This target is not used in this proposal. 0 Assigned ID: 6547 ----- Attempting Submission 1 (Thu Apr 10 17:29:16 GMT 2025) ----- We list LTT-9779 since we are going to analyze its archival data, but do not ask for new observations of this target. Changed E230M aperture to 6x0.2 instead of 0.2x0.2, with approval from STIS User Support 455390369 ----- Attempting Submission 1 (Wed Jul 30 15:25:48 GMT 2025) ----- Your proposal could not be saved. Submission aborted. ----- Attempting Submission 2 (Wed Dec 17 17:05:38 GMT 2025) ----- ----- Attempting Submission 3 (Tue Mar 03 20:25:04 GMT 2026) ----- Maximum number of buffer dumps for Visits 1 and 2 is exceeded, but we absolutely must obtain the data in TIME TAG mode because these are time series observations of exoplanet transits. The extensive census of transiting exoplanets with the Kepler satellite revealed a robust dearth of highly-irradiated Neptunes, which we think is carved by a combination of photoevaporation driven by high-energy irradiation and high-eccentricity migration. However, this hypothesis has been challenging to test with observations of atmospheric escape because most Kepler planets orbit faint stars, which are not amenable to transmission spectroscopy. The tables have since turned in our favor, as recent transit surveys discovered several planets in the hot-Neptune desert that orbit bright stars. We have identified a benchmark sample of hot planets in the desert with densities and sizes consistent with having a significant H/He primordial atmosphere, and are likely undergoing hydrodynamic escape. With regards to detectability, this key sample is unmatched by any other combination of exoplanetary and host parameters, and provide our best chances at testing photoevaporation of hot Neptunes. In this program, we aim to study signatures of hydrodynamic escape in three hot sub-Jovians worlds using the unique ultraviolet capabilities of HST. We predict that the strong planetary outflow drags heavy species, such as Mg and Fe, to the exosphere of the planet, producing detectable signatures in transmission spectroscopy. Using a suite of modeling tools to interpret these signatures, our observations will provide, for the very first time, mass loss rate constraints for planets within the hot Neptune desert. We shall observe two transits of two hot Neptunes using STIS/NUV-MAMA. The objective is to detect metals escaping from the planets, and producing in-transit absorption in emission lines between 2400 and 2900 angstrom. This program is time sensitive because it can only be executed when the planet transits. Thus, we set a periodic time constraint. It is imperative to observe as many orbits as possible in a visit to cover the entirety of the transit, as well as obtain out-of-transit baseline observations. UV observations are limited to a maximum of five orbits, so we set the phase constraints to allow five consecutive orbits per visit. There are multiple observing opportunities Cycle 33: WASP-166 is observable between November and February, and HD 149026 is observable between December and July. We will use the E230M grating centered at 2707 angstrom with the square 0.2x0.2 slit aiming for the best spectrophotometric stability. We will use the TIME-TAG mode to allow us to break down each exposure into sub-exposures, which in turn is necessary to obtain a precise time series of fluxes. In both visits, The ETC recommends a short buffer time (154 s for HD 149026, STIS.sp.2022272; 393 s for WASP-166, STIS.sp.2022205), but at this value we would require special handling for the program because the number of buffer dumps exceeds 30. No further acquisition exposures are necessary in consecutive orbits within the same visit. The wavelength calibration was set to happen after the science exposure in order to spend as much time as possible on target. We set schedulability to 100 to maximize the chances of observing our visits within Cycle 33. The Principal Investigator L. dos Santos has previously led four HST programs to pin down the high-energy environment and atmospheric escape rates of exoplanets and specializes in transmission spectroscopy techniques for transiting exoplanets, as well as modeling of planetary outflows. Co-PI Natalie Allen specializes in observations of exoplanet atmospheres using transmission spectroscopy from the ground and from space. 