Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5220 Report Date: 18-Jul-95:17:04 Version: ********** Check-in Date: ********** 1.Proposal Title: THE AURORA AND AIRGLOW OF URANUS ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID SOLAR SYSTEM GTO/WF2 Sub Category GIANT PLANETS ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Dr. John Trauger 2370 USA 818-354-9594 PROJECT SCIENTIST ------------------------------------------------------------------------------------ 7. Abstract WFPC2 observations of Uranus in the FUV will show the spatial distribution of the H Ly a and H2 Lyman and Werner band emissions with 20-80 pixels across the disk (depending on read-out and limiting sensitivity). The Uranus aurora are known to be variable, but present in the sunlit hemisphere, and spatial variations in the airglow emission appear in the Voyager UVS data. We will have a good sensitivity to discrete auroral regions, or ovals, and best measure the airglow emissions near the limb where they are enhanced in both optical depth and brightness. We will also study the extended H cloud (and in cycle 5 the possible OH cloud) coming from Uranus and its ring/satellite system. This proposal is the first phase of a WFPC2 GTO program on Uranus. ------------------------------------------------------------------------------------ 8. Scientific Key Words: JUPITER ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 1.48 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ 12. Special sched req: Time Critical obs. ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5220 PI: Dr. John Trauger Proposal Title: THE AURORA AND AIRGLOW OF URANUS ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Dr. John T. Trauger 2370 USA Prof. John T. Clarke 2660 USA Chris Burrows STSCI USA David Crisp JPL USA John Hoessel UNIV. OF WISCONSIN USA Jay Gallagher UNIV. OF WISCONSIN USA Richard Griffiths JOHNS HOPKINS UNIV USA Jeff Hester ARIZONA STATE UNIV. USA John Holtzman LOWELL OBSERVATORY USA Jeremy Mould CALTECH USA James Westphal CALTECH USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. Uranus is roughly as bright as Saturn in its FUV emissions, and has a much higher reflectivity over 1500-2100 A. Auroral/airglow images with the WFC will give 40 pixels across the 3.8 arcsec disk, and the 2x2 readout may be used for good sensitivity above the read noise. We will use F160W with and without F130LP to separate the optically thick H Lya from the optically thin H2 band emissions. Images with F160W and F165LP will measure the reflected solar component for subtraction from the images, and may show haze absorption. Short F673N images will register the limb position. The FUV images should reveal for the first time the spatial distribution of the UV emissions to identify their auroral and airglow components. The altitude resolution will be limited, but we may still find azimuthal variations in the limb airglow brightness arising from possible strong conjugate plasma flows across the terminator resulting from Uranus' particular magnetic field geometry. The images will also be co-added to image the extended H atmosphere in Ly a resonant scattering, and we can search for different scale heights in different directions revealing different exobase temperatures. Voyager data suggested UV auroral hot spots on Uranus that would be presently observable from Earth for ~30% of the time. Recent IR observations of H3+ emissions from Uranus may show evidence for auroral related structure, in which case we would time the HST observations optimized to view the aurora. ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. The far-UV emissions of Uranus's aurora and airglow can only be recorded from a space-based platform due to atmospheric absorption. The UV emissions are important because they are directly excited by the precipitating energetic articles. IUE has observed temporal variations in the disk-integrated H Ly a emissions for which the emitting region area has not been identified. It is therefore important to image these emissions with HST to resolve the auroral component, which would be spatially confined. The near-IR H3+ emissions from Uranus detected with ground-based telescopes should have an auroral component but these emissions can also be thermally excited by non-auroral processes, and are thus not sufficient to resolve the morphology of the primary auroral processes. In addition, 2x2 WF images would have at least a factor of two better spatial resolution than the ground-based H3+ images. The extended hydrogen corona particular to Uranus can only be detected in the UV. Page 3 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. The Voyager UV data show indication of auroral hot spots on Uranus' dayside that would be visible from Earth at present for only about 30% of the time. There may of course be additional auroral emission regions which were not active during the Voyager encounter. The large uncertainty in the rotation period does not allow prediction of the visibility of the auroral region from the Earth extended from the Voyager data in 1986. Recent IR observations of H3+ emissions from Uranus may show evidence for auroral related structure, and we will use any information derived from these H3+ observations to optimize the time of the HST observations to view the aurora. We will also try to coordinate simultaneous ground-based imaging of the H3+ emissions and the WFPC2 images of the aurora. This will be important to determine the relation between the different emission processes in Uranus' ionosphere. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. Scheduling during dark time is required. We are imaging FUV emissions from H (Lyman alpha) and H2 (Lyman and Werner bands), some very weak emissions, and therefore require minimum contamination from geocoronal Ly a and oxygen airglow emissions in order to obtain the best possible S/N. The exposures cannot be interrupted because of Uranus's fast rotation (~17.24 hours) and known temporal variability in the emissions, and the exposures series have been planned accordingly. