-end 123 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3238 :pcs-gap 0 ) (Tic-Orbit :proposal-id 16459 :visit-id "03" :orbit-number 2 :pcs-time 392 :si-vis-utilization 2845 :al-overhead-at-end 123 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3238 :pcs-gap 0 ) true 2 0 ETC gives a background of 10 e-/pixel, to which a FLASH of another 10 is added to reach 20 e-/pixel