18040( 2) - 15-Aug-2025 14:40:01 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 18040 Version: 2 Check-in Time: 15-Aug-2025 14:40:01 STScI Edit Number: 0 Title First UV Observations of the Negative Extremum of xi1 CMa's Complex Magnetic Field ------------------------------------------------------------------------------------ Type Cycle GO 33 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Christi Erba Space Telescope Science Institute Y CoI: Dr. Pragati Pradhan Embry-Riddle Aeronautical University N CoI: Dr. Alexander W. Fullerton Space Telescope Science Institute N CoI: Dr. Matthew E. Shultz University of Delaware N CoI: Dr. Alexandre David-Uraz Central Michigan University N ------------------------------------------------------------------------------------ Abstract The magnetic pulsating star xi1 CMa has the longest rotation period of any known magnetic B-type star (about 30 yr). It is also the only magnetic hot star for which pulsationally-induced modulations have been observed in both its X-ray light curve and its Halpha emission. Archival spectra from IUE and HST, obtained at different rotation phases, suggest xi1 CMa's UV resonance lines are also modulated on the pulsation period, a phenomenon that has not previously been observed for any magnetic hot star. A decade-long spectropolarimetric monitoring effort has now revealed xi1 CMa's complex magnetic topology; as a result, its asymmetric magnetosphere is expected to produce unique UV line profiles at the positive and negative extrema of the longitudinal field curve. xi1 CMa is currently passing through the negative magnetic extremum, a key phase in its rotation cycle that has never before been observed at UV wavelengths. We propose 4 new HST/STIS observations during Cycle 33 to obtain the first high-resolution UV spectra of xi1 CMa near its negative magnetic extremum and to measure the pulsation-induced modulation in its UV wind lines. This novel dataset will be paired with ancillary ground-based optical spectropolarimetry and X-ray spectroscopy obtained near xi1 CMa's negative magnetic extremum. Ultraviolet spectroscopy is the only way to complete a characterization of the velocity and density structure of xi1 CMa's complex magnetosphere, and HST is the only instrument with which these observations can be obtained. UV spectra are critically needed now, since an observation at this rotation phase will not be available again for at least a generation. ------------------------------------------------------------------------------------ Observations Description ------------------------ Our goal is to observe xi1 CMa near its negative magnetic extremum while sampling the ~5 hr pulsation period. The visibility period for each orbit covers about 16% of the pulsation period, so that 4 consecutive orbits cover a full pulsation cycle with minimal gaps. These four orbits must be obtained consecutively to facilitate monitoring of the pulsation cycle. The observations are achievable at any time during Cycle 33, but must be completed before the scheduled end of Cycle 33 (2026 Oct 31) in order to remain near the star's projected negative magnetic extremum. Scheduling early in Cycle 33 is preferred 18040( 2) - 15-Aug-2025 14:40:01 - [ 2] if possible. The target was observed previously at a different rotation phase = position of the stellar magnetosphere with HST/STIS/E140M during Cycle 24 GO Program 14567 (PI Oskinova). We have adopted a similar observing strategy, but have updated the ACQ strategy and exposure times to reflect the science goals of this work. Due to the brightness of the target, we will use the F25ND5 neutral density filter for the target acquisition and the narrow 0.3X0.05ND aperture (which requires a peak-up) for the scientific exposures. We plan to use the E140M grating for the science exposures. 4 FUV-MAMA integrations of 340 s duration in ACCUM mode through the 0.3X0.05ND aperture will enable us to sample the stellar pulsation period and wind structure at sufficient S/N ~10. ------------------------------------------------------------------------------------ 18040( 2) - 15-Aug-2025 14:40:01 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 -KSI01-CMA STAR, B0-B2 V-IV, RA=06H31M51.3663S +/- 0.01", J2000 V = 4.33 CIRCUMSTELLAR MATTER, DEC=-23D25'6.32" +/- 0.01" PULSATING VARIABLE Reference Frame: ICRS Extended: NO Comments: This object was generated by the targetselector and retrieved from the SIMBAD database. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -2.4352672157438562E-4 0.006157 .0021660 ------------------------------------------------------------------------------------------------------------------------------------ 18040( 2) - 15-Aug-2025 14:40:01 - [ 4] Visit: 01 (Visit 1) Visit Requirements: BEFORE 31-OCT-2026:00:00:00; SEQ 01, 02, 03, 04 WITHIN 7 H On Hold Comments: Additional Comments: Scheduling early in Cycle 33 is preferred, if possible, to maintain the best proximity to the star's negative magnetic extremum. 