----- Attempting Submission 1 (Thu May 10 20:47:03 GMT 2007) ----- Dear HST TAC We are submitting a revised HST/ACS proposal in correspondance to the recently failure of ACS. This proposal is modified from an already submitted Cycle 16 GO proposal ID 324 with the same title: "Characterization of the UV absorption feature in asteroid (1) Ceres". Thank you! Jianyang Li Assigned ID: 1387 ----- Attempting Submission 1 (Fri Feb 09 21:40:00 GMT 2007) ----- Phase I Proposal 1387 (Cycle16_Ceres_UV_rev) successfully submitted. Characterization of the UV absorption feature in asteroid (1) Ceres We propose to obtain the UV spectrum of asteroid (1) Ceres from 120 nm to 200 nm with ACS/SBC objective prism to characterize the broad and deep absorption feature within this wavelength range as reported by ACS observations of Ceres in 2003/04 (Li et al. 2006). Our scientific goals include, 1) to characterize the absorption band, 2) to determine the origin of this spectral feature and constrain the surface composition of Ceres, and 3) to understand the albedo and color features on Ceres. HST is the only observatory currently capable of obtaining spectroscopy in this wavelength range. This observation will help improve our knowledge about this largest and oldest asteroid, and support the planning of the upcoming NASA Discovery Program mission, Dawn, orbiting asteroids Vesta and Ceres.
We plan to obtain the UV spectrum of Ceres from 120 nm to 200 nm during its opposition and close approach to Earth in November 2007 through ACS/SBC objective prism PR130L. This spectrum will fill in the gap in wavelength coverage in the UV spectra of Ceres that have been measured to date, and help us confirm the absorption feature that has been recently identified, and to characterize it. We will dedicate all three orbits to building up the signal-to-noise ratio for the UV spectrum. Due to the slitless nature of ACS/SBC spectrum, and the relatively large size of Ceres (0.7"), the spectrum will be processed with deconvolution techniques to restore the spectral resolution. The results will help us understand the physical nature of this deep and broad absorption feature, identify the surface compositin of Ceres, and interpret its albedo and color features reported recently from the HST/ACS images of Ceres. The program will provide important knowledge of the surface of Ceres before the Dawn spacecraft arrives this dwarf planet. SOLAR SYSTEM 12 false 0.0 false false false false false false SUPPORTED SOLAR SYSTEM angular diameter 0.71 arcsec, surface brightness 6.25 mag arcsec-2 ASTEROID Asteroid Ceres TYPE=ASTEROID,A=2.76595642396794,E=0.07976017327383,I=10.5867116079954,O=80.4069591479241,W=73.15073411326651,M=215.800962246862,EQUINOX=J2000,EPOCH=10-APR-2007:00:00:00 ACS/SBC Imaging No No F150LP ACS/SBC Spectroscopic No No PR130L C:\Documents and Settings\Jianyang\Local Settings\Temp\OPVisit20941.xml The time requirement for this observation has two purposes: 1) to ensure high S/N; 2) to ensure large angular size for Ceres' disk for the purpose of spectral resolution restoration. The observation should be scheduled as close to the opposition of Ceres as possible, which occurs around Nov 13. 10% surface brightness drop allowance will relax the time requirement to between Nov 1 and Nov 20, and 20% allowance will relax it to between Oct 25 and Nov 27. The angular size window will be between Oct 17 and Dec 8 for less than 5% decrease from the maximum. Thus the best time of observation to ensure the quality of spectrum is between Oct 25 and Nov 27. According to Visit Planner, there are two periods of schedulable time. Perferably, the observation is scheduled close to the beginning of the second period, or close to the end of the first period if the first option is not available. (Tic-Visit :proposal-id 11109 :visit-id "01" :proposal-version -1 :trans-version "20070326" :date "10-May-2007 16:02:06.0" :trans-errors '(:WARNINGS 0 :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 222160 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11109 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11109 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2767 :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 ) (Tic-Orbit :proposal-id 11109 :visit-id "01" :orbit-number 2 :pcs-time 355 :si-vis-utilization 2762 :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 ) (Tic-Orbit :proposal-id 11109 :visit-id "01" :orbit-number 3 :pcs-time 355 :si-vis-utilization 2762 :al-overhead-at-end 0 :internal-dur-at-end 281 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3132 :pcs-gap 0 ) true 3 0 C:\Documents and Settings\Jianyang\Local Settings\Temp\OPVisit2505.xml We modified the filter for the image mode from F150LP as proposed in Phase I to F125LP, in order to obtain higher S/N for the image. As estimated from ACS ETC, the exposure will not saturate detector at any covered wavelength for any exposure time within an orbit. Therefore the exposure time for this exposure should be adjusted to the maximum allowed time within the usable time of an orbit once the visit is scheduled. We modified the filter for the image mode from F150LP as proposed in Phase I to F125LP, in order to obtain higher S/N for the image. As estimated from ACS ETC, the exposure will not saturate detector at any covered wavelength for any exposure time within an orbit. Therefore the exposure time for this exposure should be adjusted to the maximum allowed time within the usable time of an orbit once the visit is scheduled. We modified the filter for the image mode from F150LP as proposed in Phase I to F125LP, in order to obtain higher S/N for the image. As estimated from ACS ETC, the exposure will not saturate detector at any wavelength for any exposure time within an orbit. Therefore the exposure time for this exposure should be adjusted to the maximum allowed time within the usable time of an orbit once the visit is scheduled.