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. J. Seidel is an expert in studying the atmospheres of hot Jupiters using high-resolution spectroscopy and modeling planetary winds. D. Sing is a world leader in characterizing exoplanets using ground- and space-based instruments, and is involved in several large programs to perform panchromatic exoplanet studies. M. Alam and J. Kirk have extensive experience in ground-based and space-based transmission spectroscopy techniques, and will provide support in analyzing the data. S. Vissapragada has led studies of metastable He narrowband photometry in hot Jupiters, and developed theoretical frameworks to interpret them in the context of atmospheric escape. O. Attia is an expert in modeling the evolution of Neptune- sized planets using dynamical models coupled with atmospheric escape. P. McCreery has experience in fitting atmospheric escape models to transmission spectra using Gaussian Processes to eliminate systematic effects, and will contribute to the data analysis effort. L. Ramos-Rosado has an extensive experience with low-resolution transmission spectroscopy with STIS, and will contribute to the data analysis in the NUV continuum to search for cloud-precursor species. Exoplanets and Exoplanet Formation Stellar Physics and Stellar Types 6 false true false false false false false SUPPORTED EXT-STAR EXTRA-SOLAR PLANETARY SYSTEM F3-F9 NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 EXT-STAR EXTRA-SOLAR PLANETARY SYSTEM F3-F9 NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STIS/NUV-MAMA Spectroscopic No No E230M 2707 STIS/NUV-MAMA Spectroscopic No No E230M 2707 1765991003088 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. Ephemeris uncertainty by early 2026 using Kokori+2023: 2.4 minutes (Tic-Visit :proposal-id 18104 :visit-id "01" :proposal-version -1 :trans-version "20250929" :date "17-Dec-2025 14:03:22.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 2453168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18104 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18104 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "01" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "01" :orbit-number 4 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "01" :orbit-number 5 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 578 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) false 5 0 1765991003949 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 1769375352000 336.2737411140924 (Tic-Visit :proposal-id 18104 :visit-id "02" :proposal-version -1 :trans-version "20250929" :date "17-Dec-2025 14:03:23.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 2453168 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18104 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18104 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "02" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "02" :orbit-number 4 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 316 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "02" :orbit-number 5 :pcs-time 380 :si-vis-utilization 2484 :al-overhead-at-end 0 :internal-dur-at-end 578 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2864 :pcs-gap 0 ) false 5 0 1765990739021 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. Ephemeris uncertainty by early 2026 using Kokori+2023: 0.43 minutes (Tic-Visit :proposal-id 18104 :visit-id "03" :proposal-version -1 :trans-version "20250929" :date "17-Dec-2025 13:58:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 5723776 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18104 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18104 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2481 :al-overhead-at-end 81 :internal-dur-at-end 132 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "03" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2488 :al-overhead-at-end 81 :internal-dur-at-end 132 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "03" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2488 :al-overhead-at-end 81 :internal-dur-at-end 132 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "03" :orbit-number 4 :pcs-time 380 :si-vis-utilization 2488 :al-overhead-at-end 81 :internal-dur-at-end 132 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "03" :orbit-number 5 :pcs-time 380 :si-vis-utilization 2488 :al-overhead-at-end 81 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) false 5 0 1765990991559 The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18104 :visit-id "04" :proposal-version -1 :trans-version "20250929" :date "17-Dec-2025 14:03:10.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 5723776 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18104 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18104 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2481 :al-overhead-at-end 81 :internal-dur-at-end 132 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "04" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2488 :al-overhead-at-end 81 :internal-dur-at-end 132 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "04" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2488 :al-overhead-at-end 81 :internal-dur-at-end 132 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "04" :orbit-number 4 :pcs-time 380 :si-vis-utilization 2488 :al-overhead-at-end 81 :internal-dur-at-end 132 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18104 :visit-id "04" :orbit-number 5 :pcs-time 380 :si-vis-utilization 2488 :al-overhead-at-end 81 :internal-dur-at-end 394 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2868 :pcs-gap 0 ) false 5 0