0 Assigned ID: 1214 ----- Attempting Submission 1 (Fri Jan 17 17:41:40 GMT 2020) ----- HST Phase I Proposal 1214 (prop_v2.apt) successfully submitted. Receipt: # 1214-1 LONG SU LIKELY TO INTERSECT THE SAA 0 ----- Attempting Submission 1 (Thu Mar 19 20:00:29 GMT 2020) ----- SAA crossing is expected given our long 10 orbit visit. After consultation with the Contact Scientst, Joel Green, we have determined that this is unlikely to be a problem, since WFC3 can continue operating. A brief loss of data quality may be suffered, but this is preferable to shortening the observation, given the science goals. We propose to observe the transit spectrum of recently discovered young warm Jupiter V1298 Tau b using the HST/WFC3 instrument near 1.4 microns. We will measure the atmospheric properties of this likely inflated gas giant (~23Myr, 0.9 Jupiter radii, likely <90 Earth masses, 24 day period). At equilibrium temperature (650K), we expect the presence of methane in the atmosphere of this object, and we will have the precision to measure it. This will allow us to evaluate the equilibrium chemistry and temperature of the planet's atmosphere. We will place constraints on its metallicity and the clouds/hazes present. We will compare our results to the atmospheric properties of young directly imaged planets to evaluate the influence of the location within the disk and the stellar irradiation on planetary compositions. This observation represents an opportunity for HST to yet again open a new chapter of exoplanet characterization of a completely unexplored class of planets. Our observations will inform and enable future studies with JWST. We will observe V1298 Tau b during a transit using time series spectroscopy with WFC3/G141. We will collect data with the WFC3/IR camera configuration in the spectroscopic scanning mode with the G141 grism. This will provide us with a high quality transit spectrum of our target in the 1.1-1.65 micron region. In order to achieve our science goals, we require high sensitivity. Since the target star is bright (H = 8.19), we will employ the bi-directional spatial scanning mode for WFC3 in order to maximize the photon-collecting efficiency and the duty cycle of the telescope. In order to maximize the duty cycle of the telescope and estimate the signal-to-noise of our observations, we use the PandExo HST open source tool. We use input transit spectroscopy models created with the ExoTransmit package (Kempton et al. 2016), assuming solar atomic abundances, and planet mass of 90M_Earth (conservative estimate). This approach allows us to maximize the duty cycle (not including occultation by Earth) to 65%, while avoiding mid-orbit buffer dumps. We will use NSAMP = 5 and SAMP_SEQ = SPARS25. We use GRISM256 aperture to limit interference from nearby bright stars. The exposure time calculations result in optimal scan rate of 0.230 "/s, resulting in scan heights of 170 pixels (21"). This observation is time critical - it will only work if the target star is observed for the duration of the entire transit, plus out-of-transit baselines before and after transit. To ensure adequate coverage of the unusually long transit, we will observe the light curve for 10 HST orbits. The transit duration is 7 hours or 4.4 orbits, and we allow 4.6 orbits total, or 7.4 hours for pre-ingress and post-egress baselines. Dr. Todorov is an expert in transit and secondary eclipse observations both from space and from the ground (e.g., Todorov et al. 2010, 2014, 2019). He is a Co-I of HST programs GO 12495, GO 14642, GO 15131, and Spitzer GO Proposal 80128, which was also awarded 8 HST orbits. These programs have all been on transit time-series spectroscopy, primarily with WFC3, the instrument we propose to use here. He will lead the overall investigation and the analysis, and coordinate the efforts of Co-Is who are analyzing, modeling and interpreting the HST observations and ancillary data from other telescopes. Dr. Desert has more than 10 years of experience in the characterization of transiting exoplanetary atmospheres using HST, Spitzer, and ground based facilities. Desert was P.I. for four HST exoplanet characterization programs, and CoI of 27 HST programs, including two large programs. In particular, he is an expert of low-resolution transmission spectroscopy using multi-object spectrograph (MOS), and will lead the combination of the STIS/G750M observations with ground-based low-resolution spectra. He has published over 100 exoplanet characterization papers in the last decade. Co-I Pino is the PI of HST Cycle 27 program GO 15820 and has experience with complex exoplanet data sets. Co-I Arcangeli is an expert in HST/WFC3 analyses and has led several works on the topic (Arcangeli et al. 2018, 2019, 2019 in prep). Co-I Arcangeli will assist with the analysis of our data. Co-Is Baxter, Panwar and Arcangeli are graduate students; co-I Pino is a postdoc; all in Dr. Desert's group. Dr. David has extensive knowledge of the astrophysics of young stars, as well as with modeling transit photometry in the presence of strong stellar variability. As lead author of the V1298 Tau discovery papers, he has a detailed knowledge of this particular planetary system. Dr. David will assist with data analysis and manuscript preparation. Dr. Line is an expert theorist studying exoplanet atmospheres, and a prolific HST user. Dr. Line is has been a co-I of multiple HST programs to study the atmospheres of exoplanets and brown dwarfs, most recently in Cycle 27: AR 15796, GO 14782, GO 15819, and GO 15698. Dr. Line will assist with the interpretation of our observation by providing state-of-the-art models of transmission spectra. Planets and Planet Formation 6 false false false false false false false SUPPORTED STAR EXTRA-SOLAR PLANET EXTRA-SOLAR PLANETARY SYSTEM K V-IV T TAURI STAR NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 H=8.191 WFC3/IR Spectroscopic No No G141 1599163849602 /private/var/folders/46/4jpf0wpx40jbz16h87362w240001d2/T/OPVisit7330192501720124592.xml The scheduling data was generated by CASM 28.0. CASM was run in Phase II mode. 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