0 Assigned ID: 1207 ----- Attempting Submission 1 (Fri Apr 07 23:58:57 GMT 2017) ----- HST Phase I Proposal 1207 (wasp121_g102.apt) successfully submitted. Receipt: # 1207-1 ----- Attempting Submission 2 (Sat Apr 08 00:03:44 GMT 2017) ----- HST Phase I Proposal 1207 (wasp121_g102.apt) successfully submitted. Receipt: # 1207-2 ----- Attempting Submission 3 (Sat Apr 08 00:16:08 GMT 2017) ----- Resubmission on 5 Oct 2017: We reduced scan rate to 0.062 arcsec/sec. Nothing else has changed. Previous comments: We would appreciate help optimizing the POS TARG X and Y parameters. If possible, we would appreciate if the signal-to-noise of our science exposures could be double-checked. We calculate that the brightest pixel will reach 24,700 electrons per exposure. The only difference between each visit is the phase constraint specified for the acquisition image in the first orbit. This is to maximize the phase coverage of the planetary eclipse. We have attempted to place the spectrum in such a way that keeps it on a single detector throughout the scan. If this is known to be a sub-optimal strategy (e.g. placing the spectrum as close to the center of the subarray as possible is better), please let us know. 2111999550 ----- Attempting Submission 1 (Sun Jul 16 11:27:50 GMT 2017) ----- ----- Attempting Submission 2 (Thu Oct 05 14:22:17 GMT 2017) ----- The extent to which significant stratospheres form in highly-irradiated gas giant exoplanets is still a major unresolved question in the field. Using WFC3 G141, we have recently measured a thermal emission spectrum for WASP-121b (T~2700K). The 1.4 micron water band is spectrally-resolved in emission, providing a clear detection of a thermal inversion in the atmosphere. From this measurement, we conclude that the most likely cause of the inversion is absorption of impinging stellar radiation by a high-altitude optical absorber, as other heating mechanisms are almost certainly insufficient. Intriguingly, the G141 spectrum also shows a flux excess at ~1.22 micron, which can be well-explained by vanadium oxide emission. Indeed, absorption by vanadium oxide and titanium oxide has been proposed as a possible means by which to generate stratospheres in the hottest exoplanets. However, we are currently unable to draw a confident conclusion on the presence of vanadium oxide in the atmosphere of WASP-121b with the available data. We propose here to rectify this situation, by extending the wavelength coverage of the measured thermal spectrum across the 0.9-1.1 micron wavelength range using WFC3 G102. This will allow us to target the prominent vanadium oxide and titanium oxide bands at these wavelengths, where the flux from the planet is still high. If observed, a long-theorized link would be established between these important chemical species and thermal inversions in highly-irradiated atmospheres. Our WFC3 observations will provide a thermal emission spectrum for the transiting exoplanet WASP-121b across the 0.9-1.1 micron wavelength range. **Observing strategy: To construct the emission spectrum, we will observe two secondary eclipses of WASP-121b with WFC3 G102. The observations will be made in slitless spectroscopic mode. Our observing setup is very similar to that used in previous successful programs, such as Prog 14468 (PI Evans; G141 primary transit of WASP-121b), Prog 14767 (PI Sing; G141 secondary eclipse of WASP-121b ), and Prog 13467 (PI Bean; G102 transits for the somewhat fainter WASP-12b). At the start of each HST visit, a standard phase-constrained acquisition image will be taken. The subsequent observing strategy for both visits consists of taking repeated exposures for the duration of the eclipse, plus time before and after the eclipse to establish the out-of-eclipse baseline flux. Different phase constraints have been specified for each visit to maximize the phase coverage of the eclipse itself. Indeed, the only difference between each visit is the phase constraint provided for the acquisition image in the first orbit. We will use the forward spatial scanning mode with a scan rate of 0.08 arcsec/sec, using SPARS10 and NSAMP=15. We will read out a subarray size of 256 pixels to reduce overheads. Individual exposure times will be 103.1 sec, resulting in a scan across 8.25 arcsec = 68 pixels per exposure. We will apply an offset of -6 arcsec = -50 pixel along the cross-dispersion y-axis of the array at the start of each exposure. This will leave enough room on the detector above and below the scan to estimate the background flux. Each