15328( 3) - 16-Jan-2018 16:18:44 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15328 Version: 3 Check-in Time: 16-Jan-2018 16:18:44 STScI Edit Number: 0 Title Orbital period and formation process of the exceptional binary asteroid system 288P ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Jessica Agarwal Max Planck Institute for Solar System Y Research CoI: Dr. David Jewitt University of California - Los Angeles Y CoI: Max Mutchler Space Telescope Science Institute Y CoI: Dr. Harold A. Weaver The Johns Hopkins University Applied N Physics Laboratory CoI: Dr. Stephen M. Larson University of Arizona N ------------------------------------------------------------------------------------ Abstract The 288P (300163) binary asteroid system is unique and puzzling for its unusual combination of properties. It combines a wide separation with near-equal component sizes, and a high eccentricity with alignment of the mutual and heliocentric orbital planes. In addition, it is one of five known active asteroids with sublimation-driven dust production. Orbital fits to high-resolution data obtained in Cycle 24 are inconclusive regarding the orbital period and therefore the total angular momentum content, crucial to discriminate between formation of the binary system via rotational fission or impact. We request five orbits of HST/WFC3 time to measure the time evolution of the component separation under the favourable viewing geometry along the system's minor axis around the perigee passage in December 2017, to constrain with high certainty the orbital period and eccentricity of the system, and therefore its total angular momentum content. This is crucial to discriminate between the two formation scenarios and to understand the connection between the activity and the binary nature. As 288P is heading towards aphelion, the next opportunity to resolve its components will be in 2021. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to observe 288P at five epochs between 2017 August and 2018 February. The timing of each visit is flexible within +/-1 week. The first two visits will distiguish between different groups of orbit solutions compatible with Cycle 24 data. Visits 3-5 will serve to constrain the eccentricity of a Group 1 orbit, and to search for changes in the orbital elements induced by the activity. All five orbits will be suited for the search for additional satellites. We expect each component to have V~22. The orbital visibility for a solar system target near the ecliptic plane is 54 min (Section 6.3 of the HST Primer document). In each orbit, we will take 8 exposures of ~225s using the 1k subarray of WFC3 and perform a subsampling dither box pattern, obtaining 2 exposures at each dither point. We will carefully drizzle our subsampled images to a finer output 15328( 3) - 16-Jan-2018 16:18:44 - [ 2] pixel scale to extract the extra spatial information gathered by our subsampling strategy. This enhanced resolution will give us the highest accuracy in measuring the projected component distance and thus constrain their mutual orbit. The dithering will also enable us to reject hot pixels and cosmic ray hits. This strategy gives us a total exposure time of 1800s = 30min, and estimated overheads of 6min for guide-star acquisition, 2.6min for the first exposure, a total of 14.7min for the subsequent 7 exposures, and 1.5min for the three spacecraft maneuvers required for dithering, which adds up to a total execution time of 54min per orbit. This dither strategy is identical to the one employed successfully during Cycle 24, ensuring maximum comparability of the data. We will use the wide bandpass filter F606W for an optimum trade-off between sensitivity and highest resolution: the bandpass (475 -- 700 nm) covers the maximum of the solar spectrum, and is in the wavelength range where the PSF is smallest (FWHM<0.07 arcsec, from the WFC3 Instrument Handbook for Cycle 25), such that we can optimally exploit our subsampling dither strategy. In addition, F606W is the same filter we used to observe 288P in GO 12597, 14790, 14864, and 14884, enabling a direct comparison of the data sets. The WFC3 exposure time calculator returns for a solar-spectrum point source at V=22, exposure time of 225s, F606W filter, and default background values a signal-to-noise-ratio of 79 within a circle of 0.08 arcsec (ETC Request ID: WFC3UVIS.im.939003). The small aperture is needed to separate the fluxes from the two components as far as possible given the expected overlapping of the PSFs. A point source at V=27.4 will be detectable at SNR=5 in the standard 0.2arcsec aperture after stacking all eight exposures, allowing us to search for additional satellites down to a diameter of 130m that may have been hidden in the dust during all previous HST observations of the system (for an assumed geometric albedo of 0.04, heliocentric and geocentric distances of 3 and 2 AU, respectively, and during opposition). To discriminate between different orbital period regimes (Group 2 vs. Group 1+3), it is critical that the system be observed at very specific times, when the predicted component separation differs maximally between the two regimes. Therefore, Visits 1 and 2 should be scheduled within +/-1 week of 2017 August 28 and November 16. Visits 3 - 5 should follow in ~1 month steps between late December and late February to take full advantage of the perigee passage on December 31, ensuring maximum angular separation and maximum sensitivity of the component separation to the eccentricity at apoapsis. The optimum timing of Visit 1 implies that we request early implementation a month prior to the beginning of Cycle 25 (change request 88265 submitted on June 29, 2017). We could not request this observation in a Cycle 24 mid-cycle proposal, because the last data on which the current orbit fit is based were aquired only one day