8659( 68) - 01/16/03 14:10 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 8659 Version: 68 Check-in Date: 16-Jan-2003 14:09:59 1.Proposal Title: High Resolution Spectrum of the Venus Lyman-Alpha Line Profile ------------------------------------------------------------------------------------ 2. Proposal For 3. Cycle GO 9 ------------------------------------------------------------------------------------ 4. Investigators Contact? PI: Mark Bullock Southwest Research Institute CoI: William Colwell EarthWatch N CoI: Dr. Larry Esposito LASP/U. of Colorado N CoI: Dr. Randy Gladstone Southwest Research Institute N CoI: Dr. Chan Na (self) N CoI: Dr. Wayne Pryor LASP/U. of Colorado N CoI: Dr. Ian Stewart LASP/U. of Colorado N ------------------------------------------------------------------------------------ 5. Abstract We propose to record a single high spectral resolution observation of the Venus Lyman-alpha line, while HST is within Earth shadow and Venus is at 47.1 degrees solar elongation, with a supporting observation of the Lyman-alpha geocorona outside the exclusion zone (50 degrees). This Lyman-alpha line profile will be compared with emergent line profiles from Venus thermosphere radiative transfer models to assess the energetics and contributions from supra-thermal sources of hydrogen, a long- standing issue in Venus aeronomy. This information will enhance understanding of the pathways of hydrogen escape from Venus and constrain models of Venus climate evolution. The line profile will be used to assess the abundance of deuterium in the Venus atmosphere, a quantity with great importance to atmospheric evolution models. The HST STIS instrument is the only instrument capable of making these far UV observations with sufficient spectral resolution to address the details of hydrogen energetics in the Venus thermosphere and exosphere. HST previously observed Venus with Esposito as PI (P4518 and P5783). ------------------------------------------------------------------------------------ 8659( 68) - 01/16/03 14:10 - [ 2] Observations Description ------------------------ Our goal is to obtain one high resolution spectrum of the emergent Venus Lyman- alpha line. The observations will be taken with the STIS/FUV MAMA echelle spectrograph in E140H mode with the 0.2X0.09" slit to maximize spectral resolution. Data will be taken in time tag mode, while HST is in Earth shadow but Venus is above the horizon. Similar observations of Jupiter by HST in timetag mode, an object five times brighter than Venus in Lyman-alpha for 100 seconds, worked without any difficulties. We will integrate on Venus for as long as possible within Earth shadow, approximately 240 s. A second observation is of the geocorona with the same settings, but we integrate longer (960 s) to reduce the noise contribution from the background subtraction. Venus' velocity shifts the Venus lines by 0.05 Angstrom from the geocoronal background lines, (three times the width of the cold component of the Lyman-alpha line), facilitating background removal. HST will be in sunlight for the background observation. Ideally, this background observation would be taken in Earth shadow as well, but pointing timing requirements preclude this. The Lyman-alpha profile shape varies with location on Venus, due to geometric effects on radiative transfer and to spatial variation of the thermospheric photochemistry that drives the hot hydrogen production. We choose a location near the sub- solar region toward disk center to maximize signal, simplify the geometry, and examine the region most heavily modeled and best understood. The Venus disk will be at half phase. The window for observing Venus is too short to allow for pointing using guide stars. We prefer to point 4" onto the disk from the sub- solar limb to guarentee that inertial pointing will place the slit on the bright dayside of the Venus disk. There are two opportunities to observe Venus at maximum elongation during Cycle 9, each with a window approximately a week wide. Optimum dates are: Date 19 Jan 2001 8 Jun 2001 V Magnitude -4.3 -4.2 Solar Elongation 47.1 D East 45.8 D West Disk Diameter 24.8" 23.9" Doppler Shift -0.052 +0.057 Angstrom The 2001 Jan 19 date is preferred so the Doppler shift moves the Venus deuterium line away rather than toward the geocoronal Lyman-alpha line. Using the STIS ETC, we expect a S/N for the Venus Lyman-alpha peak (20 kR) of 17.5 per resolution element (2.2 pixels) at line center. A deuterium Lyman-alpha peak of 400 R will have a S/N of 2.8, but the line integrated S/N will be of order 5, adequate for a quanitative detection. The O I 1304 Angstrom triplet will have a S/N of 18.5 at line center for an average line in the