18092( 3) - 29-Jan-2026 20:04:30 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18092 Version: 3 Check-in Time: 29-Jan-2026 20:04:30 STScI Edit Number: 0 Title Connecting stellar mergers to peculiar stellar behavior with a Rosetta Stone young merger remnant ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Keri Hoadley University of Florida Y CoI: Dr. Nicole Arulanantham Schmidt Sciences N CoI: Prof. Brian Metzger Columbia University in the City of New N York CoI: Dr. Ken Shen University of California - Berkeley N CoI: Dr. Mark Seibert Carnegie Institution of Washington N CoI: Dr. Christian Schneider Christian-Albrechts Universitat zu Kiel N CoI: Dr. Hans Moritz Guenther Massachusetts Institute of Technology N CoI: Dr. Maximilian N. Guenther European Space Agency - ESTEC N CoI: Dr. Christopher Martin California Institute of Technology N CoI: Dr. James D. Neill California Institute of Technology N ------------------------------------------------------------------------------------ Abstract Binary and multi-star systems make up over 1/3 of the star systems in the Galaxy, with some ending with the complete engulfment of one star by another. The latter process is observed only in a few cases because the engulfment happens quickly, but is a likely outcome for a sizable fraction of the all binary systems. Current models of stellar mergers suggest that the merger remnant puffs up to large radius, carries additional angular momentum, and leadis to the formation of a convective zone and active dynamon. Over time, the star contracts, spinning up further and leading to the formation of a rapidly rotating star with significant stellar activity. The mergence of a convective zone may lead to the generation of a strong magnetic field. Magnetic fields may drive magnetorotational accretion of surrounding material, slow down rotation via magnetic breaking, and power jets -- all of which transport angular momentum from the merger remnant. Therefore, it remains unclear whether these systems evolve to become a rapid rotators. TYC 2597-735-1 was recently identified as a stellar merger remnant, whose collision occurred a few thousand years ago. It sits in an observationally rare category - one whose merger was old enough to emerge from its dusty aftermath, yet recent enough to still exhibit signs of a stellar merger. Our program will use HST/COS FUV and HST/STIS NUV spectroscopy to obtain a complete UV (1150 - 3000 {\AA}) spectrum at low- to moderate-resolution of TYC 2597 to disentangle the physical processes (magnetic activity, accretion, and outflows), probed using UV hot gas lines, warm circumstellar H2 features, and the UV accretion continuum, that shape its final state. ------------------------------------------------------------------------------------ Observations Description ------------------------ We request a Small GO program, comprised of 14 orbits total, to observe TYC 18092( 3) - 29-Jan-2026 20:04:30 - [ 2] 2597-735-1 (TYC 2597) using COS G130M(1291), G160M(1577), and STIS G230L spectroscopic modes. We request the following exposure times and orbits, which assume 2250 seconds of science exposure and 740 seconds of slew/settle time per orbit: COS G130M, CENWAVE=1291: 5 orbits COS G160M, CENWAVE=1577: 8 orbits STIS G230L, NUV-MAMA, 52'' x 0.2'': 1 orbit HST/COS exposure times are calculated using signal-to-noise (SN) of 10 for hot gas chromospheric and accretion lines (e.g, C III, C IV, Si IV) and the brightest H2 fluorescence lines (based on the expected Lya flux from TYC 2597, estimated from its Ha flux). The COS grating positions were chosen to maximize coverage of hot gas accretion lines (C III 1175, LyA 1216 (wings), Si IV 1402, C IV 1548, He II 1640) and warm molecular disk (H2 Lyman-Werner electronic emission (1160 - 1620 Angstroms). HST/STIS exposure times were calculated by assuming a SN = 20 at 2000 Angstroms, the lowest flux region in TYC 2597's NUV spectrum. We require high SN across the NUV-optical bandpass to accurately model the accretion shock continuum and mass accretion rates. The STIS NUV observations (1800 - 3000 Angstroms) provides simultaneous access to the peak accretion shock continuum emission through where the star's photospheric continuum begins to dominate