13199( 8) - 05-Apr-2013 11:36:01 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13199 Version: 8 Check-in Time: 05-Apr-2013 11:36:01 STScI Edit Number: 0 Title Imaging Polarimetry of the 2013 Comet ISON with ACS: A Pre-Perihelion Study of the Heterogeneous Coma ------------------------------------------------------------------------------------ Type Cycle GO/DD 20 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Dean C. Hines Space Telescope Science Institute Y CoI: Dr. Gorden Videen Space Science Institute N CoI: Dr. Yuri G. Shkuratov Kharkiv National University N CoI: Dr. Evgenij Zubko University of Helsinki N CoI: Dr. Karri Muinonen University of Helsinki N CoI: Dr. Michael L. Sitko Space Science Institute N CoI: Dr. Matthew M Knight Lowell Observatory N CoI: Dr. Carey M Lisse The Johns Hopkins University Applied N Physics Laboratory CoI: Dr. Derek Hammer Space Telescope Science Institute N ------------------------------------------------------------------------------------ Abstract We propose for Director's Discretionary time to obtain ACS/WFC polarimetric images of Comet C/2012 S1 (ISON) on its pre-perihelion approach to the inner solar system before it becomes unobservable by HST. Comet ISON is a sungrazer on a nearly parabolic trajectory, similar to that of the Great Comet of 1680, and likely carries pristine material dating to the time of the solar-system formation. Recent polarimetric observations of other comets have found that different regions of the coma produce different polarimetric light-scattering responses, indicating that different portions of the coma contain different materials. The presence of a strongly negatively polarizing circumnucleus halo region that has been observed very near the nucleus of several comets suggest a depletion of absorbing, carbonaceous particles in this region. High spatial-resolution ACS polarimetric images of Comet ISON not only can be used to place bounds on the material constituents of different regions of its coma, but can also be used to explore its dynamics and acquire an understanding of the radiation-coma interaction that accounts for coma heterogeneities. ------------------------------------------------------------------------------------ Observations Description ------------------------ We use the ACS/WFC and the POLV* + F606W polarizer/filter combinations to measure the polarization. Instead of using CR-SPLIT, we execute two separate exposures per polarizer/filter combination. This enables us to fit the observations within two consecutive orbits, and still achieve the advantages of CR-SPLIT. Real Time Justification ----------------------- Calibration Justification 13199( 8) - 05-Apr-2013 11:36:01 - [ 2] ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 13199( 8) - 05-Apr-2013 11:36:01 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: ISON ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET Comet C/2012 S1 (ISON) ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=0.01250228833615271 , E=1.000004178571949, I=61.86120174134099, O=295.7371915514632, W=345.5093083227027, T=28-NOV-2013:18:42:10, TTimeScale=TDT, EQUINOX=J2000, EPOCH=08-JAN-2013:00:00:00, EpochTimeScale=TDT ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 14.8 +/- 0.5 Target Ephemeris is from JPL Small-Body Database Browser. The solution date is 2013-Mar-24 20:50:46, and is JPL#20 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 13199( 8) - 05-Apr-2013 11:36:01 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type ACS-WFC-DITHER-LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 3.011 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 85.28 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 13199( 8) - 05-Apr-2013 11:36:01 - [ 5] Visit: 01 Visit Requirements: PCS MODE FINE; SCHED 30%; BETWEEN 07-MAY-2013 AND 09-MAY-2013 On Hold Comments: Additional Comments: These observations need to be made on or before May 7, 2013. However, they need to be scheduled as close to May 7 as possible. We definitely don't want them scheduled before May 6 if at all possible. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ISON ACS/WFC ACCUM WFC F606W, 1 710 S PATTERN 1 1 POL0V see below ------------------------------------------------------------------------------------------------------------------------------------ 2 ISON ACS/WFC ACCUM WFC F606W, 1 710 S PATTERN 1 2 POL60V see below ------------------------------------------------------------------------------------------------------------------------------------ 3 ISON ACS/WFC ACCUM WFC F606W, 1 710 S PATTERN 1 3 POL120V see below ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ ISON 1 ACS/WFC ACCUM WFC F606W, 1 none none none 1 749.0 S POL0V ISON 1 ACS/WFC ACCUM WFC F606W, 2 none none none 1 749.0 S POL0V ISON 2 ACS/WFC ACCUM WFC F606W, 1 none none none 1 655.0 S POL60V ISON 2 ACS/WFC ACCUM WFC F606W, 2 none none none 2 843.0 S POL60V ISON 3 ACS/WFC ACCUM WFC F606W, 1 none none none 2 749.0 S POL120V ISON 3 ACS/WFC ACCUM WFC F606W, 2 none none none 2 749.0 S POL120V 13199( 8) - 05-Apr-2013 11:36:01 - [ 6] Summary Form for Proposal 13199 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 07-MAY-2013 AND 09-MAY-2013, PATTERN 1 1, PATTERN 1 2, PATTERN 1 3, PCS MODE FINE, SCHED 30% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W, POL0V, POL120V, POL60V ------------------------------------------------------------------------------------------------------------------------------------ Target Names ISON ------------------------------------------------------------------------------------------------------------------------------------