triplet. We will co-add in frequency space to improve the S/N in the fainter line wings. The major source of background emission is likely to come from Lyman-alpha and O I emissions in the Earth's thermosphere. Geocoronal O I 1304 Angstrom brightnesses are on the order of 1 kR (Link et al. 1988). The H I Lyman-alpha geocoronal background will be large (8-30 kR) and requires subtraction by observing the geocoronal contribution. The different viewing geometry of the background observation can be corrected for through geocoronal modeling. The bright N I 1200 Angstrom geocoronal line will be present in the background but there is not a correspondingly bright Venus line. Real Time Justification ----------------------- Venus observations are slightly within the 50 degrees exclusion zone, and must be taken while HST is in Earth shadow but Venus is above the horizon. HST then is pointed out of the exclusion zone before sunrise. This provides an approximately four minute window for observations. Venus has been observed by HST on two previous occasions without deliterious effects (P4518 and P5783, both with Esposito as PI), and our requested solar elongation is similar, within 3 degrees of the exclusion zone. The opportunity to spectroscopically determine the Venus deuterium abundance and to directly observe the energy 8659( 68) - 01/16/03 14:10 - [ 3] distribution of hydrogen atoms in the thermosphere, both of which will provide essential insight into today's thermosphere and exosphere and into the evolutionary history of Venus, is a compelling reason to perform these observations. (none) Calibration Justification ------------------------- No wavecal requested for the VENUS target (WAVECAL=NO). The limited time available is needed for this science exposure. Wavecal is requested for the VENUS+5D target. Additional Comments ------------------- ------------------------------------------------------------------------------------ 8659( 68) - 01/16/03 14:10 - [ 4] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 3 GS-ACQ-TEST UNIDENTIFIED, RA=1H 53M 28.2178S +/- 1", J2000 V = 20 UNDESIGNATED DEC=9D 6' 25.088" +/- 1" Coordinate Source: Other_Source: MOSS Comments: This target will be used to perform a guide star acquisition test prior to the Venus obvservation. This pointing is where Venus-Cresent will be at the planned time of observation (2001-JUN-06 00:13:50 UT). The coordinates must be updated if the planned observation time changes. 4 GS-ACQ-TEST- UNIDENTIFIED, RA=259.129D +/- 0.001D, DEC=- J2000 V = 20 2 UNDESIGNATED 20.499D +/- 0.001D Coordinate Source: Other_Source: FOV Comments: This target will be used to perform a guide star acquisition test prior to the January 2003 Venus obvservation. 8659( 68) - 01/16/03 14:10 - [ 5] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 1 | TARGET NAME: VENUS-CRESCENT ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET VENUS ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=VENUS | TYPE=POS_ANGLE,RAD=9.75,ANG=0.0,REF=SUN | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | SEP OF SUN VENUS FROM EARTH GT 45.5D, | R_VEL VENUS EARTH GT 0.0 | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | F-LINE(1216)=6.2+/-2.0e-13 | W-LINE(1216)=0.015+/-0.005 | V = 4.1+/-0.2 | | Ephemeris Uncertainty: 10 S | Acquisition Uncertainty: 2 " | ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 | TARGET NAME: VENUS+5D ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET VENUS+5D ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 | TARGET POSITION LEVEL 2 | STD=VENUS | TYPE=POS_ANGLE,RAD=18000,ANG=180.0,REF=S | UN | ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 | WINDOWS | | ------------------------------------------------------------------------------------------------------------------------------------ DATA | COMMENTS | V = -4.1+/-0.2 | F-LINE(1216)=1.0+/-0.5e-12 | W-LINE(1216)=0.03+/-0.015 | | Ephemeris Uncertainty: 10 S | Acquisition Uncertainty: 30 " | ------------------------------------------------------------------------------------------------------------------------------------ 8659( 68) - 01/16/03 14:10 - [ 6] Visit: 01 Visit Priority: Visit Requirements: 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 ------------------------------------------------------------------------------------------------------------------------------------ 10 VENUS+5D S/C POINTIN V1 1 1 S G Comments: This exposure establishes a pointing near Venus but outside of HST's solar avoidance zone. Doing this minimizes the slew distance when slewing to Venus. This is a precautionary measure to protect against an unusually large pointing error after the slew to Venus. While such an error is unlikely in general, it is even