Resubmission (March 6,2020) with small changes to improve the anonymity of the original submission 1183138702 Assigned ID: 692 ----- Attempting Submission 1 (Fri Mar 06 19:25:34 GMT 2020) ----- HST Phase I Proposal 692 successfully submitted. Receipt: # 692-1 ----- Attempting Submission 2 (Fri Mar 06 19:57:39 GMT 2020) ----- Updated the flash levels for both filters in both visits. -2145748222 ----- Attempting Submission 1 (Thu Jun 18 20:06:26 GMT 2020) ----- ----- Attempting Submission 2 (Mon Oct 19 16:34:19 GMT 2020) ----- Binary systems are prevalent throughout the Kuiper Belt, with roughly 110 systems known to date. The question of how these binary systems formed is of great interest, as each proposed mechanism has its own implications for the conditions in the early Solar System during planetesimal growth. The favoured mechanism - streaming instability in a gaseous dusty disc followed by gravitational collapse of a pebble cloud (SI-GC) - naturally produces many of the observed features of Kuiper Belt binaries. This mechanism also predicts the presence of a class of relatively massive systems with nearly equal sized primary and secondary components. Such systems are virtually absent from the observed sample, with the exception of the Varda-Ilume system. Here we propose observations of the KBO 2015 RR245, the ground-based observations of which hint at a barely resolved binary. The inferred brightnesses and locations of the primary and secondary are consistent from image to image, and imply a system with mass and mass ratio very similar to the Varda system. If binarity is confirmed, RR245 and Varda together would reveal the presence of a class of binary that has simply gone unnoticed, and would solve one of the current tensions between observations and formation simulation of SI-GC. We propose a simple two orbit WFC3 program, with an aim to confirm the binarity of RR245. Observations will be tuned to avoid non-detection in the case of overlapping binary components, and will enable measure of both component's colors and relative sizes, properties that are necessary to confirm consistency with formation via SI-GC. To time our pair of observations to minimize the chances that the secondary and primary are unresolvable during both sequences, we request observations separated by roughly 15 days, or ~1/4 of our estimated orbital period. We require no special timing for the first sequence though we would like to check the proposed scheduling timing timing windows to make sure that we avoid bright star and foreground sources that would otherwise compromise the data. Once scheduling windows are determined, Benecchi will do this field check. Both visits to RR245 are identical. We make use of the WFC3's fast filter change capabilities, to gather three UVIS exposures each in the F606w and F814w filters, with 3" dithers between three different positions. This affords us some protection against cosmic ray strikes and hot pixels. Observations are to be acquired in FGS fine lock mode, slewing at the very-well known rate of motion (at most 3"/hr) of the target during each visit to preserve maximum spatial resolution. The 3-sigma ephemeris uncertainty is sub-arcsecond. We will use 358-s and 358-s exposure times for the F606w and F814w filters, respectively and have placed them in a non-interruptable sequence to avoid any rotation curve complications on the object. These exposure times have been chosen to provide high SNR while minimizing the time wasted to buffer downlinks and optimized to fit the orbit. The WFC3 UVIS imaging ETC provides an estimated SNR>100 in each filter, or ~90 and ~50 for the primary and secondary, respectively. Images will be acquired in the UVIS2-C512C-SUB sub-aperture to prevent any time lost due to mid-orbit buffer dumps. We have also put in Flash values such the total background for each filter is about 20 electrons/pixel. Dr.'s Wesley Fraser and Susan Benecchi have extensive expertice with using HST to observe Kuiper Belt Objects. Susan is one of the foremost experts in binary searches for KBOs, and Wes is a leader in photometry of KBOs bodies with HST, as well as the author of a package to model PSF behaviour of sources in WFC3 imagery. Both have extensive experience in detecting binaries with various telescope systems. Alonside Susan, Dr. JJ Kavelaars is a member of the Solar System Observations Legacy Survey, a large program on HST searching for Kuiper Belt binary objects. James Robinson is a PhD student, and a numerical model with expertice in planetesimal formation via collapse of a pebble cloud. It is his simulations which are the basis of the tension between the streaming instability and colllapse theories. Richard Smith is a PhD student who is modernizing the WFC3_PSFFit package authored by Wes Fraser to use MCMC techniques. His thesis project is a search for binaries in HST archival data using that new package. All of the above people have been chosen as experts in the various science aspects of this program. Solar System Astronomy 6 false false false false false false false SUPPORTED SOLAR SYSTEM NO ASTEROID KBO Binary TYPE=ASTEROID,A=82.03884773628791,E=0.5882820992739525,I=7.551163366915228 ,O=211.769513212333,W=260.9179682697775,M=322.1638134145541,EQUINOX=J2000,EPOCH=05-JUL-2014:00:00:00,EpochTimeScale=TDB EARTH WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F814W POS-TARG DITHER 0.145 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false 1603125207333 /private/var/folders/ty/__dmywxx5rzcc36r24sh_5800000gn/T/OPVisit1581976014558531806.xml Using ephemeris for target 16167-01-2015RR245 ephemeris data for target 16167-01-2015RR245 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 20.214 to 22.089. ephemeris interval: 20.274 to 22.274 Timing link suitability includes constraints ([02 After 01 by 14.0 to 16.0 days]) The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16167 :visit-id "01" :proposal-version -1 :trans-version "20200518" :date "19-Oct-2020 12:33:27.0" :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 27472 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16167 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16167 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2699 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 1 0 1603125184372 /private/var/folders/ty/__dmywxx5rzcc36r24sh_5800000gn/T/OPVisit13066034103626354566.xml Using ephemeris for target 16167-02-2015RR245 ephemeris data for target 16167-02-2015RR245 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 20.214 to 22.089. ephemeris interval: 20.274 to 22.274 Timing link suitability includes constraints ([02 After 01 by 14.0 to 16.0 days]) The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 16167 :visit-id "02" :proposal-version -1 :trans-version "20200518" :date "19-Oct-2020 12:33:04.0" :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 27472 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16167 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16167 :visit-id "02" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2699 :al-overhead-at-end 0 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 1 0