0 ----- Attempting Submission 1 (Thu Jul 18 14:49:16 GMT 2024) ----- 0 Assigned ID: 5923 ----- Attempting Submission 1 (Tue Jul 09 17:16:41 GMT 2024) ----- Astrometry for an Upcoming Double Occultation of Salacia-Actaea 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 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. 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. PI Proudfoot has extensive experience in modeling the orbits of TNO binaries and predicting stellar occultations of TNO companions. He has published several papers and PI'd several HST programs focused on TNO binary science. He is the lead developer of MultiMoon, the tool that will be used to model the binary orbit. Co-I Fernandez-Valenzuela is well versed in observing and analyzing occultations of TNOs. She has led a variety of successful occultation campaigns targeting TNO satellites like Hi'iaka and Weywot. Her expertise will ensure a well-run occultartion campaign. Co-I Rommel is an expert in photometry of occultation chords. She has led the analysis of a variety of occultation campaigns including the highest resolution (i.e. number of chords) TNO occultation ever. Co-I Porter provides important expertise in HST image analysis. He was the PI of the HST program to acquire precise astrometry of Arrokoth before the series of successful stellar occultations. He is the developer of the absolute astrometry tools that will be used for this effort. Co-I Ortiz is one of the leaders of the Lucky Star occultation collaboration. He is a world-renowned expert in stellar occultation of TNOs, having been the lead author on the discovery of rings around Chiron and Haumea. Solar System Astronomy 0 false SUPPORTED SOLAR SYSTEM DWARF-PLANET Dwarf planet with moon, Actaea (V ~ 23.3) 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 EARTH WFC3/UVIS Imaging No No F350LP WFC3/UVIS Imaging No No F350LP POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false Using ephemeris for target 17848-01-SALACIA ephemeris data for target 17848-01-SALACIA does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 23.274 to 25.182. ephemeris interval: 24.182 to 26.182 Timing link suitability includes constraints ([02 After 01 by 1.0 to 100.0 days]) The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 17848 :visit-id "01" :proposal-version -1 :trans-version "20240604" :date "18-Jul-2024 10:29:16.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1173296 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17848 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17848 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2440 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3005 :pcs-gap 0 ) false 1 0 Using ephemeris for target 17848-02-SALACIA ephemeris data for target 17848-02-SALACIA does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 23.274 to 25.182. ephemeris interval: 24.182 to 26.182 Timing link suitability includes constraints ([02 After 01 by 1.0 to 100.0 days]) The scheduling data was generated by CASM 32.1.1. CASM was run in Phase II mode. To be taken at least 1 day after Visit 1 (Tic-Visit :proposal-id 17848 :visit-id "02" :proposal-version -1 :trans-version "20240604" :date "18-Jul-2024 10:31:23.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 1173296 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17848 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17848 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2440 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3005 :pcs-gap 0 ) false 1 0