Thanks!!! ----- Submission 1 (Thu Nov 27 01:27:09 GMT 2003) ----- Ceres: High-Resolution Mapping and Determination of Physical Properties We propose a modest, 6-orbit HST ACS/HRC program to fully map the asteroid 1 Ceres for the first time. These high signal-to-noise, high resolution maps will be obtained in three ACS filter bandpasses from the visible to the UV. The goals of our program are to advance knowledge about Ceres dramatically, to resolve certain longstanding issues regarding Ceres, and to support planning for the Dawn Discovery mission's planned orbital tour of Ceres. The specific scientific objectives of this proposed Cycle 12 effort are: (1) To achieve dense rotational phase coverage with multi-spectral imaging over the complete rotation period of Ceres to map its surface; (2) To resolve surface features and investigate the nature of the Piazzi feature detected by HST/FOC in 1995; (3) To track surface features in order to unambigously determine Ceres' pole position; (4) To measure the three-dimensional shape of Ceres better than any existing shape model in order to significantly refine density measurements; and (5) To map Ceres' color variegation and photometric parameters in order to identify possible surface units for the first time. These goals require high resolution visible and ultraviolet imaging, which can only be obtained with HST. As we demonstrate in this proposal, the January, 2004 opposition of Ceres is the best in the next 6 years for both data quality and planning of the Dawn mission.
OVERVIEW OF VISITS: We were originally awarded 6 orbits based on the original observing plan (designed with APT) that would allow us to dither every observation and get the appropriate time sampling. When the observations were being scheduled, it was discovered that there were additional overheads for dithering on a moving object that APT did not take into account that were a serious impact on our original plan. We submitted a Program Change Request, and were awarded 3 additional orbits. So the original 6 (contiguous) orbits will now contain CRSPLIT observations to provide the appropriate timing throughout Ceres' full rotation, and the additional 3 orbits will be used for dithered observations to be taken at relative rotation phases separated by 120 degrees. Those 3 "dithered" orbits do not need to be contiguous or tightly constrained with each other or the 6 "crsplit" orbits, as long as they are still within +/-14 days of opposition and have the appropriate relative phase sampling. DETAILED DESCRIPTION OF VISITS: These observations employ 6 contiguous HST orbits to map Ceres with good rotational density in each of three ACS/HRC filter bandpasses: F220W, F330W, and F555W. 3 additional orbits are used to obtain dithered observations at rotation phases separated by roughly 120 degrees. Ceres has a 9.075-hour rotation period; with the HST orbit of ~96?minutes, we can cover a full rotation of Ceres in 6 HST orbits starting at relative rotational phases of approximately: 0, 64, 128, 191, 255, and 319 degrees. The rotational phase coverage in each filter will be even higher: three times per orbit in the F555W and the F330W filters, and two times per orbit in the F220W filter. This will allow us to obtain well-sampled, high-resolution maps, allowing for definite identification and tracking of surface features from image to image with minimal distortion due to aspect changes. We will CRSPLIT all images to optimally remove hot pixels and cosmic rays, which will allow for uncontaminated surface photometry, feature identification, and increase the S/N for photometric accuracy (e.g., determining color variegation, volatile distribution, and Minnaert parameters), and improve resolution. In the three orbits with dithered observations, we will use a 4-point dither pattern (standard pattern ACS-HRC-DITHER-BOX) for the observations in all three filters, with two sets of exposures each in the F555W and F330W filters, and one set in the F220W filter. The dithers will allow us the highest spatial resolution possible. Because of its relative brightness, most of the exposures of Ceres are relatively short. During opposition, Ceres has an integrated magnitude of V=6.8?mag, and a V-band surface brightness of 6.1?mag?arcsec-2. Using the ACS/HRC Exposure Time Calculator (ETC) using reddened analog solar spectra as well as actual IUE and visible spectra of Ceres, we estimate that the full well saturation of the brightest CCD pixel in a single image would be reached in approximately the following times: F555W?=?4.5?sec, F330W?