0 Assigned ID: 291 ----- Attempting Submission 1 (Thu Apr 09 22:20:31 GMT 2015) ----- HST Phase I Proposal 291 (Arches_Y.apt) successfully submitted. Receipt: # 291-1 ----- Attempting Submission 2 (Fri Apr 10 15:35:21 GMT 2015) ----- 0 ----- Attempting Submission 1 (Sun Jul 19 12:14:08 GMT 2015) ----- Opening a New Window towards the Nuclear Star Cluster in the Milky Way The nuclear star cluster in the Galactic Centre is the only place where we can study star formation near a massive black hole in great detail. However, due to the strong foreground extinction, previous studies have been limited to the J-band and longer wavelengths. The short wavelength coverage, from J to K, hampers attempts to accurately determine the extinction curve, to map the extinction distribution, to distinguish between massive and low-mass stars and finally, to disentangle different stellar populations through the colour magnitude diagram. Deep F105W observations with HST WFC3/IR would result in great progress toward overcoming these problems. This program can help us to make significant progress in addressing the following important astrophysics questions: 1) what are the properties of the extinction law toward the Galactic Centre environment? 2) what was the assembly history of the nuclear star cluster in the Galactic Centre? We use five HST orbits to observe the nuclear star cluster in the Milky Way at F105W band with one WFC3/IR pointing. In order to achieve our scientific goals, i.e. extinction law, extinction map and disentangling different stellar populations from the color-magnitude diagram, we need high photometry precision, especially in this extreme crowding region. We fine-tune the dithering pattern to overcome the undersample problem of the WFC3/IR detector, the main obstacle affecting the photometry accuracy. We use sub-pixel offset among dithering exposures to better sample the point spread function. Meanwhile, we also employ integer-pixel diterhng exposures to recover the information lost due to the bad pixels. Due to the huge number of visits with non-stop 5 orbits, as suggested by the Contact Scientist, we divide our 5 orbits into two visits, one with two orbits and the other one with three orbits. In these two visits, we choose 1/3 and 1/4 pixel sub-pixel offset, respectively. Meanwhile, four and three dithering exposures with integer-pixel offset are used too. In order to use each orbit efficiently, we slightly change the parameters of MULTIACCUM for different dithering exposures. As a result, we have only ~10 second left in each orbit, although the exposure time among different exposures change from 350 to 450 seconds. The total effective exposure time of the five orbits is 12.6 ks. For each dithering exposure, we employ the STEP sequence, instead of the SPARS sequence, considering the wide range of stellar magnitudes of stars in the Galactic Center. In order to compare with previous WFC3/IR observations in the F127M, F139M, F153M, we use the same coordinate and rotation angale as those used in Program 11671. RESOLVED STELLAR POPULATIONS 12 false false false false SUPPORTED STELLAR CLUSTER DUST LANE NUCLEUS OPEN CLUSTER STAR FORMING REGION The magnitude are for the brightese star in the field-of-view. J2000 J2000 J-12.2, H=9.26,K=6.5 WFC3/IR Imaging No No F105W /private/var/folders/h7/n82mj8zs28vgng7b_2wctdgm0000gn/T/OPVisit3967005816661765977.xml The scheduling data was generated by CASM 23.2. CASM was run in Phase II mode. 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CASM was run in Phase II mode. (Tic-Visit :proposal-id 14147 :visit-id "02" :proposal-version -1 :trans-version "20150609" :date "19-Jul-2015 12:35:02.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 3133632 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14147 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14147 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2867 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3229 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14147 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3002 :al-overhead-at-end 0 :internal-dur-at-end 500 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3229 :pcs-gap 0 ) true 2 0