Text improvements. -744800290 Assigned ID: 4909 ----- Attempting Submission 1 (Wed Nov 15 01:57:55 GMT 2023) ----- HST Phase I Proposal 4909 successfully submitted. Receipt: # 4909-1 ----- Attempting Submission 2 (Wed Nov 15 21:57:35 GMT 2023) ----- This is a revised phase 2. The secondary star in AR Sco is an M5 dwarf with some possibility of a major flare. To prevent damage to COS if the star were to flare during acqusition, we have switched to using MirrorB and increased the acquisition exposure to 60s. This phase 2 is again revised. This time, the grating has been shifted to 1280 to place the Lyman alpha between the detector segments as a further safety precaution. -1565578173 ----- Attempting Submission 1 (Tue Feb 13 23:26:36 GMT 2024) ----- ----- Attempting Submission 2 (Sun Jul 28 18:26:25 GMT 2024) ----- ----- Attempting Submission 3 (Tue Dec 03 20:54:28 GMT 2024) ----- This is a resubmission and nothing as changed about the target. The optical light curve of AR Scorpii has recently been found to be evolving at a rapid pace. AR Sco is the nearest and brightest white dwarf pulsar -- a binary system where synchrotron emission is powered by the spin-down of its magnetic degenerate primary. The white dwarf rotates every 1.95 minutes and generates two synchrotron pulses per spin, one from each of its magnetic poles. New observations in 2023 found that these two pulses were nearly equal in amplitude, while in 2015 the secondary pulse was half the strength of the primary. This rapid evolution has been explained as precession of the white dwarf spin axis caused by an obliquity to the binary orbital plane. However, the mechanism that accelerates the relativistic electrons is uncertain, so other physical processes could be driving the evolution. We propose COS spectroscopy of this dynamic system to test for differences in the evolution between the far-UV and optical wavelengths. By directly comparing with archival COS spectra taken in 2016, we will also search for changes in the strong emission lines that would imply evolution in the magnetic interaction between the white dwarf and secondary star. The optical light curve of AR Sco has evolved over the past decade so that the beat pulses from each pole are now nearly equal. We will make observations with COS in time-tag mode to directly compare the UV light curve and spectra of AR Sco with the COS data from 2015. The position of AR Sco is from the GSC2 in the ICRS frame. The proper motion and parallax is from GAIA EDR3. The light curve of AR Sco shows pulses separated by about 1 minute as well as an orbital modulation. The minimum flux observed in the 2015 COS data was between the pulses and around orbital phase 0. This minimum flux was 5e-16 erg/cm2/s/A. The spectrum is approximately flat, so we use this flux as that expected for acquistion using ACQ/image. From the COS acquistion ETC (COS.ta.1901985) we will reach a S/N ratio of 25 in 6s of exposure using MIRRORA/PSA. So we will take a 30s acquistion image to be certain of a high-quality image. To protect COS from a flare on the M-dwarf, we have switched to acquistion using MirrorB and extended the acqusition exposure to 60s. The original plan was to repeat the 2015 COS setup to directly compare the changes in the light curve and spectra over the decade. But the possibility of a flare from the M5 secondary required that we switch to the 1280 cenwave position. This places the Lyman alpha line between the detector segments and avoids exceeding the count-rate limit at Lyman alpha if a super-flare did occur. From the 2015 visit, the average flux of AR Sco over several orbits was 4.9e-15 erg/cm2/s/A. From the COS ETC (COS.sp.1902107), the time to fill the buffer is 10102 s. Reducing that number by 2/3 gives 6700 s. The maximum flux during the 2015 visit was a pulse that peaked at 2e-14 erg/cm2/s/A and lasted for 25s. The COS ETC estimated the buffer fill time for this flux as 4400s. Two-thirds of this is 2900s. To be safe, we are setting the Buffer Time to 1200 to 1400s depending on the exposure time. The four FP-POS have been spread over the 5 HST orbits. Members of the proposal team have published several studies of AR Sco going back to its initial discovery. Garnavich is an expert on supernovae and cataclysmic variable stars. He has led many successful HST programs. Potter is an expert on polarimetry of variable stars. He developed the accepted model that explains the light curve and polarimetry of AR Sco. Buckley is an expert on accretion processes and particularly spectroscopic, photometric and polarimetric observations of magnetic cataclysmic variables and related objects. Littlefield has extensive experience with photometry and spectroscopy of cataclysmic variable stars, particularly magnetic systems. Stellar Physics and Stellar Types 3 false false true false false true false false SUPPORTED EXT-STAR INTERMEDIATE POLAR NO The position is from the GSC2 in ICRS reference frame. The proper motion and parallax are from GAIA EDR3. J2000 J2000 COS/FUV Spectroscopic No No G140L 1105 /private/var/folders/j1/730l_tzs09jdnw98498x_l080000gr/T/OPVisit4549676814626545925.xml 1733258644846 The scheduling data was generated by CASM 32.1.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 17602 :visit-id "01" :proposal-version -1 :trans-version "20240627" :date "03-Dec-2024 15:44:04.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 5 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 765488 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 17602 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 17602 :visit-id "01" :orbit-number 1 :pcs-time 380 :si-vis-utilization 2648 :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 3028 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17602 :visit-id "01" :orbit-number 2 :pcs-time 380 :si-vis-utilization 2648 :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 3028 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17602 :visit-id "01" :orbit-number 3 :pcs-time 380 :si-vis-utilization 2647 :al-overhead-at-end 0 :internal-dur-at-end 114 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17602 :visit-id "01" :orbit-number 4 :pcs-time 380 :si-vis-utilization 2648 :al-overhead-at-end 0 :internal-dur-at-end 95 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) (Tic-Orbit :proposal-id 17602 :visit-id "01" :orbit-number 5 :pcs-time 380 :si-vis-utilization 2648 :al-overhead-at-end 0 :internal-dur-at-end 417 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3028 :pcs-gap 0 ) true 5 0 The minimum flux observed during the 2015 visit was 5e-16 erg/cm2/s/A. Using that in the ETC provides and esimate of 6s to reach a S/N=25.