0 Assigned ID: 662 ----- Attempting Submission 1 (Wed Jan 30 20:12:00 GMT 2019) ----- This target is not used in this proposal. This pattern is not used in this proposal. 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 target for visits 2+3. cut 1 minute from visits 2-3 put time back, didn't seem to make a difference 36985568 ----- Attempting Submission 1 (Mon Mar 18 17:49:01 GMT 2019) ----- HST Phase II Proposal 15706 (hst26_mc_a4a7_190318.apt) failed submission. ----- Attempting Submission 2 (Mon Mar 18 17:51:52 GMT 2019) ----- HST Phase II Proposal 15706 (hst26_mc_a4a7_190318.apt) failed submission. ----- Attempting Submission 3 (Mon Mar 18 17:52:55 GMT 2019) ----- ----- Attempting Submission 4 (Wed Apr 03 17:45:00 GMT 2019) ----- ----- Attempting Submission 5 (Wed Apr 03 19:11:05 GMT 2019) ----- ----- Attempting Submission 6 (Fri Apr 05 15:33:21 GMT 2019) ----- ----- Attempting Submission 7 (Sun Apr 14 18:13:05 GMT 2019) ----- ----- Attempting Submission 8 (Mon Apr 15 12:55:12 GMT 2019) ----- ----- Attempting Submission 10 (Mon Apr 15 16:14:03 GMT 2019) ----- The flash warnings disappear if the zodiacal light is calculated for the actual target positions. We propose to study the nuclei and dust environments of the recently discovered active asteroids P/2019 A4 and P/2019 A7 at the highest possible resolution. Our primary goal is to determine the causes of the activity, specifically if driven by the sublimation of ice or caused by an instantaneous process such as an impact or rotational instability. To this purpose, we propose to characterise the nuclei, search for potential bound or unbound companions, and study the dust environment and its evolution with time. As A4 is located in the middle main belt, sublimation-driven activity, if found, would place a strong new constraint on the location of the snow line in the early solar system. A7 is located in the outer main belt and hence more likely to contain ice, but the discovery circumstances are different from those of typical main belt comets with sublimation-driven activity. Our proposed observations will help to understand this difference. We propose three 1-orbit visits to either object between 2019 April and mid-June. Given their discovery in 2019 January, we could not propose these observations at the last regular deadline for GO proposals. Waiting for Cycle 27 will mean that the dust diagnostic of the current activity will have been dispersed by solar radiation pressure. We will observe active asteroids P/2019 A4 and P/2019 A7 during 3 1-orbit visits each between 2019 April and early June. The first visit should be scheduled as soon as possible to catch the objects at the minimum possible geocentric distance (highest angular resolution). The second and third visits should be scheduled at roughly monthly intervals to study the motion of potential fragments or a binary component and to exploit the changing angles between the line of sight from Earth and the orbital planes of the objects for analysis of the dust motion. The predicted ranges of total magnitude between 2019 April and June is V = 20.7 .. 21.7 (A4) and V = 21.5 .. 22.4 (A7). We expect that the nuclei or largest fragment will be 1-2 mag fainter, V = 22 -- 24. The orbital visibility for a solar system target near the ecliptic plane is 54 min (Section 6.3 of the HST Primer document). In each orbit, we will take 8 exposures of ~225s using the C1K1C-subarray of WFC3. We will perform a 2x2 subsampling dither box pattern, obtaining 2 exposures at each dither point. This strategy gives us a total exposure time of 1800s = 30min per orbit, and estimated overheads of 6min for guide-star acquisition, 2.6min for the first exposure, a total of 14.7min for the subsequent 7 exposures, and 1.5min for the three spacecraft maneuvers required for dithering, which adds up to a total execution time of 54min per orbit. We will use the wide bandpass filter F606W for an optimum trade-off between sensitivity and highest resolution: the bandpass (475 -- 700 nm) covers the maximum of the solar spectrum, and is in the wavelength range where the PSF is smallest (FWHM<0.07arcsec, from the WFC3 instrument handbook for Cycle 26), such that we can optimally exploit our subsampling dither strategy. The WFC3 exposure time calculator returns for a solar-spectrum point source at V=22 (24), exposure time of 225s, F606W filter, and default background values a signal-to-noise-ratio (S/N) of 80 (29) within a circle of 0.08arcsec (ETC Request IDs: WFC3UVIS.im.1312246 and WFC3UVIS.im.1312247). The small aperture is needed to separate the flux from the nucleus or fragment from that of the surrounding coma. A