! Refer to the HST Phase II Proposal Instructions to fill this out ! ! Anything after a "!" is ignored, and may be deleted ! ! All keywords with multiple entries are comma delimited except the ! Visit_Requirements and Special_Requirements keywords which can be ! delimited with carriage returns or semi-colons, but not commas ! ! For help call your Program Coordinator: Andy Lubenow ! Phone: 410 338-4928 , E-mail: lubenow@stsci.edu ! ! This partially completed template was generated from a Phase I proposal. ! Name of Phase I Proposal: nicholson-943.prop ! Date generated: Fri Dec 16 15:03:51 EST 1994 ! Revised: Sun Feb 5 1995 (pdn) - 5 targets defined ! Revised: Wed Mar 1 1995 (pdn) - visits & exposures added ! Revised: Sat Mar 4 1995 (pdn/rgf) - pos targs added ! Revised: Wed Apr 5 1995 (pdn/rgf) - visits 2 and 4 modified; new visit 5. ! Revised: Thurs May 11 1995 (pdn/ads) - visit 2 modified to fit in 7 orbits ! Revised: Thurs June 29 1995 (pdn) - visit 2 modified to 6 orbits ! Revised: Sat July 1 1995 (al/pdn) - orbits 19/20 split with 6216. ! ----------------------------------------------------------------------- Proposal_Information ! Section 4 Title: Saturn ring plane crossing observations in August and November 1995 Proposal_Category: GO Scientific_Category: Solar System Cycle: 5 Investigators PI_name: Philip Nicholson PI_Institution: Cornell University CoI_Name: Edward Danielson CoI_Institution: California Institute of Technology Contact: N ! Y or N (designate at most one contact) CoI_Name: Richard French CoI_Institution: Wellesley College Contact: N ! Y or N (designate at most one contact) CoI_Name: Steven Larson CoI_Institution: University of Arizona Contact: N ! Y or N (designate at most one contact) CoI_Name: Jack Lissauer CoI_Institution: SUNY Stony Brook Contact: N ! Y or N (designate at most one contact) CoI_Name: Patrick Seitzer CoI_Institution: University of Michigan Contact: N ! Y or N (designate at most one contact) CoI_Name: Mark Showalter CoI_Institution: Stanford University Contact: N ! Y or N (designate at most one contact) CoI_Name: Bruno Sicardy CoI_Institution: Observatoire de Paris, Meudon Contact: N ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) The plane of Saturn's rings passes through the earth on 10 August 1995, and through the sun on 17-21 November 1995, providing a rare opportunity to determine the thickness, vertical distortions, and pole orientation of the rings. A similar opportunity will not recur until the year 2038. We will obtain time series of images using the Wide Field Camera and methane filter at each crossing time, in order to measure the radial profile of apparent ring thickness, to determine the moment of the earth's crossing to within a few minutes, and to look for the expected warp in the ring plane due to satellite perturbations. In addition, the Planetary Camera will be used to recover the small satellites Pan and Atlas and thus refine their orbital periods. A series of multi-color WFC observations will be used to probe the structure and particle size distribution within the faint E and G rings. Questions ! Free format text (please update) Observing_Description: We propose to observe the passage of the Earth through Saturn's ring plane on 10--11 August 1995 for a total of 9 consecutive orbits, and the passage of the Sun through the ring plane on 21 November 1995 for 6 orbits. VISIT 1: Prior to the actual RPX time on 10 August, we will use 2 orbits to study the color and spatial distribution of the E Ring, with an emphasis on UV imaging. Long WFC exposures of the west ansa (to avoid contamination by bright satellites) will be obtained with the wide-U (F300W) filter, plus shorter exposures with wide-B (F450W) and V and R filters, in order to constrain the particle size distribution and its spatial variations. The wide filters, though non-standard, are necessary because of the very faint signals expected. VISIT 2: On the remaining 7 orbits in August 1995, while looking at the `dark side' of the rings and during the Earth crossing itself, we will obtain a 600 sec exposure WFC image (FQCH4N filter, CR-SPLIT) covering both ring ansae to determine the radial profile of ring brightness, as well as a series of 100 sec PC exposures (FQCH4P15 filter) of the east and west ansa of the rings to detect and follow the orbital motions of the small satellites Pan and Atlas. Longer exposures would result in significant image smear. The 8922 Angstrom methane band filters will be used to minimize scattered light from Saturn. From linear fits to the pre-RPX and post-RPX branches of the ring light curve, we can interpolate to determine both the time of crossing and the edge-on brightness profile as a function of radius. Because all the major satellites will saturate in 600 sec, we will also obtain a 15 sec exposure in the same filter for astrometric and photometric calibration on each orbit. VISIT 3: We also propose to obtain PC images of both ring ansae in the six hours (4 orbits) immediately prior to the time of solar RPX on 21 November 1995, again