the continuum emission. Exposure times were estimated for each instrument using a normalized UV spectrum of a pre-main sequence star (RECX-11) and re-scaling the spectrum to TYC 2597's FUV magnitude (20.5 AB). TYC 2597 has a distance of 1.93 kpc (GaiaDR2), an effective temperature of T = 5850 K, and an observed radial velocity ~8.7 km/s. TYC 2597 is at a high galactic latitude (+39.4 degrees above the galactic plane). IRSA extinction maps show E(B-V) = 0.04 +/- 0.02 for a 3' radius around TYC, strongly suggesting that absorption by interstellar dust and hydrogen will not play a significant role in attenuating our FUV observations (A(V) ~ 0.13, assuming R(V) = 3.1). ------------------------------------------------------------------------------------ 18092( 3) - 29-Jan-2026 20:04:30 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 TYC25977351 STAR, ACCRETION DISK, RA=16H48M37.4122S +/- 0.0083", J2000 V = 11.13 20.5 (FUV), 15.4 (NUV), 11.71 CIRCUMSTELLAR MATTER, DEC=+35D12'9.44" +/- 0.01" (B), 10.95 (G), 9.98 (J) F0-F2, F3-F9, WIND Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -2.328507589596735E-4 0.002012 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 18092( 3) - 29-Jan-2026 20:04:30 - [ 4] Visit: 01 (STIS NUV G230L) Visit Requirements: On Hold Comments: Additional Comments: Orbit 1 (out of 1) 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 TYC25977351 STIS/CCD ACQ F28X50LP MIRROR 1 0.1 S (0.1 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 TYC25977351 STIS/NUV ACCUM 52X0.2 G230L 2376 1 2143 S -MAMA (2143 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 | ------------------------------------------------------------------------------------------------------------------------------------ TYC25977351 1 STIS/CCD ACQ F28X50LP MIRROR none none none none 1 N/A TYC25977351 2 STIS/NUV ACCUM 52X0.2 G230L 2376 none none none none 1 N/A -MAMA 18092( 3) - 29-Jan-2026 20:04:30 - [ 5] Visit: 02 (COS FUV G130M Visit 1) Visit Requirements: On Hold Comments: Additional Comments: Orbits 1 - 3 (out of 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 TYC25977351 COS/NUV ACQ/IMA PSA MIRRORB 1 5 S (5 S) GE ------------------------------------------------------------------------------------------------------------------------------------ 2 TYC25977351 COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=4160, FP-POS=4 1 2172 S G (2172 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 TYC25977351 COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=4160, FP-POS=3 1 2552 S G (2552 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 TYC25977351 COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=4160, FP-POS=4 1 2552 S G (2552 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 | ------------------------------------------------------------------------------------------------------------------------------------ TYC25977351 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE TYC25977351 2 COS/FUV TIME-TA PSA G130M 1291 none none none none 1 N/A G TYC25977351 3 COS/FUV TIME-TA PSA G130M 1291 none none none none 2 N/A G TYC25977351 4 COS/FUV TIME-TA PSA G130M 1291 none none none none 3 N/A G 18092( 3) - 29-Jan-2026 20:04:30 - [ 6] Visit: 03 (COS FUV G130M Visit 2) Visit Requirements: On Hold Comments: Additional Comments: Orbits 4 - 5 (out of 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 TYC25977351 COS/NUV ACQ/IMA PSA MIRRORB 1 5 S (5 S) GE ------------------------------------------------------------------------------------------------------------------------------------ 2 TYC25977351 COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=4160, FP-POS=3 1 2172 S G (2172 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 TYC25977351 COS/FUV TIME-TA PSA G130M 1291 BUFFER-TIME=4160, FP-POS=4 1 2552 S G (2552 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 | ------------------------------------------------------------------------------------------------------------------------------------ TYC25977351 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE TYC25977351 2 COS/FUV TIME-TA PSA G130M 1291 none none none none 1 N/A G TYC25977351 3 COS/FUV TIME-TA PSA G130M 1291 none none none none 2 N/A G 18092( 3) - 29-Jan-2026 20:04:30 - [ 