Cannot find file /Users/jewitt/Dropbox/C28_Borisov/Borisov_Cycle28.pdf 0 Assigned ID: 89 ----- Attempting Submission 1 (Mon Mar 02 21:49:43 GMT 2020) ----- HST Phase I Proposal 89 successfully submitted. Receipt: # 89-1 ----- Attempting Submission 2 (Fri Mar 06 21:29:46 GMT 2020) ----- These need to be done as 1 orbit visits. So I broke them into single orbit visits. -777761846 ----- Attempting Submission 1 (Mon Jun 15 20:33:55 GMT 2020) ----- ----- Attempting Submission 2 (Tue Dec 08 17:17:15 GMT 2020) ----- ----- Attempting Submission 3 (Wed Dec 09 14:37:37 GMT 2020) ----- ----- Attempting Submission 4 (Mon Feb 22 15:59:16 GMT 2021) ----- ----- Attempting Submission 5 (Fri Feb 26 13:35:36 GMT 2021) ----- Your proposal could not be saved. Submission aborted. ----- Attempting Submission 6 (Mon Mar 15 15:22:19 GMT 2021) ----- C/2019 Q4 (Borisov) is the first interstellar comet and only the second interstellar object (after 'Oumuamua) ever identified within the solar system. We propose high resolution observations with WFC3 and HST in order to probe the development of this body in Cycle 28. During this time we will use HST and WFC3 to constrain the nucleus and dust properties. Observation as the Earth passes through the projected orbit plane early in the Cycle will provide a model-free estimate of the dust extent and velocity perpendicular to the plane. Additional, spaced observations provide perspectives as the object recedes from about 9 to about 13 AU. The high resolution of HST is needed to resolve faint near-nucleus structures (jets, fans) and fragments at the growing distance to the comet. The proposed observations extend the temporal coverage of the evolution of this unique object and take advantage of new perspectives. We request 8 HST orbits spread over Cycle 28. The proposed observations span the outbound heliocentric distance range 9.0 AU to 13.7 AU. 2I emerges from the HST Sun-exclusion zone on 2021 January 28, at rH = 9.0, delta = 9.5 AU, and with phase angle 5 deg. This date also corresponds to orbit plane crossing, needed to detect ultra-low surface brightness trail material consisting of the largest, most slowly moving particles. In this geometry, the direction of trailing of field objects is parallel to the direction of the extended dust emission, placing especially stringent constraints on the need for accurate background removal. For this reason, we request four orbits with WFC3 and the F350LP filter to image 2I on the plane-crossing date at the highest sensitivity using the broad F350LP filter (effective center 6230A, FWHM 4760A). These four orbits will be dithered and combined to optimize the rejection of field object trails, especially from hard-to-remove low surface brightness galaxies. Subsequent visits will be used to measure the brightness and morphological evolution of 2I, as well as to obtain sub-arcsecond astrometry. These single-orbit visits will secure six 270s integrations each, with dithering to provide protection from chip defects. According to the WFC3 ETC, a single exposure of this length reaches V = 26.5 at SNR = 5. Combing 6 images from one orbit will take us 1 magnitude fainter and will also provide protection from cosmic ray strikes on individual images. Combining data from 4 orbits will give us another 0.6 magnitudes, taking us to a point-source sensitivity V = 28.1 for the plane-crossing V1. As noted above, the expected apparent magnitude of a 0.5 km radius nucleus (albedo 0.04) is V = 28 AU at V1, so that detection of the nucleus will be challenging. We do expect to find the largest, slowest particles aligned in a trail behind the nucleus; the 0.04 arcsec PSF of HST projects to 300 km at the comet. Sub-pixel astrometry will assist with orbit fitting and the determination of non-gravitational acceleration. The currently predicted 1 arcsec ephemeris uncertainty (from JPL Horizons) is 2 arcsec on UT 2021 January 28. This is already small enough compared to the WFC3 field of view that ephemeris uncertainty poses no threat to the proposed observations. Moreover, as with all high profile targets, continuous additions to the astrometric database by astronomers around the world will shrink this uncertainty month-by-month up until the comet reaches elongations < 50 degree (in 2020 October). Astrometry from this work will also be used to update the orbit. The ephemeris accuracy for HST observations is expected to be of no concern to these observations. All observations are with WFC3 and the F350LP (effective center 6230A, FWHM 4760A) filter to provide the highest sensitivity. The division of the requested orbits is as follows. For visits V1 and V2, 2I emerges from