prior to the second mid-cycle deadline. ------------------------------------------------------------------------------------ 15328( 3) - 16-Jan-2018 16:18:44 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: 288P ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET Comet 288P (300163, VW139) ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=2.433757796112896, E=0.201280124072449, I=3.240701450960771, O=83.19018988764668, W=281.3064762224968, T=16-JUL-2011:11:50:43, TTimeScale=TDB, EQUINOX=J2000, EPOCH=18-AUG-2013:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 22 +/- 1 Ephemeris Center: EARTH Extended: NO ------------------------------------------------------------------------------------------------------------------------------------ 15328( 3) - 16-Jan-2018 16:18:44 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 15328( 3) - 16-Jan-2018 16:18:44 - [ 5] Visit: 01 Visit Requirements: BETWEEN 21-AUG-2017:00:00:00 AND 04-SEP-2017:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 288P WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO 2 230 S PATTERN 1 1 S 1C-SUB (1840 S) Comments: The flash warning is not triggered if running the ETC with the zodiacal light calculated for the actual sky positions of the target at the targeted epochs of visits 1-5. The background is on Aug-20 45 e-/px, and between 17 and 20 e-/px for visits 2-5. (ETC runs WFC3UVIS.im.1004647, 1004651, 1004654, 1004655, 1004656). ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 2 none 1 N/A S K1C-SUB 15328( 3) - 16-Jan-2018 16:18:44 - [ 6] Visit: 02 Visit Requirements: BETWEEN 09-NOV-2017:00:00:00 AND 23-NOV-2017:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 288P WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO 2 230 S PATTERN 1 1 S 1C-SUB (1840 S) Comments: The flash warning is not triggered if running the ETC with the zodiacal light calculated for the actual sky positions of the target at the targeted epochs of visits 1-5. The background is on Aug-20 45 e-/px, and between 17 and 20 e-/px for visits 2-5. (ETC runs WFC3UVIS.im.1004647, 1004651, 1004654, 1004655, 1004656). ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 2 none 1 N/A S K1C-SUB 15328( 3) - 16-Jan-2018 16:18:44 - [ 7] Visit: 03 Visit Requirements: BETWEEN 24-DEC-2017:00:00:00 AND 07-JAN-2018:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 288P WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO 2 230 S PATTERN 1 1 S 1C-SUB (1840 S) Comments: The flash warning is not triggered if running the ETC with the zodiacal light calculated for the actual sky positions of the target at the targeted epochs of visits 1-5. The background is on Aug-20 45 e-/px, and between 17 and 20 e-/px for visits 2-5. (ETC runs WFC3UVIS.im.1004647, 1004651, 1004654, 1004655, 1004656). ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 2 none 1 N/A S K1C-SUB 15328( 3) - 16-Jan-2018 16:18:44 - [ 8] Visit: 04 Visit Requirements: BETWEEN 24-JAN-2018:00:00:00 AND 07-FEB-2018:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 288P WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO 2 230 S PATTERN 1 1 S 1C-SUB (1840 S) Comments: The flash warning is not triggered if running the ETC with the zodiacal light calculated for the actual sky positions of the target at the targeted epochs of visits 1-5. The background is on Aug-20 45 e-/px, and between 17 and 20 e-/px for visits 2-5. (ETC runs WFC3UVIS.im.1004647, 1004651, 1004654, 1004655, 1004656). ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 2 none 1 N/A S K1C-SUB 15328( 3) - 16-Jan-2018 16:18:44 - [ 9] Visit: 05 Visit Requirements: BETWEEN 24-FEB-2018:00:00:00 AND 10-MAR-2018:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 288P WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO 2 230 S PATTERN 1 1 S 1C-SUB (1840 S) Comments: The flash warning is not triggered if running the ETC with the zodiacal light calculated for the actual sky positions of the target at the targeted epochs of visits 1-5. The background is on Aug-20 45 e-/px, and between 17 and 20 e-/px for visits 2-5. (ETC runs WFC3UVIS.im.1004647, 1004651, 1004654, 1004655, 1004656). ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 2 none 1 N/A S K1C-SUB 15328( 3) - 16-Jan-2018 16:18:44 - [ 10] Visit: 06 Visit Requirements: BETWEEN 06-MAY-2018:00:00:00 AND 20-MAY-2018:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 288P WFC3/UVI ACCUM UVIS2-C1K F606W CR-SPLIT=NO 2 230 S PATTERN 1 1 S 1C-SUB (1840 S) Comments: The flash warning is not triggered if running the ETC with the zodiacal light calculated for the actual sky positions of the target at the targeted epoch of visit 6. The background on May-15 is 15 e-/px (ETC runs WFC3UVIS.im.1045051). ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 1 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 2 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 3 none 2 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 1 none 1 N/A S K1C-SUB 288P 1 WFC3/UVI ACCUM UVIS2-C1 F606W 4 none 2 none 1 N/A S K1C-SUB 15328( 3) - 16-Jan-2018 16:18:44 - [ 11] Summary Form for Proposal 15328 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C1K1C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 06-MAY-2018:00:00:00 AND 20-MAY-2018:00:00:00, BETWEEN 09-NOV-2017:00:00:00 AND 23-NOV-2017:00:00:00, BETWEEN 21-AUG-2017:00:00:00 AND 04-SEP-2017:00:00:00, BETWEEN 24-DEC-2017:00:00:00 AND 07-JAN-2018:00:00:00, BETWEEN 24-FEB-2018:00:00:00 AND 10-MAR-2018:00:00:00, BETWEEN 24-JAN-2018:00:00:00 AND 07-FEB-2018:00:00:00, PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F606W ------------------------------------------------------------------------------------------------------------------------------------ Target Names 288P ------------------------------------------------------------------------------------------------------------------------------------