7314( 5) - 09/01/98 17:32 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7314 Version: 5 Check-in Date: 01-Sep-1998 17:31:38 1.Proposal Title: Albedos and Sizes of Planetary Ring Particles ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 7 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Amanda Bosh Lowell Observatory CoI: Catherine B. Olkin Lowell Observatory N CoI: Wendy M. Calvin United States Geological Survey N ------------------------------------------------------------------------------------ 5. Abstract Compositions of the rings of Saturn are poorly understood, even after spacecraft visits. Knowledge of compositions is important for understanding the origin and evolution of ring systems. We propose a series of observations of Saturn's rings to obtain high spatial-resolution spectra from 0.17 to 1.15 micron. We will obtain 1 set of spectra, near phase angle 0 degrees. With known dependence of reflectivity on phase angle and wavelength (via radiative transfer and Mie scattering), we will be able to determine the variation in particle albedo with ring region. This information will be used to search for clues to the compositions of the rings and to study the differences in composition among ring regions. The high spatial resolution possible with HST will allow us to determine properties of individual rings or ring regions as small as 325 km at Saturn. ------------------------------------------------------------------------------------ 7314( 5) - 09/01/98 17:32 - [ 2] Observations Description ------------------------ Acquire Rhea when it is more than 17.4 arcsec from Saturn center. This ensures that Saturn's limb will not be in the acquisition aperture. Peakup is not required because centering accuracy (on Saturn's rings) is required to just 0.1 arcsec. Obtain spectra of Rhea with G750L, G430L, and G230LB gratings to be used for calibration of solar lines in ring spectra. Blind offset to center of Saturn, with slit in proper orientation such that it goes along the long axis of the apparent ellipse of the rings, cutting ansa to ansa. Positioning accuracy here is 0.1 arcsec and 0.5 degrees in slit orientation. Obtain spectra of Saturn's rings with G750L, G430L, and G230LB gratings. For all G750L grating observations, we will obtain only a single grating step, not using the far red end. As the last exposure, obtain an image of Saturn and its rings in the OIII filter, to check centering of the slit on the rings. This should be the last exposure and should not be moved earlier. Real Time Justification ----------------------- None. Calibration Justification ------------------------- None. Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 7314( 5) - 09/01/98 17:32 - [ 3] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: SATURN-RING ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: RING SATURN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 7.0 | B-V = 0.6 | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: RHEA ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE RHEA ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | STD=RHEA | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | SEP OF RHEA SATURN FROM EARTH GT 17.4" | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 9.7 | B-V = 0.78 | | ------------------------------------------------------------------------------------------------------------------------------------ 7314( 5) - 09/01/98 17:32 - [ 4] Visit: 01 Visit Priority: Visit Requirements: PCS MODE FINE ORIENT 316.2D TO 316.5D BETWEEN 20-Oct-1998 AND 24-Oct-1998 SCHED 100% On Hold Comments: Additional Comments: Also acceptable: ORIENT 137.2D TO 138.2D Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 RHEA STIS/C ACQ F28X50O MIRROR ACQTYPE=DIFFUSE,CHECKBOX=7 1 5 S ONBOARD ACQ FOR 20-80 CD III Comments: Acquire Rhea, blind offset to Saturn location. Peakup not required because Saturn is extended, slit positioning required only to 0.1 arcsec. ------------------------------------------------------------------------------------------------------------------------------------ 20 RHEA STIS/C ACCUM 52X0.1 G750L 7751 1 45 S CD ------------------------------------------------------------------------------------------------------------------------------------ 30 RHEA STIS/C ACCUM 52X0.1 G430L 4300 1 200 S CD ------------------------------------------------------------------------------------------------------------------------------------ 40 RHEA STIS/C ACCUM 52X0.5 G230LB 2375 1 600 S CD Comments: RPS2 tries to expand this, and in doing so pushes it over the limit for this orbit. If it would just leave it alone, it would fit fine. ------------------------------------------------------------------------------------------------------------------------------------ 50 SATURN-RING STIS/C ACCUM 52X0.1 G750L 7751 1 60 S CD ------------------------------------------------------------------------------------------------------------------------------------ 60 SATURN-RING STIS/C ACCUM 52X0.1 G430L 4300 1 270 S CD ------------------------------------------------------------------------------------------------------------------------------------ 70 SATURN-RING STIS/C ACCUM 52X0.5 G230LB 2375 1 600 S CD Comments: EXPAND. I want this exposure to be the one expanded if possible, but I want 80 to be the last exposure in the orbit. If I put EXPAND in this exp as a special requirement, it expands it so much that 80 is then pushed into the next orbit. ------------------------------------------------------------------------------------------------------------------------------------ 80 SATURN-RING STIS/C ACCUM F28X50O MIRROR CR-SPLIT=NO 1 10 S CD III ------------------------------------------------------------------------------------------------------------------------------------ 7314( 5) - 09/01/98 17:32 - [ 5] Summary Form for Proposal 7314 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50OIII 52X0.1 52X0.5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=DIFFUSE CHECKBOX=7 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PCS MODE FINE ORIENT 316.2D TO 316.5D BETWEEN 20-Oct-1998 AND 24-Oct-1998 SCHED 100% ONBOARD ACQ FOR 20-80 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G750L G430L G230LB ------------------------------------------------------------------------------------------------------------------------------------ Target Names RHEA SATURN-RING ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 7751 4300 2375 ------------------------------------------------------------------------------------------------------------------------------------