0 Assigned ID: 177 ----- Attempting Submission 1 (Wed Mar 04 20:19:47 GMT 2020) ----- HST Phase I Proposal 177 successfully submitted. Receipt: # 177-1 ----- Attempting Submission 2 (Wed Mar 04 20:38:52 GMT 2020) ----- HST Phase I Proposal 177 successfully submitted. Receipt: # 177-2 ----- Attempting Submission 3 (Thu Mar 05 21:48:14 GMT 2020) ----- 0 ----- Attempting Submission 2 (Fri Jun 19 18:40:35 GMT 2020) ----- HST Phase II Proposal 16168 successfully submitted. Receipt: # 16168-2 ----- Attempting Submission 3 (Tue Jul 28 19:31:00 GMT 2020) ----- Hot Jupiters are compelling targets for thermal emission observations because their high signal-to-noise allows precise atmospheric characterization. Theory predicts a continuum of thermal structures and resulting emission spectra for these objects. Planets with dayside temperatures (Tday) below ~2100 K are expected to have uninverted atmospheres and display absorption features in their spectra. Planets with Tday>2100 K should have inverted atmospheres, but only those with 2100<Tday<2500 are expected to show emission features, as those with Tday>2500 are expected to have featureless, blackbody-like spectra. While we have observed cooler planets with absorption features and warmer planets with blackbody-like spectra, we have not observed any intermediate-temperature planets at high enough precision to understand the transition between these regimes. We propose to use the Hubble Space Telescope (HST)/WFC3+G141 grism to observe the thermal emission spectrum of the hot Jupiter WASP-77Ab. WASP-77Ab planet sits at a temperature where the models predict the widest range of potential atmospheric structures and resulting secondary eclipse spectra, and it is the only planet in this transition region whose spectrum can be measured precisely with only two eclipse observations. The resulting spectrum will be as precise as that of the benchmark hot Jupiter WASP-43b, and if it shows absorption or emission features we will place equally tight constraints on the water abundance of WASP-77Ab. Its high signal-to-noise means WASP-77Ab has the potential to become a new archetype hot Jupiter and will likely be targeted for extensive JWST observations if its spectrum shows interesting features. We will perform time-series spectroscopy using HST to measure two secondary eclipses of WASP-77Ab. We will use the WFC3/IR instrument with the G141 grism to measure the thermal emission spectra of WASP-77Ab from 1.1 to 1.7 microns. We used PandExo to simulate the observations and predict the S/N values for each secondary eclipse (Batalha et al., 2017). The observations will be done with the 256 x 256 subarray. We will use the SPARS25, NSAMP=5 sampling sequence (total time per exposure of 89.7 s) and the spatial scan mode with bi-directional scans to maximize the duty cycle (expected to be 66%). We will use a scan rate of 0.195"/s, which will give peak counts of roughly 30k electrons/pixel and a scan height of 144 pixels. The scan will fit comfortably in the 256 subarray and leave plenty of empty detector space to estimate the background. We expect a photon-limited signal-to-noise ratio of about 3,200 per pixel in each extracted 1D spectrum. A total of 20 exposures will be obtained in each orbit, and 1 orbit during each visit will occur during the secondary eclipse. Each visit will consist of 5 orbits. Each orbit will begin with a direct image through the F126N filter for wavelength calibration. WASP-77A has a companion star (WASP-77B) with a projected separation of 3.2". In order to correct for contamination from this companion star, the first orbit of each visit contains a single G141 stare mode spectrum to measure the relative flux of the two stars. We have placed orient constraints on each visit such that the spectra of WASP-77A and WASP-77B do not overlap in this stare mode image. PI Megan Mansfield has analyzed many HST+WFC3 data sets as a graduate student under the supervision of Co-I Jacob Bean, and has published two papers on HST observations of hot Jupiters. Jacob Bean has extensive experience with HST observations and data analysis, having led programs totaling 200+ orbits and with 20+ papers utilizing HST data. Vivien Parmentier, Michael Line, Jonathan Fortney, Eliza Kempton, and Matej Malik have done extensive work on the theory of hot Jupiters described in the proposal and are experts in atmospheric retrieval. Jean-Michel Desert, Kevin Stevenson, Brian Klipatrick, Jacob Arcangeli, and Laura Kreidberg are experts in HST observations and data analysis. Exoplanets and Exoplanet Formation 6 false false false false false false false SUPPORTED STAR EXTRA-SOLAR PLANET This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/IR Spectroscopic No No G141 1603715096736 The scheduling data was generated by CASM 28.2. CASM was run in Phase II mode. The position angle from WASP-77A to WASP-77B is 153.6 degrees. This position angle must be >10 pixels (which corresponds to ~24.9 degrees) from the WFC3 IR x-axis. 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CASM was run in Phase II mode. /private/var/folders/bl/s7q0tqnn5gbcbyvcfnrhj2rh0004nc/T/OPVisit7656778510677946625.xml The position angle from WASP-77A to WASP-77B is 153.6 degrees. This position angle must be >10 pixels (which corresponds to ~24.9 degrees) from the WFC3 IR x-axis. The WFC3 IR instrument has a y offset angle of 13.5 degrees, which we used to calculate the below allowable orient ranges. 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