Switched from F606W to F350LP and revised the discussion on observing details. -1696047873 Assigned ID: 1047 ----- Attempting Submission 1 (Sun Feb 24 14:12:55 GMT 2013) ----- HST Phase I Proposal 1047 (HST_MBC_TOO_2013_v4_submitted.pdf.apt) successfully submitted. ----- Attempting Submission 2 (Sun Feb 24 23:53:57 GMT 2013) ----- Please schedule V2 as soon as possible, consistent with being a "non-disruptive" ToO. After analysis of the V1 data, we see that another set of observations at the earliest feasible date is scientifically desired. I updated the target's orbital elements to JPL2. Also, since V1 has already executed using the JPL1 elements, I created a new target for V2. It's the same target, but with improved orbital elements. -344523276 ----- Attempting Submission 1 (Sat Jun 15 14:20:53 GMT 2013) ----- ----- Attempting Submission 2 (Wed Aug 28 12:49:06 GMT 2013) ----- ----- Attempting Submission 3 (Wed Aug 28 17:32:44 GMT 2013) ----- HST Phase II Proposal 13475 (13475.apt) successfully submitted. ----- Attempting Submission 4 (Wed Aug 28 18:10:05 GMT 2013) ----- ----- Attempting Submission 5 (Wed Aug 28 20:39:24 GMT 2013) ----- ----- Attempting Submission 6 (Fri Aug 30 12:29:59 GMT 2013) ----- ----- Attempting Submission 7 (Wed Sep 11 17:09:31 GMT 2013) ----- I didn't run any of the Orbit Planner tools so as to not mess up any of the planning already done by the PC. Main-belt comets (MBCs, or ``active asteroids'') have the orbital characteristics of asteroids but also show transient, comet-like activity. Examples of mass-loss likely caused by ice sublimation and by impact 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 MBC discovered in order to help determine the process driving mass-loss. This proposal is a straightforward continuation of our (so-far un-triggered) ToO approved in Cycle 20. 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 (as with P/2010 A2, for instance), the initial observations alone will be enough to determine whether the morphology is more consistent with sublimation or another origin. In others, careful study of the photometry and evolution over long intervals will be needed for this purpose. Our observing strategy is to take both short and long exposures using WFC3 and a single filter (F606W). Asteroid Scheila, with its ultra-bright nucleus V~13.7, represents an end-member case. We used an exposure time of 0.5 sec (the shortest available) to obtain S/N~200 on the nucleus itself in search of structure at ~100 km scales. An intermediate exposure time of ~40 s brought out the near-nucleus environment without saturating too many pixels, while long exposures of ~400 s provided the deepest search for debris. We plan to take a sequence of at least 3 images (one for each exposure time) at one location on the CCD and then repeat that sequence of images at a dithered location (offset by 0.2'' in each dimension). Dithered, multiple images provide protection from bad pixels and cosmic ray strikes that otherwise might compromise the photometry. Previous HST observations show that the timescale for substantial change ranges from several weeks (Scheila) to several months (P/2010 A2). 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 two 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 (at ~60 km/pixel at 2 AU geocentric distance). 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 typically ~50''/hr, 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 of 162x162''. 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 1" to 2" 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. 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. 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 6 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=1.93384934892737,E=0.1173619073956487,I=4.981097557209049,O=279.3844915611511,W=144.9317439481429,T=17-APR-2014:21:25:27,TTimeScale=TDT,EQUINOX=J2000,EPOCH=22-AUG-2013:00:00:00,EpochTimeScale=TDT EARTH SOLAR SYSTEM Updated to JPL #2 orbital elements COMET Main Belt Comet TYPE=COMET,Q=1.936403971304516,E=0.1152027633258743,I=4.967974595638397,O=279.2852123089732,W=144.2069632687044,T=15-APR-2014:17:39:45,TTimeScale=TDT,EQUINOX=J2000,EPOCH=28-AUG-2013,EpochTimeScale=TDT EARTH WFC3/UVIS Imaging No No F350LP 1377712778468 52.5 1378830973000 95.19208741735628 (Tic-Visit :proposal-id 13475 :visit-id "01" :proposal-version -1 :trans-version "20130722" :date "28-Aug-2013 13:59:38.0" :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 1732496 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13475 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13475 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2817 :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 3150.0 :pcs-gap 0 ) false 1 0 1377712779765 52.5 (Tic-Visit :proposal-id 13475 :visit-id "02" :proposal-version -1 :trans-version "20130722" :date "28-Aug-2013 13:59:39.0" :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 1732496 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 13475 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 13475 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2817 :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 3150.0 :pcs-gap 0 ) false 1 0