Hi Alison, This is P. Feldman's ACS/GTO program on a TOO comet. As he mentioned in an earlier message, he will update the ephemeris when available. (1) The program is 4 visits, 1 orbit per visit. Can you make sure this is correct i.e. total of 4 orbits. (2) Can you also make sure the BUFFER-TIME is reasonable ? (I assume Paul did it ok) Andre' ----- Submission 1 (Fri May 16 18:00:45 GMT 2003) ----- ----- Submission 48 (Tue Apr 27 14:52:30 GMT 2004) ----- Orbital elements will need to be updated as target (a comet) becomes available. Comets: Gas in the Inner Coma Our target of opportunity program aims at understanding the nucleus-coma interface in comets. Imaging of the near-nucleus region, from both the in situ spacecraft missions to comet Halley in 1986, and more recently with the WFPC2 Planetary Camera, has revealed the structure and evolution of the dust jets associated with active areas on the surface of the nucleus. These dust jets are thought to be driven by the vaporization of the volatiles trapped in the cometary ice. However, the total source inventory of the gaseous component of the coma is not known as there has not been to date direct imaging of a "parent" molecule vaporized directly from the nucleus. In the spectral range of the SBC, the dominant emissions are the Fourth Positive band system of CO and the resonance transitions of its dissociation products carbon and oxygen (oxygen is also produced by the photodissociation of water). The latter, as dissociation products, are rather extended but the CO emission is concentrated close to the nucleus (McPhate et al. 1999). Thus, imaging with the SBC using the BaF_2 filter to remove the OI 1304 A will provide a measure of the gas flow leaving the comet's nucleus. In the event of outbursts (often associated with the rotation of active areas into the sunlit hemisphere), sequential images can provide a direct measure of the gas outflow velocity. The possible presence of a distributed source of CO (such as the purported "CHON" grains invoked to explain the distribution recorded by the Giotto neutral mass spectrometer at Halley) will also be determined. We note that while CO can be detected spectroscopically from the ground at both infrared and millimeter wavelengths, both of these require very high spectral resolving power and the techniques are not suitable for direct imaging of the CO.
This is a Target of Opportunity program to observe any newly-discovered comet that achieves a water production rate of about 2E29 at 1 AU. This roughly maps into a total visual magnitude limit of about 6. This criterion is easily met by comet C/2002 T7 (LINEAR) whose perihelion is on 23-Apr-2004. The comet emerges from inside the solar exclusion zone (50 degree elongation) on 22-May-2004 and is favorably place for HST observations until the end of May. Because of the comet's motion, 1 visit corresponds to 1 orbit because it is virtually certain that the same GS pair will NOT be available for more than 1 orbit. The timeline for the observations is as follows: Visit 1 : STIS/FUV-MAMA spectroscopy of the CO Fourth Positive bands Visit 2: ACS/HRC imaging of the visible coma followed by SBC difference images Visits 3-4 : SBC difference images to isolate the CO Fourth Positive emissions The elements used are from JPL ephemeris #65, and the positions are likely to be off by several arcmins. About 2 weeks prior to the observations, we anticipate that the ephemeris accuracy will be about 1 arcmin, or somewhat less. About 1 week before the observation, we hope that the ephemeris accuracy will be within 30 arcsec, so that GS selection and bright object checking could reasonably be done at that time. At the time of program execution, we expect to know the ephemeris to a few arcsec accuracy. Thus, the offset pointing command that we uplink prior to starting the observations (i.e., the offset specified by the REQ EPHEM CORR special requirement) should place the comet within the 30 x 30 arcsec HRC and SBC apertures. The apparent motion of the comet will be about 0.25 arcsec/sec. Thus, the comet motion should be about 600 arcsec, or 10 arcmin during the 40 mins that we will be trying to track it. If necessary, a part of the tracking will have to be done under GYRO control. None None None 12 false false false false false SUPPORTED SOLAR SYSTEM Elements from JPL/Horizons ephemeris #65 B-V = 0.8, V-R = 0.4 COMET Comet C/2002 T7 (Linear) TYPE=COMET,Q=0.61453796505,E=1.00046060456,I=160.581998192,O=94.8556364616,W=157.740291777,T=23-APR-2004:01:38:46,EQUINOX=J2000,EPOCH=25-JUL-2003:00:00:00,A1=0.0,A2=0.0,A3=0.0 (Tic-Visit :proposal-id 9985 :visit-id "01" :proposal-version -1 :trans-version "20040225" :date "27-Apr-2004 09:20:19.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 504880 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9985 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9985 :visit-id "01" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2588 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3004 :pcs-gap 0 ) false (Tic-Visit :proposal-id 9985 :visit-id "02" :proposal-version -1 :trans-version "20040225" :date "27-Apr-2004 09:20:21.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 92240 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9985 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9985 :visit-id "02" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2587 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3004 :pcs-gap 0 ) false (Tic-Visit :proposal-id 9985 :visit-id "03" :proposal-version -1 :trans-version "20040225" :date "27-Apr-2004 09:20:23.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 37040 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9985 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9985 :visit-id "03" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2587 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3004 :pcs-gap 0 ) false (Tic-Visit :proposal-id 9985 :visit-id "04" :proposal-version -1 :trans-version "20040225" :date "27-Apr-2004 09:20:24.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 37040 :tdrss-contact-duration 0 ) (Tic-Obset :proposal-id 9985 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 9985 :visit-id "04" :orbit-number 1 :pcs-time 365 :si-vis-utilization 2587 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3004 :pcs-gap 0 ) false