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. NONE ------------------------------------------------------------------------------------ 9. Description of previous HST work. No images of Uranus in the UV have been obtained with HST or any other instrument. We estimate that WFPC2 with the Na metal filter will have 4-5 times higher efficiency and a much larger dynamic range than would be possible with the FOC. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Unix workstations are available with IDL and the WFPC2 system SPICA software packages. ------------------------------------------------------------------------------------ 13. Uranus and Neptune form a class of giant planet substantially smaller than Jupiter and Saturn, with much colder lower atmospheres (changing the composition), and with bizarrely tilted and offset magnetic fields. Uranus is roughly as bright as Saturn in the FUV despite being twice as far from the Sun and can be imaged with WFPC2. In addition to bright and highly variable FUV airglow and auroral emissions, Uranus has an extensive hydrogen corona resulting from the planet's low gravity and hot (~800K) upper atmospheric temperature. IUE has observed strong and highly variable H Ly a emissions from Uranus, and it is now known from Voyager and IUE data that these emissions are composed of resonant scattering components combined with poorly understood airglow and auroral emissions. The difficulty in understanding the observed variations with time is due in part to the lack of spatial resolution combined with a large uncertainty in the planetary (magnetic) rotation period of 17.24 +/- 0.01 hours derived in 1986 from Voyager data. We will therefore attempt to resolve the spatial distribution of the H Ly a and the H2 auroral and airglow emissions and help understand the nature of the observed changes with time with WFPC2 images in cycle 4. In cycle 5, with repeated FUV observations we will study the temporal variations and may refine Uranus' rotational period. We may also image (in the NUV) Uranus' extended OH cloud sputtered from the icy ring particles and/or satellites. Page 4 ------------------------------------------------------------------------------------ 11. Address Information Name: JOHN T. TRAUGER Category: PI Institution: 2370 Address: MS 179-225 4800 Oak Grove Drive City: Pasadena State: CA Zip Code: 91109 Country: USA Telephone: 818-354-9594 Telex (or e-mail): ------------------------------------------------------------------------------------ Name: JOHN T. CLARKE Category: Institution: 2660 Address: City: State: Zip Code: Country: Telephone: 313-747-3540 Telex (or e-mail): ------------------------------------------------------------------------------------ Name: GILDA E. BALLESTER Category: Institution: 2660 Address: City: State: Zip Code: Country: Telephone: 313-747-3670 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST b)Solar System Targets ID = 5220 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: URANUS-AUR1 ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET URANUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD = URANUS | | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | OLG OF URANUS BETWEEN 330 60 | ------------------------------------------------------------------------------------------------------------------------------------ REF | DATA | COMMENTS | | 1 |V = -0.6 +/- 0.5 | URANUS AURORA/AIRGLOW FUV IMAGES 2 |F-LINE(1400)=1+/-3E-14,W-LINE(1400)=420 | WITH WFC AND WITH 2 FILTER 3 |F-CONT(1800) = 2 +/- 5 E-13 | COMBINATIONS TO BE MADE IN 4 |SIZE = 3.9 +/- 1 | SEQUENTIAL ORBITS. THE F160BW 5 |F-CONT(5500) = 2.1 +/- 1 E-12 | EXPOSURES SHOULD SCHEDULED ACCORDING 6 |SIZE = 1.1 | TO THE LATEST POSSIBLE INFORMATION | | ON H3+ IR OBSERVATIONS TO HAVE BEST | | CHANCE TO OBSERVE THE AURORA. OLG | | WINDOWS CAN BE EXPANDED SOMEWHAT IF | | NEEDED FOR SCHEDULING. SCHEDULE | | DURING DARK TIME. | ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5220 [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1.1 URANUS-AUR1 WFPC2 IMAGE WF4-FIX F673N ATD-GAIN=15 1 12.0 S 120 5 1 CYCLE 4 CR-SPLIT=NO 6 GROUP 1.1 - 1.5 NO GAP PCS MODE F POS TARG -4.2,0.0 /1.1-1.5 Comments: RED IMAGES OF URANUS WITH SAME GUIDE STARS AS IN LINENUM 1.2 TO IDENTIFY LIMB OF PLANET. ------------------------------------------------------------------------------------------------------------------------------------ 1.2 URANUS-AUR1 WFPC2 IMAGE WF4-FIX F160BW, ATD-GAIN=7 1 1000.0 3 3 1 CYCLE 4 F165LP CR-SPLIT=NO 4 PCS MODE F Comments: IMAGE OF URANUS' BACKGROUND UV SCATTERED LIGHT TO SUBTRACT FROM FUV IMAGES OF AURORA. ------------------------------------------------------------------------------------------------------------------------------------ 1.3 URANUS-AUR1 WFPC2 IMAGE WF4-FIX F160BW ATD-GAIN=7 4 1000.0 10 2 1 CYCLE 4 CR-SPLIT=NO 3 PCS MODE F 4 Comments: FUV IMAGE OF URANUS' AURORA/ AIRGLOW H AND H2 EMISSIONS. DARK TIME. ------------------------------------------------------------------------------------------------------------------------------------ 1.4 URANUS-AUR1 WFPC2 IMAGE WF4-FIX F160BW, ATD-GAIN=7 1 1000.0 10 2 1 CYCLE 4 F165LP CR-SPLIT=NO 3 PCS MODE F 4 Comments: FUV IMAGE OF URANUS' AURORA/ AIRGLOW H AND H2 EMISSIONS. DARK TIME. ------------------------------------------------------------------------------------------------------------------------------------ 1.5 URANUS-AUR1 WFPC2 IMAGE WF4-FIX F673N ATD-GAIN=15 1 12.0 S 120 5 1 CYCLE 4 CR-SPLIT=NO 6 PCS MODE F Comments: RED IMAGES OF URANUS WITH SAME GUIDE STARS AS IN LINENUM 1.4 TO IDENTIFY LIMB OF PLANET AND TELESCOPE POINTING. ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5220 [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GTO/WF2 ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 1.48 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category SOLAR SYSTEM ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category GIANT PLANETS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; GROUP 1.1 - 1.5 NO GAP; PCS MODE F; POS TARG -4.2,0.0 /1.1-1.5 PCS MODE F ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F673N F160BW, F165LP F160BW ------------------------------------------------------------------------------------------------------------------------------------ Target Names URANUS-AUR1 ------------------------------------------------------------------------------------------------------------------------------------