For G160M observations, please consult Chapter 9 of the COS Instrument Handbook to estimate overheads and the number of exposures per orbit, and consequently the correct lifetime position. Use of LP4 with G160M requires justification in the "Special Requirements" section of the Phase I PDF. Use of the default LP6 with G160M requires no justification. Proposals can be submitted with the warning present. 0 Assigned ID: 6581 ----- Attempting Submission 1 (Thu Apr 10 18:14:26 GMT 2025) ----- HST Phase I Proposal 6581 successfully submitted. Receipt: # 6581-1 ----- Attempting Submission 2 (Thu Apr 10 20:02:32 GMT 2025) ----- We are aware of the LP4 consideration and planned our proposal accordingly. For the best data quality, it is generally required to use all four FP-POS positions at a given COS cenwave (or 2 positions for certain exception cases). See extended explanation in the diagnostic browser. For the best data quality, it is generally required to use all four FP-POS positions at a given COS cenwave (or 2 positions for certain exception cases). See extended explanation in the diagnostic browser. As recommended, we have made the following changes in this resubmission: 1. ACQ/IMAGE exposure is updated to 2 seconds. 2. Buffer times have been updated according to new ETC calculations that take into account E(B-V) = 0.3 (previously 0.42) based on reddening maps provided by Gorski et al. (2020, ApJ, 889, 179) and Skowron et al. (2021, ApJS, 252, 23). 242181074 ----- Attempting Submission 1 (Wed Aug 06 17:20:16 GMT 2025) ----- ----- Attempting Submission 2 (Fri Sep 12 07:23:52 GMT 2025) ----- ----- Attempting Submission 3 (Wed Oct 01 15:24:49 GMT 2025) ----- We were recommended to use all FP_POS settings individually rather than using the ALL option for each exposure. VFTS 812: A Quiescent Eccentric Black Hole Binary in the LMC? Understanding how black holes form in massive binary systems is a central question in modern astrophysics, with direct implications for the origin of gravitational-wave sources. VFTS 812, an eccentric 17-day period binary in the sub-solar metallicity environment of the Tarantula Nebula was identified as a prime candidate hosting an O4V star with a possible black hole companion. Current optical observations strongly suggest a non-luminous companion exceeding the typical mass threshold for black holes, but cannot definitively exclude a faint, non-degenerate star. Furthermore, the primary mass and atmospheric properties are not constrained enough to trace its past evolution. We propose HST UV observations to decisively determine if the unseen companion in VFTS 812 is indeed a black hole, clarify the physical properties of the O4V primary, and reveal signatures of past mass-transfer episodes. A UV spectroscopic analysis will precisely constrain the rotation and wind characteristics key to understanding the systems evolutionary history. Confirming the black hole companion candidate will provide critical insights into supernova natal kicks, the evolution of massive stars in low-metallicity environments, and the formation of merging binary black holes. We aim to obtain UV spectra with the G160M (1533 & 1623) grating of the O+black-hole binary candidate VFTS 812 during two randomly timed visits. Each visit requested includes two orbits, one each for the two wavelength settings. The SNR in each wavelength setting is expected to reach 15-20 based on ETC calculations. The team has the full necessary expertise in topics including past experience with HST/STIS, UV spectroscopic analysis, stellar evolution and dust extinction. Deshmukh, Shenar and Sana are experts in observations of massive stars using ground- and space-based instruments and applying spectral disentangling techniques. Shenar and Verhamme are experts in atmospheric modeling of massive stars using state-of-the-art modeling tools such as PoWR and FASTWIND. Ludwig is experienced in SWIFT UV photometry in the Magellanic Clouds, including PSF fitting in dense fields, and has driven the search for stripped stars in the Magellanic Clouds. Willcox is expert in using Bayesian inference techniques to study supernova natal kicks using observations of OB+BH binaries. Stellar Physics and Stellar Types 6 false true false false false false SUPPORTED STAR MAIN SEQUENCE O NO 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. VFTS812 J2000 J2000 Swift UVOT UVW2 = 15.14 +/- 0.01, Spectral type O4 V COS/FUV Spectroscopic No No G160M 1533 COS/FUV Spectroscopic No No G160M 1623 /private/var/folders/k5/23v0lgn160sgtmrf_rtth14hdpkh5m/T/OPVisit17612405545501878895.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 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CASM was run in Phase II mode. (Tic-Visit :proposal-id 18118 :visit-id "02" :proposal-version -1 :trans-version "20250624" :date "01-Oct-2025 16:41:24.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 269728 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18118 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18118 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2702 :al-overhead-at-end 0 :internal-dur-at-end 105 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3092 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18118 :visit-id "02" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2711 :al-overhead-at-end 0 :internal-dur-at-end 405 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3092 :pcs-gap 0 ) true 2 0