the 55 deg HST exclusion zone on UT 2021 January 28 at rH = 9.0, delta = 9.5 AU and with phase angle 5 deg. Fortuitously, the Earth will pass through the orbit plane on this date providing us with the maximum sensitivity to large particles confined to the orbit plane of the body. Thus, early observation of 2I in Cycle 28 provides our best chance to detect a large particle trail. In this geometry, the direction of trailing of field objects is parallel to the direction of the extended dust emission, placing especially stringent constraints on the need for accurate background removal. For this reason we request three orbits to be dithered and combined to optimize the rejection of field object trails. The four orbits in V1 and V2 should be as close together as possible, although they do not need to be consecutive. (We realize that no more than two consecutive orbits are possible on a moving target because of the gyro problem). In fact, spaced orbits would be an advantage by giving enough time for background objects to completely leave the field of view. Image alignment between two consecutive HST orbits is excellent but alignment after a dither or other alignment change is less secure, particularly on a faint target that might not be readily identified in a single, heavily cosmic-ray impacted orbit. From experience, we feel confident in achieving good alignment in four plane-crossing orbits separated by a gyro gap. The in-plane angle changes by about 0.08 deg/day near plane crossing. Therefore, we need to be within 2 to 3 days of January 28 in order to attain the in-plane geometry and the closer to this time the better. Visit V3 is a single orbit visit near UT 2021 April 1 (rH = 10.1 AU), requested to sample the changing morphology and photometry of the comet. Visit V4 is a single orbit visit near UT 2021 June 1 (rH = 11.4 AU), requested to sample the changing morphology and photometry of the comet. Visit V5 is a single orbit visit near UT 2021 August 1 (rH = 12.6 AU), requested to sample the changing morphology and photometry of the comet. The Earth again passes through the orbital plane of 2I at this time but the increased distance will substantially reduce our sensitivity to a large particle trail. Therefore, we have focused our in-plane attention primarily on V1 and V2. Visit V6 is a single orbit visit within 2 weeks of the end of Cycle 28 (UT 2021 September 30, rH = 13.7 AU), requested to complete the study. The end of Cycle 28 is followed by entry of 2I into the Sun exclusion zone from 2021 October 26 - 2022 February 7. V6 marks the likely end of any possible observations of 2I/Borisov. 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. The team has expertise in all aspects of the program, including physics of active asteroids, origin of active asteroids, dynamics of dust under the action of radiation and gravity, operational details of HST, reduction and analysis of WFC3 data and prompt publication of the data. David Jewitt has an extensive record of research into the study of small solar system bodies, especially the Kuiper belt objects and the cometary nuclei. In the last decade he has written 19 refereed papers based on Hubble data. Max Mutchler is an expert in planning the aquisition of HST data and interpreting its properties. Jessica Agarwal and Yoonyoung Kim are experts in modeling the dynamics of dust under the combined action of solar gravity and radiation pressure, with experience in the application to many comets. Jing Li is experienced in CCD data reduction techniques. Harold Weaver is a long-term user of HST with experience in all aspects of its operation. Man-To Hui will examine the near-nucleus surface brightness structure of the comet. We will all cooperate to promptly write the papers. Solar System Astronomy 6 false false false false false false false SUPPORTED SOLAR SYSTEM NO COMET interstellar comet TYPE=COMET,Q=2.006581893840375,E=3.356215101434632,I=44.05257068647377 ,O=308.1487262895379,W=209.12367864468,T=08-DEC-2019:13:04:54,TTimeScale=TDB,EQUINOX=J2000,EPOCH=01-AUG-2020:00:00:00,EpochTimeScale=TDB,R0=2.808 ,DT=87.2916 ,A1=7.093444347382E-8,A2=-1.443811535835E-8,A3=6.534734368324E-10 ,ALN=0.1112620426,NM=2.15,NN=5.093,NK=4.6142,AMRAT=0. EARTH WFC3/UVIS Imaging No No F350LP 1614346155670 Using ephemeris for target 16310-01-2I-BORISOV ephemeris data for target 16310-01-2I-BORISOV does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 20.366 to 22.089. ephemeris interval: 21.031 to 23.032 Timing link suitability includes constraints ([Group (01 02) Within 0.7 days]) The scheduling data was generated by CASM 29.0. 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