We propose to observe the newly discovered comet C/2011 W3 Lovejoy at one epoch near its closest approach to the Earth in early-January 2012. Lovejoy is a member of the Kreutz group of sungrazing comets and is the first sungrazing comet known to have survived perihelion during the era of modern observations (since 1970). Its size is currently unconstrained but is critical for understanding Lovejoy’s place in the Kreutz group hierarchy (either as one of the 1600+ known “pygmy” fragments or one of a handful of major fragments of the parent body, which support and fuel the rest). Kreutz comets are known to fragment frequently, and we expect that Hubble’s high spatial resolution will reveal individual fragments undetectable by any other means. We will estimate the size distribution of these fragments. Due to Lovejoy’s extreme southern declination, small solar elongation, and 300+ year orbit, these observations can only be obtained using Hubble, and cannot be accomplished at any other epoch.

We will obtain 6 x 350s exposures using the F606W filter. We will use two different dither positions (3 images at each dither location) to fill-in the gap between the two CCDs and to mitigate the effects of bad pixels. If necessary, the exposure time for the sixth image should be reduced to fit the observations into one orbit. SOLAR SYSTEM 0 false 0.0 0.0 false false false false SUPPORTED SOLAR SYSTEM COMET Newly discovered sungrazing comet TYPE=COMET,Q=0.005554772513974684,E=0.9999271792540354,I=134.4069584659192,O=326.520935644692,W=53.61581727191412,T=16-DEC-2011:00:20:00,TTimeScale=TDB,EQUINOX=J2000,EPOCH=08-JAN-2012,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 WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F814W 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 WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F814W 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 WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F475W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F814W WFC3/UVIS Imaging No No F814W Using ephemeris for target 12792-01-LOVEJOY ephemeris data for target 12792-01-LOVEJOY does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 11.213 to 13.091. ephemeris interval: 11.365 to 12.091 The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12792 :visit-id "01" :proposal-version -1 :trans-version "20110825" :date "22-Dec-2011 21:33:28.0" :trans-errors '(:WARNINGS 1 :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 12792 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12792 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2944 :al-overhead-at-end 0 :internal-dur-at-end 670 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) false 1 1