0 Assigned ID: 6580 ----- Attempting Submission 1 (Thu Apr 10 18:12:41 GMT 2025) ----- HST Phase I Proposal 6580 successfully submitted. Receipt: # 6580-1 0 ----- Attempting Submission 1 (Wed Aug 13 21:44:44 GMT 2025) ----- First UV Observations of the Negative Extremum of xi1 CMa's Complex Magnetic Field 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. 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 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. Erba (PI) is an expert in massive star atmospheres and magnetospheres, specializing in optical and ultraviolet spectroscopy, optical spectropolarimetry, and stellar atmosphere modeling. Erba is an expert on the star xi1 CMa. She is also the co-PI of SpecPolFlow -- a newly-developed software suite for spectropolarimetric analyses using Python. Erba has successfully led a past HST AR proposal with multiple papers resulting from that work. Pradhan (co-I) is an Assistant Professor in Astrophysics at Embry Riddle Aeronautical University. Pradhan's research interests include stellar wind diagnostics of massive OB, WR and cool stars from their high resolution spectra in X-rays as well as accreting neutron stars and their transient behavior. David-Uraz (co-I) is an expert in massive star winds and magnetism, with experience leading a successful HST proposal (resulting in multiple publications). David-Uraz's expertise includes the analysis of spectroscopic data (including HST data), and performing UV radiative transfer and numerical simulations. Fullerton (co-I) is an expert in the UV spectroscopy of early-type stars. Fullerton's experience in reducing and analyzing STIS data is also required for this project. Shultz (co-I) is an expert in stellar magnetism, specializing in the surface magnetic fields and circumstellar magnetospheres of early-type stars, and with a focus on the analysis of spectropolarimetric, spectroscopic, and photometric data. Shultz has pioneered studies of xi1 CMa, including the discovery of the star's extraordinarily long rotation period, as well as the (so far unique) pulsational modulation of the Halpha emission probing the cool plasma of its magnetosphere. Stellar Physics and Stellar Types 6 false true false false false false SUPPORTED STAR B0-B2 V-IV CIRCUMSTELLAR MATTER PULSATING VARIABLE NO This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STIS/FUV-MAMA Spectroscopic No No E140M 1425 /Users/cerba/Documents/000-Projects/020-Grants/021-Funded/2025_hstGO-18040_xi1CMa/OP-cache/xi1cma_hstCycle33_PH2-v01.xml Timing link suitability includes constraints ([Sequence (01 02 03 04) within 0.3 days] [02 After 01 by 0.1 to 0.1 days]) The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. Scheduling early in Cycle 33 is preferred, if possible, to maintain the best proximity to the star's negative magnetic extremum. (Tic-Visit :proposal-id 18040 :visit-id "01" :proposal-version -1 :trans-version "20250624" :date "13-Aug-2025 17:27:06.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 296256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18040 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18040 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 450 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 /Users/cerba/Documents/000-Projects/020-Grants/021-Funded/2025_hstGO-18040_xi1CMa/OP-cache/xi1cma_hstCycle33_PH2-v02.xml Timing link suitability includes constraints ([Sequence (01 02 03 04) within 0.3 days] [02 After 01 by 0.1 to 0.1 days] [03 After 02 by 0.1 to 0.1 days]) The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18040 :visit-id "02" :proposal-version -1 :trans-version "20250624" :date "13-Aug-2025 17:27:06.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 296256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18040 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18040 :visit-id "02" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 450 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 /Users/cerba/Documents/000-Projects/020-Grants/021-Funded/2025_hstGO-18040_xi1CMa/OP-cache/xi1cma_hstCycle33_PH2-v03.xml Timing link suitability includes constraints ([Sequence (01 02 03 04) within 0.3 days] [03 After 02 by 0.1 to 0.1 days] [04 After 03 by 0.1 to 0.1 days]) The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18040 :visit-id "03" :proposal-version -1 :trans-version "20250624" :date "13-Aug-2025 17:27:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 296256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18040 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18040 :visit-id "03" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 450 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0 /Users/cerba/Documents/000-Projects/020-Grants/021-Funded/2025_hstGO-18040_xi1CMa/OP-cache/xi1cma_hstCycle33_PH2-v04.xml Timing link suitability includes constraints ([Sequence (01 02 03 04) within 0.3 days] [04 After 03 by 0.1 to 0.1 days]) The scheduling data was generated by CASM 33.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 18040 :visit-id "04" :proposal-version -1 :trans-version "20250624" :date "13-Aug-2025 17:27:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 296256 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18040 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18040 :visit-id "04" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2598 :al-overhead-at-end 0 :internal-dur-at-end 450 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 1 0