6803( 13) - 10/12/98 09:54 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6803 Version: 13 Check-in Date: 12-Oct-1998 09:52:41 1.Proposal Title: Disk-resolved Spectrophotometry of the Dark Side of Iapetus ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 6 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Tilmann Denk Deutsches Zentrum fuer Luft- und Raumfahrt CoI: Keith S. Noll Space Telescope Science Institute N CoI: Dale P. Cruikshank NASA Ames Research Center N CoI: Ralf Jaumann Deutsches Zentrum fuer Luft- und Raumfahrt N CoI: Gerhard Neukum Deutsches Zentrum fuer Luft- und Raumfahrt N CoI: Yvonne J. Pendleton NASA Ames Research Center N CoI: Ted L. Roush San Francisco State University N ------------------------------------------------------------------------------------ 5. 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 (335-1020 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 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 nine different narrow band filters. We will observe near eastern elongation and close to Saturn opposition. Under such conditions, Iapetus will have an angular diameter of about 0.23", or more than 5 PC-pixels. This is sufficient for disk-resolved spectrophotometry of Cassini Regio. ------------------------------------------------------------------------------------ 6803( 13) - 10/12/98 09:54 - [ 2] Observations Description ------------------------ We propose to get spectrophotometry of Iapetus by imaging with WFPC2 at nine different wavelengths (Table). One image offset by half pixel step will be obtained for four filters (F410M, F588N, F656N, and F1042M) in order to evaluate effects of pixelization. Table Iapetus HST observation filter set and exposure times. Approx. ADU Calculated Central for Cassini SNR for HST exp. Filter wavelength D Regio [ ] Cass. Reg. time [sec]-------- ---------- - ------ ----- ---------- ---------- F336W* 3342 A 130 42.0 140 F410M* 4090 A x 124 41.6 120 F502N 5012 A 103 37.4 160 F588N* 5894 A x 157 46.4 40 F656N 6564 A x 147 44.8 100 FR680N 6950 A 173 48.7 40 FR680N18 7630 A 157 46.4 40 FQCH4P15 8929 A 169 48.1 140 F1042M 10184 A x 148 45.0 200-------- ---------- - ----------- --- ------- ---------- * = Close relation to Voyager filter D = Dither image FR680N and FR680N18, Linear Ramp filters The SNR will be between 37 and 48 for all images (Cassini Regio). For the bright polar regions, the SNR will be between 140 and 215. The ADU (gain=14) will be between 1350 and 3260 for "polar pixels". Real Time Justification ----------------------- We require observation within approximately 1 week of Iapetus eastern elongation. Because of the small angular size of Iapetus, we also require observations close to opposition. For 1998, the first week in November (approx. 45th week of the year) fits these requirements best. Calibration Justification ------------------------- None. Additional Comments ------------------- Justification for Solar_System_Targets, Window CML OF IAPETUS FROM EARTH BETWEEN 50 90 Observation of the DARK SIDE of IAPETUS -- CASSINI REGIO -- when as much as possible of this area is visible for HST, when as few as possible of the bright surrounding terrain is visible, and as close as possible to Saturn opposition. [ Because the preferred Iapetus eastern elongation in 1998 is after Saturn opposition, the window 50-90 has been selected instead of a wider 50-130 in order to keep the observation as close as possible to the Saturn opposition date. The original Phase 2 request was 85-95. This was relaxed to get a more flexible observing schedulability. ] Justification for Visit_Requirements BETWEEN 13-SEP-1998 AND 02-DEC-1998 Best opportunity for HST imaging of Iapetus will be close to Saturn opposition (23-Oct-1998 in 1998). 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. ------------------------------------------------------------------------------------ 6803( 13) - 10/12/98 09:54 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 6803( 13) - 10/12/98 09:54 - [ 4] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: IAPETUS-CASSINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: FEATURE IAPETUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | STD=IAPETUS | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | TYPE=PGRAPHIC,LONG=90,LAT=0 | CML OF IAPETUS FROM EARTH BETWEEN 50 90 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(V) = 12.2+/-0.5 | None. | ------------------------------------------------------------------------------------------------------------------------------------ 6803( 13) - 10/12/98 09:54 - [ 5] Visit: 01 Visit Priority: Visit Requirements: BETWEEN 13-Sep-1998 AND 02-Dec-1998 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 ------------------------------------------------------------------------------------------------------------------------------------ 112 IAPETUS-CAS WFPC2 IMAGE PC1 F410M 4090 ATD-GAIN=15,DITHER-TYPE=LINE 1 120 S SINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ 134 IAPETUS-CAS WFPC2 IMAGE PC1 F588N 5894 ATD-GAIN=15,DITHER-TYPE=LINE 1 40 S SINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ 159 IAPETUS-CAS WFPC2 IMAGE PC1 F1042M 10184 ATD-GAIN=15,DITHER-TYPE=LINE 1 200 S SINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ 216 IAPETUS-CAS WFPC2 IMAGE LRF LRF 6950 ATD-GAIN=15 1 40 S SINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ 227 IAPETUS-CAS WFPC2 IMAGE LRF LRF 7630 ATD-GAIN=15 1 40 S SINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ 235 IAPETUS-CAS WFPC2 IMAGE PC1 F656N 6564 ATD-GAIN=15,DITHER-TYPE=LINE 1 100 S SINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ 251 IAPETUS-CAS WFPC2 IMAGE PC1 F336W 3342 ATD-GAIN=15 1 140 S SINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ 268 IAPETUS-CAS WFPC2 IMAGE FQCH4P1 FQCH4P15 8929 ATD-GAIN=15 1 140 S SINI-REGIO 5 ------------------------------------------------------------------------------------------------------------------------------------ 273 IAPETUS-CAS WFPC2 IMAGE PC1 F502N 5012 ATD-GAIN=15 1 160 S SINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ 6803( 13) - 10/12/98 09:54 - [ 6] Summary Form for Proposal 6803 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PC1 LRF FQCH4P15 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=15 DITHER-TYPE=LINE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 13-Sep-1998 AND 02-Dec-1998 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F410M F588N F1042M LRF F656N F336W FQCH4P15 F502N ------------------------------------------------------------------------------------------------------------------------------------ Target Names IAPETUS-CASSINI-REGIO ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 4090 5894 10184 6950 7630 6564 3342 8929 5012 ------------------------------------------------------------------------------------------------------------------------------------