Phase 1 for Active Asteroid (MBC) Target of Opportunity proposal. -407358174 Assigned ID: 148 ----- Attempting Submission 1 (Thu Apr 10 01:30:59 GMT 2014) ----- I changed to the JPL #2 orbital elements for the target. These elements are sufficiently accurate to do the final scheduling. No other changes were made. -1169784061 ----- Attempting Submission 1 (Wed Jul 09 20:17:16 GMT 2014) ----- ----- Attempting Submission 2 (Wed Jul 23 00:32:12 GMT 2014) ----- ----- Attempting Submission 3 (Tue Sep 30 13:14:20 GMT 2014) ----- ----- Attempting Submission 4 (Tue Sep 30 14:45:08 GMT 2014) ----- ----- Attempting Submission 5 (Tue Sep 30 17:10:03 GMT 2014) ----- ----- Attempting Submission 6 (Tue Sep 30 23:19:07 GMT 2014) ----- I'm using APT version 22.2.1, and I'm once again having problems getting the orbit planner to work. Active asteroids (aka Main-Belt comets or MBCs) have the orbital characteristics of asteroids but also show transient, comet-like activity caused by mass-loss. Examples of mass-loss likely caused by sublimation, impact, and rotational effects have been established, while numerous additional processes are capable of launching material from asteroids. We propose two orbits of non-disruptive, target-of-opportunity observations of the next discovered active asteroid in order to help determine the process driving mass loss. This proposal extends our very productive ToO program approved in Cycle 21 (triggered on P/2013 P5; Jewitt et al. 2013). We request two single-orbit HST visits to image a newly-discovered MBC. The basic objective is to characterize the early-time morphology and establish the initial rates of change in the appearance, so that the need for additional HST observations and their optimum cadence can be realistically determined. In some cases the initial observations alone may be enough to determine whether the morphology is more consistent with sublimation or another origin. In others (as with P/2013 P5), the ToO orbits motivate follow-up through the DDT program. Our basic observing strategy is to take multiple long exposures (348 s) using WFC3 and a wide bandpass filter (F350LP) for maximum sensitivity. If the nucleus is bright, we also plan some shorter exposures, possibly with a filter having a narrower bandpass (e.g., F621M). Asteroid Scheila, with its ultra-bright nucleus V = 13.7, represents an end-member case. We used an exposure time of 4 s with the F621M filter to obtain S/N 200 on the nucleus itself in search of structure at 100 km scales. We used long exposures of 390 s through the F606W filter to provide a deep search for debris. The F350LP filter provides an 1.6 higher count rate for a target with a solar-type spectrum, so we used that filter for cycle 21 and plan to use it in cycle 22. If the target requires two different exposure times (Scheila did, but other MBCs did not), we plan to use the M1K1C-SUB aperture for the short exposures (only the region around the nucleus is important in this case, and using the subarray prevents the loss of observing efficiency associated with CCD memory dumps) and the full UVIS aperture for the long exposures. We also plan to dither the exposures to mitigate the effects from bad pixels, cosmic rays, and the inter-chip gap. Previous HST observations show that the timescale for substantial change ranges from weeks (P/2013 P5, Scheila, P/2013 R3) to several months (P/2010 A2, 300163). Therefore, while the first observation should be scheduled as soon as possible after discovery of activity, the science does not require that the first visit be secured within the first three weeks. So ours is a non-disruptive Target of Opportunity program, which will not require heroic scheduling. The first visit will set the scene, by establishing the high-resolution morphology of the object. The second visit, ideally separated from the first by 14 days, will reveal the changes. The two visits together will allow us to make a rational decision about the need for further observations with HST. Main-belt targets have apparent rates of motion 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 numbered asteroids is negligible (sub-arcsecond), compared to the WFC3 field-of-view. For newly discovered objects the uncertainty can be larger but, as we showed even for the low surface brightness and morphologically complex example set by P/2010 A2, attaining the required accuracy is straightforward. 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. Finally, we note that our team can prepare and submit a Phase 2 proposal within hours of activation of this ToO program. The trigger for these observations is the discovery of an object in the main-belt having a Tisserand parameter TJ > 3.1 and showing a coma or tail. Comets have TJ < 3, asteroids have TJ > 3. The parameter is useful only in the context of the circular, restricted three-body approximation. As a result, objects with TJ very close to 3 can be either cometary or asteroidal in nature. In practice, we take TJ > 3.1 as the dividing line, since objects with larger TJ cannot be dynamically linked to the classical comets. The Tisserand constraint is quite stringent, and avoids any possibility of confusion with classical comets (the blue dots in Figure 1). With one exception, the known MBCs have been discovered serendipitously by sky surveys conducted for other purposes. We expect this mode of discovery to continue. Co-I Larson is PI of the Catalina Sky Survey (CSS) which discovered coma at (596) Scheila and co-discovered P/2013 R3. The CSS will be used to obtain astrometric and photometric data on objects discovered elsewhere (or by CSS itself) in support of the HST observations in this proposal. Over the last 7 yrs MBCs have been discovered by on-going surveys at the average rate of about one per year. From this, and bearing in mind statistical fluctuations, we estimate that the probability that an MBC will be discovered in the next HST Cycle is 50% to 100%. SOLAR SYSTEM Default false false false false false SUPPORTED SOLAR SYSTEM ASTEROID Main Belt Comet TYPE=COMET,Q=2.391662587768245,E=0.2420719086106455 ,I=10.96709082187444,O=106.50360151037,W=253.4153978927824,T=28-AUG-2014:05:17:20,TTimeScale=TDB,EQUINOX=J2000,EPOCH=19-SEP-2014:00:00:00,EpochTimeScale=TDB EARTH WFC3/UVIS Imaging No No F350LP 1412096771712 Using ephemeris for target 13864-01-2014S4-GIBBS ephemeris data for target 13864-01-2014S4-GIBBS does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 14.213 to 16.090. ephemeris interval: 14.243 to 16.245 Timing link suitability includes constraints ([02 After 01 by 10.0 to 20.0 days]) The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13864 :visit-id "01" :proposal-version -1 :trans-version "20140605" :date "30-Sep-2014 13:05:24.0" :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 1443744 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13864 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13864 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2866 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) false 1 0 1412096847387 Using ephemeris for target 13864-02-2014S4-GIBBS ephemeris data for target 13864-02-2014S4-GIBBS does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 14.213 to 16.090. ephemeris interval: 14.243 to 16.245 Timing link suitability includes constraints ([02 After 01 by 10.0 to 20.0 days]) The scheduling data was generated by CASM 22.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 13864 :visit-id "02" :proposal-version -1 :trans-version "20140605" :date "30-Sep-2014 13:06:41.0" :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 1443744 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13864 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13864 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2866 :al-overhead-at-end 0 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3222 :pcs-gap 0 ) false 1 0