fragment with V=26 will be detected at S/N=8 (WFC3UVIS.im.1285906), such that we expect to detect fragments down to 180m diameter for standard assumptions on a C-type asteroid with geometric albedo p=0.06 (Nugent et al., 2016) and phase function coefficient G=0.15 (Bowell et al., 1989). The position uncertainty predicted for A4 in early April is currently of order 10 arcsec. We request a late ephemeris update option at the phase 2 stage to be able to flexibly deal with possible late updates of the ephemeris based on new astrometric measurements. The ephemeris uncertainty for A7 is small compared to the WFC3 field of view. The maximum apparent motion of the targets is only ~62 arcsec/hr (0.02 arcsec/s), which is well within Hubble's tracking capabilities. PI Agarwal previously analyzed HST data on active asteroids to place constraints on the dust ejection process from the dust dynamics and photometry. She will measure the nucleus sizes and probe the potential binary nature of the targets through PSF fitting, contribute the analysis of the dust dynamics and to publishing the results. Co-I Kim is an expert in the dynamical modeling of dust moving under the action of gravity, solar radiation pressure and initial velocity distribution. She will provide the three-dimensional dust dynamics model to determine the cause of the observed activity (e.g., sublimation or other effects like impacts or rotational disruption). Co-I Jewitt will contribute to the measurement, analysis and interpretation of the data and to writing up the results for publication. Co-I Mutchler is an expert on Hubble's cameras. He will contribute to the subsampling observing strategy, and special image processing for moving targets. Co-I 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. Co-I Larson is an experienced investigator of small Solar system bodies and the PI of the Catalina Sky Survey, from which previous HST targets including the outburst of (596) Scheila, P/2013 R3 and 313P were discovered. He will contribute to continuously updating the target ephemeris and to the data interpretation. Solar System 3 false false false false false false false SUPPORTED SOLAR SYSTEM YES ASTEROID Active asteroid TYPE=ASTEROID,A=2.613583746324236,E=0.08960734196836118,I=13.32039689241388 ,O=119.2995371407606,W=341.7814697490555,M=10.258094656676,EQUINOX=J2000,EPOCH=18-JAN-2019:00:00:00,EpochTimeScale=TDB EARTH SOLAR SYSTEM YES ASTEROID Active asteroid TYPE=ASTEROID,A=2.613548561710995,E=0.0896028018538064,I=13.31897611728256 ,O=119.3001705986976,W=341.9095170765762,M=12.716814643128,EQUINOX=J2000,EPOCH=29-JAN-2019:00:00:00,EpochTimeScale=TDB EARTH SOLAR SYSTEM YES ASTEROID Active asteroid TYPE=ASTEROID,A=2.613583746324236,E=0.08960734196836118,I=13.32039689241388 ,O=119.2995371407606,W=341.7814697490555,M=10.258094656676,EQUINOX=J2000,EPOCH=18-JAN-2019:00:00:00,EpochTimeScale=TDB EARTH SOLAR SYSTEM YES ASTEROID Active asteroid TYPE=ASTEROID,A=3.188304552499178,E=0.1607480733255885,I=17.772656582968 ,O=280.5213002812847,W=119.5461347673522,M=46.56029697759,EQUINOX=J2000,EPOCH=04-OCT-2018:00:00:00,EpochTimeScale=TDB EARTH WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F606W WFC3/UVIS Imaging No No F606W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false POS-TARG DITHER 0.145 LINE false false 2 46.84 WFC3-UVIS-DITHER-LINE 2 false 1555265488757 Using ephemeris for target 15706-01-P2019A4-V1 ephemeris data for target 15706-01-P2019A4-V1 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 19.060 to 20.092. ephemeris interval: 19.090 to 21.091 The scheduling data was generated by CASM 27.0. CASM was run in Phase II mode. 1554114614000 98.82874251010918 (Tic-Visit :proposal-id 15706 :visit-id "01" :proposal-version -1 :trans-version "20181130" :date "14-Apr-2019 20:11:28.0" :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 142608 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15706 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15706 :visit-id "01" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2594 :al-overhead-at-end 0 :internal-dur-at-end 192 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) false 1 0 The flash-warning disappears if the ETC is run with calculating the zodiacal light for the actual target position on 2019 April 01. 1555331324209 Using ephemeris for target 15706-02-P2019A4-V2 ephemeris data for target 15706-02-P2019A4-V2 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 19.060 to 20.092. ephemeris interval: 19.090 to 21.091 Timing link suitability includes constraints ([Group (02 03) Within 2.0 days]) The scheduling data was generated by CASM 27.