18129( 3) - 17-Sep-2025 14:52:24 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18129 Version: 3 Check-in Time: 17-Sep-2025 14:52:24 STScI Edit Number: 0 Title Intersection of Extremes: Probing the Wind of BP Cru ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Matheus Bernini Peron Astronomisches Rechen-Institut Heidelberg Y CoI: Dr. Andreas Sander Astronomisches Rechen-Institut Heidelberg N CoI: Mr. Joris Josiek Universitat Heidelberg N CoI: Elisa Clara Schosser Universitat Heidelberg N CoI: Roel Lefever Astronomisches Rechen-Institut Heidelberg N CoI: Mr. Timothy N Parsons University College London N CoI: Dr. Varsha Ramachandran Universitat Heidelberg N CoI: Dr. Gemma Gonzalez-Tora Astronomisches Rechen-Institut Heidelberg N CoI: Dr. Daniel Pauli Institute of Astronomy, KU Leuven N CoI: Dr. Wolf-Rainer Hamann Universitat Potsdam N CoI: Dr. Rainer Hainich Universitat Potsdam N CoI: Prof. Lidia Oskinova Universitat Potsdam N CoI: Dr. Helge Todt Universitat Potsdam N CoI: Ms. Sabela Reyero Serantes Universitat Potsdam N ------------------------------------------------------------------------------------ Abstract 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. ------------------------------------------------------------------------------------ Observations Description ------------------------ 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 18129( 3) - 17-Sep-2025 14:52:24 - [ 2] 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 ------------------------------------------------------------------------------------ 18129( 3) - 17-Sep-2025 14:52:24 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V-BP-CRU STAR, B0-B2 III-I RA=12H26M37.5605S +/- J2000 V = 10.803 0.0000120", DEC=-62D46'13.26" +/- 0.0000133" 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 -7.615790077857849E-4 -0.0020710000626422698 2.5059999999999997E-4 ------------------------------------------------------------------------------------------------------------------------------------ 18129( 3) - 17-Sep-2025 14:52:24 - [ 4] Visit: 01 Visit Requirements: Period 41.5 D AND ZERO-PHASE HJD2453531.65 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 V-BP-CRU COS/NUV ACQ/IMA PSA MIRRORB 1 10 S (10 PHASE 0.2 TO 0.7 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=1, BUFFER-TIME=9850 1 1990 S PHASE 0.2 TO 0.7 G (1990 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=2, BUFFER-TIME=9850 1 2618 S PHASE 0.2 TO 0.7 G (2618 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-BP-CRU 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE V-BP-CRU 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 N/A G V-BP-CRU 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 2 N/A G 18129( 3) - 17-Sep-2025 14:52:24 - [ 5] Visit: 04 Visit Requirements: Period 41.5 D AND ZERO-PHASE HJD2453531.65 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 V-BP-CRU COS/NUV ACQ/IMA PSA MIRRORB 1 10 S (10 PHASE 0.2 TO 0.7 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-BP-CRU COS/NUV TIME-TA PSA G230L 2635 FP-POS=1, BUFFER-TIME=1164 1 600 S (600 PHASE 0.2 TO 0.8 G S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-BP-CRU COS/NUV TIME-TA PSA G230L 2635 FP-POS=2, BUFFER-TIME=1164 1 738 S (738 PHASE 0.2 TO 0.8 G S) ------------------------------------------------------------------------------------------------------------------------------------ 4 V-BP-CRU COS/NUV TIME-TA PSA G230L 2950 FP-POS=3, BUFFER-TIME=1090 1 2655 S PHASE 0.2 TO 0.8 G (2655 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 V-BP-CRU COS/NUV TIME-TA PSA G230L 2950 FP-POS=4, BUFFER-TIME=1090 1 2655 S PHASE 0.2 TO 0.7 G (2655 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-BP-CRU 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE V-BP-CRU 2 COS/NUV TIME-TA PSA G230L 2635 none none none none 1 N/A G V-BP-CRU 3 COS/NUV TIME-TA PSA G230L 2635 none none none none 1 N/A G V-BP-CRU 4 COS/NUV TIME-TA PSA G230L 2950 none none none none 2 N/A G V-BP-CRU 5 COS/NUV TIME-TA PSA G230L 2950 none none none none 3 N/A G 18129( 3) - 17-Sep-2025 14:52:24 - [ 6] Visit: 05 Visit Requirements: Period 41.5 D AND ZERO-PHASE HJD2453531.65 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 V-BP-CRU COS/NUV ACQ/IMA PSA MIRRORB 1 10 S (10 PHASE 0.2 TO 0.7 