15098( 11) - 07-Dec-2017 03:42:48 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 15098 Version: 11 Check-in Time: 07-Dec-2017 03:42:48 STScI Edit Number: 8 Title Calibrating ACS-SBC Using STIS at Lyman Alpha (121.567 nm) ------------------------------------------------------------------------------------ Type Cycle GO 25 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Dolon Bhattacharyya Boston University Y CoI: Prof. John T. Clarke Boston University N CoI: Dr. Majd A Mayyasi Boston University N ------------------------------------------------------------------------------------ Abstract This short calibration program is needed to correctly interpret existing STIS and ACS data on the exospheres of several solar system objects. It will allow us to calibrate observations of planetary exospheres, and to quantitatively determine the atmospheric escape flux, from Mars, Uranus, Titan and other solar system objects, and to contribute to the calibration of the MAVEN IUVS instrument. The need for added calibration is driven by the large uncertainty in the sensitivity of ACS/SBC images at H Lyman alpha (121.6 nm) and also by the lack of a Lyman alpha flat field for STIS G140L long aperture spectra, in both cases for diffuse emissions. The STIS instrument sensitivity is well calibrated at Lyman alpha in the G140L mode through calibration star observations, but there is no flat field specifically at Lyman alpha for diffuse emissions filling the aperture. The ACS/SBC F115 mode is calibrated for a mean wavelength in the bandpass, but as an imaging instrument the specific sensitivity at Lyman alpha has not been measured. These calibrations could be obtained through observations of the geocoronal Lyman alpha emission, comparing the count rates of STIS G140L and ACS/SBC for the same diffuse source brightness, and obtaining the STIS Lyman alpha flat field from the observations of diffuse emission. This study will be beneficial for both the planetary and the astrophysics community as hydrogen is the most abundant element in our universe and Lyman alpha is the most probable transition in H atoms. The flat field for STIS in Lyman alpha will benefit the analysis of past and future GO program data and will be delivered to STScI for use by the observational community. ------------------------------------------------------------------------------------ Observations Description ------------------------ We propose to take ACS/SBC F115LP and STIS UV-MAMA observations of the geocorona + interplanetary hydrogen (IPH) in the G140L grating mode with the 52" x 2" slit in order to calibrate ACS SBC at Lyman alpha. This observing campaign will be executed in 2 HST orbits with the first one involving observations with ACS and the second one involving observations only with STIS. The ACS orbit will utilize the F115LP (clear) filter to image the geocorona+IPH, which allows all FUV wavelengths up to 115 nm including Lyman alpha (121.6 nm). The STIS orbit will observe the geocorona + IPH with the G140L grating. This will allow us to compare the brightness of the same diffuse Lyman alpha emission (geocorona + IPH) using both STIS (whose sensitivity at Lyman alpha is known) and ACS thereby making it possible for us to calculate the absolute calibration of the ACS/SBC detector at Lyman alpha. One important 15098( 11) - 07-Dec-2017 03:42:48 - [ 2] thing to note about this observation is that it has to be conducted in conjunction with the second visit of another proposal selected for this cycle (#15097). Proposal #15097 is to observe Mars with the ACS-SBC detector and they require background calibration images of the geocorona + IPH with ACS-SBC, which are critical for the analysis of those images. Those calibration images would be provided by the ACS orbit executed in this proposal which will image the sky background 5 arcminutes away from Mars and has to be executed immediately after the Mars observation orbit from visit 2 of proposal #15097. Most of the ACS observations will be conducted in the Earth's shadow to minimize the count rate from Lyman alpha photons scattered by the geocorona. The expected sky background count rate with Lyman alpha will be well below the limit of 200, 000 counts/sec, and the local count rate limits will also not be exceeded. Our earlier observations of the geocorona with ACS had maximum count rates of ~70, 000 counts/sec which is well below the maximum limit of 200, 000 counts/sec for solar maximum conditions. For the proposed observations, the solar Lyman alpha flux would be lower as the solar cycle is in its minimum and the HST-Sun angle would not go below 50 degrees. The STIS observations will be conducted looking at the same part of the sky as ACS with the G140L grating and with the 52" x 2' aperture. It is important to observe