0 Assigned ID: 6153 ----- Attempting Submission 1 (Tue Apr 08 11:28:10 GMT 2025) ----- HST Phase I Proposal 6153 successfully submitted. Receipt: # 6153-1 ----- Attempting Submission 2 (Thu Apr 10 11:53:29 GMT 2025) ----- HST Phase I Proposal 6153 successfully submitted. Receipt: # 6153-2 ----- Attempting Submission 3 (Thu Apr 10 22:08:22 GMT 2025) ----- 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. 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. 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. Final submission after discussions with CS. 1063146599 ----- Attempting Submission 1 (Thu Aug 07 11:50:05 GMT 2025) ----- HST Phase II Proposal 18129 successfully submitted. Receipt: # 18129-1 ----- Attempting Submission 2 (Wed Sep 17 14:40:36 GMT 2025) ----- The visits were organized as such to improve the schedulability. Intersection of Extremes: Probing the Wind of BP Cru Massive stars are frequently found in binary or multiple systems. Within the diverse types of multiples, high-mass X-ray binaries (HMXBs) are a particularly intriguing class of objects. They are characterized by strong X-ray emissions due to the accretion of material from a massive donor star onto a compact remnant. Their analysis offers unique insights into the physics of stellar winds and binary evolution. Using the unique capabilities of the HST, we aim to conduct a pilot and pioneering study of BP Cru, a HMXB system whose mass donor is a B hypergiant (BHG) - a B-type star close to the Eddington-limit with hybrid characteristics of "typical" B supergiants and luminous blue variables. Marking a crucial intersection among the evolution of massive stars, probing the wind of BP Cru provides a unique opportunity to investigate the nature of BHGs as well as wind-fed HMXBs. Obtaining the first high-quality UV spectra of this singular target and combining them with archival data for other spectral regions as well as state-of-the-art atmosphere models, we will (1) shed light into the evolutionary status of BP Cru, (2) measure the wind properties, and (3) constrain the conditions for wind accretion by the compact remnant, an aspect still highly uncertain in HMXBs. Additionally, this study will also boost our knowledge on radiatively driven winds for cooler regimes by evaluating the conditions and mechanisms for wind launching. We propose to observe BP Cru using HST/COS spectroscopy within 15 orbits, aiming for a S/N of ~10 in the FUV range using the G140L/1280 grating and of ~35 in the NUV range using G230L/2950. While medium-resolution settings would be ideal for obtaining detailed wind signatures, the reddening of the target makes this unfeasible. Yet, the COS low resolution gratings will provide spectra comparable with IUE high dispersion data -- which proved to be sufficient to obtain detailed wind properties of, for example, the less extreme BHGs zet1 Sco and HD190603 (Clark et al. 2012). We calculated detailed synthetic spectra using available optical spectra and a state-of-the-art stellar atmosphere code (e.g. CMFGEN) to estimate the necessary exposure time. The UV data will contain major wind lines of different ionization stages (e.g., Si IV 1398-1402 Angstroms, C IV 1548-51 Angstroms, Mg II 2790-2805 Angstroms, dee Fig. 1), which, as illustrated in the figure, some are very sensitive to the X-ray emission in the wind. This will enable us to perform a spectral analysis that will reveal the detailed structure of a BHG wind and HMXB donor. While the optical lines show some wind features, many wind-driving ions, as well as the true wind velocity (and thus also the mass-loss rate), can only be determined from the spectral lines found in the UV range. Our observations will be performed in TIME-TAG mode. Wherever possible, we will use all four FP-POS positions for each target to enhance the lifetime of the detector. Following the new COS Lifetime Usage Policy, the number of science counts per pixel does not exceed the 1% count limit (270 counts per second) per LP. The X-ray emission increases considerably moments before the periastron (at phi ~ 0.95) and the apastron (phi ~ 0.50). We expect that the UV spectrum is affected by the amount of X-rays present in the wind. Thus, if the observations happen in multiple random orbital phases (which might include these special phases), spectra whose morphology differ considerably might be added. With the proposed data, we aim to quantify the general atmospheric properties of BP Cru. Therefore, we need spectra that will not be (strongly) contaminated by such transient events. Hence, we require that all of our observations are taken between phi = 0.65 and phi = 0.85 to ensure the neutron star is far from the apsides. These phase constraints correspond to a time window of around 8 days during each period The proposing team consists of established researchers and PhD students. A. Sander, V. Ramaschandran, L. Oskinova, D. Pauli, and W-R. Hamann all have experience with quantitative spectroscopy including HST UV data. W-R. Hamann, L. Oskinova, A. Sander, V. Ramaschandran, D. Pauli, H. Todt, R. Hainich, R. Lefever, J. Josiek, E. C. Schoesser, S. Reyero Serantes, and M. Bernini Peron have detailed experience with non-LTE atmosphere modelling. T. Parsons have experience modelling UV spectra using SEI method. G. Gonzalez-Tora is an expert in spectral modeling of massive stars across all evolutionary phases. A. Sander, H. Todt, and W.-R. Hamann are lead developers of PoWR, a state-of-the-art non-LTE stellar atmosphere code, especially designed to cope with radiatively-driven winds of hot stars. Moreover, D. Pauli, V. Ramachandran, and M. Bernini Peron have experience in modelling of the evolution of massive stars with the publicly available MESA code, and J. Josiek have experience within the same field but with GENEC. Stellar Physics and Stellar Types 6 false true false false false false SUPPORTED STAR B0-B2 III-I 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. J2000 J2000 COS/FUV Spectroscopic No No G140L 800 COS/NUV Spectroscopic No No G230L 2950 /tmp/OPVisit12923546227381965516.xml The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. 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