using the FQCH4P15 methane-band filter to suppress scattered light from Saturn and exposure times of ~400 sec. VISITS 4 & 5: After the sun sets on the rings, we will obtain WFC images of the E and G rings (east and west ansae) in broadband F555W and F675W filters on 2 separate orbits. Observations are timed to avoid contamination of the fields by bright satellites. Real_Time_Justification: Almost all of the proposed observations are time-critical, but do not depend on the exact phasing of the HST orbit relative to Saturn. We request those orbits which will permit observations of Saturn closest to the dates and times specified below. Uncertainties of +/-50 min in the specific observing times are acceptable, and have been factored into our requests. The predicted time of Earth's ring plane crossing (RPX) is 20:54 +/-16 min UT on 10 August, for the nominal pole precession rate and the Saturn pole determined by French et al. (1993). Allowing for a maximum plausible error of +/-100\ overall uncertainty in the time of RPX is +/ -102 min, spanning three HST orbits. In order to determine accurately the exact crossing time, it is necessary to have at least two observations of the brightness of the rings on consecutive HST orbits both before and after the moment of crossing, leading to a total requirement of 7 consecutive orbits. Therefore we request that these 7 orbits be centered on the nominal RPX time, so that we observe between August 10, 16:06 UT and August 11, 1:42 UT, or the nearest practicable approximation. The E Ring observations are not as time-critical, but should be made (1) shortly prior to August 10, when the dark side of the rings is visible, and (2) at a time when bright satellites are not present between distances of 2.5 and 8 Saturn radii (25-80'') from the planet on the ansa being observed. Prior to the above 7 orbits at Aug 9.75 - 10.3 is the optimal time, as it satifies both constraints and the ring brightness will be at a minimum. The predicted mid-time of the solar RPX is 15:09 +/-30 min UT on 19 November 1995, with an additional uncertainty of +/-137 min associated with a maximum +/-100\ rate. Because of the finite solar angular diameter, the solar crossing takes place over a period of 3.71 days, centered on the above time. The critical time is when the last rays of the sun strike the observed (northern) side of the rings, on November 21, 11:59 UT and we wish to observe the main rings on the 4 orbits immediately prior to this time. The E and G rings will be observed shortly afterwards, optimally on November 27 and Nov 28 when bright satellites interfere least. Calibration_Justification: Additional_Comments: Solar_System_Targets ! Section 5.2 Target_Number: 1 Target_Name: SATURN Description: PLANET SATURN Level_1: STD = SATURN ! Satellite of Sun Window: Flux: SURF(V) = 6.6 ! Include at least V and B-V B-V = 1.0 Comments: Target center of Saturn disk. Target_Number: 2 Target_Name: SATURN-EAST-ANSA Description: RING SATURN Level_1: STD = SATURN ! Satellite of Sun Level_2: TYPE = TORUS, ! Satellite of Level_1 LONG = 270, LAT = 0, RAD = 1.37E05, POLE_LAT = +90 Window: Flux: SURF(V) = 15.0 ! Include at least V and B-V B-V = 0.65 Comments: Eastern ansa of Saturn rings centered on outer edge of the A ring. Flux is edge-on ring brightness per LINEAR arcsecond. Target_Number: 3 Target_Name: SATURN-WEST-ANSA Description: RING SATURN Level_1: STD = SATURN ! Satellite of Sun Level_2: TYPE = TORUS, ! Satellite of Level_1 LONG = 90, LAT = 0, RAD = 1.37E05, POLE_LAT = +90 Window: Flux: SURF(V) = 15.0 ! Include at least V and B-V B-V = 0.65 Comments: Western ansa of Saturn rings centered on outer edge of the A ring. Flux is edge-on brightness per LINEAR arcsecond. Target_Number: 4 Target_Name: SATURN-EAST-ERING Description: RING SATURN Level_1: STD = SATURN ! Satellite of Sun Level_2: TYPE = TORUS, ! Satellite of Level_1 LONG = 270, LAT = 0, RAD = 3.25E05, POLE_LAT = +90 Window: Flux: SURF(V) = 18.6 ! Include at least V and B-V B-V = 0.58 Comments: Eastern ansa of Saturn E ring centered 50 arcsec from center of Saturn. Target_Number: 5 Target_Name: SATURN-WEST-ERING Description: RING SATURN Level_1: STD = SATURN ! Satellite of Sun Level_2: TYPE = TORUS, ! Satellite of Level_1 LONG = 90, LAT = 0, RAD = 3.25E05, POLE_LAT = +90 Window: Flux: SURF(V) = 18.6 ! Include at least V and B-V B-V = 0.58 Comments: Eastern ansa of Saturn E ring centered 50 arcsec from center of Saturn. ! Clarke's target Target_Number: 33 Target_Name: SAT-RPX-IMAGE-3 Description: PLANET SATURN Level_1: STD = SATURN level_2: type = pos_angle, rad = 50.3, ang = 274.6, ref = north Window: WND FROM 10-AUG-95:15 TO 10-AUG-95:18 Flux: V = -0.6 +/- 0.5 SIZE = 19 +/- 3 F-CONT(5500) = 7.8 +/- 5E-12 comments: Imaging East ansa of rings on WF3 with Saturn offset onto WF2. Visits ! Section 6 ! =================================================================== Visit_Number: 1 Visit_Requirements: ! Section 7.1 ! PCS MODE [Fine | Gyro] ! TBD ! GUIDing TOLerance ! TBD BETWEEN 09-AUG-95:18:00 AND 10-AUG-95:05:00 ! GROUP WITHIN