7204( 12) - 12/16/96 16:15 - [ 0] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7204 Version: 12 Check-in Date: 16-Dec-1996 16:12:54 1.Proposal Title: Pre-Perihelion Observations of the International Rosetta Mission Target Comet 46P/Wirtanen in Support of UV Spectrometer Design and Comet Characterization ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GO/DD 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Alan Stern Southwest Research Institute CoI: Michael A'Hearn University of Maryland N CoI: Jean-Loup Bertaux Service de Aeronomie, France N CoI: Michel C. Festou Observatoire Midi-Pyrenees, France N CoI: Paul D. Feldman Johns Hopkins University N CoI: Rita Schulz Max Planck Institute, Germany N ------------------------------------------------------------------------------------ 6. Abstract The ALICE Ultraviolet Spectrometer team for the International Rosetta mission (a collaboration between ESA and NASA) requests HST DD time to obtain observations of the Rosetta Mission target, comet 46P/Wirtanen, as a part of our instrument design activity. Our specific objectives are to: (i) characterize the variation in UV emissions (particularly, OH) with heliocentric distance in the critical 2-3 AU distance regime where Rosetta will rendezvous with the comet, and (ii) to obtain reflectance spectra of the nucleus, before the comet reaches 2.8 AU and becomes very active, so that far-UV design requirements can be based on data rather than supposition. We propose to use the FOS with grating G270H to meet these objectives. Comet P/Wirtanen has never been observed in the UV, and will reach perihelion in Cycle 6. This is the last perihelion before the launch of Rosetta in 2003. HST is the only observatory capable of obtaining UV spectra of P/Wirtanen. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to use FOS/RD (grating G270H) to obtain the first UV survey observations of comet P/Wirtanen. As described above, we request these observations at three epochs during the period from July to early-November 1996. More specifically, the observing windows we request are: Early July 1996: r_H ~ 2.8 AU, elongation ~ 135 deg, geocentric distance ~ 1.9 AU. Early September 1996: r_H ~ 2.4 AU, elongation ~ 150 deg, geocentric distance ~ 1.5 AU. Early November 1996: r_H ~ 1.9 AU, elongation ~ 85 deg, geocentric distance ~ 1.7 AU. Together, this set of three observations will allow us to span the region of expected activity increase as water becomes the dominant sublimator. With three observations we are confident that a good, logarithmic heliocentric production rate dependence relation can be determined. At 2.8 AU, the predicted OH brightness of Wirtanen (calculated according to the method described by Budzien et al. (1994)) will be 8 R. If Wirtanen is not active when HST makes its observation near 2.8 AU, we will obtain a nearly- uncontaminated nuclear surface reflectance spectrum, as well as a strong upper limit on the rate of water sublimation, which to first order controls the release rates of other coma species once comets are inside 2.5-3 AU. Our second measurement point is design to provide an intermediate measurement, and is located at 2.4 AU (OH ~ 21 R). Our third observing point, at 1.9 AU, is near the end of the period of observability of the comet by HST, when the OH is predicted to be 155 R. These mid-UV measurements are not achievable from the ground. Assuming an OH flux of 1.2x10e-16 erg/cm^2/s/arcsec^2 at r_H = 2.8 AU, a spectrum which detects the integrated OH band at S/N = 7 can be taken with the FOS 4.3" aperture in 20 minutes. Assuming a typical cometary behavior, signal strengths will increase such that at 2.4 and 1.9 AU, the estimated FOS exposure times will be 4 minutes and 1 minute, respectively. However, the range of uncertainty in cometary behavior is such that these estimates could be in error by factors of 5 to 10. This uncertainty is, of course, what we propose to eliminate with these observations, so that the Rosetta UVS can be optimized and its observation plan can be accurately designed. In addition to the OH emissions, which are expected to be the brightest in the mid-UV, we will measure or constrain the brightness of CO2+ (2890 A) and CS (2576 