6803( 4) - 09/12/97 17:37 - [ 1]
PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only
ID: 6803
Version: 4
Check-in Date: 12-Sep-1997
17:36:31
1.Proposal Title:
Disk-resolved Spectrophotometry of the Dark Side of Iapetus
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2. Scientific Category 3. Proposal For 4. Cycle
SOLAR SYSTEM GO 6
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5. Investigators
Contact?
PI: TILMANN DENK DEUTSCHE FORSCHUNGSANSTALT FUER LUFT UND
RAUMFAHRT
CoI: Yvonne Pendleton NASA Ames Research Center N
CoI: Ted Roush San Francisco State University N
CoI: Keith Noll Space Telescope Science Institute N
CoI: Dale Cruikshank NASA Ames Research Center N
CoI: Ralf Jaumann Deutsche Forschungsanstalt fuer Luft- und N
Raumfahrt
CoI: Gerhard Neukum Deutsche Forschungsanstalt fuer Luft- und N
Raumfahrt
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6. Abstract
With this HST observation, we will obtain the first spectrum of pure dark material
on Iapetus' Cassini Regio from near UV to near IR (320-1040 nm). It will allow us to
calibrate higher resolution, earth-based spectra of the leading side of Iapetus. The
origin of the dark material on Iapetus is still currently unknown. A direct
measurement of the spectrum will allow an unbiased comparison of Cassini Regio with
spectra of laboratory samples and spectra of other outer solar system objects and
therefore offer an additional key to the origin question. We will image the leading
hemisphere of Iapetus in 11 narrow band filters. We will observe at eastern
elongation when the visible disk is most completely covered by the dark material
with the minimum coverage by bright polar ice. Near opposition Iapetus will have an
angular diameter of 0.23", or more than 5 PC-pixels. This is sufficient for disk-
resolved spectrophotometry of Cassini Regio. HST is the only astronomical instrument
capable of this observation.
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Observations Description
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We propose to get spectrophotometry of Iapetus by imaging with WFPC2 at 11
different wavelengths (Table). The following criteria have been used for the
Phase-II filter selection: - Choice of filters with central wavelengths
comparable to Voyager-ISS filters (for shorter wavelengths). - Choice of
filters with longer central wavelengths for search of spectral features of
water ice. - Continuous steps throughout the WFPC2 wavelength range as far as
limited observing time allows. One image offset by half pixel step will be
obtained for one or two filters (F410M and possibly F656N) in order to evaluate
effects of pixelization. Table: Iapetus HST observation filter set and exposure
times. Count rate HST exp. Filter D [e-/(sec*pxl)] time [sec] -------- - ------
-------- ---------- F336W* 13 200 F410M* x 14 180 F467M* 38 70 LRF554* 27 100
F588N* 55 50 F656N (x) 21 140 LRF763 55 50 LRF835 43 60 FQCH4P15 20 140 F953N
9.4 300 F1042M 10 260 -------- - -------------- ---------- * = Relation to
Voyager filter D = Dither image LRF554 designates the linear ramp filter at a
wavelength of 554 nm. The two other LRF entries have a similar meaning. All LRF
wavelengths were chosen to fall of the PC. The SNR will be about 50 for all
images (dark area). For the bright polar regions, the SNR will be more than
200. The ADU (for gain=14) will be about 200 for "Cassini Regio pixels", and
approximately 3000 for "polar pixels".
Real Time Justification
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We require observation within 1 day of Iapetus eastern elongation. Because of
the small angular size of Iapetus, we also require observations close to
opposition. One such opportunity in cycle 6 will occur on 01 September 1996.
Calibration Justification
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None.
Additional Comments
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Justification for: Solar_System_Targets, Window: CML OF IAPETUS FROM EARTH
BETWEEN 85 95: Observation of the DARK SIDE of IAPETUS - CASSINI REGIO - when
as much as possible of this area is visible for HST, and when as few as
possible of the bright surrounding terrain is visible. Justification for:
Visit_Requirements: BETWEEN 16-AUG-1996 AND 06-NOV-1996: Best opportunity for
HST imaging of Iapetus will be close to Saturn opposition (26-SEP-1996 during
Cycle 6). Iapetus has a revolution period of nearly 80 days. Therefore, a time
span of 40 days before and after opposition will provide by far the best
observing conditions.