7] Visit: 04 (COS FUV G160M Visit 1) Visit Requirements: On Hold Comments: Additional Comments: Orbits 1 - 2 (out of 8) 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 TYC25977351 COS/NUV ACQ/IMA PSA MIRRORB 1 5 S (5 S) GE ------------------------------------------------------------------------------------------------------------------------------------ 2 TYC25977351 COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=10300, FP-POS=1 1 2243 S G (2243 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 TYC25977351 COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=10300, FP-POS=2 1 2548 S G (2548 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 | ------------------------------------------------------------------------------------------------------------------------------------ TYC25977351 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE TYC25977351 2 COS/FUV TIME-TA PSA G160M 1577 none none none none 1 N/A G TYC25977351 3 COS/FUV TIME-TA PSA G160M 1577 none none none none 2 N/A G 18092( 3) - 29-Jan-2026 20:04:30 - [ 8] Visit: 05 (COS FUV G160M Visit 2) Visit Requirements: On Hold Comments: Additional Comments: Orbits 3 - 5 (out of 8) 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 TYC25977351 COS/NUV ACQ/IMA PSA MIRRORB 1 5 S (5 S) GE ------------------------------------------------------------------------------------------------------------------------------------ 2 TYC25977351 COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=10300, FP-POS=3 1 2243 S G (2243 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 TYC25977351 COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=10300, FP-POS=4 1 2548 S G (2548 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 TYC25977351 COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=10300, FP-POS=4 1 2548 S G (2548 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 | ------------------------------------------------------------------------------------------------------------------------------------ TYC25977351 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE TYC25977351 2 COS/FUV TIME-TA PSA G160M 1577 none none none none 1 N/A G TYC25977351 3 COS/FUV TIME-TA PSA G160M 1577 none none none none 2 N/A G TYC25977351 4 COS/FUV TIME-TA PSA G160M 1577 none none none none 3 N/A G 18092( 3) - 29-Jan-2026 20:04:30 - [ 9] Visit: 06 (COS FUV G160M Visit 3) Visit Requirements: On Hold Comments: Additional Comments: Orbits 6 - 8 (out of 8) 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 TYC25977351 COS/NUV ACQ/IMA PSA MIRRORB 1 5 S (5 S) GE ------------------------------------------------------------------------------------------------------------------------------------ 2 TYC25977351 COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=10300, FP-POS=1 1 2243 S G (2243 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 TYC25977351 COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=10300, FP-POS=2 1 2548 S G (2548 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 TYC25977351 COS/FUV TIME-TA PSA G160M 1577 BUFFER-TIME=10300, FP-POS=3 1 2548 S G (2548 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 | ------------------------------------------------------------------------------------------------------------------------------------ TYC25977351 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE TYC25977351 2 COS/FUV TIME-TA PSA G160M 1577 none none none none 1 N/A G TYC25977351 3 COS/FUV TIME-TA PSA G160M 1577 none none none none 2 N/A G TYC25977351 4 COS/FUV TIME-TA PSA G160M 1577 none none none none 3 N/A G 18092( 3) - 29-Jan-2026 20:04:30 - [ 10] Summary Form for Proposal 18092 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 52X0.2, F28X50LP, PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV, STIS/CCD, STIS/NUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=10300, BUFFER-TIME=4160, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G130M, G160M, G230L, MIRROR, MIRRORB ------------------------------------------------------------------------------------------------------------------------------------ Target Names TYC25977351 ------------------------------------------------------------------------------------------------------------------------------------