0 Assigned ID: 1218 ----- Attempting Submission 1 (Wed Sep 30 04:53:08 GMT 2020) ----- HST Phase I Proposal 1218 successfully submitted. Receipt: # 1218-1 ----- Attempting Submission 2 (Wed Sep 30 04:55:12 GMT 2020) ----- HST Phase I Proposal 1218 successfully submitted. Receipt: # 1218-2 ----- Attempting Submission 3 (Wed Sep 30 19:29:04 GMT 2020) ----- HST Phase I Proposal 1218 successfully submitted. Receipt: # 1218-3 ----- Attempting Submission 4 (Thu Oct 01 03:24:00 GMT 2020) ----- HST Phase I Proposal 1218 successfully submitted. Receipt: # 1218-4 0 ----- Attempting Submission 1 (Mon Nov 30 01:21:38 GMT 2020) ----- We are moving from an era of exoplanet discovery into an era of exoplanet characterization, but small (R < 1.5 Rearth), potentially-rocky planets orbiting bright, nearby stars that are suitable for atmospheric characterization studies are relatively scarce. Amongst these candidates for atmospheric characterization is L 98-59 c. This 1.35 Rearth planet is one of three known to orbit the bright (H = 7.4), nearby (10.6 pc), M3V star L 98-59. HST/WFC3 observed a transit of L 98-59 c earlier this year. These data revealed the first tentative signs of a atmosphere on a predominantly rocky exoplanet. However, this detection was of fairly low signal-to-noise, and independent analyses did not yield wholly consistent results. Here we propose to observe two additional transits of L 98-59 c using the same instrument setup as the archival data. With these new data, the significance of the atmospheric features, if supported, would be increased by greater than 5-sigma. Moreover, these new data will provide sufficient signal to measure the chemical composition of the atmosphere. With the robust detection of an atmosphere, L 98-59 c will become a touchstone exoplanet for atmospheric studies and a key planet for demonstrating the precision of JWST. The program will obtain time series spectroscopy of L 98-59 c. We will use WFC3's G141 grism and the 512x512 subarray. We will cover 2 transits of the planet. Each transit is covered by a single visit, and each visit consists of four sequential orbits to obtain quasi-continuous coverage of the transits. The actual planet transits will occur in the third orbit of each visit, with two pre-transit orbits and one post-transit orbit. We will use the first orbit of each visit in our construction of the out-of-transit baseline flux if instrument systematics allow. Each orbit begins with a direct image of the target with the F130N filter for wavelength calibration. The remainder of each orbit will consist of MULTIACCUM exposures with the NSAMP = 4, SPARS25 readout pattern. To keep the fluence near 30,000 photoelectrons, we will use spatial scan mode with a 0.496 arcsec/sec scan rate, yielding a total scan height of 285.3 pixels), as recommended by Pandexo. To maximize the duty cycle of the observations (~60%), we will alternate between forward and reverse scanning along the detector. The proposed investigation relies on the precise planning of exoplanet transit observations with HST and the careful reduction and analysis of WFC3 data. Our team has experience and proven expertize in all aspects of this investigation. The observations that motivated this proposal was lead by our team (GO-15856). Within this proposal we have demonstrated that we know how to plan, reduce, and analyze transmission spectroscopy data. Our team performed three different data reduction methods and two different atmospheric retrieval methods to analyze these data. If selected, we will use the same algorithms and methods to analyze the new data. Specifically, Dr. Knicole Colon, Dr. Laura Kreidberg, Dr. Christina Hedges. and Dr. Ian Crossfield have lead HST transmission spectroscopy proposal and are accomplished at analyzing, and publishing the data (e.g., Kreidberg et al. 2014a,b, 2015, 2018a,b). Drs. Colon and Kreidberg were the PI and Co-PI on HST GO-15255 and led the planning and implementation of WFC3 transit observations of KELT-11b. Dr. Kreidberg led the reduction and analysis of those WFC3 transit observations. Dr. Barclay, Dr. Mullally, Dr. Schlieder and Dr. Youngblood have expertise in stellar and exoplanet characterization using a variety of photometric and spectroscopic tools. Dr. Kostov was the lead author on the L 98-59 discovery paper and has experience modeling transits. The data reduction will be performed independently by team members Dr. Damiano, Dr. Hedges, and Mr. Sheppard. Aside from Hedges method, the other pipelines used are public and open sources, and the team members have experience using and publishing with these algorithms. Hedges plans to publish a paper on her method within the next few months. The retrieval analyses will be performed by Dr. Mandell/Mr. Mang and Dr. Hu/Dr. Damiano. They also use public, open sources tools to perform the analyses. Dr. Morley, Dr. Kite, Dr. Kopparapu, Dr Hu, Dr. Fauchez, and Dr. Lopez have expertise in interpreting exoplanet transmission spectroscopy, and will lead the theoretical modeling aspects of the proposal. Dr Lopez is an expert in formation, evolution, and interior models of exoplanets, which will be applied to this investigations to interpret the findings from HST. Exoplanets and Exoplanet Formation 6 false false false false false false false SUPPORTED EXT-STAR EXTRA-SOLAR PLANET M V-IV This object was generated by the targetselector and retrieved from the SIMBAD database. 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