Dust emission process in newly discovered active asteroids P/2021 L4

0 Assigned ID: 2545 ----- Attempting Submission 1 (Thu Jun 24 15:26:25 GMT 2021) ----- HST Phase I Proposal 2545 successfully submitted. Receipt: # 2545-1 ----- Attempting Submission 2 (Thu Jun 24 15:36:09 GMT 2021) ----- FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser FLASH level may be too low for this exposure or a short subexposure. See extended explanation in the diagnostic browser Updated the orbit solution for target 3. -1792628970 Your proposal could not be saved. Submission aborted. ----- Attempting Submission 1 (Thu Jul 08 12:59:29 GMT 2021) ----- ----- Attempting Submission 2 (Tue Jul 13 16:01:40 GMT 2021) ----- ----- Attempting Submission 3 (Wed Jul 28 15:41:06 GMT 2021) ----- ----- Attempting Submission 4 (Wed Jul 28 18:40:27 GMT 2021) ----- ----- Attempting Submission 5 (Fri Aug 20 13:03:32 GMT 2021) ----- ----- Attempting Submission 7 (Tue Aug 31 19:48:26 GMT 2021) ----- ----- Attempting Submission 8 (Fri Sep 03 13:37:44 GMT 2021) ----- When running the ETC with the zodiacal light background for the actual target position in July 2021 (WFC3UVIS.im.1522864), the background flux increases to 16 electrons/pixel. Due to the presence of extended dust, we expect the actual flux to be even higher, and therefore expect the CTE to be acceptable. Dust emission process in newly discovered active asteroids P/2021 L4 We request 3 orbits of DD time to identify the cause of dust emission in newly discovered active asteroid P/2021 L4. The orbit of L4 is in the outer main belt, and similar to those of two other asteroids with confirmed activity likely driven by the sublimation of ice. However, the activity in L4 can be dated to an epoch more than 1.5 years after perihelion, which make sublimation-driven activity questionable, with possible alternatives being an impact or rotational mass shedding. We here seek to find out about the cause of activity from studying the distribution and dynamical evolution of dust and debris near the nucleus and in the dust tail, and to characterise the nucleus itself. This will help us to constrain the depth of buried ice in this outer-main-belt object, and lay the basis for follow-up observations during the next perihelion passage in 2025. We request DD time because L4 was discovered after the last regular GO proposal deadline, and because we expect the debris to disperse on timescales of weeks to a few months. The goal of this program is to characterise the nucleus and dust environment of newly detected active asteroid L4. The first orbit (out of a total 3) should be scheduled as soon as possible to catch the dust field in its current state. The second visit should be scheduled 2-4 weeks after the first to study the motion of potential fragments or a binary system. The third visit should be scheduled as close as possible to October 03 (when L4 will enter HST's solar exclusion zone). The predicted total magnitude of L4 is V=21 in July, decreasing to 22 by late September. We expect that the nucleus or largest fragment will be 1-2 mag fainter, V = 23 - 24. Since this is a newly discovered asteroid with a short arc of observations, the JPL ephemeris will be updated as new astrometry is being reported to the Minor Planet Center and JPL. We will monitor this and request to update the ephemeris in APT when a new orbit solution has been published. To mitigate the ephemeris uncertainty, we would like to use the 2K2C sub-detector of WFC3/UVIS (instead of the 1K-subarray as in the phase 1 proposal). This will give us maximum protection against the position uncertainty, at the moderate cost of increased readout time. To compensate for increased readout time, we plan to reduce the number of exposures from 8 to 6, such that now in each orbit, we plan to take 6 exposures of 205s and perform a 2-point dither pattern to mitigate hot pixels and cosmic ray hits, obtaining 3 exposures at each dither point. We plan to use the wide bandpass filter F606W. The exposure time is flagged with a CTE warning. However, when running the ETC with the zodiacal light background for the actual target position in July 2021 (WFC3UVIS.im.1522864), the background flux increases to 16 electrons/pixel. Due to the presence of extended dust, we expect the actual flux to be even higher, and therefore expect the CTE to be acceptable. Jessica Agarwal previously analyzed HST data on active asteroids to place constraints on the dust ejection process from the dust dynamics and photometry. She is the PI of several HST programs that lead to the discovery and further analysis of the unusual binary main-belt comet 288P. She will carry out the PSF fitting to measure the size of the nucleus and potential fragments. Yoonyoung Kim is an expert in the dynamical modeling of dust moving under the action of gravity, solar radiation pressure and initial velocity distribution, and will constrain these parameters from comparison of simulated and observed images. 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 >20 refereed papers based on Hubble data. He will contribute to the measurement, analysis and interpretation of the data and to writing up the results for publication. Max Mutchler is an expert on Hubble's cameras. He will contribute to the subsampling observing strategy, and special image processing for moving targets. Harold Weaver is a veteran Hubble observer, mostly of comets, with many Hubble-related publications. He will contribute to optimizing the observation strategy and to interpreting the data. Maria Mastropietro is a fresh PhD student planning to study the dust size distribution and orbital range of activity in main-belt comets from comparison of new and archival images to model calculations. Solar System Astronomy 0 false SUPPORTED SOLAR SYSTEM YES The ephemeris will need to be updated regularly, in particular for visits 2 and 3. We do not expect the necessity of late ephemeris updates. ASTEROID Active Asteroid TYPE=ASTEROID,A=3.165314289622532,E=0.1193576578627996,I=16.97017863084731 ,O=243.2235429431992,W=234.7512400659903,M=113.7169141429207,EQUINOX=J2000,EPOCH=16-JUN-2021:00:00:00,EpochTimeScale=TDB EARTH SOLAR SYSTEM YES The ephemeris will need to be updated regularly, in particular for visits 2 and 3. We do not expect the necessity of late ephemeris updates. ASTEROID Active Asteroid TYPE=ASTEROID,A=3.165095001722153,E=0.1187392431431302,I=16.96260314419682 ,O=243.2248890332734,W=234.6698922988284,M=119.8238708365419,EQUINOX=J2000,EPOCH=20-JUL-2021:00:00:00,EpochTimeScale=TDB EARTH SOLAR SYSTEM YES ASTEROID Active Asteroid TYPE=ASTEROID,A=3.165057892850544,E=0.1186608143484228,I=16.96177845929909 ,O=243.2250068856324,W=234.6547896738686,M=120.0241691048568,EQUINOX=J2000,EPOCH=21-JUL-2021:00:00:00,EpochTimeScale=TDB EARTH WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F606W POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 1

