7242( 3) - 08/22/97 13:58 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 7242 Version: 3 Check-in Date: 22-Aug-1997 13:58:07 1.Proposal Title: NEPTUNE CLOUD COMPOSITION ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle SOLAR SYSTEM GTO/NIC 7 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: BRADFORD A. SMITH INSTITUTE FOR ASTRONOMY CoI: RICHARD TERRILE JET PROPULSION LABORATORY N CoI: ROLAND MEIER UNIVERSITY OF HAWAII N ------------------------------------------------------------------------------------ 6. Abstract Voyager dramatically extended the results of groundbased observations that had already revealed the presence of clouds on Neptune. Brilliant white clouds were observed at visible wavelengths, contrasting sharply with the blue background of the planet. In the near-infrared groundbased observations, these clouds stand out against the dark background caused by atmospheric methane absorption. It is generally assumed that these clouds are composed of methane ice crystals, but there is no spectroscopic evidence for this. To the contrary, it is curious that the clouds are so prominent in the K band, since solid methane absorbs strongly at several wavelengths in this region. To secure identification of composition, precise spectrophotometry at the highest possible spatial resolution is needed. The filters used in this observation should distinguish methane ice from water ice, and either one of these from neutral scatterers such as carbon monoxide, argon, etc. Because the distribution of bright clouds in Neptune's atmosphere is difficult to predict, two identical visits will be made. ------------------------------------------------------------------------------------ 7242( 3) - 08/22/97 13:58 - [ 2] Observations Description ------------------------ Images of Neptune are taken through 4 filters, F180M, F204M, F222M, and F237M. These moderatly wide bandpasses should distinguish methane ice from water ice or a neutral scatterer such as carbon monoxide, argon, etc. As this program involves precise photometric ratioing and differencing, it is important that we achieve the highest possible S/N. We use a four point spiral dither at the cost of an additional overhead of 6 min 00 sec for Pre-/Post MTO manoevres and a hard to understand additional penalty due to a NIC buffer dump. The dither step of 2.4375 arcsec is slightly larger than the diameter of Neptune and will shift the image by (x + 0.5) pixels per move. Our dither pattern will allow to remove bad pixels and increase the spatial resolution by a factor of 2. While we will not have independent background data at the longest wavelengths, Neptune covers only a small fraction of the field of view and thus leaves adequate empty space to assess the background level. Note that the detector-corrected background is essentially a dc level without any structure. With the exposure times of this proposal and assuming fluxes of 0.02 Jy arcsec-2 for filter F180M, 0.01 Jy arcsec-2 for filter F204M, 0.004 Jy arcsec-2 for filter F222M, and 0.001 Jy arcsec-2 for filter F237M we expect S/N levels as follows (we reduced the S/N produced by the exposure calculator by a factor of 0.66 to account for more recent sensitivity measurements). F180M ---> S/N = 42 at a total exposure time of 4 x 32 sec = 2 min 8 sec F204M ---> S/N = 36 at a total exposure time of 4 x 32 sec = 2 min 8 sec F222M ---> S/N = 25 at a total exposure time of 8 x 48 sec = 6 min 24 sec F237M ---> S/N = 7 at a total exposure time of 8 x 160 sec = 21 min 20 sec Time spend on overhead is as follows 7 min 07 sec for Guide Star Acquisition including extra penalty for moving target 4 min 10 sec for Pre / Post MTO manoevres 2 min 30 sec NIC buffer dump which sums up to a total of 13 minutes 47 sec compared to 32 min 00 sec spent on Neptune. Real Time Justification ----------------------- None Calibration Justification ------------------------- We added darks to this proposal in order to ensure that darks are available for the filters used at the time of our observations. Additional Comments ------------------- None ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: Rodger Thompson*University of Arizona*Steward Obs./NICMOS*933 N. Cherry Ave*Tucson, AZ 85721-0065 Ship Via: Email: thompson@as.arizona.edu ------------------------------------------------------------------------------------ 7242( 3) - 08/22/97 13:58 - [ 3] TARGET LIST b)Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: NEPTUNE ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET NEPTUNE ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=NEPTUNE | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = +7.9+/-0.1 | SIZE=+2.2+/-0.1 | J = +9.5+/-0.7 | J-H = -0.1+/-0.2 | J-K = -1.8+/-0.9 | | ------------------------------------------------------------------------------------------------------------------------------------ 7242( 3) - 08/22/97 13:58 - [ 4] Visit: 01 Visit Requirements: SCHED 40% 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 NEPTUNE NIC2 MULTIAC NIC2 F180M 1.80000 PATTERN = SPIRAL-DITH,NUM-POS = 4 1 DEF CUM ,DITH-SIZE = 2.4375,SAMP-SEQ = STEP16,NSAMP = 8 ------------------------------------------------------------------------------------------------------------------------------------ 2 NEPTUNE NIC2 MULTIAC NIC2 F204M 2.04000 PATTERN = SPIRAL-DITH,NUM-POS = 4 1 DEF CUM ,DITH-SIZE = 2.4375,SAMP-SEQ = STEP16,NSAMP = 8 ------------------------------------------------------------------------------------------------------------------------------------ 3 NEPTUNE NIC2 MULTIAC NIC2 F222M 2.22500 PATTERN = SPIRAL-DITH,NUM-POS = 4 2 DEF CUM ,DITH-SIZE = 2.4375,SAMP-SEQ = STEP16,NSAMP = 9 ------------------------------------------------------------------------------------------------------------------------------------ 4 NEPTUNE NIC2 MULTIAC NIC2 F237M 2.37500 PATTERN = SPIRAL-DITH,NUM-POS = 4 2 DEF CUM ,DITH-SIZE = 2.4375,SAMP-SEQ = STEP64,NSAMP = 10 ------------------------------------------------------------------------------------------------------------------------------------ 5 DARK NIC2 MULTIAC NIC2 BLANK SAMP-SEQ = STEP16,NSAMP = 8 8 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 6 DARK NIC2 MULTIAC NIC2 BLANK SAMP-SEQ = STEP16,NSAMP = 9 8 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7 DARK NIC2 MULTIAC NIC2 BLANK SAMP-SEQ = STEP64,NSAMP = 10 8 DEF CUM ------------------------------------------------------------------------------------------------------------------------------------ 7242( 3) - 08/22/97 13:58 - [ 5] Summary Form for Proposal 7242 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters PATTERN = SPIRAL-DITH NUM-POS = 4 DITH-SIZE = 2.4375 SAMP-SEQ = STEP16 NSAMP = 8 NSAMP = 9 NSAMP = 10 SAMP-SEQ = STEP64 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GTO/NIC ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SCHED 40% ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F180M F204M F222M F237M BLANK ------------------------------------------------------------------------------------------------------------------------------------ Target Names NEPTUNE DARK ------------------------------------------------------------------------------------------------------------------------------------