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 -KSI01-CMA STIS/CCD ACQ F25ND5 MIRROR 1 1.4 S (1.4 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 -KSI01-CMA STIS/CCD ACQ/PEA 0.3X0.05N MIRROR 1 0.1 S (0.1 K D S) ------------------------------------------------------------------------------------------------------------------------------------ 3 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 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 | ------------------------------------------------------------------------------------------------------------------------------------ -KSI01-CMA 1 STIS/CCD ACQ F25ND5 MIRROR none none none none 1 N/A -KSI01-CMA 2 STIS/CCD ACQ/PEA 0.3X0.05 MIRROR none none none none 1 N/A K ND -KSI01-CMA 3 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 4 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 5 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 6 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND 18040( 2) - 15-Aug-2025 14:40:01 - [ 5] Visit: 02 (Visit 2) Visit Requirements: AFTER 01 BY 0.9 Orbits TO 1.1 Orbits 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 -KSI01-CMA STIS/CCD ACQ F25ND5 MIRROR 1 1.4 S (1.4 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 -KSI01-CMA STIS/CCD ACQ/PEA 0.3X0.05N MIRROR 1 0.1 S (0.1 K D S) ------------------------------------------------------------------------------------------------------------------------------------ 3 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 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 | ------------------------------------------------------------------------------------------------------------------------------------ -KSI01-CMA 1 STIS/CCD ACQ F25ND5 MIRROR none none none none 1 N/A -KSI01-CMA 2 STIS/CCD ACQ/PEA 0.3X0.05 MIRROR none none none none 1 N/A K ND -KSI01-CMA 3 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 4 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 5 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 6 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND 18040( 2) - 15-Aug-2025 14:40:01 - [ 6] Visit: 03 (Visit 3) Visit Requirements: AFTER 02 BY 0.9 Orbits TO 1.1 Orbits 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 -KSI01-CMA STIS/CCD ACQ F25ND5 MIRROR 1 1.4 S (1.4 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 -KSI01-CMA STIS/CCD ACQ/PEA 0.3X0.05N MIRROR 1 0.1 S (0.1 K D S) ------------------------------------------------------------------------------------------------------------------------------------ 3 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 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 | ------------------------------------------------------------------------------------------------------------------------------------ -KSI01-CMA 1 STIS/CCD ACQ F25ND5 MIRROR none none none none 1 N/A -KSI01-CMA 2 STIS/CCD ACQ/PEA 0.3X0.05 MIRROR none none none none 1 N/A K ND -KSI01-CMA 3 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 4 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 5 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 6 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND 18040( 2) - 15-Aug-2025 14:40:01 - [ 7] Visit: 04 (Visit 4) Visit Requirements: AFTER 03 BY 0.9 Orbits TO 1.1 Orbits 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 -KSI01-CMA STIS/CCD ACQ F25ND5 MIRROR 1 1.4 S (1.4 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 -KSI01-CMA STIS/CCD ACQ/PEA 0.3X0.05N MIRROR 1 0.1 S (0.1 K D S) ------------------------------------------------------------------------------------------------------------------------------------ 3 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 S) ------------------------------------------------------------------------------------------------------------------------------------ 6 -KSI01-CMA STIS/FUV ACCUM 0.3X0.05N E140M 1425 1 340 S -MAMA D see below (343 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 | ------------------------------------------------------------------------------------------------------------------------------------ -KSI01-CMA 1 STIS/CCD ACQ F25ND5 MIRROR none none none none 1 N/A -KSI01-CMA 2 STIS/CCD ACQ/PEA 0.3X0.05 MIRROR none none none none 1 N/A K ND -KSI01-CMA 3 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 4 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 5 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND -KSI01-CMA 6 STIS/FUV ACCUM 0.3X0.05 E140M 1425 none none none none 1 343.0 S -MAMA ND 18040( 2) - 15-Aug-2025 14:40:01 - [ 8] Summary Form for Proposal 18040 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures 0.3X0.05ND, F25ND5 ------------------------------------------------------------------------------------------------------------------------------------ Configurations STIS/CCD, STIS/FUV-MAMA ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM, ACQ, ACQ/PEAK ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements AFTER 01 BY 0.9 Orbits TO 1.1 Orbits, AFTER 02 BY 0.9 Orbits TO 1.1 Orbits, AFTER 03 BY 0.9 Orbits TO 1.1 Orbits, BEFORE 31-OCT-2026:00:00:00, SEQ 01, 02, 03, 04 WITHIN 7 H ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements E140M, MIRROR ------------------------------------------------------------------------------------------------------------------------------------ Target Names -KSI01-CMA ------------------------------------------------------------------------------------------------------------------------------------