14458( 3) - 24-Nov-2015 13:49:30 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14458 Version: 3 Check-in Time: 24-Nov-2015 13:49:30 STScI Edit Number: 0 Title Hubble Investigation of Active Asteroid 324P/La Sagra ------------------------------------------------------------------------------------ Type Cycle GO 23 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. David Jewitt University of California - Los Angeles Y CoI: Dr. Harold A. Weaver The Johns Hopkins University Applied Y Physics Laboratory CoI: Max Mutchler Space Telescope Science Institute Y CoI: Dr. Jessica Agarwal Max Planck Institute for Solar System N Research CoI: Dr. Stephen M. Larson University of Arizona N ------------------------------------------------------------------------------------ Abstract Active asteroid 324P/La Sagra has recently reactivated. We propose WFC3 observations to characterize the activity, to measure the size distribution of the ejected dust, its velocity and the time profile of the mass production rate. These Mid-Cycle observations will be combined with observations from our Cycle 23 (2-orbit) ToO program GO 14263 in order to produce the best possible dataset for this body. Reactivation of an active asteroid near perihelion suggests that sublimating ice is the activity driver. 324P/La Sagra orbits near 3 AU, widely posited as a likely source region for the Earth's oceans and other volatiles. Characterizing ice in the asteroid belt is scientifically interesting in the broad context of the origin of planetary volatiles. ------------------------------------------------------------------------------------ Observations Description ------------------------ We request four HST orbits to image La Sagra, with one scheduled as early as possible in November and three as close as possible to December 19 to study the nucleus and capture the object from an in-plane perspective, which provides data that are particularly diagnostic of the dust velocity distribution. Our basic observing strategy is to take multiple long exposures (400 s) using WFC3 and a wide bandpass filter (F350LP) for maximum sensitivity. (In some previous HST programs we used long exposures through the F606W filter to provide maximum sensitivity. The F350LP filter provides an 1.6 higher count rate for a target with a solar-type spectrum.) We also plan to dither the exposures to mitigate the effects from bad pixels, cosmic rays, and the inter-chip gap. We already have observations from Sep 29 (orbit plane angle 10 degrees), and observations for Oct 8 are already scheduled under our two-orbit ToO program 14263. Two additional visits, as early in November as practical (3 degrees) and as close as possible to the Dec 19 Sun exclusion zone (0 degrees), will provide sufficient input to derive the properties of the dust coma from the dynamical models. To test the role of spin in 324P, we request 3 consecutive or near-consecutive orbits to sample the nucleus lightcurve over a 3 hour interval. Observations over 3 hours will allow us to measure the lightcurve over slightly more than one period, in order to ensure that periodicity has 14458( 3) - 24-Nov-2015 13:49:30 - [ 2] been detected. The apparent rates of motion are 30 arcsec per hour, which are easily within Hubble's tracking capabilities. This rate of motion is also slow enough to keep a single pair of guide stars within the FGS pickles for an entire visibility window. The ephemeris uncertainty of La Sagra is negligible (sub-arcsecond), compared to the WFC3 field-of-view. Ephemeris issues are of no concern to this observation. We understand that we will have essentially no control over the spacecraft roll angle, which means we will not be able to optimize the orientation of the dust tail on the CCD (i.e., to orient the tail along the longest dimension of the detector). However, the field-of-view of the camera is large enough that we should obtain excellent data on a portion of the tail, no matter what spacecraft roll angle is used. ------------------------------------------------------------------------------------ 14458( 3) - 24-Nov-2015 13:49:30 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 TARGET NAME: 324P-LA-SAGRA ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: ASTEROID active asteroid, Main Belt Comet ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 TYPE=COMET, Q=2.619823310911345, E=.153784445570409, I=21.41695747394586, O=270.6516569004608, W=58.56915804482286, T=29-NOV-2015:22:58:09, TTimeScale=UTC, EQUINOX=J2000, EPOCH=28-AUG-2015:00:00:00, EpochTimeScale=TDB ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 23 +/- 2 Ephemeris Center: EARTH Extended: YES ------------------------------------------------------------------------------------------------------------------------------------ 