0 Assigned ID: 7808 ----- Attempting Submission 1 (Thu Apr 16 23:45:19 GMT 2026) ----- STIS TIME-TAG EXPOSURE GENERATES HEAVY DATA VOLUME Dear Instrument Scientists, I am submitting our Phase-2 proposal, which needs some attention and your recommendations. The target is bright, therefore we must follow instrument safety considerations. We prefer TIME-TAG mode observations, but can accept ACCUM as well. The current Phase-2 is written up for TIME-TAG mode and 31x0.05 slit with the NDA filter. This requires target acqusition, slit ilumination measurement (ACQ-PEAK) and then three science exposures in three consecutive orbits in one visit. This is efficeint and allows optimal calibrations. We wish to perform the WAVE exposures after the science exposures during occultation. However, APT did not allow to use the same aperture for WAVE as for the science frames. Unfortunately, this setup is very close to the buffer limit of STIS and this gives a heavy data warning. I wonder if there is any alternative way to maintain instrument safety and increase the SNR in TIME-TAG mode. I have considered usig ACCUM mode, which would eliminate most of the safety risks, although the orbital smearing may reduce the high resolution. Using the 0.2x0.2 slit we could increase the science time, maximuse the troughput and the resulting SNR by 50%. We are looking for a well exposed spectrum and accurate line profiles across the FUV and not for the variability of the object. I would appreciate your advice! Sincerely yours, Peter Nemeth -613942022 ----- Attempting Submission 1 (Tue Aug 18 18:44:48 GMT 2026) ----- We seek for recommendations from the Instrument Scientist to reduce the heavy data production in TIME-TAG mode. The nature of the quasi-Wolf-Rayet (qWR) primary in the binary HD 45166 remains fundamentally uncertain: it may be either a low-mass stripped helium star analogous to hot subdwarfs or a genuinely massive Wolf-Rayet star. Resolving this ambiguity requires a precise mass determination, which in this non-eclipsing system depends critically on composite spectral modeling. Current optical analyses are limited by degeneracies in wind structure, chemical abundances, and flux contributions. We propose high-resolution far-ultraviolet spectroscopy with STIS to constrain the atmospheric properties of the qWR component. Resonance lines such as C IV 1548A/1550A, N V 1238A/1242A, and Si IV 1393A/1402A directly probe the wind kinematics, ionization structure, and mass-loss rate, providing diagnostics inaccessible from optical data. By anchoring the wind and abundance structure, the FUV data will remove the dominant systematic uncertainties in the spectral modeling and enable a robust mass determination. These observations also serve as a feasibility test for a planned ultraviolet survey of massive stars in the PLATO fields, complementing previous surveys focused on low-metallicity and low-mass populations. HD 45166 is the key benchmark system for establishing this methodology and distinguishing between massive-star and stripped-star evolutionary channels. We will obtain far-UV spectroscopy of HD 45166 with HST/STIS using the E140H grating and the 31X0.05NDA aperture. The observations are divided into three single-orbit visits, each using TIME-TAG mode, with no special scheduling constraints. The three E140H settings together provide the required FUV spectral coverage at a resolving power of approximately R = 14,000. The neutral-density aperture is required because of the high UV brightness of HD 45166. Each orbit will provide an exposure of approximately 2300 s, yielding an expected S/N of 23 near 1550 Agstrom. The resulting spectra will resolve the narrow photospheric and wind features of the qWR component and provide key diagnostics of its ionization structure, chemical abundances, wind velocity field, and mass-loss properties. P. Nemeth has extensive experience in quantitative spectral analysis of hot stars and binaries. He is proficient in the use of state-of-the-art non-LTE model atmosphere codes, including TLUSTY and CMFGEN, enabling the simultaneous modeling of photospheric and wind-affected spectra. His work focuses on composite-spectrum systems, where he has developed and applied advanced spectral decomposition and disentangling techniques to derive reliable stellar parameters from multi-component observations. This expertise is particularly relevant for HD 45166, where accurate modeling of both the qWR and B-type components, including wind effects, is essential for determining the system parameters and the mass of the qWR star. E. de Almeida is an expert in the analysis of hot, massive stars using state-of-the-art non-LTE atmosphere models. He has extensive experience with the CMFGEN code, including the modeling of stellar winds and emission-line spectra of evolved hot stars. In addition, he has strong expertise in optical and infrared stellar interferometry, enabling the interpretation of spatially resolved observations of binary systems and stellar environments. His combined experience in spectroscopic modeling and interferometric analysis is particularly valuable for constraining the physical properties and geometry of complex systems such as HD 45166. Stellar Physics and Stellar Types 0 false true false false false false false SUPPORTED STAR B6-B9.5 V-IV COMPOSITE SPECTRAL TYPE EMISSION LINE STAR WOLF RAYET 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.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. J2000 J2000 STIS/FUV-MAMA Spectroscopic No No E140H 1234 STIS/FUV-MAMA Spectroscopic No No E140H 1416 STIS/FUV-MAMA Spectroscopic No No E140H 1598 1787076564491 /tmp/OPVisit17781500145428010235.xml The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18414 :visit-id "01" :proposal-version -1 :trans-version "20260618" :date "18-Aug-2026 20:09:24.0" :trans-errors '(:WARNINGS 1 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 3114304 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18414 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18414 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2597 :al-overhead-at-end 0 :internal-dur-at-end 367 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2977 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18414 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2597 :al-overhead-at-end 0 :internal-dur-at-end 371 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2977 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18414 :visit-id "01" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2597 :al-overhead-at-end 0 :internal-dur-at-end 629 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2977 :pcs-gap 0 ) true 3 0 Exposure time (seconds) = 1,694.0000 at wavelength 1400.00 A gives: SNR = 25.2033 (per resolution element) https://etc.stsci.edu/etc/results/STIS.sp.2366731/ Exposure time (seconds) = 2,395.0000 at wavelength 1200.00 A gives: SNR = 19.8204 (per resolution element) https://etc.stsci.edu/etc/results/STIS.sp.2366736/ Exposure time (seconds) = 2,395.0000 at wavelength 1600.00 A gives: SNR = 19.6822 (per resolution element) https://etc.stsci.edu/etc/results/STIS.sp.2366737/