18245( 2) - 28-Apr-2026 18:34:00 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18245 Version: 2 Check-in Time: 28-Apr-2026 18:34:00 STScI Edit Number: 0 Title Characterizing the Accreting Protoplanet Embedded in the Protoplantary Disk ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Jun Hashimoto National Astronomical Observatory of Japan Y (NAOJ) CoI: Dr. Yasuhiro Hasegawa Jet Propulsion Laboratory N CoI: Dr. Yuhiko Aoyama Sun Yat-Sen University N CoI: Dr. Gabriel-Dominique Marleau Universitat Duisburg-Essen N CoI: Dr. Taichi Uyama National Institute for Basic Biology N CoI: Dr. Nagayoshi Ohashi Academia Sinica, Institute of Astronomy N and Astrophysics CoI: Dr. Michihiro Takami Academia Sinica, Institute of Astronomy N and Astrophysics ------------------------------------------------------------------------------------ Abstract The planetary growth rate, specifically the mass accretion rate, is a key parameter in planet formation, as it ultimately determines a planet's final mass. Traditionally, accretion rates have been estimated using hydrogen emission lines based on the accretion flow model, originally developed for stars. However, Aoyama et al. recently proposed the accretion shock model as an alternative mechanism for hydrogen line emission. For planetary-mass objects, the shock model predicts accretion rates up to an order of magnitude higher than the flow model, making it crucial to determine which mechanism dominates. We propose a joint JWST-HST observing program of the protoplanet WISPIT 2 b to distinguish between the two models using hydrogen line ratios. For the first time, this study will enable more accurate estimates of accretion rates in accreting planets embedded within protoplanetary disks. Our pilot observations pave the way for applying these models to characterize future discoveries with JWST and the ELTs. ------------------------------------------------------------------------------------ Observations Description ------------------------ We request contemporaneous JWST and HST observations as described in Science Justification. While Pa-alpha and Pa-beta will be observed with JWST, H-beta will be observed with HST/WFC3. Below, we provide the observing description for the HST observations. We propose a two-orbit campaign to observe the accreting planet WISPIT 2 b using the F487N filter. The C512C-SUB array of the WFC3/UVIS2 detector will be employed to minimize readout overheads. Since we will apply the Reference Star Differential Imaging (RDI) technique for PSF subtraction to mitigate self-subtraction, one orbit will be allocated to the target and the other to the reference star. We request that Visit-01 for the target (WISPIT 2 b) be fully scheduled within the JWST observing window. In contrast, Visit-02 for the 18245( 2) - 28-Apr-2026 18:34:00 - [ 2] reference star does not need to overlap with JWST observations. Each orbit will consist of four 224 s exposures to improve spatial sampling (see below), resulting in a total integration time of 896 s per orbit in F487N. Note that the exposure time has been reduced from 720 s in the Phase I proposal to 224 s to avoid saturation. The expected SNR is 7, which is sufficient to achieve our science goals. We adopt a four-point box dithering pattern to improve the spatial sampling of the images. The native pixel scale of 40 mas in the UVIS channel is undersampling for the spatial resolution of 70 mas in the F487N filter. The dithering distance will be half a pixel (20 mas) in either direction. At each dithering position, eight 28-second exposures will be taken to mitigate cosmic rays. The total integration times per orbit will be 896 s. The same procedure is applied to both the target and the reference star. The background flux at the planets' locations is expected to be high because the planets are embedded in the bright stellar halo. Therefore, we choose to ignore the warnings regarding the FLASH levels and do not apply additional FLASH. ------------------------------------------------------------------------------------ 18245( 2) - 28-Apr-2026 18:34:00 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 IRAS-19205-0 STAR, EXTRA-SOLAR RA=19H23M17.0332S, J2000 V = 11.197 746 PLANETARY SYSTEM DEC=-07D40'55.08" Reference Frame: ICRS Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 4.2434166330108643E-4 -0.027137999904880417 0.0074649 ------------------------------------------------------------------------------------------------------------------------------------ 2 TYC-5709-28- STAR, K III-I RA=19H21M47.6414S, J2000 V = 11.31 1 DEC=-07D57'3.78" Reference Frame: ICRS Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -5.220856808208548E-4 0.0013460000000000002 6.826E-4 ------------------------------------------------------------------------------------------------------------------------------------ 18245( 2) - 28-Apr-2026 18:34:00 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.02 Line_Spacing 0.02 Coordinate_Frame POS-TARG Pattern_Orient 0 Angle_Between_Sides 90 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 18245( 2) - 28-Apr-2026 18:34:00 - [ 5] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: 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 IRAS-19205- WFC3/UVI ACCUM UVIS2-C51 F487N 8 28 S (896 POS TARG 0, 0; PATTERN 1 0746 S 2C-SUB S) 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 1 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 2 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 3 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 4 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 5 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 6 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 7 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 8 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 1 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 2 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 3 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 4 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 5 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 6 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 7 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 8 none 1 N/A S 12C-SUB 18245( 2) - 28-Apr-2026 18:34:00 - [ 6] 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 | ------------------------------------------------------------------------------------------------------------------------------------ IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 1 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 2 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 3 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 4 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 5 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 6 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 7 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 8 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 1 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 2 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 3 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 4 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 5 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 6 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 7 none 1 N/A S 12C-SUB IRAS-19205-0746 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 8 none 1 N/A S 12C-SUB 18245( 2) - 28-Apr-2026 18:34:00 - [ 7] Visit: 02 Visit Requirements: AFTER 01 BY 0 Orbits TO 1 Orbits On Hold Comments: Additional Comments: 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 TYC-5709-28 WFC3/UVI ACCUM UVIS2-C51 F487N 8 28 S (896 POS TARG 0, 0; PATTERN 1 -1 S 2C-SUB S) 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 1 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 2 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 3 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 4 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 5 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 6 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 7 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 1 none 8 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 1 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 2 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 3 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 4 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 5 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 6 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 7 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 2 none 8 none 1 N/A S 12C-SUB 18245( 2) - 28-Apr-2026 18:34:00 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 1 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 2 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 3 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 4 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 5 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 6 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 7 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 3 none 8 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 1 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 2 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 3 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 4 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 5 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 6 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 7 none 1 N/A S 12C-SUB TYC-5709-28-1 1 WFC3/UVI ACCUM UVIS2-C5 F487N 4 none 8 none 1 N/A S 12C-SUB 18245( 2) - 28-Apr-2026 18:34:00 - [ 9] Summary Form for Proposal 18245 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS2-C512C-SUB ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 0 Orbits TO 1 Orbits, PATTERN 1 1, POS TARG 0, 0 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F487N ------------------------------------------------------------------------------------------------------------------------------------ Target Names IRAS-19205-0746, TYC-5709-28-1 ------------------------------------------------------------------------------------------------------------------------------------