8158( 40) - 10/13/00 16:09 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8158 Version: 40 Check-in Date: 13-Oct-2000 16:08:36 1.Proposal Title: FUV diagnostic of Saturn's stratosphere with STIS. Water influx from the ring and polar haze ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 8 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Renee Prange Institut d'Astrophysique Spatiale CoI: Dr. J.E.C. Connerney NASA Goddard Space Flight Center N CoI: Dr. Regis Courtin DESPA, Observatoire de Paris N CoI: Pr. J.C. McConnell York University N CoI: Chris Parkinson York University N ------------------------------------------------------------------------------------ 5. Abstract This program addresses several outstanding issues concerning Saturn's upper stratosphere by means of UV long slit spectroscopy with STIS (6 orbits). In the wavelength range of interest, 1150 - 3100 Angstrom, lie the signatures of scattering by aerosols and of absorption by stratospheric species, and the auroral H and H_2 emissions. The issues cover thermochemical equilibrium and dynamics of the atmosphere through the abundance and latitudinal distribution of the species (hydrocarbons, phosphine, water). We will particularly focus on two particular issues for which we have obtained promising preliminary results in Cycle 4 with GHRS: (i) The distribution of the abundance of heavy hydrocarbons (identified in Cycle 4 spectra) and aerosols in the polar haze with respect to the locus of the aurorae (their assumed source), in order to investigate haze generation processes and transport. (ii) The latitudinal profile of exogenous water in the atmosphere of Saturn (for which we have d etected a strong maximum at southern mid latitudes near the B-C ring footprint in Cycle 4) . The effect of this influx on the composition of Saturn's atmosphere will be inferred from photochemical models and compared to observations (e.g. observed anomalies in CO, H and ionospheric densities). A quantitative and accurate latitudinal profile of water abundance would be an essential test of electromagnetic theories of ring erosion and of the age of the rings. ------------------------------------------------------------------------------------ 8158( 40) - 10/13/00 16:09 - [ 2] Observations Description ------------------------ We will take a series of exposures during 6 HST orbits using STIS in the spectroscopic mode. We will use consecutively the gratings G140L and G230L with FUV/MAMA detector to cover the spectral range ~ 1150 - 3000 Angstrom\ ), We will use the long slit 52x0.5 (G140L) or 52x0.2 (G230L). Its length covers a diameter of Saturn in a single shot, and its width is a good compromise between count-rate and spectral resolution. The slit must follow the central meridian, which means (i) that its orientation is critical, and (ii) that pointing must be more accurate than 1 arcsec, and that the acquisition will be done by an offset from a satellite., The spectral resolution for an extended source using the 0.5 arcsec wide slit is ~ 20 pixels with G140L and 8 pixels with G230L/0.2 arcsec wide slit (Tables 13.34, 13.35), resulting in 20 x 0.6 = 12 Angstrom\ and 1.35 x 8 = 10.8 Angstrom\, respectively. This is about twice the resolution we had with GHRS (which we had to degrade significantly a t short wavelength because of low S/N), and is enough for the kind of absorption spectra we study., Calculation of exposure time, As an estimate of the incident energy flux per arc sec^2 (extended source), we use the values derived from our 1994 observations, as a function of wavelength. To determine the count-rate, we scale the Manual extended source sensitivity (right axis) to the width of the slit, and we sum over 1 arsec along the slit, in order to have a spatial resolution comparable with our GHRS data (we had used the 1.7x1.7 aperture, which was ~ 45^degrees off the rotation axis, so that it extended ~ 2.4 arcsec along CML, and 1 arc sec at half maximum)., , Lambda (Angstrom).............1500....1550.....1600.....1700.....175 0.....1850.....1950.....2050......2250......2350, . , ergcm^- 2s^-1 ..5E- 17...1E-16...3E-16...6E-16...1E-15...3E-15...8E- 15..1.5E-14..7.5E-14..9.5E-14, AA^-1$ arcsec^-2, , cts pix^- 1......1.3E13..9.2E12..6E12...3.4E12, in (1x0.5)''per unit flu x a rcsec^-2 (G140L), idem (G230LB).................................. ...........6E12...1 .1E13..1.7E13..2.8E13 ..5.6E13...7.6E13, , cts pix^-1s^- 1......6E-3...9.2E- 3...1.8E-3...2E-3....6E-3...3.3E-2...1.4E- 2...4.1E-1...4.2E0...6.5E0, in (1x0.5)'', , cts pix^- 1..............7.........10........20.........22, G140L, t=180mn,(1x0.5)'', , cts pix^- 1............................................................ ..15........70........300.......5E3......5E4......7.8E4, G230LB, t= 36 mn,(1x0.5)'', , With these exposure times, we increase the signal by an order of magnitude or more (depending on wavelength) compared to our past data, and in addition, the PFS is significantly oversampled, so that we will easily detect broad band absorption at the 10\ wavelength. In addition, we extend the wavelength range significantly, which will help to improve the model fit: down to ~ 1500 Angstrom, this will help differentiate the spectral signatures of water and hydrocarbons, and up to ~ 3000 An gs trom, this will allow to better constrain the amount of aerosol we must use in the model. , In fact, there is little chance that we can schedule 6 orbits in a row. Therefore, we will have to split the observations into 2 visits. In order to check whether the pointing is similar enough to coadd directly the spectra (Saturn satellite's position is known within 0.5 arc sec only) and the orientation (the orientation accuracy is +/- 4D according to the Manual), and to check that the aurora (responsible for the polar haze) has not varied too much, we will need an additional image in each visit, if it is not possible to fit the 6 orbits in the same visit. Real Time Justification ----------------------- The slit must be oriented along Saturn's CML., The observations should be taken not to far from opposition in order to limit the geocoronal contamination on the FUV/MAMA., Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 8158( 40) - 10/13/00 16:09 - [ 3] Data Distribution Paper Products: NO Media: ELECTRONIC Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 8158( 40) - 10/13/00 16:09 - [ 4] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: SATURN-SOUTH ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET PLANET SATURN ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | TYPE=TORUS,LONG=00,LAT=- | 30,RAD=58600,POLE_LAT=+90,POLE_LONG=00 | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | SURF(1750)=1.5+/-0.7e-15 | Center at south latitude to minimize SURF(2150)=2.0+/-0.5e-14 | the effect of the orientation V = 0.0+/-0.2 | uncertainty on observations of the SIZE=19+/-1.5 | south hemisphere. | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: ENCELADUS-OFFSET ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: SATELLITE SATELLITE ENCELADUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=SATURN | STD=ENCELADUS | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | SEP OF ENCELADUS MIMAS FROM EARTH GT | 10", SEP OF ENCELADUS TETHYS FROM EARTH | GT 10", SEP OF ENCELADUS RHEA FROM EARTH | GT 10", SEP OF ENCELADUS DIONE FROM | EARTH GT 10", OLG OF SATURN BETWEEN 327 | 5 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = 11.7+/-0.1 | If another satellite of Saturn is | used, the position, windows and flux | values must be changed accordingly. | THETYS V0=10.2, MIMAS V0=12.9, RHEA | V0=9.7, DIONE V0=10.4 | ------------------------------------------------------------------------------------------------------------------------------------ 8158( 40) - 10/13/00 16:09 - [ 5] Visit: 01 Visit Priority: Visit Requirements: ORIENT 43.1D TO 43.5D GROUP 01-02 WITHIN 2 D VISIBILITY INTERVAL 52 M On Hold Comments: Additional Comments: SPECIAL REQUIREMENT: The STIS long slit must be along Saturn's CML. The orientation accuracy is critical. ALTERNATE ORIENT 223.1D TO 223.5D. Removed as a special requirement due to problem with implementation of multiple ORIENT ranges in HST ground system. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 110 ENCELADUS-O STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.2 S FFSET CD P Comments: If a brighter satellite was to be used (Tethys, Dione and Rhea)., the exposure time should be adjusted to 0.1sec and ACQTYPE to DIFFUSE with CHECK-BOX=5 and DIFFUSE-CENTER=GEOMETRIC-CENTER ------------------------------------------------------------------------------------------------------------------------------------ 111 SATURN-SOUT STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=120 1 8 M NO SPLIT H UV-MAM G A Comments: Control image to cross check pointing, orientation of Visits 1 and 2, and object variability. ------------------------------------------------------------------------------------------------------------------------------------ 112 SATURN-SOUT STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1000,WAVECAL=NO 1 18.25 M NO SPLIT END ORBIT H UV-MAM G A Comments: What about 1575 A which is proposed by RPS2? ------------------------------------------------------------------------------------------------------------------------------------ 121 WAVE STIS/N ACCUM 52X0.2 G230L 2376 1 30 S NO SPLIT UV-MAM A Comments: G230LB: 1680-3060A, dispersion 1.35A/pix - G230L: 1570-3180A, dispersion 1.58A/pix ------------------------------------------------------------------------------------------------------------------------------------ 122 SATURN-SOUT STIS/N ACCUM 52X0.2 G230L 2376 1 17.85 M NO SPLIT SEQ 121-123 H UV-MAM NON-INT MAX DUR 100.5% A Comments: G230LB: 1680-3060A, dispersion 1.35A/pix - G230L: 1570-3180A, dispersion 1.58A/pix ------------------------------------------------------------------------------------------------------------------------------------ 123 SATURN-SOUT STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1000 1 22.5 M NO SPLIT END ORBIT H UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 131 WAVE STIS/N ACCUM 52X0.2 G230L 2376 1 30 S NO SPLIT UV-MAM A Comments: G230LB: 1680-3060A, dispersion 1.35A/pix - G230L: 1570-3180A, dispersion 1.58A/pix ------------------------------------------------------------------------------------------------------------------------------------ 8158( 40) - 10/13/00 16:09 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 132 SATURN-SOUT STIS/N ACCUM 52X0.2 G230L 2376 1 17.85 M NO SPLIT MAX DUR 100.5% H UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 133 SATURN-SOUT STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1000 1 22.5 M NO SPLIT END ORBIT SEQ H UV-MAM G 131-133 NON-INT A ------------------------------------------------------------------------------------------------------------------------------------ 8158( 40) - 10/13/00 16:09 - [ 7] Visit: 02 Visit Priority: Visit Requirements: ORIENT 43.1D TO 43.5D VISIBILITY INTERVAL 52 M On Hold Comments: Additional Comments: 1 - SPECIAL REQUIREMENT: The STIS long slit must be along Saturn's CML. The orientation accuracy is critical. 2 - If the 6 orbits of this program could be scheduled in a single visit, exposure 210 should be removed and the observing time of exposure 212 should be increased accordingly. ALTERNATE ORIENT 223.1D TO 223.5D. Removed as a special requirement due to problem with implementation of multiple ORIENT ranges in HST ground system. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 210 ENCELADUS-O STIS/C ACQ F28X50L MIRROR ACQTYPE=POINT 1 0.2 S FFSET CD P Comments: 1 - If the 6 orbits of this program could be scheduled in a single visit, this onboard acquisition exposure should be canceled, and the exposure time of exposure 212 should be increased accordingly.******* 2 - If a brighter satellite was to be used (Tethys, Dione and Rhea)., the exposure time should be adjusted to 0.1sec and ACQTYPE to DIFFUSE with CHECK-BOX=5 and DIFFUSE-CENTER=GEOMETRIC-CENTER ------------------------------------------------------------------------------------------------------------------------------------ 211 SATURN-SOUT STIS/F TIME-TA F25SRF2 MIRROR BUFFER-TIME=120 1 8 M NO SPLIT H UV-MAM G A Comments: Control image to cross check pointing, orientation, and object variability between Visits 1 and 2. ------------------------------------------------------------------------------------------------------------------------------------ 212 SATURN-SOUT STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1000,WAVECAL=NO 1 18.25 M NO SPLIT END ORBIT H UV-MAM G A Comments: What about 1575 A which is proposed by RPS2? ------------------------------------------------------------------------------------------------------------------------------------ 221 WAVE STIS/N ACCUM 52X0.2 G230L 2376 1 30 S NO SPLIT SEQ 221-223 UV-MAM NON-INT A ------------------------------------------------------------------------------------------------------------------------------------ 222 SATURN-SOUT STIS/N ACCUM 52X0.2 G230L 2376 1 17.85 M NO SPLIT SEQ 221-223 H UV-MAM NON-INT MAX DUR 100.5% A ------------------------------------------------------------------------------------------------------------------------------------ 223 SATURN-SOUT STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1000 1 22.5 M NO SPLIT END ORBIT H UV-MAM G A ------------------------------------------------------------------------------------------------------------------------------------ 231 WAVE STIS/N ACCUM 52X0.2 G230L 2376 1 30 S NO SPLIT UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 8158( 40) - 10/13/00 16:09 - [ 8] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 232 SATURN-SOUT STIS/N ACCUM 52X0.2 G230L 2376 1 17.85 M NO SPLIT MAX DUR 100.5% H UV-MAM A ------------------------------------------------------------------------------------------------------------------------------------ 233 SATURN-SOUT STIS/F TIME-TA 52X0.5 G140L 1425 BUFFER-TIME=1000 1 22.5 M NO SPLIT END ORBIT SEQ H UV-MAM G 231-233 NON-INT A ------------------------------------------------------------------------------------------------------------------------------------ 8158( 40) - 10/13/00 16:09 - [ 9] Summary Form for Proposal 8158 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures F28X50LP F25SRF2 52X0.5 52X0.2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD STIS/FUV-MAMA STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ TIME-TAG ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT BUFFER-TIME=120 WAVECAL=NO BUFFER-TIME=1000 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 43.1D TO 43.5D GROUP 01-02 WITHIN 2 D VISIBILITY INTERVAL 52 M NO SPLIT NO SPLIT END ORBIT NO SPLIT SEQ 121-123 NON-INT MAX DUR 100.5% NO SPLIT MAX DUR 100.5% NO SPLIT END ORBIT SEQ 131-133 NON-INT ORIENT 43.1D TO 43.5D VISIBILITY INTERVAL 52 M NO SPLIT SEQ 221-223 NON-INT NO SPLIT SEQ 221-223 NON-INT MAX DUR 100.5% NO SPLIT END ORBIT SEQ 231-233 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G140L G230L ------------------------------------------------------------------------------------------------------------------------------------ Target Names ENCELADUS-OFFSET SATURN-SOUTH WAVE ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1425 2376 ------------------------------------------------------------------------------------------------------------------------------------