17460( 5) - 30-Jul-2025 12:50:09 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17460 Version: 5 Check-in Time: 30-Jul-2025 12:50:09 STScI Edit Number: 3 Title Heavy metals escaping from a hot Neptune ------------------------------------------------------------------------------------ Type Cycle GO 31 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Antonija Oklopcic Universiteit van Amsterdam Y CoI: Dr. Heather A. Knutson California Institute of Technology N CoI: Dr. Jessica Spake Carnegie Institution of Washington Y CoI: Dion Linssen Universiteit van Amsterdam N ------------------------------------------------------------------------------------ Abstract A large fraction of known exoplanets orbit their host stars at very short periods. Due to such close proximity to the parent star, their atmospheres are exposed to high levels of stellar radiation and stellar wind, as well as strong tidal interactions, which can lead to atmospheric escape operating in a regime much more efficient than in the Solar System planets. Efficient atmospheric mass loss has the power to radically transform planets by changing their atmospheric structure or by removing the atmosphere altogether. Even though the first evidence of ongoing atmospheric escape in exoplanets was acquired for close-in gas giants, exoplanet demographics suggest that this process likely plays a much greater evolutionary role in planets the size of Neptune and smaller. It is believed to be responsible for shaping the so-called 'hot Neptune desert', the observed paucity of intermediate-sized planets at close orbital separations. LTT 9779b is a rare example of a planet residing well within this desert, in the part of the parameter space where atmospheric escape driven by stellar high-energy radiation can be further assisted by Roche lobe overflow, resulting in extremely high mass-loss rates. The goal of our proposal is to observe the ongoing atmospheric escape for this ultra-hot Neptune through transmission spectroscopy at NUV wavelengths with STIS. The NUV wavelength range gives us the best opportunity to observe the upper atmosphere in multiple lines of different species, which is necessary in order to break modeling degeneracies and constrain the atmospheric mass-loss rate. ------------------------------------------------------------------------------------ Observations Description ------------------------ We will observe the transiting exoplanet system LTT 9779 with five visits of three orbits each. Each visit will be centered around a transit of the planet LTT 9779b, which has an orbital period of 0.79 days, allowing for frequent observing opportunities. Each of the five visits must be a non-interrupted sequence in order to cover a pre-transit baseline with the first orbit, the transit itself in the second orbit, and the post-transit baseline with the third orbit. Target acquisition will be performed with the recommended F28X50LP filter, and 0.2s exposure times. This is below the saturation time of 0.33s. The rest of the observing time will be dedicated to spectroscopy with the E230M echelle. The buffer time given by the exposure time calculator is 617 s. We have therefore used the recommended 4/5 value of 493 s. ------------------------------------------------------------------------------------ 17460( 5) - 30-Jul-2025 12:50:09 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 LTT9779 EXT-STAR, EXTRA-SOLAR RA=23H54M40.5304S, J2000 V = 9.76 PLANETARY SYSTEM, G DEC=-37D37'41.61" V-IV Reference Frame: ICRS Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2015.5 0.020844902538697366 -0.06975199999033066 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17460( 5) - 30-Jul-2025 12:50:09 - [ 3] Visit: 01 (LTT 9779 E230M Visit 1) Visit Requirements: SCHED 100%; Period 0.7920641 D AND ZERO-PHASE HJD2459043.31061 On Hold Comments: Additional Comments: It is essential that the three orbits be scheduled in a coninuous block. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LTT9779 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 0.2 S (0.2 PHASE 0.8977 TO 0.9078; S) SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2100 S -MAMA G see below (1952 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ LTT9779 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A LTT9779 2 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 1 1952.0 S -MAMA G LTT9779 3 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 2 2484.0 S -MAMA G LTT9779 4 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 3 2484.0 S -MAMA G 17460( 5) - 30-Jul-2025 12:50:09 - [ 4] Visit: 02 (LTT 9779 E230M Visit 2) Visit Requirements: SCHED 100%; Period 0.7920641 D AND ZERO-PHASE HJD2459043.31061 On Hold Comments: Additional Comments: It is essential that the three orbits be scheduled in a coninuous block. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LTT9779 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 0.2 S (0.2 PHASE 0.8977 TO 0.9078; S) SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2100 S -MAMA G see below (1952 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ LTT9779 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A LTT9779 2 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 1 1952.0 S -MAMA G LTT9779 3 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 2 2484.0 S -MAMA G LTT9779 4 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 3 2484.0 S -MAMA G 17460( 5) - 30-Jul-2025 12:50:09 - [ 5] Visit: 03 (LTT 9779 E230M Visit 3) Visit Requirements: SCHED 100%; Period 0.7920641 D AND ZERO-PHASE HJD2459043.31061 On Hold Comments: Additional Comments: It is essential that the three orbits be scheduled in a coninuous block. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LTT9779 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 0.2 S (0.2 PHASE 0.8977 TO 0.9078; S) GS ACQ SCENARIO BASE1O3; SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2100 S -MAMA G see below (1952 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ LTT9779 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A LTT9779 2 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 1 1952.0 S -MAMA G LTT9779 3 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 2 2484.0 S -MAMA G LTT9779 4 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 3 2484.0 S -MAMA G 17460( 5) - 30-Jul-2025 12:50:09 - [ 6] Visit: 04 (LTT 9779 E230M Visit 4) Visit Requirements: SCHED 100%; Period 0.7920641 D AND ZERO-PHASE HJD2459043.31061 On Hold Comments: Additional Comments: It is essential that the three orbits be scheduled in a coninuous block. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LTT9779 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 0.2 S (0.2 PHASE 0.8977 TO 0.9078; S) GS ACQ SCENARIO BASE1O3; SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2100 S -MAMA G see below (1952 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ LTT9779 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A LTT9779 2 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 1 1952.0 S -MAMA G LTT9779 3 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 2 2484.0 S -MAMA G LTT9779 4 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 3 2484.0 S -MAMA G 17460( 5) - 30-Jul-2025 12:50:09 - [ 7] Visit: 05 (LTT 9779 E230M Visit 5) Visit Requirements: SCHED 100%; Period 0.7920641 D AND ZERO-PHASE HJD2459043.31061 On Hold Comments: Additional Comments: It is essential that the three orbits be scheduled in a coninuous block. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LTT9779 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 0.2 S (0.2 PHASE 0.8977 TO 0.9078; S) GS ACQ SCENARIO BASE1O3; SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2100 S -MAMA G see below (1952 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ LTT9779 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A LTT9779 2 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 1 1952.0 S -MAMA G LTT9779 3 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 2 2484.0 S -MAMA G LTT9779 4 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 3 2484.0 S -MAMA G 17460( 5) - 30-Jul-2025 12:50:09 - [ 8] Visit: 55 (LTT 9779 E230M Visit 5) Visit Requirements: SCHED 100%; Period 0.7920641 D AND ZERO-PHASE HJD2459043.31061 On Hold Comments: Additional Comments: It is essential that the three orbits be scheduled in a coninuous block. HOPR repeat of visit 5. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 LTT9779 STIS/CCD ACQ F28X50LP MIRROR ACQTYPE=POINT 1 0.2 S (0.2 PHASE 0.8977 TO 0.9078; S) GS ACQ SCENARIO BASE1O3; SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ 2 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2100 S -MAMA G see below (1952 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 LTT9779 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 BUFFER-TIME=493 1 2700 S -MAMA G see below (2484 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ LTT9779 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A LTT9779 2 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 1 1952.0 S -MAMA G LTT9779 3 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 2 2484.0 S -MAMA G LTT9779 4 STIS/NUV TIME-TA 0.2X0.2 E230M 2707 none none none none 3 2484.0 S -MAMA G 17460( 5) - 30-Jul-2025 12:50:09 - [ 9] Summary Form for Proposal 17460 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.2, F28X50LP ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ACQTYPE=POINT, BUFFER-TIME=493 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements GS ACQ SCENARIO BASE1O3, PHASE 0.8977 TO 0.9078, Period 0.7920641 D AND ZERO-PHASE HJD2459043.31061, SCHED 100%, SEQ 1-2 NON-INT ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E230M, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names LTT9779 ------------------------------------------------------------------------------------------------------------------------------------