15094( 15) - 27-Jun-2018 20:10:11 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15094 Version: 15 Check-in Time: 27-Jun-2018 20:10:11 STScI Edit Number: 12 Title Stellar Occultation by Saturn's Rings in the UV ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Tracy M Becker Southwest Research Institute Y CoI: Dr. Kurt David Retherford Southwest Research Institute N CoI: Dr. Joshua E Colwell University of Central Florida N CoI: Dr. Nathaniel J. Cunningham Nebraska Wesleyan University N CoI: Dr. Lorenz Roth Royal Institute of Technology N CoI: Dr. Pippa Molyneux Southwest Research Institute N CoI: Mr. Richard Jerousek University of Central Florida N ------------------------------------------------------------------------------------ Abstract We propose to capitalize on the unique opportunity to observe the July 2018 stellar occultation of the star HD 168233 by Saturn's rings using the COS G230L mode on HST. Our program will characterize the particle size distribution of the rings through analyses of the starlight diffracted by the ring particles. It will also define the shape and structure of the rings through measurements of the optical depth of the variable F ring, the characterization of the self-gravity wakes, and by constraining the A ring edge dynamics six months after the radial swap of the co-orbital moons Janus and Epimetheus, which maintain the ring's outer edge. Saturn's rings are very dark at UV wavelengths; therefore, stellar occultations in the UV have a significantly lower background signal from the ring-reflected sunlight than at longer wavelengths. Furthermore, occultations at UV wavelengths are sensitive to the smallest particles in the rings. The geometry and wavelengths of the stellar occultation from HST COS will complement and extend the science return from the Cassini spacecraft nearly one year after the mission's end. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to observe the stellar occultation of HD 168233 by Saturns rings with one visit consisting of five HST orbits to ensure we encompass the entire occultation. Each orbit will remain fixed on the star as Saturn and its rings pass through the instrument field of view (FOV). We will use the COS G320 L mode centered on 300 nm in Time-Tag mode to obtain spectral information with a high SNR for short integration periods. We will implement the COS observation technique described by Cunningham et al. (2015), which offsets the primary signal source (in our case, the star) by 0.35 arcseconds in the cross-dispersion (COS +y) direction. We can then use the signal observed in the lower half of the COS aperture as an estimate of the background flux, the majority of which will emanate from the ring-reflected sunlight and terrestrial airglow. ------------------------------------------------------------------------------------ 15094( 15) - 27-Jun-2018 20:10:11 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD-168233 STAR, A4-A9 V-IV RA=18H19M39.7480S +/- 0.02417", J2000 V = V = 9.24 DEC=-22D31'43.94" +/- 0.02182" -45.6 Reference Frame: Other: SIMBAD Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 4.1861241362834263E-4 -0.0086 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 15094( 15) - 27-Jun-2018 20:10:11 - [ 3] Visit: 01 (Orbit1) Visit Requirements: BETWEEN 11-JUL-2018:23:40:00 AND 12-JUL-2018:05:20:00 On Hold Comments: Additional Comments: All orbits will be the same setup. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD-168233 COS/NUV ACQ/IMA BOA MIRRORB 1 42 S (42 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 HD-168233 COS/NUV TIME-TA PSA G230L 3000 FP-POS=3, BUFFER-TIME=120 1 1937 S G see below (585 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HD-168233 1 COS/NUV ACQ/IMA BOA MIRRORB none none none none 1 N/A GE HD-168233 2 COS/NUV TIME-TA PSA G230L 3000 none none none none 1 585 S G 15094( 15) - 27-Jun-2018 20:10:11 - [ 4] Visit: 02 (Orbit2) Visit Requirements: AFTER 01 BY 0 Orbits TO 1.8 Orbits; BETWEEN 11-JUL-2018:23:40:00 AND 12-JUL-2018:05:20:00 On Hold Comments: Additional Comments: All orbits will be the same setup. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD-168233 COS/NUV TIME-TA PSA G230L 3000 FP-POS=3, BUFFER-TIME=120 1 1937 S G see below (660 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HD-168233 1 COS/NUV TIME-TA PSA G230L 3000 none none none none 1 660 S G 15094( 15) - 27-Jun-2018 20:10:11 - [ 5] Visit: 03 (Orbit3) Visit Requirements: AFTER 02 BY 0 Orbits TO 1.8 Orbits; BETWEEN 11-JUL-2018:23:40:00 AND 12-JUL-2018:05:20:00 On Hold Comments: Additional Comments: All orbits will be the same setup. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD-168233 COS/NUV TIME-TA PSA G230L 3000 FP-POS=3, BUFFER-TIME=120 1 1937 S G see below (870 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HD-168233 1 COS/NUV TIME-TA PSA G230L 3000 none none none none 1 870 S G 15094( 15) - 27-Jun-2018 20:10:11 - [ 6] Visit: 04 (Orbit4) Visit Requirements: AFTER 03 BY 0 Orbits TO 1.8 Orbits; BETWEEN 11-JUL-2018:23:40:00 AND 12-JUL-2018:05:20:00 On Hold Comments: Additional Comments: All orbits will be the same setup. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD-168233 COS/NUV TIME-TA PSA G230L 3000 FP-POS=3, BUFFER-TIME=120 1 1937 S G see below (2285 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 HD-168233 COS/NUV ACQ/IMA BOA MIRRORB 1 42 S (42 GE S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HD-168233 1 COS/NUV TIME-TA PSA G230L 3000 none none none none 1 2285 S G HD-168233 2 COS/NUV ACQ/IMA BOA MIRRORB none none none none 1 N/A GE 15094( 15) - 27-Jun-2018 20:10:11 - [ 7] Visit: 05 (Orbit5) Visit Requirements: AFTER 04 BY 0 Orbits TO 1.8 Orbits; BETWEEN 11-JUL-2018:23:40:00 AND 12-JUL-2018:05:20:00 On Hold Comments: Additional Comments: All orbits will be the same setup. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 HD-168233 COS/NUV TIME-TA PSA G230L 3000 FP-POS=3, BUFFER-TIME=120 1 1937 S G see below (2792 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ HD-168233 1 COS/NUV TIME-TA PSA G230L 3000 none none none none 1 2792 S G 15094( 15) - 27-Jun-2018 20:10:11 - [ 8] Summary Form for Proposal 15094 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures BOA, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=120, FP-POS=3 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 0 Orbits TO 1.8 Orbits, AFTER 02 BY 0 Orbits TO 1.8 Orbits, AFTER 03 BY 0 Orbits TO 1.8 Orbits, AFTER 04 BY 0 Orbits TO 1.8 Orbits, BETWEEN 11-JUL-2018:23:40:00 AND 12-JUL-2018:05:20:00 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G230L, MIRRORB ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD-168233 ------------------------------------------------------------------------------------------------------------------------------------