16886( 4) - 10-Dec-2021 18:42:02 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16886 Version: 4 Check-in Time: 10-Dec-2021 18:42:02 STScI Edit Number: 0 Title A Remarkable Inbound Long-Period Comet at Record Heliocentric Distances ------------------------------------------------------------------------------------ Type Cycle GO 29 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Man-To Hui Macau University of Science and Technology Y CoI: Dr. David Jewitt University of California - Los Angeles Y CoI: Max Mutchler Space Telescope Science Institute Y CoI: Dr. Liang-Liang Yu Macau University of Science and Technology N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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 16886( 4) - 10-Dec-2021 18:42:02 - [ 2] 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. ------------------------------------------------------------------------------------ 16886( 4) - 10-Dec-2021 18:42:02 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: 2014UN271 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET Distantly active comet ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 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 ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 20 +/- 1 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 16886( 4) - 10-Dec-2021 18:42:02 - [ 4] Visit: 01 Visit Requirements: ORIENT 62D TO 74 D; BETWEEN 07-JAN-2022:18:00:00 AND 09-JAN-2022:12:00:00 On Hold Comments: Additional Comments: Schedule this visit as soon as possible. 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 2014UN271 WFC3/UVI ACCUM UVIS2-2K2 F350LP CR-SPLIT=NO 3 285 S (855 POS TARG 15, 15; SEQ 1-2 S C-SUB S) NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 2014UN271 WFC3/UVI ACCUM UVIS2-2K2 F350LP CR-SPLIT=NO 2 285 S (570 POS TARG 15.4, 15.4 S C-SUB 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 | ------------------------------------------------------------------------------------------------------------------------------------ 2014UN271 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 2014UN271 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 2014UN271 1 WFC3/UVI ACCUM UVIS2-2K F350LP none none 3 none 1 N/A S 2C-SUB 2014UN271 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 1 none 1 N/A S 2C-SUB 2014UN271 2 WFC3/UVI ACCUM UVIS2-2K F350LP none none 2 none 1 N/A S 2C-SUB 16886( 4) - 10-Dec-2021 18:42:02 - [ 5] Summary Form for Proposal 16886 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-2K2C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 07-JAN-2022:18:00:00 AND 09-JAN-2022:12:00:00, ORIENT 62D TO 74 D, POS TARG 15, 15, POS TARG 15.4, 15.4, SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names 2014UN271 ------------------------------------------------------------------------------------------------------------------------------------