eclipse of WASP-121b lasts 173 minutes. We therefore require 5 consecutive HST orbits for each visit. The first orbit serves to allow the telescope to thermally relax into its new pointing position and for the detector charge-traps to fill, which is a standard procedure adopted by all HST WFC3 transiting exoplanet observations. The remaining orbits will provide good phase coverage during eclipse, and allow for sufficient time (2 HST orbits - one before eclipse, one after eclipse) to establish the baseline stellar flux necessary to accurately measure the eclipse depth. We will obtain 17 science exposures per HST orbit, coming to a total of 34 in-eclipse and 34 out-of-eclipse science exposures per visit. We choose not to use bi-directional spatial scanning, e.g. as has been done for WASP-12b in Program 13467 (PI Bean). This is because although bi-directional spatial scanning would allow an additional 2 exposures to be acquired per HST orbit (i.e. 19 per orbit), the instrumental systematics are different for each scan direction, which is likely more of a disadvantage. **Signal-to-noise estimates: WASP-121b is a bright target in the conventional sense (V=10.5mag, J=9.6mag). The challenge with exoplanet emission spectroscopy is to measure subtle changes in the system brightness across different wavelength channels, via variations in the transit depth. We used the HST Exposure Time Calculator with the observational setup described above to calculate a SNR of ~1800 per resolution element per exposure. Note that this flux will be spread over ~68 pixel columns due to the spatial scan (see above), so there is no risk of saturation. According to the HST Exposure Time Calculator, with this setup the brightest pixel per exposure will reach 24,700 electrons (see linked ETC Run #'s in the observing sequences). Planets and Planet Formation 6 false false false false false false SUPPORTED EXT-STAR EXTRA-SOLAR PLANETARY SYSTEM F3-F9 This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/IR Spectroscopic No No G102 WFC3/IR Spectroscopic No No G102 1510141436532 The scheduling data was generated by CASM 25.2. CASM was run in Phase II mode. /private/var/folders/zc/ljhf1lgn10b1yd9ytmwlp4jr00070l/T/OPVisit8111219854411406176.xml It is essential that the five HST orbits be scheduled in a contiguous block. We have defined each HST orbit within a non-interruptible sequence, to ensure that all exposures defined within the sequence are taken during the same HST orbit. We will use forward spatial scanning mode to avoid saturation on relatively long exposures and increase observing efficiency. Visit orientation requirements have been defined to avoid spectra from nearby stars overlapping the target spectrum. 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CASM was run in Phase II mode. It is essential that the five HST orbits be scheduled in a contiguous block. We have defined each HST orbit within a non-interruptible sequence, to ensure that all exposures defined within the sequence are taken during the same HST orbit. We will use forward spatial scanning mode to avoid saturation on relatively long exposures and increase observing efficiency. Visit orientation requirements have been defined to avoid spectra from nearby stars overlapping the target spectrum. 1509976878000 310.0 (Tic-Visit :proposal-id 15135 :visit-id "02" :proposal-version -1 :trans-version "20170613" :date "30-Oct-2017 06:52:09.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1502736 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15135 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15135 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2420 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3118 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15135 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2692 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3118 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15135 :visit-id "02" :orbit-number 3 :pcs-time 222 :si-vis-utilization 2692 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3118 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15135 :visit-id "02" :orbit-number 4 :pcs-time 222 :si-vis-utilization 2692 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3118 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15135 :visit-id "02" :orbit-number 5 :pcs-time 222 :si-vis-utilization 2692 :al-overhead-at-end 0 :internal-dur-at-end 457 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3118 :pcs-gap 0 ) false 5 0 Phase-constrained