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 15706 :visit-id "02" :proposal-version -1 :trans-version "20181130" :date "15-Apr-2019 08:28:43.0" :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 71312 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15706 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15706 :visit-id "02" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2690 :al-overhead-at-end 0 :internal-dur-at-end 114 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) false 1 0 The target ephemeris and position uncertainty need to be updated before the visit executes. The flash-warning disappears if the ETC is run with calculating the zodiacal light for the actual target position on 2019 May 01. 1555331511159 Using ephemeris for target 15706-03-P2019A4-V2 ephemeris data for target 15706-03-P2019A4-V2 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 19.060 to 20.092. ephemeris interval: 19.090 to 21.091 Timing link suitability includes constraints ([Group (02 03) Within 2.0 days]) The scheduling data was generated by CASM 27.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 15706 :visit-id "03" :proposal-version -1 :trans-version "20181130" :date "15-Apr-2019 08:31:51.0" :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 71312 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15706 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15706 :visit-id "03" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2630 :al-overhead-at-end 0 :internal-dur-at-end 114 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) false 1 0 The target ephemeris and position uncertainty need to be updated before the visit executes. The flash-warning disappears if the ETC is run with calculating the zodiacal light for the actual target position on 2019 June 01. 1555265493287 Using ephemeris for target 15706-04-P2019A7 ephemeris data for target 15706-04-P2019A7 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 19.060 to 20.092. ephemeris interval: 19.090 to 21.091 The scheduling data was generated by CASM 27.0. CASM was run in Phase II mode. 1554274903000 87.58118330057619 (Tic-Visit :proposal-id 15706 :visit-id "04" :proposal-version -1 :trans-version "20181130" :date "14-Apr-2019 20:11:32.0" :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 142608 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15706 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15706 :visit-id "04" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2594 :al-overhead-at-end 0 :internal-dur-at-end 192 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 1 0 The flash-warning disappears if the ETC is run with calculating the zodiacal light for the actual target position on 2019 April 01. 1555265405871 Using ephemeris for target 15706-05-P2019A7 ephemeris data for target 15706-05-P2019A7 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 19.060 to 20.092. ephemeris interval: 19.090 to 21.091 Timing link suitability includes constraints ([06 After 05 by 0.1 to 0.1 days]) The scheduling data was generated by CASM 27.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 15706 :visit-id "05" :proposal-version -1 :trans-version "20181130" :date "14-Apr-2019 20:10:05.0" :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 142608 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15706 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15706 :visit-id "05" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2674 :al-overhead-at-end 0 :internal-dur-at-end 192 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 1 0 The flash-warning disappears if the ETC is run with calculating the zodiacal light for the actual target position on 2019 May 01. 1555265409322 Using ephemeris for target 15706-06-P2019A7 ephemeris data for target 15706-06-P2019A7 does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 19.060 to 20.092. ephemeris interval: 19.090 to 21.091 Timing link suitability includes constraints ([06 After 05 by 0.1 to 0.1 days]) The scheduling data was generated by CASM 27.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 15706 :visit-id "06" :proposal-version -1 :trans-version "20181130" :date "14-Apr-2019 20:10:08.0" :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 142608 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15706 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15706 :visit-id "06" :orbit-number 1 :pcs-time 393 :si-vis-utilization 2674 :al-overhead-at-end 0 :internal-dur-at-end 192 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 1 0 The flash-warning disappears if the ETC is run with calculating the zodiacal light for the actual target position on 2019 June 01.