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Data Distribution
Media: 8MM
Blocking Factor: 10
Ship To: PI_Address
Ship Via: UPS
Email:
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6803( 4) - 09/12/97 17:37 - [ 3]
TARGET LIST b)Solar System Targets
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TARGET NUMBER: 1 | TARGET NAME: IAPETUS-CASSINI-REGIO
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TARGET DESCRIPTION: FEATURE IAPETUS
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TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2
|
STD=SATURN | STD=IAPETUS
|
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TARGET POSITION LEVEL 3 | WINDOWS
|
TYPE=PGRAPHIC,LONG=90,LAT=0 | CML OF IAPETUS FROM EARTH BETWEEN 85 95
|
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DATA | COMMENTS
|
SURF(V) = 12.2+/-0.5 | None.
|
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Visit: 01
Visit Priority: <none>
Visit Requirements: BETWEEN 1-NOV-1998 AND 15-NOV-1998
On Hold Comments: <none>
Additional Comments: [1] If expanding of exposure time is possible, expand all images of each
orbit proportionally to fill the orbit. [2] If the 13 proposed exposures (11
exposures, two of them with 'dither' parameter) cannot be fitted into the
two allocated orbits, the following rules should be used: 2A) Change the
exposure numbers in order to find a sequence which fits into the two orbits
(and which could not have been found by using RPS2). If this doesn't work:
2B) Reduce the exposure times if necessary, but by no more than 20%. It is
not necessary to reduce them proportionally, although this might be
preferred. A reduction of exposure times for the longer exposures combined
with a change of the gain state may also be considered. If this doesn't
work, too: 2C) Remove the dither option of exposure no. 231 (filter F656N).
Exposures
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Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special
Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements
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11 IAPETUS-CAS WFPC2 IMAGE PC1 F588N 5894 ATD-GAIN=15 1 50 S
SINI-REGIO
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12 IAPETUS-CAS WFPC2 IMAGE PC1 F467M 4669 ATD-GAIN=15 1 70 S
SINI-REGIO
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13 IAPETUS-CAS WFPC2 IMAGE PC1 F336W 3342 ATD-GAIN=15 1 200 S
SINI-REGIO
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14 IAPETUS-CAS WFPC2 IMAGE PC1 F1042M 10184 ATD-GAIN=15 1 260 S
SINI-REGIO
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15 IAPETUS-CAS WFPC2 IMAGE PC1 F953N 9545 ATD-GAIN=15 1 300 S
SINI-REGIO
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16 IAPETUS-CAS WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=15 1 140 S
SINI-REGIO 5
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22 IAPETUS-CAS WFPC2 IMAGE LRF LRF 5540 ATD-GAIN=15 1 100 S
SINI-REGIO
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23 IAPETUS-CAS WFPC2 IMAGE LRF LRF 7630 ATD-GAIN=15 1 50 S
SINI-REGIO
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24 IAPETUS-CAS WFPC2 IMAGE LRF LRF 8350 ATD-GAIN=15 1 60 S
SINI-REGIO
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25 IAPETUS-CAS WFPC2 IMAGE PC1 F410M 4090 ATD-GAIN=15,DITHER-TYPE=LINE 1 180 S
SINI-REGIO
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Exposures
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Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special
Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements
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231 IAPETUS-CAS WFPC2 IMAGE PC1 F656N 6564 ATD-GAIN=15,DITHER-TYPE=LINE 1 140 S
SINI-REGIO
Comments: If the proposed observations can not be
executed within the two allocated orbits, the
'dither' option of this exposure might be
sacrified.
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Summary Form for Proposal 6803
Item Used in this proposal
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Configurations WFPC2
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Opmodes IMAGE
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Optional Parameters ATD-GAIN=15 DITHER-TYPE=LINE
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Proposal Category GO
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Scientific Category SOLAR SYSTEM
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Special Requirements BETWEEN 1-NOV-1998 AND 15-NOV-1998
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Spectral Elements F588N F467M F336W F1042M F953N FQCH4P15 LRF F410M F656N
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Target Names IAPETUS-CASSINI-REGIO
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