14458( 3) - 24-Nov-2015 13:49:30 - [ 4] Visit: 01 Visit Requirements: BEFORE 09-DEC-2015:00:00:00 On Hold Comments: Additional Comments: Please 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 324P-LA-SAG WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 3 420 S SEQ 1-2 NON-INT RA S (1260 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 324P-LA-SAG WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 2 420 S (840 POS TARG 0.2, 2.0 RA 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 | ------------------------------------------------------------------------------------------------------------------------------------ 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 1 none 1 N/A S 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 2 none 1 N/A S 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 3 none 1 N/A S 324P-LA-SAGRA 2 WFC3/UVI ACCUM UVIS2 F350LP none none 1 none 1 N/A S 324P-LA-SAGRA 2 WFC3/UVI ACCUM UVIS2 F350LP none none 2 none 1 N/A S 14458( 3) - 24-Nov-2015 13:49:30 - [ 5] Visit: 02 Visit Requirements: BETWEEN 18-DEC-2015:00:00:00 AND 20-DEC-2015:00:00:00; SEQ 02, 03, 04 WITHIN 3.2 Orbits On Hold Comments: Additional Comments: Please schedule visits 2, 3, 4 in sequence as late as possible before solar exclusion begins. 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 324P-LA-SAG WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 3 420 S SEQ 1-2 NON-INT RA S (1260 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 324P-LA-SAG WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 2 420 S (840 POS TARG 0.2, 2.0 RA 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 | ------------------------------------------------------------------------------------------------------------------------------------ 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 1 none 1 N/A S 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 2 none 1 N/A S 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 3 none 1 N/A S 324P-LA-SAGRA 2 WFC3/UVI ACCUM UVIS2 F350LP none none 1 none 1 N/A S 324P-LA-SAGRA 2 WFC3/UVI ACCUM UVIS2 F350LP none none 2 none 1 N/A S 14458( 3) - 24-Nov-2015 13:49:30 - [ 6] Visit: 03 Visit Requirements: On Hold Comments: Additional Comments: Please schedule visits 2, 3, 4 in sequence as late as possible before solar exclusion begins. 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 324P-LA-SAG WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 3 420 S SEQ 1-2 NON-INT RA S (1260 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 324P-LA-SAG WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 2 420 S (840 POS TARG 0.2, 2.0 RA 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 | ------------------------------------------------------------------------------------------------------------------------------------ 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 1 none 1 N/A S 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 2 none 1 N/A S 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 3 none 1 N/A S 324P-LA-SAGRA 2 WFC3/UVI ACCUM UVIS2 F350LP none none 1 none 1 N/A S 324P-LA-SAGRA 2 WFC3/UVI ACCUM UVIS2 F350LP none none 2 none 1 N/A S 14458( 3) - 24-Nov-2015 13:49:30 - [ 7] Visit: 04 Visit Requirements: On Hold Comments: Additional Comments: Please schedule visits 2, 3, 4 in sequence as late as possible before solar exclusion begins. 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 324P-LA-SAG WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 3 420 S SEQ 1-2 NON-INT RA S (1260 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 324P-LA-SAG WFC3/UVI ACCUM UVIS2 F350LP CR-SPLIT=NO 2 420 S (840 POS TARG 0.2, 2.0 RA 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 | ------------------------------------------------------------------------------------------------------------------------------------ 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 1 none 1 N/A S 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 2 none 1 N/A S 324P-LA-SAGRA 1 WFC3/UVI ACCUM UVIS2 F350LP none none 3 none 1 N/A S 324P-LA-SAGRA 2 WFC3/UVI ACCUM UVIS2 F350LP none none 1 none 1 N/A S 324P-LA-SAGRA 2 WFC3/UVI ACCUM UVIS2 F350LP none none 2 none 1 N/A S 14458( 3) - 24-Nov-2015 13:49:30 - [ 8] Summary Form for Proposal 14458 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 09-DEC-2015:00:00:00, BETWEEN 18-DEC-2015:00:00:00 AND 20-DEC-2015:00:00:00, POS TARG 0.2, 2.0, SEQ 02, 03, 04 WITHIN 3.2 Orbits, SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F350LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names 324P-LA-SAGRA ------------------------------------------------------------------------------------------------------------------------------------