=?55?sec, F220W =4000 sec. It is desirable to have the highest S/N possible in these images to obtain the best surface feature contrast. However, to allow for bright albedo spots, which could be several times brighter than the average albedo, exposure times for each dithered sub-image should be no more than about 20% of these saturation times. Using the ETC, we determined that for our observing plan for Ceres as described herein, each sub-image exposure (before combining dithered sets) is predicted to obtain acceptably high signal-to-noise ratios for each 2x2 resolution element; specifically, the ETC predicts: F555W S/N=350 in 1 sec, F330W S/N=320 in 10 sec, and F220W S/N=150 in 180 sec. We are including one deep, 20 sec, CRSPLIT=4 F555W image at the end of orbits 2,3,5,6 (orbits that use GS Re-Acq) using the full CCD (the HRC aperture), to look for faint satellite companions and to improve dynamic range on faint, low-contrast features. TIMING OF OBSERVATIONS: In Cycle 12, Ceres is at opposition on 2004 January 11. We can allow +/-14?days on either side of this optimal date while retaining an adequate combination of surface brightness and resolution on Ceres. Within this range of time, the resolution varies by <10%, and the S/N will vary by < 20%. The ideal plan would be to get 6 contiguous HST orbits for these observations, which would provide even-sampling of phase coverage over a short period of time so that temporal changes (illumination, surface effects, etc.) will not be a factor. According to Section 2.3.2 of the HST Primer, the longest possible set of contiguous orbits without SAA intersection is 5 to 6 orbits. To this end, we have grouped the 6 orbits into 2 visits (each containing 3 orbits), with the requested constraint that these visits be contiguous (i.e. Visit 02 to be immediately after Visit 01). Please check that Visit 02 will, indeed, immediately follow Visit 01. We believe we have defined this correctly using the AFTER scheduling constraint, but since the timing of the observations is critical, this is an imporant point to verify. Also please check that the timing of Visits 03, 04, and 05 meet the intended goal of sampling at 120 degree intervals throughout Ceres' 9.1 hour rotation period. SOLAR SYSTEM 12 false false false false SUPPORTED SOLAR SYSTEM ASTEROID ASTEROID 1 CERES TYPE=ASTEROID,A=2.7659574,E=0.0795184,I=10.58343,O=80.4794,W=74.06844,M=317.77388,EQUINOX=J2000,EPOCH=27-DEC-2003:00:00:00 false false ACS-HRC-DITHER-BOX false 19.89 1 0.15 DITHER 4 LINE POS-TARG false false ACS-HRC-DITHER-LINE false 44.28 2 0.198 DITHER 3 LINE POS-TARG VISIT 02 SHOULD IMMEDIATELY FOLLOW VISIT 01. THE TWO VISITS SHOULD BE CONTIGUOUS TO ALLOW FOR REGULAR SAMPLING ROTATIONAL PHASES. IF SCHEDULING DOES NOT PREMIT THE TWO VISITS TO BE CONTIGUOUS, PLEASE CONTACT THE PI. Visit 01 contains the first 3 (out of 6) orbits, at nominal relative phases: 0.0, 63.7, 127.5 degrees. Visit 02 contains the last 3 (out of 6) orbits, at nominal relative phases: 191.1, 254.8, 318.5 degrees. Each orbit contains: Three CRSPLIT=4 F555W exposures; Three CRSPLIT=4 F330W exposures; Two CRSPLIT=3 F220W exposures; Also, the second and third orbit each end with one "long F555W" CRSPLIT=3 exposure (not included in first orbit of visit). All observations on Visits 01 and 02 are CRSPLIT. The observing plan is identical for both visits. The order of exposures in each orbit are: F555W, F330W, F220W, F555W, F330W, F22OW, F330W, F555W, "long F555W". All images except the "long F555W" use the HRC-512 subarray (less readout time, fewer/shorter dumps). The "long F555W" exposure uses the full CCD ("HRC" aperture), and is to look for satellites and faint/low-contrast features. We include more than one orbit per visit, which saves overhead by not doing a new GS Acq each orbit. We split the first six orbits into two visits because for scheduling and GS assignment, it will help to have a full GS Acq after 3 orbits. (Tic-Visit :proposal-id 9748 :visit-id "01" :proposal-version -1 :trans-version "20030714" :date "26-Nov-2003 17:58:02.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 517968 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9748 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9748 :visit-id "01" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2833 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) (Tic-Orbit :proposal-id 9748 :visit-id "01" :orbit-number 2 :pcs-time 300 :si-vis-utilization 2898 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) (Tic-Orbit :proposal-id 9748 :visit-id "01" :orbit-number 3 :pcs-time 300 :si-vis-utilization 2898 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) true VISIT 02 SHOULD IMMEDIATELY FOLLOW VISIT 01. THE TWO VISITS SHOULD BE CONTIGUOUS TO ALLOW FOR