0 Assigned ID: 2549 ----- Attempting Submission 1 (Fri Sep 03 06:28:40 GMT 2021) ----- In this resubmission, I have set an ORIENT range consistent with the nominal roll available for the 7-10 Jan 2022 scheduling window. I also added a POS TARG of 15x15 arcsec to the existing small dither to better place the comet tail, which extends towards the NE, within the aperture. -- Max Mutchler -1388058723 ----- Attempting Submission 1 (Wed Dec 01 07:41:43 GMT 2021) ----- ----- Attempting Submission 3 (Wed Dec 08 22:59:12 GMT 2021) ----- ----- Attempting Submission 4 (Fri Dec 10 18:38:41 GMT 2021) ----- C/2014 UN271 (Bernardinelli-Bernstein) is a recently discovered long-period comet that was observed at unprecedentedly large inbound distances from the Sun (~29 au). Here we seek one HST mid-cycle orbit using the WFC3 camera to observe the remarkable comet at heliocentric distance ~20 au. Our primary scientific objective is to determine the nucleus size by photometrically isolating the nucleus signal from the surrounding coma. The proposed HST program will enable us to study an inbound comet at a rarely-seen distance from the Sun in good detail. Here we request one mid-cycle orbit primarily to characterize the nucleus of distantly active comet C/2014 UN271 (Bernardinelli-Bernstein) with WFC3-UVIS and the F350LP filter. As the comet is nearing the Sun, resulting in intensifying activity, our observation should be performed as early as possible lest the nucleus signal is overwhelmed by the surrounding dust in the coma. According to the Orbit Planner, in the single orbit, we will obtain five individual exposures each of 285 s duration, with an image dithering executed in the middle. All of the images should be tracked at the nonsidereal motion rate of the target, which will be no more than ~0.14"/min due to its great distance, easily within the tracking capacity of the telescope. Combining all of these five images will improve the signal-to-noise ratio of the comet and will also effectively mitigate effects from CCD defects and cosmic ray strikes. Within the entire observability window, the individual images will be also used to search for possible variability of the near-nucleus region of the comet due to the spin of the nucleus, which can be only achieved through the WFC3 camera thanks to its supreme sensitivity, stability, and angular resolution. Given the small apparent size of the observed coma of the comet (~20"), reading out 2k x 2k subarrays only, which has a square field of view (FOV) of ~80" x 80", will be sufficient for our program. According to the WFC3 user document, amp C on CCD chip2 outperforms others because of milder geometric distortion and fewer ghosts from bright background sources. Therefore, we choose WFC3's UVIS2-2K2C-SUB for our program. The current 3-sigma ephemeris uncertainty of the comet is only at a subarcsec level, much smaller than the FOV of the subarrays, and therefore will not cause any problem to telescope pointing. Ideally, we prefer that the CCD can be oriented to place the tail (extended approximately in the NE direction) roughly along the diagonal of the subarrays. However, given that the FOV of the subarrays is large enough and we will have no control over the roll angle of the spacecraft, we should be able to obtain high-quality data of the distant comet regardless of the roll angle used in our program. Man-To Hui is experienced in observational studies of comets and modeling the dynamics of cometary dust and has participated in and led HST programs. David Jewitt has led a multitude of studies using HST on different small bodies, from comets, asteroids, to Kuiper-belt objects. Max Mutchler is an expert in HST cameras and observing plannings, especially for acquisition of high-quality imaging of small bodies. Liang-Liang Yu is an expert on thermodynamics and has the capability to simulate and model various thermodynamical processes on icy small bodies. We will all collaborate and write the paper expeditiously once we have results from the HST observation. Solar System Astronomy 3 false false false false false false true false SUPPORTED SOLAR SYSTEM YES COMET Distantly active comet TYPE=COMET,Q=10.95346775840689,E=0.9995433744217906,I=95.56709024101407 ,O=190.1002771851635,W=326.267349724131,T=24-JAN-2031:00:22:52,TTimeScale=TDB,EQUINOX=J2000,EPOCH=11-APR-2017:00:00:00,EpochTimeScale=TDB EARTH WFC3/UVIS Imaging No No F350LP 1639161037151 /private/var/folders/tj/27ygn_756lz3w1z19s6wtgtm0006vh/T/OPVisit7282771946131726597.xml Using ephemeris for target 16886-01-2014UN271 ephemeris data for target 16886-01-2014UN271 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 21.213 to 23.089. ephemeris interval: 21.334 to 23.335 The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. Schedule this visit as soon as possible. (Tic-Visit :proposal-id 16886 :visit-id "01" :proposal-version -1 :trans-version "20210514" :date "10-Dec-2021 13:30:37.0" :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 351936 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16886 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16886 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2386 :al-overhead-at-end 0 :internal-dur-at-end 421 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2782 :pcs-gap 0 ) true 1 0