the same part of the sky as ACS in order to calibrate ACS using STIS, because the sky background which is mainly the geocorona is changing constantly with HST's orbit and cannot be modeled accurately. The exposure time for STIS would be close to 40 minutes so as to allow us to construct a flat field for STIS with reduced noise fluctuations in the signal. This will help in the analysis of HST data of Uranus obtained through a previous proposal (GO-10502) to the HST program. ------------------------------------------------------------------------------------ 15098( 11) - 07-Dec-2017 03:42:48 - [ 3] TARGET LIST Solar System Targets ------------------------------------------------------------------------------------------------------------------------------------ TARGET NUMBER: 2 TARGET NAME: SKY-NEAR-MARS ------------------------------------------------------------------------------------------------------------------------------------ TARGET DESCRIPTION: PLANET Lyman alpha emission from geocorona and interplanetary medium near Mars ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 1 TARGET POSITION LEVEL 2 STD=MARS TYPE=POS_ANGLE, RAD=295, ANG=0, REF=NORTH ------------------------------------------------------------------------------------------------------------------------------------ TARGET POSITION LEVEL 3 WINDOWS ------------------------------------------------------------------------------------------------------------------------------------ DATA COMMENTS V = 0 +/- 0 Sky emission ranging from 1-18 kRayleigh Ephemeris Center: EARTH ------------------------------------------------------------------------------------------------------------------------------------ 15098( 11) - 07-Dec-2017 03:42:48 - [ 4] Visit: 01 Visit Requirements: ORIENT 283D TO 290 D On Hold Comments: Additional Comments: To be executed just after the Mars observing orbit of visit 2 of GO-15097. 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 SKY-NEAR-MA ACS/SBC ACCUM SBC F115LP 13 100 S RS (1300 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 SKY-NEAR-MA ACS/SBC ACCUM SBC F140LP 6 100 S (600 RS 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 | ------------------------------------------------------------------------------------------------------------------------------------ SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 1 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 2 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 3 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 4 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 5 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 6 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 7 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 8 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 9 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 10 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 11 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 12 none 1 N/A SKY-NEAR-MARS 1 ACS/SBC ACCUM SBC F115LP none none 13 none 1 N/A SKY-NEAR-MARS 2 ACS/SBC ACCUM SBC F140LP none none 1 none 1 N/A SKY-NEAR-MARS 2 ACS/SBC ACCUM SBC F140LP none none 2 none 1 N/A SKY-NEAR-MARS 2 ACS/SBC ACCUM SBC F140LP none none 3 none 1 N/A SKY-NEAR-MARS 2 ACS/SBC ACCUM SBC F140LP none none 4 none 1 N/A SKY-NEAR-MARS 2 ACS/SBC ACCUM SBC F140LP none none 5 none 1 N/A SKY-NEAR-MARS 2 ACS/SBC ACCUM SBC F140LP none none 6 none 1 N/A 15098( 11) - 07-Dec-2017 03:42:48 - [ 5] Visit: 02 Visit Requirements: ORIENT 283D TO 290 D; AFTER 01 BY 0.5 Orbits TO 1.5 Orbits On Hold Comments: Additional Comments: To be executed just after the Mars observing orbit of visit 2 of GO-15097. 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 SKY-NEAR-MA STIS/FUV TIME-TA 52X2 G140L 1425 BUFFER-TIME=445, WAVECAL=NO 1 2714 S RS -MAMA G (2714 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 WAVE STIS/FUV ACCUM 52X0.05 G140L 1425 1 DEF (0 S) -MAMA ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ SKY-NEAR-MARS 1 STIS/FUV TIME-TA 52X2 G140L 1425 none none none none 1 N/A -MAMA G WAVE 2 STIS/FUV ACCUM 52X0.05 G140L 1425 none none none none 1 N/A -MAMA 15098( 11) - 07-Dec-2017 03:42:48 - [ 6] Summary Form for Proposal 15098 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.05, 52X2, SBC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/SBC, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=445, WAVECAL=NO ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 0.5 Orbits TO 1.5 Orbits, ORIENT 283D TO 290 D ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F115LP, F140LP, G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names SKY-NEAR-MARS, WAVE ------------------------------------------------------------------------------------------------------------------------------------