16087( 17) - 28-Jul-2020 12:21:58 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16087 Version: 17 Check-in Time: 28-Jul-2020 12:21:58 STScI Edit Number: 9 Title Optical Evolution of Interstellar Object 2I/Borisov ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: 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 Y Physics Laboratory CoI: Dr. Yoonyoung Kim Max Planck Institute for Solar System N Research CoI: Dr. Man-To Hui University of Hawaii N CoI: Dr. Jessica Agarwal Technische Universitaet Braunschweig N ------------------------------------------------------------------------------------ Abstract We propose a 5 orbit study designed to continue characterization of the changing activity of interstellar object 2I/Borisov (formerly C/2019 Q4) in the post-perihelion phase. We will assess the dust particle ejection using data from a range of viewing perspectives as input to an established Monte Carlo dynamics model, to infer particle size, size distribution, velocity and velocity distribution, for comparison with dust populations in solar system comets. Observations as the HST crosses the projected orbit plane will probe the out-of-plane distribution of dust. As the comet recedes (to 6 AU at the end of Cycle 27) and consequently cools and fades, we will probe the near-nucleus region with less and less contamination by dust. The proposed observations capitalize on the high angular resolution of HST, and will extend time-sequence observations of this unique object obtained in public-domain data with the same observational set-up under GO 16009 and 16041. ------------------------------------------------------------------------------------ Observations Description ------------------------ We request 5 mid-cycle orbits using WFC3 and the F350LP filter to image 2I in the remainder of Cycle 27 (ending 2020 Sep 30, when rH = 6.6 AU). The broad F350LP filter (effective center 6230A, FWHM 4760A) gives maximum sensitivity to faint coma. The orbits would be spaced by about one month to give sampling complementary to that already obtained. In one month, 2I moves away from the Sun by another 0.5 AU. Precise timing of the visits is not critical, except for V4, which is designed to image 2I from a vantage point in the orbit plane of the object (on UT 2020 July 31). This perspective provides unique constraints on the out-of- plane distribution of dust, and will be used to assess the dust ejection velocity. Mid-Cycle observations extending from the first visit on 2019 Oct 12 (GO 16009) to the end of Cycle 27 on 2020 September 30 (this proposal) will provide the most complete and yet economical sampling of the time-varying activity of this remarkable object. We expect that all of the observations will be immediately in the public domain. We will secure six 270 s integrations in each orbit, with dithering to provide protection from chip defects. According to the WFC3 ETC, a single 270 s exposure reaches V=26.5 at 16087( 17) - 28-Jul-2020 12:21:58 - [ 2] SNR=5. Combing 6 images will take us 1 magnitude fainter, to V=27.5, and will also provide protection from cosmic ray strikes on individual images. Deep imaging is needed to assess the near-nucleus environment and identify fragments, or set limits to their presence. We will also use individual images to examine photometric stability of the core on the (~1 hour) orbital timescale. Sub-pixel astrometry from all orbits will assist with orbit fitting and the search for non- gravitational acceleration. The 3-sigma ephemeris uncertainty is currently < 5 arcsec through the remainder of this Cycle and will shrink as more astrometry is added to the orbit fit. Therefore, ephemeris uncertainties are of no concern to the proposed observations. 2I is outside the 55 deg HST Sun exclusion zone for the entire proposal period. Visits V1, V2, V3 are single-orbit visits spaced approximately monthly in order to monitor the time- dependence of the morphology and photometry at the highest resolution. The first observation, V1, is requested near DOY 105+/-10 days, in order to observe the comet from the maximum angle of the Earth above the orbital plane. This perspective provides the clearest separation of particle trajectories in the orbital plane, essential for accurate Monte Carlo modeling. Visits V2 (DOY 145+/-10) and V3 (DOY 180+/-10) span the interval to V4 and plane-crossing. Visit V4 is requested to coincide with orbit plane crossing on UT 2020 July 31. The angle above the plane varies by about 0.1 degree per day at this time, so that observations to within < 0.1 degree of plane crossing provide should be readily scheduled and will provide a strong measure of the out-of-plane extent of the coma. Visit V5 is requested as close as possible to the end of Cycle 27, by which time 2I will be outbound at 6.6 AU from the Sun (greater than the discovery distance) and Earth will be 5 degrees below the orbit plane. V4 is the only orbit for which the constraint is tight: we need to be within 1 day of July 31d 03h in order to attain the in-plane geometry and the closer to this time the better. We understand that we will have essentially no control over the spacecraft roll angle, which means that we will not be able to optimize the orientation of the dust coma on the CCD (e.g., to orient the tail along the longest dimension of the detector). However, the field-of-view of the camera is large enough and the target coma small enough that we should obtain excellent data, no matter what spacecraft roll angle is used. ------------------------------------------------------------------------------------ 16087( 17) - 28-Jul-2020 12:21:58 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 3 TARGET NAME: C2019-Q4-V11 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET Interstellar comet ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=2.006615476559197, E=3.357057274677898, I=44.05348671638512 , O=308.1499528970442, W=209.124397765598, T=08-DEC-2019:13:18:12, TTimeScale=TDB, EQUINOX=J2000, EPOCH=05-JAN-2020:00:00:00, EpochTimeScale=TDB, R0=2.808 , DT=0. , A1=-4.111801624298E-8, A2=-2.939796209335E-8, A3=-1.149449539185E-7 , ALN=0.1112620426, NM=2.15, NN=5.093, NK=4.6142, AMRAT=0. ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 16 +/- 2 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 16087( 17) - 28-Jul-2020 12:21:58 - [ 4] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 4 TARGET NAME: C2019-Q4-V12 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET Interstellar comet ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=2.006624008587265, E=3.356191268153205, I=44.05262620283894 , O=308.1489154698829, W=209.1246056235187, T=08-DEC-2019:13:04:38, TTimeScale=TDB, EQUINOX=J2000, EPOCH=31-JUL-2020:00:00:00, EpochTimeScale=TDB, R0=2.808 , DT=0. , A1=7.312064170837E-8, A2=-3.252092599869E-8, A3=0. , ALN=0.1112620426, NM=2.15, NN=5.093, NK=4.6142, AMRAT=0. ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 16 +/- 2 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 16087( 17) - 28-Jul-2020 12:21:58 - [ 5] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type LINE Pattern_Purpose DITHER Number_Of_Points 2 Point_Spacing 0.8 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 45 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 16087( 17) - 28-Jul-2020 12:21:58 - [ 6] Visit: 11 Visit Requirements: BETWEEN 30-MAR-2020:06:00:00 AND 30-MAR-2020:13:00:00; BETWEEN 01-APR-2020:12:00:00 AND 02-APR-2020:01:00:00 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 C2019-Q4-V1 WFC3/UVI ACCUM UVIS2-2K2 F350LP CR-SPLIT=NO 3 260 S POS TARG 10, 15; SEQ 1 1 S C-SUB (1560 S) NON-INT; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ C2019-Q4-V11 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 1 none 1 N/A S 2C-SUB C2019-Q4-V11 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 2 none 1 N/A S 2C-SUB C2019-Q4-V11 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 3 none 1 N/A S 2C-SUB C2019-Q4-V11 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 1 none 1 N/A S 2C-SUB C2019-Q4-V11 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 2 none 1 N/A S 2C-SUB C2019-Q4-V11 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 3 none 1 N/A S 2C-SUB 16087( 17) - 28-Jul-2020 12:21:58 - [ 7] Visit: 12 Visit Requirements: BETWEEN 13-APR-2020:10:00:00 AND 15-APR-2020:13:00:00 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 C2019-Q4-V1 WFC3/UVI ACCUM UVIS2-2K2 F350LP CR-SPLIT=NO 3 260 S POS TARG 15, 15; SEQ 1 2 S C-SUB (1560 S) NON-INT; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 1 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 2 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 3 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 1 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 2 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 3 none 1 N/A S 2C-SUB 16087( 17) - 28-Jul-2020 12:21:58 - [ 8] Visit: 13 Visit Requirements: BETWEEN 19-APR-2020:00:00:00 AND 20-APR-2020:16:00:00 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 C2019-Q4-V1 WFC3/UVI ACCUM UVIS2-2K2 F350LP CR-SPLIT=NO 3 260 S (780 POS TARG 15, 15; SEQ 1-2 2 S C-SUB S) NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 C2019-Q4-V1 WFC3/UVI ACCUM UVIS2-2K2 F350LP CR-SPLIT=NO 2 260 S (520 POS TARG 16, 16 2 S C-SUB S) ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB C2019-Q4-V12 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB C2019-Q4-V12 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 16087( 17) - 28-Jul-2020 12:21:58 - [ 9] Visit: 14 Visit Requirements: SCHED 30%; BETWEEN 30-JUL-2020:22:00:00 AND 01-AUG-2020:03:00:00 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 C2019-Q4-V1 WFC3/UVI ACCUM UVIS2-2K2 F350LP CR-SPLIT=NO 3 260 S POS TARG 15, 15; SEQ 1 2 S C-SUB (1560 S) NON-INT; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 1 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 2 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 3 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 1 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 2 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 3 none 1 N/A S 2C-SUB 16087( 17) - 28-Jul-2020 12:21:58 - [ 10] Visit: 15 Visit Requirements: BETWEEN 09-SEP-2020:00:00:00 AND 17-SEP-2020:21:00:00 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 C2019-Q4-V1 WFC3/UVI ACCUM UVIS2-2K2 F350LP CR-SPLIT=NO 3 260 S POS TARG 15, 15; SEQ 1 2 S C-SUB (1560 S) NON-INT; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 1 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 2 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 1 none 3 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 1 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 2 none 1 N/A S 2C-SUB C2019-Q4-V12 1 WFC3/UVI ACCUM UVIS2-2K F350LP 2 none 3 none 1 N/A S 2C-SUB 16087( 17) - 28-Jul-2020 12:21:58 - [ 11] Summary Form for Proposal 16087 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-2K2C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-APR-2020:12:00:00 AND 02-APR-2020:01:00:00, BETWEEN 09-SEP-2020:00:00:00 AND 17-SEP-2020:21:00:00, BETWEEN 13-APR-2020:10:00:00 AND 15-APR-2020:13:00:00, BETWEEN 19-APR-2020:00:00:00 AND 20-APR-2020:16:00:00, BETWEEN 30-JUL-2020:22:00:00 AND 01-AUG-2020:03:00:00, BETWEEN 30-MAR-2020:06:00:00 AND 30-MAR-2020:13:00:00, PATTERN 1 1, POS TARG 10, 15, POS TARG 15, 15, POS TARG 16, 16, SCHED 30%, SEQ 1 NON-INT, SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names C2019-Q4-V11, C2019-Q4-V12 ------------------------------------------------------------------------------------------------------------------------------------