11109( 2) - 05/11/07 06:54 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11109 Version: 2 Check-in Time: 11-May-2007 10:53:51 STScI Edit Number: 0 Title Characterization of the UV absorption feature in asteroid (1) Ceres ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO 16 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Jian-Yang Li University of Maryland CoI: Dr. Lucy-Ann McFadden University of Maryland N CoI: Dr. Christopher T. Russell University of California - Los Angeles N CoI: Dr. Michael F. A'Hearn University of Maryland N CoI: Dr. Eleonora Ammannito CNR, Istituto di Radioastronomia N CoI: Dr. A. Coradini CNR, Istituto di Radioastronomia N CoI: Dr. Cristina De Sanctis CNR, Istituto di Radioastronomia N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ 11109( 2) - 05/11/07 06:54 - [ 2] Observations Description ------------------------ 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. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 11109( 2) - 05/11/07 06:54 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: CERES ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: ASTEROID Asteroid Ceres ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE=ASTEROID,A=2.76595642396794,E=0.079 | 76017327383,I=10.5867116079954,O=80.4069 | 591479241,W=73.15073411326651,M=215.8009 | 62246862,EPOCH=10-Apr-2007,EQUINOX=J2000 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 7.25+/-0.1 | angular diameter 0.71 arcsec | surface brightness 6.25 mag arcsec-2 | | ------------------------------------------------------------------------------------------------------------------------------------ 11109( 2) - 05/11/07 06:54 - [ 4] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 25-OCT-2007:00:00:00 AND 27-NOV-2007:23:59:59 On Hold Comments: Additional Comments: 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. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 CERES ACS/SBC ACCUM SBC F125LP 1 600 S Comments: 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. ------------------------------------------------------------------------------------------------------------------------------------ 2 CERES ACS/SBC ACCUM SBC PR130L 3 630 S Comments: 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. ------------------------------------------------------------------------------------------------------------------------------------ 3 CERES ACS/SBC ACCUM SBC F125LP 1 600 S Comments: 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. ------------------------------------------------------------------------------------------------------------------------------------ 4 CERES ACS/SBC ACCUM SBC PR130L 3 625 S Comments: 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. ------------------------------------------------------------------------------------------------------------------------------------ 11109( 2) - 05/11/07 06:54 - [ 5] Exposures ----------------------------------------------------------------------------------------------------------------------------------- Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ----------------------------------------------------------------------------------------------------------------------------------- 5 CERES ACS/SBC ACCUM SBC F125LP 1 600 S Comments: 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. ------------------------------------------------------------------------------------------------------------------------------------ 6 CERES ACS/SBC ACCUM SBC PR130L 3 625 S Comments: 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. ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ CERES 1 ACS/SBC ACCUM SBC F125LP none none none none 1 N/A CERES 2 ACS/SBC ACCUM SBC PR130L none none 1 none 1 N/A CERES 2 ACS/SBC ACCUM SBC PR130L none none 2 none 1 N/A CERES 2 ACS/SBC ACCUM SBC PR130L none none 3 none 1 N/A CERES 3 ACS/SBC ACCUM SBC F125LP none none none none 2 N/A CERES 4 ACS/SBC ACCUM SBC PR130L none none 1 none 2 N/A CERES 4 ACS/SBC ACCUM SBC PR130L none none 2 none 2 N/A CERES 4 ACS/SBC ACCUM SBC PR130L none none 3 none 2 N/A CERES 5 ACS/SBC ACCUM SBC F125LP none none none none 3 N/A CERES 6 ACS/SBC ACCUM SBC PR130L none none 1 none 3 N/A CERES 6 ACS/SBC ACCUM SBC PR130L none none 2 none 3 N/A CERES 6 ACS/SBC ACCUM SBC PR130L none none 3 none 3 N/A 11109( 2) - 05/11/07 06:54 - [ 6] Summary Form for Proposal 11109 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures SBC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/SBC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 25-OCT-2007 00 00 00 AND 27-NOV-2007 23 59 59; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F125LP PR130L ------------------------------------------------------------------------------------------------------------------------------------ Target Names CERES ------------------------------------------------------------------------------------------------------------------------------------