more unlikely for a small slew. ------------------------------------------------------------------------------------------------------------------------------------ 20 VENUS-CRESC STIS/F TIME-TA 0.2X0.0 E140H 1234 BUFFER-TIME=600,WAVECAL=NO 1 4.25 M SHADOW GS ACQ SCENARIO ENT UV-MAM G 9 SINGLE SEQ 20-40 NON-INT A GSPAIR 0624100797F10000000000F0 Comments: (1) Maximize duration of VENUS target exposure. (2) Venus' maximum elongation is 47.1 degrees, within the 50 degree exclusion zone. It will be observed while HST is within the Earth's shadow. Exposure time for Venus will be severly constrained, and this observation is designed to maximize the time available for the Venus science exposure. (3) No wavecal requested for the VENUS target (WAVECAL=NO). The limited time available is needed for this science exposure. (4) Optimum observing date is 17 Jan 2001, +/- 5 days, when Venus will be at maximum solar elongation and its deuterium Lyman-alpha line will be Doppler shifted away from the geocoronal Lyman-alpha line. The actual time range of the observing window will be dictated by the operational goal of maximizing the solar elongation of Venus. ------------------------------------------------------------------------------------------------------------------------------------ 8659( 68) - 01/16/03 14:10 - [ 7] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 30 VENUS+5D STIS/F TIME-TA 0.2X0.0 E140H 1234 BUFFER-TIME=1000 1 16 M NEW OBSET FULL ACQ UV-MAM G 9 A Comments: (1) Geocoronal Lyman-alpha foreground and interplanetary Lyman-alpha background, for subtraction from the Venus Lyman-alpha line. (2) Pointing accuracy needed is 10', so GS Aquisition is adequate. (3) Target is outside the 50 degree solar elongation exclusion zone. Here i have referred to the location from Venus center (5 degrees anti-sunward). The rps2 software appears to indicate it as unschedualable because Venus is within the exclusion zone even though this target/exposure is not. RA and Declination can be provided or calculated instead of an offset once the date of the observation is known, if RA, Dec. is preferred. (4) Wavecal is requested for the VENUS+5D target. ------------------------------------------------------------------------------------------------------------------------------------ 40 WAVE STIS/F ACCUM 0.2X0.0 E140H 1234 1 DEF UV-MAM 9 A ------------------------------------------------------------------------------------------------------------------------------------ 8659( 68) - 01/16/03 14:10 - [ 8] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Guide star acquisition test. BETWEEN may need to be modified if planned time for Venus observations (visit 1) changes. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 GS-ACQ-TEST STIS/C ACCUM 0.2X0.0 MIRROR 1 1 S GS ACQ SCENARIO SINGLE CD 9 GSPAIR 0062300194F20000000000F0 ------------------------------------------------------------------------------------------------------------------------------------ 8659( 68) - 01/16/03 14:10 - [ 9] Visit: 03 Visit Priority: Visit Requirements: BEFORE 01-Jan-2003 On Hold Comments: Additional Comments: Guide star acquisition test. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 10 GS-ACQ-TEST S/C POINTIN V1 1 1 S GS ACQ SCENARIO SINGLE -2 G GSPAIR 0624100797F10000000000F0 ------------------------------------------------------------------------------------------------------------------------------------ 8659( 68) - 01/16/03 14:10 - [ 10] Summary Form for Proposal 8659 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures V1 0.2X0.09 ------------------------------------------------------------------------------------------------------------------------------------ Configurations S/C STIS/FUV-MAMA STIS/CCD ------------------------------------------------------------------------------------------------------------------------------------ Opmodes POINTING TIME-TAG ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=600 WAVECAL=NO BUFFER-TIME=1000 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements SHADOW GS ACQ SCENARIO SINGLE SEQ 20-40 NON-INT GSPAIR 0624100797F10000000000F0 NEW OBSET FULL ACQ GS ACQ SCENARIO SINGLE GSPAIR 0062300194F20000000000F0 BEFORE 01-Jan-2003 GS ACQ SCENARIO SINGLE GSPAIR 0624100797F10000000000F0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E140H MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names VENUS+5D VENUS-CRESCENT WAVE GS-ACQ-TEST GS-ACQ-TEST-2 ------------------------------------------------------------------------------------------------------------------------------------ Wavelengths 1234 ------------------------------------------------------------------------------------------------------------------------------------