0 Assigned ID: 1228 ----- Attempting Submission 1 (Wed Sep 30 16:32:08 GMT 2020) ----- HST Phase I Proposal 1228 successfully submitted. Receipt: # 1228-1 ----- Attempting Submission 2 (Wed Sep 30 20:29:33 GMT 2020) ----- HST Phase I Proposal 1228 successfully submitted. Receipt: # 1228-2 0 ----- Attempting Submission 1 (Mon Nov 30 12:30:43 GMT 2020) ----- HST Phase II Proposal 16462 successfully submitted. Receipt: # 16462-1 ----- Attempting Submission 2 (Mon Nov 30 12:31:11 GMT 2020) ----- ----- Attempting Submission 4 (Sun Feb 21 00:03:43 GMT 2021) ----- ----- Attempting Submission 5 (Thu Jul 29 23:17:28 GMT 2021) ----- The newborn planetary system comprising of four gas giants transiting the bright 23 Myr old star V1298 Tau presents an exciting opportunity to probe the atmospheric properties of planetary systems immediately post-formation, and to do so within one system. We propose to observe a transit of the hottest gas giant in the system, V1298 Tau c, using the HST/WFC3/G141 grism, to measure the strength of water absorption features. The NIR transmission spectrum of this hot Neptune planet will be used to constrain its metallicity and cloud or haze coverage, which in turns will inform planet formation and evolution models. In conjunction with the previous WFC3/G141 observations of the warm gas giant V1298 Tau b in the system, our observations will enable comparative exoplanetology of planets within a multiplanet system fresh after formation. When put in the context of directly imaged planets at wider orbital separations but similar age as the V1298 Tau system, the inferences from our comparative study of a close-in multiplanet system will put constraints on the effect of insolation and location in the planet-forming disks on the bulk planetary composition and properties. We will observe V1298 Tau c during a transit of the planet using time series spectroscopy with WFC3/G141 in drift scan mode. The planet b exhibit 30 mins TTV, and 12 mins uncertainty on mid-transit times by the end of 2022. We currently have a restrictive phase constraint (+/-30mins) starting 3 HST orbits before primary transit and ending 1-2 orbits after transit. The observing start window is relaxed (60 minutes) to ensure we cover properly the transit. This observing window could be relaxed more to enable as many observing opportunities as possible. We plan to get updated ephemeris by the end of the year which will help constraining the TTVs. 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. 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 4.66 hours, and will allow 4 hours for pre-ingress and post-egress baselines. Jean-Michel Desert and Jacob Bean have extensive experience with HST observations of exoplanet atmospheres and have led programs totaling more than 300 orbits and with 30+ papers utilizing HST data. Vatsal Panwar, Bob Jacobs, Lorenzo Pino, and Claire Baxter are experts on ground and space based transit spectroscopy of exoplanets. Michael Line and Antonija Oklopcic are experts on modeling exoplanet atmospheres. Niloofar Khorshid is an expert on modeling planet formation and evolution. Trevor David and John Livingston are experts on exoplanets around young stars. Exoplanets and Exoplanet Formation 6 false 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.This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 H=8.191 WFC3/IR Spectroscopic No No G141 1633717980108 /System/Volumes/Data/solaris/user1/csoto/OP-cache/16462-v01.xml The scheduling data was generated by CASM 29.2. 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