false

1630676047620 Using ephemeris for target 16795-01-P2021L4 ephemeris data for target 16795-01-P2021L4 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 21.177 to 22.244. ephemeris interval: 21.243 to 23.244 The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. /tmp/OPVisit12805167124164858.xml 1627283100000 100.0 (Tic-Visit :proposal-id 16795 :visit-id "01" :proposal-version -1 :trans-version "20210514" :date "03-Sep-2021 15:34:07.0" :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 422320 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16795 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16795 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2368 :al-overhead-at-end 0 :internal-dur-at-end 498 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2782 :pcs-gap 0 ) true 1 0 1630676052151 Using ephemeris for target 16795-02-P2021L4-2 ephemeris data for target 16795-02-P2021L4-2 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 21.177 to 22.244. ephemeris interval: 21.243 to 23.244 The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. /tmp/OPVisit9390598147475005505.xml 1629959648000 98.80000000000001 (Tic-Visit :proposal-id 16795 :visit-id "02" :proposal-version -1 :trans-version "20210514" :date "03-Sep-2021 15:34:10.0" :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 422320 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16795 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16795 :visit-id "02" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2338 :al-overhead-at-end 0 :internal-dur-at-end 498 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2782 :pcs-gap 0 ) true 1 0 1630676055166 Using ephemeris for target 16795-03-P2021L4-3 ephemeris data for target 16795-03-P2021L4-3 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 21.177 to 22.244. ephemeris interval: 21.243 to 23.244 Timing link suitability includes constraints ([04 After 03 by 0.1 to 0.1 days] [05 After 03 by 0.1 to 0.2 days]) The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. /tmp/OPVisit18139660306829492337.xml (Tic-Visit :proposal-id 16795 :visit-id "03" :proposal-version -1 :trans-version "20210514" :date "03-Sep-2021 15:34:15.0" :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 422320 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16795 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16795 :visit-id "03" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2368 :al-overhead-at-end 0 :internal-dur-at-end 498 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2782 :pcs-gap 0 ) true 1 0 1630676058357 Using ephemeris for target 16795-04-P2021L4-3 ephemeris data for target 16795-04-P2021L4-3 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 21.177 to 22.244. ephemeris interval: 21.243 to 23.244 Timing link suitability includes constraints ([04 After 03 by 0.1 to 0.1 days]) The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. /tmp/OPVisit16894037739980750776.xml (Tic-Visit :proposal-id 16795 :visit-id "04" :proposal-version -1 :trans-version "20210514" :date "03-Sep-2021 15:34:18.0" :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 422320 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16795 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16795 :visit-id "04" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2368 :al-overhead-at-end 0 :internal-dur-at-end 498 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2782 :pcs-gap 0 ) true 1 0 1630676060393 Using ephemeris for target 16795-05-P2021L4-3 ephemeris data for target 16795-05-P2021L4-3 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 21.177 to 22.244. ephemeris interval: 21.243 to 23.244 Timing link suitability includes constraints ([05 After 03 by 0.1 to 0.2 days]) The scheduling data was generated by CASM 29.2. CASM was run in Phase II mode. /tmp/OPVisit14093805557486741398.xml (Tic-Visit :proposal-id 16795 :visit-id "05" :proposal-version -1 :trans-version "20210514" :date "03-Sep-2021 15:34:20.0" :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 422320 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 16795 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 16795 :visit-id "05" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2368 :al-overhead-at-end 0 :internal-dur-at-end 498 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2782 :pcs-gap 0 ) true 1 0