We propose to carry out a dedicated satellite search program for asteroids Vesta and Ceres. Despite being the two largest asteroids, and having clear evidence of a violent collisional history for Vesta, Vesta and Ceres do not have any satellites found so far, neither have there been any dedicated satellite search program for them reported. We propose to take short and long exposure mosaics to cover the whole Hill sphere while using specific observing strategies and image processing techniques to search in close to the center body. In addition to its significant scientific merit, this proposed project will be important for the planning of NASA's Dawn mission. Currently Ceres is moving close to the Earth, making it more difficuilt to cover the whole stability region of satellites with minimal HST orbit requirement. Similar geometry will not repeat until the second half of 2009. Therefore we request DD time.

Vesta will not have the visibility to be scheduled until late 2009. Therefore we plan all 4 approved orbits for Ceres. We emphasize searching deep to both cover the whole Hill shpere of Ceres, and as close to Ceres as possible. Four one-orbit visits are planned for this purpose. The four visits are grouped into two two-visit groups, separated by one day. And each visit has one orbit. In the first group, we will put Ceres near the apex in each of the four WFPC2 CCD chips, and take long exposures to search faint objects around Ceres. Also, short, unsaturated, exposures with Ceres at the center of PC1 chip will be taken to be stacked together to model the PSF. In the second group, we will repeat the exposures for near apex pointing of Ceres, but replace the PC1 centered exposures with a four pointing mosaics, taking long exposures, to search for faint objects in a large region around Ceres. In order to avoid potential problem of moving objects tracking, we put together the pointings that are almost along a straightline into one one-orbit visit in each group. Out detailed observing plan is: Group 1: Visit 1, total 17 exposures: PC1 near-apex pointing, 1 short, 3 intermediate, 2 long WF3 near-apex pointing, 1 short, 3 intermediate, 2 long PC1 center pointing, 5 short Visit 2, total 17 exposures: WF2 near-apex pointing, 1 short, 3 intermediate, 2 long WF4 near-apex pointing, 1 short, 3 intermediate, 2 long PC1 center pointer, 5 short Group 2, 1 day after the first group: Visit 3, total 16 exposures: PC1 with Ceres (30",30") from apex, 1 short, 2 long PC1 near-apex pointing, 1 short, 2 intermediate, 2 long WF3 near-apex pointing, 1 short, 2 intermediate, 2 long WF3 with Ceres (50",50") from apex, 1 short, 2 long Visit 4, total 16 exposures: WF2 with Ceres (50",50") from apex, 1 short, 2 long WF2 near-apex pointing, 1 short, 2 intermediate, 2 long WF4 near-apex pointing, 1 short, 2 intermediate, 2 long WF4 with Ceres (50",50") from apex, 1 short, 2 long We will use F606W filter for all exposures. For WF chips, short exposure is 0.12 sec, intermediate 20 sec, and long 40 sec. For PC1 chips, short exposure is 0.6 sec, long exposure 40 sec. Two visits in each group should be scheduled together (Separation < 2 orbits). Two groups should be scheduled one day apart. SOLAR SYSTEM 0 false 0.0 0.0 false false false false false SUPPORTED SOLAR SYSTEM ASTEROID Asteroid 1 Ceres TYPE=ASTEROID,A=2.766791532351548,E=.07947462245028122,I=10.58571555748677,O=80.40447317892902,W=72.89568694749072,M=344.5452233474741,EQUINOX=J2000,EPOCH=30-NOV-2008:00:00:00 EARTH WFPC2 Imaging No F547M WFPC2 Imaging No F547M WFPC2 Imaging No F702W WFPC2 Imaging No F702W POS-TARG MOSAIC 25 LINE false false 2 45 LINE 3 false POS-TARG MOSAIC 25 LINE false false 2 315 LINE 4 false Using ephemeris for target 11969-01-CERES ephemeris data for target 11969-01-CERES does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 07.182 to 09.335. ephemeris interval: 08.335 to 10.317 Timing link suitability includes constraints ([Sequence (01 02) within 0.1 days]) The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 11969 :visit-id "01" :proposal-version -1 :trans-version "20080807" :date "06-Jan-2009 12:51:49.0" :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 761872 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11969 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11969 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2659 :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 3132 :pcs-gap 0 ) true 1 0 Short exposure with gain=15 to avoid saturation Long saturated exposure to detect faint satellites Long saturated exposure to detect faint satellites Short exposure with gain=15 to avoid saturation Using ephemeris for target 11969-02-CERES ephemeris data for target 11969-02-CERES does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 07.182 to 09.335. ephemeris interval: 08.335 to 10.317 Timing link suitability includes constraints ([Sequence (01 02) within 0.1 days] [03 After 02 by 1.0 to 1.0 days]) The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 11969 :visit-id "02" :proposal-version -1 :trans-version "20080807" :date "06-Jan-2009 12:51:53.0" :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 761872 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11969 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11969 :visit-id "02" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2659 :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 3132 :pcs-gap 0 ) true 1 0 Short exposure with gain=15 to avoid saturation Long saturated exposure to detect faint satellites Long saturated exposure to detect faint satellites Short exposure with gain=15 to avoid saturation Using ephemeris for target 11969-03-CERES ephemeris data for target 11969-03-CERES does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 07.182 to 09.335. ephemeris interval: 08.335 to 10.317 Timing link suitability includes constraints ([Sequence (03 04) within 0.1 days] [03 After 02 by 1.0 to 1.0 days]) The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 11969 :visit-id "03" :proposal-version -1 :trans-version "20080807" :date "06-Jan-2009 12:51:58.0" :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 717056 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11969 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11969 :visit-id "03" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2754 :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 3132 :pcs-gap 0 ) true 1 0 Short exposure with gain=15 to avoid saturation Long saturated exposure to detect faint satellites Short exposure with gain=15 to avoid saturation Long saturated exposure to detect faint satellites Long saturated exposure to detect faint satellites Short exposure with gain=15 to avoid saturation Long saturated exposure to detect faint satellites Using ephemeris for target 11969-04-CERES ephemeris data for target 11969-04-CERES does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 07.182 to 09.335. ephemeris interval: 08.335 to 10.317 Timing link suitability includes constraints ([Sequence (03 04) within 0.1 days]) The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 11969 :visit-id "04" :proposal-version -1 :trans-version "20080807" :date "06-Jan-2009 12:53:49.0" :trans-errors '(:WARNINGS 2 :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 717056 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11969 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Obset :proposal-id 11969 :visit-id "04" :obset-id "A4" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11969 :visit-id "04" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2754 :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 3132 :pcs-gap 0 ) true 1 0 Short exposure with gain=15 to avoid saturation Long saturated exposure to detect faint satellites Short exposure with gain=15 to avoid saturation Long saturated exposure to detect faint satellites Long saturated exposure to detect faint satellites Short exposure with gain=15 to avoid saturation Long saturated exposure to detect faint satellites