REGULAR SAMPLING ROTATIONAL PHASES. IF SCHEDULING DOES NOT PREMIT THE TWO VISITS TO BE CONTIGUOUS, PLEASE CONTACT THE PI. Visit 01 contains the first 3 (out of 6) orbits, at nominal relative phases: 0.0, 63.7, 127.5 degrees. Visit 02 contains the last 3 (out of 6) orbits, at nominal relative phases: 191.1, 254.8, 318.5 degrees. Each orbit contains: Three CRSPLIT=4 F555W exposures; Three CRSPLIT=4 F330W exposures; Two CRSPLIT=3 F220W exposures; Also, the second and third orbit each end with one "long F555W" CRSPLIT=3 exposure (not included in first orbit of visit). All observations on Visits 01 and 02 are CRSPLIT. The observing plan is identical for both visits. The order of exposures in each orbit are: F555W, F330W, F220W, F555W, F330W, F22OW, F330W, F555W, "long F555W". All images except the "long F555W" use the HRC-512 subarray (less readout time, fewer/shorter dumps). The "long F555W" exposure uses the full CCD ("HRC" aperture), and is to look for satellites and faint/low-contrast features. We include more than one orbit per visit, which saves overhead by not doing a new GS Acq each orbit. We split the first six orbits into two visits because for scheduling and GS assignment, it will help to have a full GS Acq after 3 orbits. (Tic-Visit :proposal-id 9748 :visit-id "02" :proposal-version -1 :trans-version "20030714" :date "26-Nov-2003 17:59:04.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 517968 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9748 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9748 :visit-id "02" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2833 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) (Tic-Orbit :proposal-id 9748 :visit-id "02" :orbit-number 2 :pcs-time 300 :si-vis-utilization 2898 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) (Tic-Orbit :proposal-id 9748 :visit-id "02" :orbit-number 3 :pcs-time 300 :si-vis-utilization 2898 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) true All observations on Visits 03, 04, and 05 are dithered: the F555W and F330W exposures use a 4-point ACS-HRC-DITHER-BOX pattern, and the F220W exposure uses a 3-point ACS-HRC-DITHER-LINE pattern. In addition, the F220W is a CRSPLIT=3 at each dither position. The observing plan is identical for all three visits. The order of exposures in each orbit are: F555W, F330W, F220W, F330W, F555W. All images use the HRC-512 subarray (less readout time, fewer/shorter dumps). (Tic-Visit :proposal-id 9748 :visit-id "03" :proposal-version -1 :trans-version "20030714" :date "26-Nov-2003 17:59:38.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 113216 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9748 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9748 :visit-id "03" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2450 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) false All observations on Visits 03, 04, and 05 are dithered: the F555W and F330W exposures use a 4-point ACS-HRC-DITHER-BOX pattern, and the F220W exposure uses a 3-point ACS-HRC-DITHER-LINE pattern. In addition, the F220W is a CRSPLIT=3 at each dither position. The observing plan is identical for all three visits. The order of exposures in each orbit are: F555W, F330W, F220W, F330W, F555W. All images use the HRC-512 subarray (less readout time, fewer/shorter dumps). (Tic-Visit :proposal-id 9748 :visit-id "04" :proposal-version -1 :trans-version "20030714" :date "26-Nov-2003 16:34:39.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 113216 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9748 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9748 :visit-id "04" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2450 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) false All observations on Visits 03, 04, and 05 are dithered: the F555W and F330W exposures use a 4-point ACS-HRC-DITHER-BOX pattern, and the F220W exposure uses a 3-point ACS-HRC-DITHER-LINE pattern. In addition, the F220W is a CRSPLIT=3 at each dither position. The observing plan is identical for all three visits. The order of exposures in each orbit are: F555W, F330W, F220W, F330W, F555W. All images use the HRC-512 subarray (less readout time, fewer/shorter dumps). (Tic-Visit :proposal-id 9748 :visit-id "05" :proposal-version -1 :trans-version "20030714" :date "26-Nov-2003 15:16:38.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 113216 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9748 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9748 :visit-id "05" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2450 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3200 :pcs-gap 0 ) false