16089( 7) - 08-Apr-2020 17:23:33 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 16089 Version: 7 Check-in Time: 08-Apr-2020 17:23:33 STScI Edit Number: 4 Title A new member of a new comet group: characterization of C/2019 Y4 (ATLAS) ------------------------------------------------------------------------------------ Type Cycle GO 27 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Quanzhi Ye University of Maryland Y CoI: Dr. Man-To Hui University of Hawaii N ------------------------------------------------------------------------------------ Abstract The recently discovered long-period comet C/2019 Y4 (ATLAS) has an orbit resembling comet C/1844 Y1 (Great Comet), suggesting a common origin. This is only the third identified long-period comet group. Here we request 1 (one) HST orbit to constrain the nucleus size of C/2019 Y4 and to search for smaller, young fragments in its vicinity, with the goal being to understand the mechanism that drives the disintegration of its progenitor. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will spend one HST/WFC3 orbit to image C/2019 Y4. The observation will be conducted right before the comet enters the HST solar exclusion zone (UT 2020 Apr 30 04:00) at a heliocentric distance of 0.9 au. Since the situation is highly dynamic and the brightness of the comet around the observation date is uncertain, we will use two different exposure schemes: a large number of short, sub-array exposures aiming for near-nucleus features and fragments, and a small number of full-frame exposures aiming for fragments far from the nucleus. In case the comet disintegrates well before the time of observation, we will only conduct long, full-frame exposures to characterize the debris field, as the nucleus no longer exists and there is no concern of saturation. ------------------------------------------------------------------------------------ 16089( 7) - 08-Apr-2020 17:23:33 - [ 2] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: C2019Y4-OFFSET ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET Comet ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=0.2528606942259004, E=0.9992079311528602, TYPE=POS_ANGLE, RAD=30, ANG=90, REF=NORTH I=45.37858785518691 , O=120.567065117029, W=177.4112843664408, T=31-MAY-2020:00:25:43, TTimeScale=TDB, EQUINOX=J2000, EPOCH=06-MAR-2020:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 15 Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 16089( 7) - 08-Apr-2020 17:23:33 - [ 3] Visit: 01 Visit Requirements: BETWEEN 20-APR-2020:08:30:00 AND 21-APR-2020:12:00:00 On Hold Comments: Additional Comments: 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 C2019Y4-OFF WFC3/UVI ACCUM UVIS F350LP 1 388 S (388 SEQ 1-5 NON-INT SET S S) ------------------------------------------------------------------------------------------------------------------------------------ 2 C2019Y4-OFF WFC3/UVI ACCUM UVIS F350LP 1 385 S (385 POS TARG 0, .4 SET S S) ------------------------------------------------------------------------------------------------------------------------------------ 3 C2019Y4-OFF WFC3/UVI ACCUM UVIS F350LP 1 385 S (385 POS TARG .4, 0 SET S S) ------------------------------------------------------------------------------------------------------------------------------------ 4 C2019Y4-OFF WFC3/UVI ACCUM UVIS F350LP 1 385 S (385 POS TARG 0, -.4 SET S S) ------------------------------------------------------------------------------------------------------------------------------------ 5 C2019Y4-OFF WFC3/UVI ACCUM UVIS F350LP 1 385 S (385 POS TARG -0.4, 0 SET S 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 | ------------------------------------------------------------------------------------------------------------------------------------ C2019Y4-OFFSET 1 WFC3/UVI ACCUM UVIS F350LP none none none none 1 N/A S C2019Y4-OFFSET 2 WFC3/UVI ACCUM UVIS F350LP none none none none 1 N/A S C2019Y4-OFFSET 3 WFC3/UVI ACCUM UVIS F350LP none none none none 1 N/A S C2019Y4-OFFSET 4 WFC3/UVI ACCUM UVIS F350LP none none none none 1 N/A S C2019Y4-OFFSET 5 WFC3/UVI ACCUM UVIS F350LP none none none none 1 N/A S 16089( 7) - 08-Apr-2020 17:23:33 - [ 4] Summary Form for Proposal 16089 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 20-APR-2020:08:30:00 AND 21-APR-2020:12:00:00, POS TARG -0.4, 0, POS TARG .4, 0, POS TARG 0, -.4, POS TARG 0, .4, SEQ 1-5 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names C2019Y4-OFFSET ------------------------------------------------------------------------------------------------------------------------------------