16077( 3) - 07-Apr-2020 20:41:09 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16077 Version: 3 Check-in Time: 07-Apr-2020 20:41:09 STScI Edit Number: 1 Title Determining the cause of activity of the first active Trojan, 2019 LD2 ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Bryce Bolin California Institute of Technology Y CoI: Dr. Dennis Bodewits Auburn University N CoI: Dr. Yanga Fernandez University of Central Florida N CoI: Dr. Carey Michael Lisse The Johns Hopkins University Applied N Physics Laboratory ------------------------------------------------------------------------------------ Abstract We request three orbits of observing time to study the recently discovered activity of 2019 LD2, the first Jupiter Trojan asteroid observed to have a comet-like, active appearance. Dynamical models predict that most Trojan Asteroids originated in the TransNeptunian belt and should, therefore, contain volatiles that should be active at the present-day heliocentric distances of the Trojans. The main objective of this program is to observe the coma and near-nucleus region of 2019 LD2 to constrain the cause of its activity as to whether caused by the sublimation of volatiles as the origins of Trojans might suggest, or if the activity is caused by impact or rotational disruption. Thus we will be constraining the possible volatile content of Trojan asteroids by studying 2019 LD2 with HST. We will accomplish this goal by using the high-resolution capabilities to observe the dust behavior of 2019 LD2 and its evolution as it approaches perihelion in March and April 2020 where the sublimation of volatiles is expected to increase and when the orbital plane angle is minimized allowing for the measurement of the perpendicular velocity component of the ejected dust. We will also constrain the 2019 LD2's nucleus size using the advanced high-resolution capabilities of HST. The discovery and confirmation of the activity of 2019 LD2 did not occur until after the regular GO proposal deadline and waiting for cycle 28 will mean the dispersal of dust diagnosing the activity by Solar Radiation pressure. The detection of volatile-driven activity on the first known active Trojan will be tremendously exciting and will be useful for leveraging subsequent observations of this novel type of object. ------------------------------------------------------------------------------------ Observations Description ------------------------ We request a total of three visits each consisting of 1 orbit to characterize the coma of 2019 LD2 with WFC3/UVIS at three different epochs around when the Earth crosses its orbital plane during the first week of April 2020, a few weeks after perihelion passage of this comet on 2020 April 4 UTC and a few weeks to a month after the second visit. Our observation dates for the last two observations are flexible, but we require stricter scheduling for the first observation at around the orbital plane crossing during early April for our science goal of measuring the dust ejection velocity. We will acquire images in the F350LP filter for a maximum throughput of a Solar-like source which is expected for 2019 LD2. Each visit will consist of five 380 s exposures using 16077( 3) - 07-Apr-2020 20:41:09 - [ 2] the F350LP filter and the UVIS2 detector set up. This filter gives us the maximum throughput enabled by WFC3/UVIS in the 300 nm - 800 nm wavelength range for a Solar-like source which is expected of Solar System objects while allowing for a 0.04'' pixel scale. We will use the methodology of Jewitt et al. 2020 for color calibrations of the F350LP filter observations. This will give us a total exposure time of 1900 s while also providing image stacks robust to cosmic-rays. We will use line dithering to reduce the noise from flat-field calibration errors, cosmic rays, and residual images. We also request moving object support due to the nature of the target. 2019 LD2's apparent motion rate is currently ~25''/hr, which is well within the tracking capability of HST. According to the ephemerides provided by the JPL HORIZONS system (on 2019-10-08 UT), the positional uncertainty of 2019 LD2 is less than a few arcseconds in early April 2020, and should not pose any problem to the pointing. We understand that we have no control over the spacecraft roll angle and will plan our observations so that they place the target within the center of the UVIS2 chip so that the entire extent of the target will appear in the chip regardless of roll angle. ------------------------------------------------------------------------------------ 16077( 3) - 07-Apr-2020 20:41:09 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: 2019LD2 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET 2019_LD2 ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=4.581143657178035, E=0.1462955970904501, I=11.54447123343416 , O=181.0493574718406, W=120.7533777397608, T=27-MAR-2020:01:04:37, TTimeScale=TDB, EQUINOX=J2000, EPOCH=20-NOV-2018:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 19.7 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 16077( 3) - 07-Apr-2020 20:41:09 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type LINE Pattern_Purpose OTHER Number_Of_Points 5 Point_Spacing 0.03 Line_Spacing Coordinate_Frame CELESTIAL Pattern_Orient 0 Angle_Between_Sides Center_Pattern YES ------------------------------------------------------------------------------------------------------------------------------------ 16077( 3) - 07-Apr-2020 20:41:09 - [ 5] Visit: 01 Visit Requirements: BETWEEN 15-MAR-2020:00:00:00 AND 04-APR-2020:00:00:00 On Hold Comments: Additional Comments: I have a strong preference for this observations being carried out as soon as possible so that we can observe as close as possible to the orbital plane crossing occuring in the last week of March. 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 2019LD2 WFC3/UVI ACCUM UVIS2 F350LP 1 380 S POS TARG 0.099, 0.106; S see below PATTERN 1 1 (1925 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 1 none none none 1 385.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 2 none none none 1 385.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 3 none none none 1 385.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 4 none none none 1 385.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 5 none none none 1 385.0 S S 16077( 3) - 07-Apr-2020 20:41:09 - [ 6] Visit: 02 Visit Requirements: BETWEEN 08-MAY-2020:00:00:00 AND 12-JUN-2020:00:00:00 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 2019LD2 WFC3/UVI ACCUM UVIS2 F350LP 1 380 S POS TARG 0.297, 0.318; S see below PATTERN 1 1 (1925 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 1 none none none 1 385.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 2 none none none 1 385.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 3 none none none 1 385.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 4 none none none 1 385.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 5 none none none 1 385.0 S S 16077( 3) - 07-Apr-2020 20:41:09 - [ 7] Visit: 03 Visit Requirements: BETWEEN 18-JUL-2020:00:00:00 AND 20-AUG-2020:00:00:00 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 2019LD2 WFC3/UVI ACCUM UVIS2 F350LP 1 380 S POS TARG 0.198, 0.212; S see below PATTERN 1 1 (1850 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 1 none none none 1 370.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 2 none none none 1 370.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 3 none none none 1 370.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 4 none none none 1 370.0 S S 2019LD2 1 WFC3/UVI ACCUM UVIS2 F350LP 5 none none none 1 370.0 S S 16077( 3) - 07-Apr-2020 20:41:09 - [ 8] Summary Form for Proposal 16077 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 08-MAY-2020:00:00:00 AND 12-JUN-2020:00:00:00, BETWEEN 15-MAR-2020:00:00:00 AND 04-APR-2020:00:00:00, BETWEEN 18-JUL-2020:00:00:00 AND 20-AUG-2020:00:00:00, PATTERN 1 1, POS TARG 0.099, 0.106, POS TARG 0.198, 0.212, POS TARG 0.297, 0.318 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names 2019LD2 ------------------------------------------------------------------------------------------------------------------------------------