17848( 3) - 19-Jul-2024 15:07:21 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17848 Version: 3 Check-in Time: 19-Jul-2024 15:07:21 STScI Edit Number: 1 Title Astrometry for an Upcoming Double Occultation of Salacia-Actaea ------------------------------------------------------------------------------------ Type Cycle GO/DD 31 ------------------------------------------------------------------------------------ Investigators Contact? PI: Mr. Benjamin Proudfoot University of Central Florida Board of Y Trustees CoI: Dra. Estela Fernandez-Valenzuela University of Central Florida Board of N Trustees CoI: Dra. Flavia Luane Rommel University of Central Florida Board of N Trustees CoI: Dr. Simon Bernard Porter Southwest Research Institute N CoI: Dr. Jose Luis Ortiz Instituto de Astrofisica de Andalucia N (IAA) ------------------------------------------------------------------------------------ Abstract Binary trans-Neptunian objects (TNOs) are some of the most powerful tracers of solar system formation and evolution. One of the highest resolution way to study binary TNOs is by using stellar occultations, which enable direct determinations of the size and shape of each binary component. Although considerable effort has been expended targeting individual binary components, very few occultation campaigns have been able to simultaneously observe both binary components. On August 17th 2024, Salacia and its binary companion Actaea will occult a relatively bright star within 5 minutes of each other. This double occultation event will be visible along the same shadow path, allowing for a focused campaign to observe both bodies. Currently, uncertainties on the exact location of the shadow path are ~2500 km. We request two single-orbit visits to acquire both absolute and relative astrometry of the Salacia-Actaea system to allow for a more precise determination of the shadow path. Our observations will enable updated event predictions with uncertainties of ~300 km. The secondary science opportunities provided by the ultra-precise astrometry of the system are also substantial. ------------------------------------------------------------------------------------ Observations Description ------------------------ Observations are to be used for both relative (Actaea's position relative to Salacia) and absolute astrometry to provide precise predictions for an August 17 double occultation of Salacia and Actaea. To maximize efficiency of our observations during each visit, we request 4 images with a subarray to get relative astrometry, followed by 4 images with the full UVIS2 aperture. This maximizes exposure time over the orbit, with only one long buffer dump during the observations, and allows us to observe as many reference stars as possible during the observations. The "No gyro bias update" option was chosen to increase the orbital visibility to maximize exposure time on our single-orbit visits. Our observations use the a box dither to minimize per-pixel effects and optimally sample the PSFs of Salacia and Actaea. 17848( 3) - 19-Jul-2024 15:07:21 - [ 2] Visits are to occur at least 1 day apart to allow for orbital motion to accumulate. This also provides redundancy in the event of a guiding (or other) failure, as a HOPR would likely not allow rapid enough turnaround to reschedule observations before the August 17 occultation event. We have checked background fields to ensure that nearby bright field stars will not contaminate the relative astrometry, while also ensuring that enough reference stars are within the large aperture images. Both visits leave some "unused orbital visibility" when using the Orbit Planner. This has been purposefully included to increase the schedulability of the observations. If difficulties arrive in scheduling, we are happy to change number of exposures and/or exposure time to allow for better schedulability. ------------------------------------------------------------------------------------ 17848( 3) - 19-Jul-2024 15:07:21 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: SALACIA ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: DWARF-PLANET Dwarf planet with moon, Actaea (V ~ 23.3) ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=ASTEROID, A=41.91864340424245, E=0.1098795382573878, I=23.9261520468926 , O=279.9835651860334, W=309.1996740556897, M=122.8445075195537, EQUINOX=J2000, EPOCH=04-NOV-2017:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 20.8 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 17848( 3) - 19-Jul-2024 15:07:21 - [ 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 ------------------------------------------------------------------------------------------------------------------------------------ 17848( 3) - 19-Jul-2024 15:07:21 - [ 5] Visit: 01 Visit Requirements: BEFORE 03-AUG-2024:00:00:00; VISIBILITY INTERVAL NO GYRO BIAS UPDATE ON MOVING TARGET 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 SALACIA WFC3/UVI ACCUM UVIS2-C51 F350LP FLASH=7 1 120 S (480 GS ACQ SCENARIO ONEB1O3; S 2C-SUB S) SEQ 1-2 NON-INT; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 SALACIA WFC3/UVI ACCUM UVIS2 F350LP FLASH=12 1 60 S (240 PATTERN 1 2 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ SALACIA 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none none none tbd N/A S 12C-SUB SALACIA 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none none none tbd N/A S 12C-SUB SALACIA 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none none none tbd N/A S 12C-SUB SALACIA 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 4 none none none tbd N/A S 12C-SUB SALACIA 2 WFC3/UVI ACCUM UVIS2 F350LP 1 none none none tbd N/A S SALACIA 2 WFC3/UVI ACCUM UVIS2 F350LP 2 none none none tbd N/A S SALACIA 2 WFC3/UVI ACCUM UVIS2 F350LP 3 none none none tbd N/A S SALACIA 2 WFC3/UVI ACCUM UVIS2 F350LP 4 none none none tbd N/A S 17848( 3) - 19-Jul-2024 15:07:21 - [ 6] Visit: 02 Visit Requirements: AFTER 01 BY 1 D TO 100 D; BEFORE 03-AUG-2024:00:00:00; VISIBILITY INTERVAL NO GYRO BIAS UPDATE ON MOVING TARGET On Hold Comments: Additional Comments: To be taken at least 1 day after Visit 1 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 SALACIA WFC3/UVI ACCUM UVIS2-C51 F350LP FLASH=7 1 120 S (480 GS ACQ SCENARIO ONEB1O3; S 2C-SUB S) SEQ 1-2 NON-INT; PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ 2 SALACIA WFC3/UVI ACCUM UVIS2 F350LP FLASH=12 1 60 S (240 PATTERN 1 2 S 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 | ------------------------------------------------------------------------------------------------------------------------------------ SALACIA 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 1 none none none tbd N/A S 12C-SUB SALACIA 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 2 none none none tbd N/A S 12C-SUB SALACIA 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 3 none none none tbd N/A S 12C-SUB SALACIA 1 WFC3/UVI ACCUM UVIS2-C5 F350LP 4 none none none tbd N/A S 12C-SUB SALACIA 2 WFC3/UVI ACCUM UVIS2 F350LP 1 none none none tbd N/A S SALACIA 2 WFC3/UVI ACCUM UVIS2 F350LP 2 none none none tbd N/A S SALACIA 2 WFC3/UVI ACCUM UVIS2 F350LP 3 none none none tbd N/A S SALACIA 2 WFC3/UVI ACCUM UVIS2 F350LP 4 none none none tbd N/A S 17848( 3) - 19-Jul-2024 15:07:21 - [ 7] Summary Form for Proposal 17848 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2, UVIS2-C512C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=12, FLASH=7 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 1 D TO 100 D, BEFORE 03-AUG-2024:00:00:00, GS ACQ SCENARIO ONEB1O3, PATTERN 1 1, PATTERN 1 2, SEQ 1-2 NON-INT, VISIBILITY INTERVAL NO GYRO BIAS UPDATE ON MOVING TARGET ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names SALACIA ------------------------------------------------------------------------------------------------------------------------------------