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=3, BUFFER-TIME=9850 1 1990 S PHASE 0.2 TO 0.7 G (1990 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=4, BUFFER-TIME=9850 1 2618 S PHASE 0.2 TO 0.7 G (2618 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-BP-CRU 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE V-BP-CRU 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 N/A G V-BP-CRU 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 2 N/A G 18129( 3) - 17-Sep-2025 14:52:24 - [ 7] Visit: 06 Visit Requirements: Period 41.5 D AND ZERO-PHASE HJD2453531.65 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 V-BP-CRU COS/NUV ACQ/IMA PSA MIRRORB 1 10 S (10 PHASE 0.2 TO 0.7 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=1, BUFFER-TIME=9850 1 1990 S PHASE 0.2 TO 0.7 G (1990 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=2, BUFFER-TIME=9850 1 2618 S PHASE 0.2 TO 0.7 G (2618 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-BP-CRU 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE V-BP-CRU 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 N/A G V-BP-CRU 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 2 N/A G 18129( 3) - 17-Sep-2025 14:52:24 - [ 8] Visit: 07 Visit Requirements: Period 41.5 D AND ZERO-PHASE HJD2453531.65 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 V-BP-CRU COS/NUV ACQ/IMA PSA MIRRORB 1 10 S (10 PHASE 0.2 TO 0.7 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=3, BUFFER-TIME=9850 1 1990 S PHASE 0.2 TO 0.7 G (1990 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=4, BUFFER-TIME=9850 1 2618 S PHASE 0.2 TO 0.7 G (2618 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-BP-CRU 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE V-BP-CRU 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 N/A G V-BP-CRU 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 2 N/A G 18129( 3) - 17-Sep-2025 14:52:24 - [ 9] Visit: 08 Visit Requirements: Period 41.5 D AND ZERO-PHASE HJD2453531.65 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 V-BP-CRU COS/NUV ACQ/IMA PSA MIRRORB 1 10 S (10 PHASE 0.2 TO 0.7 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=1, BUFFER-TIME=9850 1 1990 S PHASE 0.2 TO 0.7 G (1990 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=2, BUFFER-TIME=9850 1 2618 S PHASE 0.2 TO 0.7 G (2618 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-BP-CRU 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE V-BP-CRU 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 N/A G V-BP-CRU 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 2 N/A G 18129( 3) - 17-Sep-2025 14:52:24 - [ 10] Visit: 09 Visit Requirements: Period 41.5 D AND ZERO-PHASE HJD2453531.65 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 V-BP-CRU COS/NUV ACQ/IMA PSA MIRRORB 1 10 S (10 PHASE 0.2 TO 0.7 GE S) ------------------------------------------------------------------------------------------------------------------------------------ 2 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=3, BUFFER-TIME=9850 1 1990 S PHASE 0.2 TO 0.7 G (1990 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-BP-CRU COS/FUV TIME-TA PSA G140L 1280 FP-POS=4, BUFFER-TIME=9850 1 2618 S PHASE 0.2 TO 0.7 G (2618 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 | ------------------------------------------------------------------------------------------------------------------------------------ V-BP-CRU 1 COS/NUV ACQ/IMA PSA MIRRORB none none none none 1 N/A GE V-BP-CRU 2 COS/FUV TIME-TA PSA G140L 1280 none none none none 1 N/A G V-BP-CRU 3 COS/FUV TIME-TA PSA G140L 1280 none none none none 2 N/A G 18129( 3) - 17-Sep-2025 14:52:24 - [ 11] Summary Form for Proposal 18129 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=1090, BUFFER-TIME=1164, BUFFER-TIME=9850, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PHASE 0.2 TO 0.7, PHASE 0.2 TO 0.8, Period 41.5 D AND ZERO-PHASE HJD2453531.65 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, G230L, MIRRORB ------------------------------------------------------------------------------------------------------------------------------------ Target Names V-BP-CRU ------------------------------------------------------------------------------------------------------------------------------------