18115( 2) - 11-Aug-2025 15:25:34 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18115 Version: 2 Check-in Time: 11-Aug-2025 15:25:34 STScI Edit Number: 0 Title HD 96670: A pilot study to characterise low luminosity stripped stars around bright O stars ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Koushik Sen University of Arizona Y CoI: Dr. Yael Naze Universite de Liege N CoI: Dr. Nikolay Britavskiy Universite de Liege N CoI: Prof. Gregor Rauw Universite de Liege N CoI: Prof. Mathieu Renzo University of Arizona N ------------------------------------------------------------------------------------ Abstract Massive stars stripped of their hydrogen-rich envelopes are one of the most common products of binary interaction. They are the progenitors of stripped-envelope supernovae and binary compact object mergers. Uncertain assumptions in binary mass transfer, including the efficiency of mass and angular momentum transfer, affect our understanding of stripped-envelope supernovae and gravitational wave merger progenitors. Without empirical constraints from stripped stars, parameter-space degeneracies are likely to persist despite the anticipated growth in data in the coming decade. Observationally, only a few stripped stars have been detected because the light from their much brighter B- or O-star companions dominates the spectral signature. Recent simulations indicate that high-quality FUV spectra from HST/STIS are ideal for identifying low-luminosity stripped stars with O-star companions. We propose a pilot study requiring only six orbits to characterise the first discovered stripped star+O star binary, HD 96670, in the Milky Way. We will cross-correlate model spectra of stripped stars with the observed spectrum to derive the radial velocities of the stripped star. Combined with the O-star radial velocity curve from the literature, we will provide the first dynamical mass estimate for a stripped star+O star binary. This project will pave the way for more extensive programs to identify populations of stripped star+O star binaries with luminosity contrasts down to 1%. We demonstrate how our analysis of HD 96670 will serve as a cornerstone for providing robust empirical constraints on mass and angular momentum transfer efficiency in massive binary evolution. ------------------------------------------------------------------------------------ Observations Description ------------------------ We request 2 epochs of high-resolution R ~ 45800 spectra (using the FUV-MAMA detector and the E140M echelle grating) of HD96670 (1144 - 1710 Angstrom) at a signal-to-noise ratio SNR ~ 120 at 1425 Angstrom (global SNR ~ 170 for 2 epochs). For the E140M grating with a 0.2 x 0.06 aperture, a Pickles O9 star spectrum with V = 7.43 and E(B - V ) = 0.483 (Gomez et al. 2021), the exposure time required to reach an SNR of 120 at 1425 Angstrom is ~ 5208 s or ~ 87 min, accounting for the minimum buffer time of 99 s (count rate > 20000/s). The target visibility is 52 min per orbit (APT). The total overhead is calculated as the sum of the initial acquisition overhead (6 min) + target acquisition overhead (6 min) + first scientific exposure in MAMA (8 min) ~ 20 min. This 18115( 2) - 11-Aug-2025 15:25:34 - [ 2] allows for 52-20 ~ 32 mins of science exposure time per orbit. As such, 88/32 ~ 3 orbits are required per epoch to reach SNR ~ 120. ------------------------------------------------------------------------------------ 18115( 2) - 11-Aug-2025 15:25:34 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 HD-96670 STAR, MAIN SEQUENCE O RA=11H07M13.9343S +/- 0.0231", J2000 V = V = 7.43 U 6.86, B 7.60, R 8.38, G DEC=-59D52'23.18" +/- 0.0225" -9.00 7.35, J 7.056, H 7.07, K 7.00 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 -8.962973219159579E-4 0.001693 