0 Assigned ID: 1676 ----- Attempting Submission 1 (Thu Apr 08 18:40:06 GMT 2021) ----- HST Phase I Proposal 1676 successfully submitted. Receipt: # 1676-1 ----- Attempting Submission 2 (Fri Apr 09 17:40:54 GMT 2021) ----- Adjusted phase requirement of Visit 52 to guarantee that we will have a better exoplanet transit phase coverage. -1577751394 ----- Attempting Submission 1 (Wed Jul 21 12:54:11 GMT 2021) ----- HST Phase II Proposal 16723 successfully submitted. Receipt: # 16723-1 ----- Attempting Submission 2 (Wed Jul 28 12:57:41 GMT 2021) ----- ----- Attempting Submission 3 (Wed Nov 10 13:42:36 GMT 2021) ----- ----- Attempting Submission 4 (Thu Aug 11 01:39:25 GMT 2022) ----- ----- Attempting Submission 5 (Wed Jan 04 20:29:05 GMT 2023) ----- Resolving the dichotomy of atmospheric escape in the young planet DS Tuc A b One of the biggest aims in exoplanet science is to understand how planets and their atmospheres evolve. Among the several challenges faced while inching towards this goal is the severe lack of observational constraints on the high-energy environments of young exoplanets and their early history of atmospheric escape. In particular, we do not know how well Neptune-sized and smaller planets can survive atmospheric erosion during the first billion years and retain their primary atmospheres. In this context, the recently discovered planet DS Tuc A b (45 Myr) is the best target to study atmospheric escape in the first 100 Myr in the life of a Neptune-sized exoplanet, and is likely going to become a testbed to investigate the primordial chemistry of exoplanetary atmospheres with JWST. A previous transit observation with HST suggest that this planet is currently undergoing intense hydrodynamic escape, but the result is ambiguous due to insufficient phase coverage and potential stellar activity contamination. In this program, we aim to observe two more transits, which are necessary to confirm that the feature is not spurious and to study the shape of the planet's exosphere. Either a detection or a non-detection will be crucial to interpret the evolution of exoplanetary atmospheres of this young planet and other similar worlds. We will observe two transits of DS Tuc A b using HST/STIS with the G140M grating centered on 122.2 nm. Since DS Tuc is a binary (separation = 5 arcsec = 100 pixels), it is imperative to insert the correct star in the slit. In principle, it could advantageous to set both stars in the slit to allow for differential spectroscopy, but that would introduce an ORIENT constraint, and this is not strictly necessary for the program. The target DS Tuc A is approximately 1 magnitude brighter than DS Tuc B at visible wavelengths, so the telescope should automatically center the correct target assuming everything goes well. There is also another bright star 3 arcmin east of the DS Tuc system. We will use the narrowest slit width (0.05") to minimize airglow contamination as much as possible. We understand that this choice can introduce slit losses, but we can correct for these losses when analyzing the data (on the other hand, the extra noise introduced by the airglow cannot be corrected). The ACQ exposure is performed following the recommendations from the ETC. Our target star is very bright, so we always get warnings for the ACQ/PEAK when running it in the ETC. We decided to use the same ACQ/PEAK configuration as in program GO#16085, which also observed this target. We set the timing constraints in the SCIENCE exposure to match an observing window of 10 hours around the exoplanet transit midcenter (period = 8.138268 days), which roughly corresponds to 5 orbits and some "wiggle room" for flexibility; this timing constraint covers the transit and the baseline flux of the star in the most reliable, yet flexible way. In addition, iin Visit 1 we also shift the phase constraints by -96 minutes (one HST orbit) in relation to program GO#16085 to provide a more extensive out-of-transit baseline; Visit 2 is shifted by +96 minutes. We set the schedulability constraint to 100 in order to maximize observation opportunities. L. dos Santos has experience in data reduction and interpretation of HST/STIS and COS stellar spectra, ground- based spectra, as well as transmission spectroscopy of exoplanets, interpretation and correction of instrumental systematics and stellar activity in the far-ultraviolet and visible wavelengths. D. Ehrenreich and V. Bourrier have an extensive experience on UV data analysis of planet-hosting stars, space- and ground-based transmission spectra and have several publications on ground-breaking discoveries about exoplanetary atmospheres. Moreover, V. Bourrier developed empirical and analytical tools to analyze and interpret observations of atmospheric escape from exoplanets. M. Lendl is an expert in ground-based photometric monitoring of exoplanet-host stars. L. Nielsen is an expert in stellar spectroscopy, radial velocity measurements and analysis of stellar activity indexes. B. Morris specializes in stellar activity and its impact in space-based photometry and spectroscopy of planet-hosting stars. J. D. Lothringer is an expert in both observing exoplanet atmospheres with HST, as well as atmosphere modeling with PHOENIX with extensive experience studying ultra-hot Jupiters. A. Vidotto specializes in simulating the space weather and stellar wind interactions of exoplanet upper atmospheres using hydrodynamical models, whose work has extensively been used to interpret HST observations. B. Morris is a specialist in stellar activity and is analyzing the simultaneous TESS observation from program GO-16085 to understand the impact of spots in the HST results. We are currently performing the first 3-dimensional models of the atmospheric escape of DS Tuc Ab aiming to better understand the effects of stellar wind in the Lya atmospheric signature. Exoplanets and Exoplanet Formation Stellar Physics and Stellar Types 6 false false true false false false false SUPPORTED STAR EXTRA-SOLAR PLANETARY SYSTEM G V-IV RS CVN STAR NO This object was generated by the targetselector and retrieved from the SIMBAD database. DS-TUC-A J2000 J2000 STIS/FUV-MAMA Spectroscopic No No G140M 1222 STIS/FUV-MAMA Spectroscopic No No G140M 1222 The scheduling data was generated by CASM 30.3. 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