0 Assigned ID: 1341 ----- Attempting Submission 1 (Tue Jan 31 23:28:05 GMT 2017) ----- HST Phase I Proposal 1341 (phase1-GO_wasp107_2.pdf.apt) successfully submitted. Receipt: # 1341-1 ----- Attempting Submission 2 (Wed Feb 01 00:09:56 GMT 2017) ----- 0 ----- Attempting Submission 1 (Wed Mar 29 16:46:50 GMT 2017) ----- WASP-107b is a new, relatively cool (~770K) transiting exoplanet that our team confirmed in January 2017. It has a mass lower than Saturn (0.12MJ), a radius almost as large as Jupiter's (0.94RJ), and a bright host star (H ~ 8.6). These properties make it an outstanding target for transmission spectroscopy. With HST, it will be possible to measure a transmission spectrum rivaling the quality of the canonical planets HD 209458b and HD 189733b. Its low equilibrium temperature places WASP-107b well below the predicted transition from hot, CO-dominated exoplanet atmospheres to cooler, CH4 dominated ones. We propose to use WFC3+G102 and WFC+G141 to measure its near-infrared transmission spectrum. This, combined with allocated K2 photometry will allow us to classify WASP-107b as clear or cloudy, and search for evidence of CH4. If such evidence is detected, WASP-107b would become a prime target for JWST Cycle 1, which is why these observations should be made as soon as possible. Our WFC3 observations will provide a transmission spectrum for the transiting exoplanet WASP-107b across the 0.8-1.1 micron wavelength range. We are targeting the absorption signatures of water and methane. **Observing strategy: To construct the transmission spectrum, we require a single transit of WASP-107b to be observed with WFC3 G102. The observations will be made in slitless spectroscopic mode. Our observing setup is very similar to that used in previous successful exoplanet transit programs, such as for the similar-brightness GJ1214 in Program 13021 (PI Bean). At the start of the HST visit, a standard phase-constrained acquisition image will be taken. The subsequent observing strategy consists of taking repeated exposures for the duration of the transit, plus time before and after the transit to establish the out-of-transit baseline flux. We will use the forward spatial scanning mode with a scan rate of 0.068 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 7.0 arcsec = 54 pixels per exposure, leaving plenty of room on the detector to estimate the background flux. Each transit of WASP-107b lasts 165 minutes. We therefore require 5 consecutive HST orbits. The first orbit serves to allow the telescope to thermally relax into its new pointing position, which is a standard procedure adopted by all HST transiting exoplanet observations. The remaining orbits will provide good phase coverage during transit, and allow for sufficient time (2 HST orbits - one before transit, one after transit) to establish the baseline stellar flux necessary to accurately measure the transit depth. We will obtain 17 science exposures per HST orbit, coming to a total of 34 in-transit and 34 out-of-transit exposures. We choose not to use bi-directional spatial scanning, e.g. as has been done for GJ1214 in Program 13021 (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-107b is a bright target in the conventional sense (V=11.5mag, J=9.4mag). The challenge with exoplanet transmission 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 54 pixel columns due to the spatial scan (see above), so there is no risk of saturation. Extrasolar Planets and Planet Formation 3 false false false true false false SUPPORTED STAR EXTRA-SOLAR PLANETARY SYSTEM K V-IV 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 G141 /private/var/folders/08/r9w2chf12pbdjf7vsvgyzlkh002hyc/T/OPVisit1453646979203647238.xml 1490805253726 The scheduling data was generated by CASM 25.0. CASM was run in Phase II mode. It is essential that the five HST orbits be scheduled in a contiguous block, free of the SAA. 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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