3.11E-4 ------------------------------------------------------------------------------------------------------------------------------------ 18115( 2) - 11-Aug-2025 15:25:34 - [ 4] Visit: 01 (Epoch 1) Visit Requirements: Period 5.28387625 D AND ZERO-PHASE HJD2460064.890 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 HD-96670 STIS/CCD ACQ F28X50OII MIRROR 1 1 S (1 S) PHASE 0.15 TO 0.35 ------------------------------------------------------------------------------------------------------------------------------------ 2 HD-96670 STIS/CCD ACQ/PEA 0.2X0.06 G430L 4300 1 1 S (1 S) PHASE 0.15 TO 0.35 K ------------------------------------------------------------------------------------------------------------------------------------ 3 HD-96670 STIS/FUV ACCUM 0.2X0.06 E140M 1425 1 1074 S PHASE 0.15 TO 0.35 -MAMA (1074 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 HD-96670 STIS/FUV ACCUM 0.2X0.06 E140M 1425 1 2634 S PHASE 0.15 TO 0.35 -MAMA (2634 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 HD-96670 STIS/FUV ACCUM 0.2X0.06 E140M 1425 1 2634 S PHASE 0.15 TO 0.35 -MAMA (2634 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 | ------------------------------------------------------------------------------------------------------------------------------------ HD-96670 1 STIS/CCD ACQ F28X50OI MIRROR none none none none 1 N/A I HD-96670 2 STIS/CCD ACQ/PEA 0.2X0.06 G430L 4300 none none none none 1 N/A K HD-96670 3 STIS/FUV ACCUM 0.2X0.06 E140M 1425 none none none none 1 N/A -MAMA HD-96670 4 STIS/FUV ACCUM 0.2X0.06 E140M 1425 none none none none 2 N/A -MAMA HD-96670 5 STIS/FUV ACCUM 0.2X0.06 E140M 1425 none none none none 3 N/A -MAMA 18115( 2) - 11-Aug-2025 15:25:34 - [ 5] Visit: 02 (Epoch 2) Visit Requirements: Period 5.28387625 D AND ZERO-PHASE HJD2460064.890 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 HD-96670 STIS/CCD ACQ F28X50OII MIRROR 1 1 S (1 S) PHASE 0.65 TO 0.85 ------------------------------------------------------------------------------------------------------------------------------------ 2 HD-96670 STIS/CCD ACQ/PEA 0.2X0.06 G430L 4300 1 1 S (1 S) PHASE 0.65 TO 0.85 K ------------------------------------------------------------------------------------------------------------------------------------ 3 HD-96670 STIS/FUV ACCUM 0.2X0.06 E140M 1425 1 1074 S PHASE 0.65 TO 0.85 -MAMA (1074 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 HD-96670 STIS/FUV ACCUM 0.2X0.06 E140M 1425 1 2634 S PHASE 0.65 TO 0.85 -MAMA (2634 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 HD-96670 STIS/FUV ACCUM 0.2X0.06 E140M 1425 1 2634 S PHASE 0.65 TO 0.85 -MAMA (2634 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 | ------------------------------------------------------------------------------------------------------------------------------------ HD-96670 1 STIS/CCD ACQ F28X50OI MIRROR none none none none 1 N/A I HD-96670 2 STIS/CCD ACQ/PEA 0.2X0.06 G430L 4300 none none none none 1 N/A K HD-96670 3 STIS/FUV ACCUM 0.2X0.06 E140M 1425 none none none none 1 N/A -MAMA HD-96670 4 STIS/FUV ACCUM 0.2X0.06 E140M 1425 none none none none 2 N/A -MAMA HD-96670 5 STIS/FUV ACCUM 0.2X0.06 E140M 1425 none none none none 3 N/A -MAMA 18115( 2) - 11-Aug-2025 15:25:34 - [ 6] Summary Form for Proposal 18115 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.2X0.06, F28X50OII ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, ACQ/PEAK ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PHASE 0.15 TO 0.35, PHASE 0.65 TO 0.85, Period 5.28387625 D AND ZERO-PHASE HJD2460064.890 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E140M, G430L, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names HD-96670 ------------------------------------------------------------------------------------------------------------------------------------