A) emission. Also, the FOS will detect the continuum emission from the cometary nucleus (and inside 2.5 AU, the nucleus+dust). We will use these data to measure the reflectance slope below 3000 A, both before and after the onset of significant H_2O sublimation, in support of Rosetta mid-UV imaging objectives. We propose to obtain all these data using the 3.7x3.7 arcsec FOS acquisition aperture, which both maximizes sensitivity and minimizes acquisition overhead time. Each Wirtanen observation will require 1 orbit. On each orbit we will acquire the object in the FOS/ACQ aperture, obtain an image using the flat mirror, peak up using ACQ/BIN (~9-10 minutes), and then obtain a set of spectra in the 4-minute, ACCUM mode. This is exactly how we are studying the larger but more distant comet-like object 2060 Chiron around its perihelion in 1996 using the FOS. Three orbits are requested in toto, in order to obtain a good understanding of the power-law dependence of emission brightnesses with heliocentric distance. However, a 2-orbit program would provide sufficient observations to meet our minimum objectives. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: , ------------------------------------------------------------------------------------ 7204( 12) - 12/16/96 16:15 - [ 1] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: COMET-WIRTANEN ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: COMET Comet P/Wirtanen ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | TYPE=COMET,Q=1.0637469,E=0.6567490,I=11. | 72255,O=82.20387,W=356.34322,T = 14-Mar- | 1997:03:25:54.0,EQUINOX=J2000,EPOCH=13- | Mar-1997,A1=+0.42,A2=-0.1769,A3=0 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF-LINE(3075)=1.2e-16 | | Ephemeris Uncertainty: 15000 KM | Acquisition Uncertainty: 10 " | ------------------------------------------------------------------------------------------------------------------------------------ 7204( 12) - 12/16/96 16:15 - [ 2] Visit: 01 Visit Requirements: BEFORE 26-Jul-1996 SCHED 50% On Hold Comments: Additional Comments: PLEASE SCHEDULE THIS OBSERVATION AS SOON AS POSSIBLE. It is very important to observe the target before it becomes active. The latest acceptable observation date (26 July 1996) is determined for when comet is at a heliocentric distance of 2.7 AU, but it could be already active by that date. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 COMET-WIRTA FOS/RD ACQ/PEA 4.3 MIRROR SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 60 S REQ EPHEM CORR ECORR1 NEN K SCAN-STEP-Y=1.23 ONBOARD ACQ FOR 2 SEQ 1-2 NON-INT Comments: Time est. from Table 2-4 in FOS Inst. Handbook (v. 6.0). For G2V star, V=20: MIRROR Peak/up time=30s. If comet V<21.8 (estimate from Marsden based on March obs.), then time=189s. A time=300s gives us 0.7mag buffer. ------------------------------------------------------------------------------------------------------------------------------------ 2 COMET-WIRTA FOS/RD ACCUM 4.3 G270H 1 1500 S END ORBIT REQ EPHEM CORR NEN ECORR1 ------------------------------------------------------------------------------------------------------------------------------------ 7204( 12) - 12/16/96 16:15 - [ 3] Visit: 02 Visit Requirements: BETWEEN 22-Aug-1996 AND 16-Sep-1996 SCHED 100% On Hold Comments: Additional Comments: Range of observation dates is determined for when comet is between heliocentric distances of 2.5 and 2.3 AU. Optimal observation date is 04-Sep -1996 when the comet is at a heliocentric distance of 2.4 AU. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 COMET-WIRTA FOS/RD ACQ/PEA 4.3 MIRROR SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 60 S REQ EPHEM CORR ECORR1 NEN K SCAN-STEP-Y=1.23 ONBOARD ACQ FOR 2 SEQ 1-2 NON-INT Comments: Time est. from Table 2.1.6 in FOS Inst. Handbook (v. 5.0). For G2V star, V=15: MIRROR Peak/up time=0.3s. If comet V<21.8 (estimate from Marsden based on March obs.), then time=156s. A time=300s gives us 0.7mag buffer. ------------------------------------------------------------------------------------------------------------------------------------ 2 COMET-WIRTA FOS/RD ACCUM 4.3 G270H 1 25 M END ORBIT REQ EPHEM CORR NEN ECORR2 ------------------------------------------------------------------------------------------------------------------------------------ 7204( 12) - 12/16/96 16:15 - [ 4] Visit: 52 Visit Requirements: BETWEEN 22-Aug-1996 AND 16-Sep-1996 SCHED 100% On Hold Comments: Additional Comments: Range of observation dates is determined for when comet is between heliocentric distances of 2.5 and 2.3 AU. Optimal observation date is 04-Sep -1996 when the comet is at a heliocentric distance of 2.4 AU. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 COMET-WIRTA FOS/RD ACQ/PEA 4.3 MIRROR SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 60 S REQ EPHEM CORR ECORR1 NEN K SCAN-STEP-Y=1.23 ONBOARD ACQ FOR 2 SEQ 1-2 NON-INT Comments: Time est. from Table 2.1.6 in FOS Inst. Handbook (v. 5.0). For G2V star, V=15: MIRROR Peak/up time=0.3s. If comet V<21.8 (estimate from Marsden based on March obs.), then time=156s. A time=300s gives us 0.7mag buffer. ------------------------------------------------------------------------------------------------------------------------------------ 2 COMET-WIRTA FOS/RD ACCUM 4.3 G270H 1 24 M END ORBIT REQ EPHEM CORR NEN ECORR2 ------------------------------------------------------------------------------------------------------------------------------------ 7204( 12) - 12/16/96 16:15 - [ 5] Visit: 03 Visit Requirements: BETWEEN 23-Oct-1996 AND 16-Nov-1996 SCHED 100% On Hold Comments: Additional Comments: Range of observation dates is determined for when comet is between heliocentric distances of 2.0 and 1.8 AU. Optimal observation date is 04-Nov -1996 when the comet is at a heliocentric distance of 1.9 AU. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 COMET-WIRTA FOS/RD ACQ/PEA 4.3 MIRROR SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 60 S REQ EPHEM CORR ECORR1 NEN K SCAN-STEP-Y=1.23 ONBOARD ACQ FOR 2 SEQ 1-2 NON-INT Comments: Time est. from Table 2.1.6 in FOS Inst. Handbook (v. 5.0). For G2V star, V=15: MIRROR Peak/up time=0.3s. If comet V<21.8 (estimate from Marsden based on March obs.), then time=156s. A time=300s gives us 0.7mag buffer. ------------------------------------------------------------------------------------------------------------------------------------ 2 COMET-WIRTA FOS/RD ACCUM 4.3 G270H 1 25 M END ORBIT REQ EPHEM CORR NEN ECORR3 ------------------------------------------------------------------------------------------------------------------------------------ 7204( 12) - 12/16/96 16:15 - [ 6] Visit: 13 Visit Requirements: SCHED 100% On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 COMET-WIRTA FOS/RD ACQ/PEA 4.3 MIRROR SEARCH-SIZE-X=1,SEARCH-SIZE-Y=3, 1 60 S REQ EPHEM CORR ECOR13 NEN K SCAN-STEP-Y=1.23 ONBOARD ACQ FOR 2 SEQ 1-2 NON-INT Comments: Time est. from Table 2.1.6 in FOS Inst. Handbook (v. 5.0). For G2V star, V=15: MIRROR Peak/up time=0.3s. If comet V<21.8 (estimate from Marsden based on March obs.), then time=156s. A time=300s gives us 0.7mag buffer. ------------------------------------------------------------------------------------------------------------------------------------ 2 COMET-WIRTA FOS/RD ACCUM 4.3 G270H 1 25 M END ORBIT REQ EPHEM CORR NEN ECOR13 ------------------------------------------------------------------------------------------------------------------------------------ 7204( 12) - 12/16/96 16:15 - [ 7] Summary Form for Proposal 7204 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters SEARCH-SIZE-X=1 SEARCH-SIZE-Y=3 SCAN-STEP-Y=1.23 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO/DD ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 26-Jul-1996 SCHED 50% REQ EPHEM CORR ECORR1 ONBOARD ACQ FOR 2 SEQ 1-2 NON-INT END ORBIT REQ EPHEM CORR ECORR1 BETWEEN 22-Aug-1996 AND 16-Sep-1996 SCHED 100% END ORBIT REQ EPHEM CORR ECORR2 BETWEEN 23-Oct-1996 AND 16-Nov-1996 SCHED 100% END ORBIT REQ EPHEM CORR ECORR3 REQ EPHEM CORR ECOR13 ONBOARD ACQ FOR 2 SEQ 1-2 NON-INT END ORBIT REQ EPHEM CORR ECOR13 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G270H ------------------------------------------------------------------------------------------------------------------------------------ Target Names COMET-WIRTANEN ------------------------------------------------------------------------------------------------------------------------------------