resubmission after HOPR for visits 4 and 5 ----- Submission 3 (Wed May 30 22:04:22 GMT 2007) ----- Even after using "Run All Tools", warnings are still coming up that "orbit filling information is not available"... Complexity in the Smallest Galaxies: Star Formation History of the Sculptor Dwarf Spheroidal The Sculptor dwarf spheroidal galaxy (Scl dSph) is one of the most luminous of the Milky Way dSph satellites, suffers virtually no foreground confusion or reddening because of its high galactic latitude, and is nearby at 80 kpc from the Sun. It is of great interest to astronomy to understand the detailed histories of dSph galaxies because they may be survivors of the hierarchical merging process that created giant galaxies like our own. Despite this, the age distribution of stars in Scl dSph remains remarkably poorly constrained because of a dearth of high-quality color-magnitude diagrams (CMDs) of its central regions. Scl dSph is known to be complex on the basis of shallower photometry, radial velocity studies, and investigations of the metallicity; however, the age range of significant star-formation and the proportion of stars older and younger than 10 Gyr is still completely unknown. The age of the centrally concentrated, metal-rich population has never been measured. We propose to obtain deep optical images of the core of Scl dSph with WFPC2 in order to measure the temporal evolution of its star-formation rate over its entire lifetime. The ONLY way to reliably measure the variation in star-formation rate on Gyr timescales at ages of 10-13 Gyr is with photometry of a large number of stars at and below the oldest main-sequence turnoffs to magnitudes of (B,I) = (25.1, 24.5). Because of the high stellar density and resulting image crowding, it is impossible to achieve the required level of photometric precision except with diffraction-limited imaging. These data will permit the first reliable measurement of the star-formation history of the main body of Scl dSph; limited inferences from WFPC2 data in an outer field have been made, but they were hindered not only by small number statistics but by the subsequent revelation of extremely strong population gradients in Scl dSph, such that the stars in the existing WFPC2 field are not representative of the galaxy as a whole. Our proposed program will shed strong new light on the formation processes of the smallest galaxies. Only by measuring the detailed early histories of galaxies like Scl dSph can we evaluate the impact of outside influences like ram-pressure stripping, tidal stirring, and photoionization feedback on the evolution of small galaxies.
We will image the core region of the Sculptor dwarf spheroidal (ESO351-30) using the F450W and F814W filters of WFPC2. This proposal was originally intended to use ACS/WFC and has been reassigned to WFPC2 The exposures are designed to optimize the combination of sensitivity and age/metallicity resolution for the main-sequence turnoffs of stellar populations older than ~6 billion years. Our science goal requires high signal-to-noise, highly complete photometry down to magnitudes of (B, I) ~ (25.5, 24.5), two magnitudes below the oldest main-sequence turnoff. The WFCP2 online ETC shows that S/N > 25 can be achieved in ~8800 sec per filter, or approximately 4 orbits each given the visibility of the Sculptor dwarf. To minimize overheads, we will implement a standard line dither pattern by means of POS-TARG commands between visits, and fill each of the first 6 orbits with long CR-SPLIT exposures. To extend our dynamic range up the red giant branch, we use the GAIN=14 setting, and we will use a set of 4x400sec exposures in our last visit to ensure that accurate photometry can be obtained for upper RGB stars. The radius of Sculptor is many times larger than the WFPC2 field of view, so no constraints on the orientation are required as long as all four visits are oriented the same. The Sculptor dwarf spheroidal was observed with WFPC2 under program #6866 in F555W and F814W. However, the observations were taken ~15 arcmin along the minor axis from the galaxy's center and only measured one component of the complex stellar population mix now known to be present. Our goal here is to rectify that shortcoming; the existing CMD (Monkiewicz et al. 1999) will be a valuable resource to constrain the population gradient in Sculptor. RESOLVED STELLAR POPULATIONS 12 false 0.0 false false false false false SUPPORTED GALAXY DWARF SPHEROIDAL This object was generated by the targetselector and retrieved from the NED database. surface brightness 23.5 Vmag/arcsec^2 stellar field SCULPTOR-DSPH J2000 01 00 9.3000 -33 42 33.00 J2000 GALAXY DWARF SPHEROIDAL This object was generated by the targetselector and retrieved from the NED database. surface brightness 23.5 Vmag/arcsec^2 stellar field SCULPTOR-DSPH J2000 01 00 9.3000 -33 42 33.00 J2000 ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F814W WFPC2 Imaging No F555W WFPC2 Imaging No F814W POS-TARG DITHER 0.3535 LINE false false 2 45.0 WFPC2-LINE 1 false /private/tmp/OPVisit6122.xml (Tic-Visit :proposal-id 10888 :visit-id "02" :proposal-version -1 :trans-version "20051113" :date "30-May-2007 16:43:48.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10888 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10888 :visit-id "02" :orbit-number 1 :pcs-time 339 :si-vis-utilization 2760 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10888 :visit-id "02" :orbit-number 2 :pcs-time 339 :si-vis-utilization 2760 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) true 2 0 /private/tmp/OPVisit6123.xml (Tic-Visit :proposal-id 10888 :visit-id "03" :proposal-version -1 :trans-version "20051113" :date "30-May-2007 16:43:54.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10888 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10888 :visit-id "03" :orbit-number 1 :pcs-time 339 :si-vis-utilization 2760 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10888 :visit-id "03" :orbit-number 2 :pcs-time 339 :si-vis-utilization 2760 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) true 2 0 /private/tmp/OPVisit6124.xml (Tic-Visit :proposal-id 10888 :visit-id "04" :proposal-version -1 :trans-version "20051113" :date "30-May-2007 16:44:01.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10888 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10888 :visit-id "04" :orbit-number 1 :pcs-time 339 :si-vis-utilization 2760 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10888 :visit-id "04" :orbit-number 2 :pcs-time 339 :si-vis-utilization 2760 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) true 2 0 /Users/andrewcole/ESO351-30/OP-cache/postHOPR_10888-v05.xml (Tic-Visit :proposal-id 10888 :visit-id "05" :proposal-version -1 :trans-version "20051113" :date "30-May-2007 15:26:26.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 358528 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10888 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10888 :visit-id "05" :orbit-number 1 :pcs-time 339 :si-vis-utilization 2360 :al-overhead-at-end 160 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10888 :visit-id "05" :orbit-number 2 :pcs-time 339 :si-vis-utilization 2340 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) true 2 0 /Users/andrewcole/ESO351-30/OP-cache/postHOPR_10888-v54.xml (Tic-Visit :proposal-id 10888 :visit-id "54" :proposal-version -1 :trans-version "20051113" :date "30-May-2007 15:25:17.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 89632 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10888 :visit-id "54" :obset-id "54" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10888 :visit-id "54" :orbit-number 1 :pcs-time 339 :si-vis-utilization 2760 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) true 1 0 /Users/andrewcole/ESO351-30/OP-cache/postHOPR_10888-v55.xml (Tic-Visit :proposal-id 10888 :visit-id "55" :proposal-version -1 :trans-version "20051113" :date "30-May-2007 15:37:50.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 358528 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10888 :visit-id "55" :obset-id "55" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10888 :visit-id "55" :orbit-number 1 :pcs-time 339 :si-vis-utilization 2360 :al-overhead-at-end 160 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10888 :visit-id "55" :orbit-number 2 :pcs-time 339 :si-vis-utilization 2340 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3283 :pcs-gap 0 ) true 2 0