17276( 5) - 04-Aug-2023 15:54:54 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 17276 Version: 5 Check-in Time: 04-Aug-2023 15:54:54 STScI Edit Number: 1 Title A new radio pulsing white dwarf? ------------------------------------------------------------------------------------ Type Cycle GO 30 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Ingrid Pelisoli The University of Warwick Y CoI: Prof. Boris T. Gaensicke The University of Warwick N CoI: Dr. David Buckley South African Astronomical Observatory N CoI: Dr. Stephen Potter South African Astronomical Observatory N CoI: Ian Heywood CSIRO, Australia Telescope National N Facility CoI: Dr. Axel Schwope Leibniz-Institut für Astrophysik Potsdam N (AIP) CoI: Dr. Patrick Woudt University of Cape Town N CoI: Jaco Brink South African Astronomical Observatory N ------------------------------------------------------------------------------------ Abstract In April this year, we have discovered a system showing strong optical pulses on a period of 5.3 minutes, during which the flux increases by up to a factor of four. Optical spectroscopy revealed a blue continuum added to the red spectrum of an M-type dwarf, with strong Balmer and neutral helium lines in emission. The radial velocity of the lines varies on a period of 4.03 hours, consistent with a photometric modulation observed on TESS data and clearly identifying the system as a compact binary. Perhaps most fascinating of all, the 5.3 minute pulses are also identified in radio. While radio pulses are reminiscent of neutron star or black hole binaries, the 5.3 min modulation is archetypical of the spin period of a strongly magnetic white dwarf. Only one other white dwarf binary is known to show this behaviour: the white dwarf pulsar AR Scorpii, in which the combination of a magnetic field and rapid rotation results in the acceleration of relativisitic particles that blast the inner hemisphere of the M-dwarf companion, akin to the well-known milli-second pulsars. We believe our system to be the first ever AR Sco twin, establishing white dwarf pulsars as a class. The ultimate proof of our hypothesis relies on the unambiguous identification of the white dwarf, which will be achieved through the detection of hydrogen absorption in the requested COS/G140L observations. This discovery will provide the first opportunity to test models proposed to explain the origin of AR Sco and shed light onto the evolution of close binaries. ------------------------------------------------------------------------------------ Observations Description ------------------------ We require FUV spectroscopy of J1912 in TIME-TAG mode, which allows to re-bin the data in both time and wavelength. We will generate ultraviolet light curves and time-resolved spectra that we will bin both on the orbital period of the binary, and the spin period of the white dwarf. With these data in hand, we will (i) confirm the presence of a white dwarf in the system, (ii) measure the UV amplitude of the pulses, (iii) probe for the occurrence of flares, and (iv) 17276( 5) - 04-Aug-2023 15:54:54 - [ 2] probe for Zeeman splitting indicating a magnetic field. For covering the FUV, we will use COS with the G140L grating centred at 1105 A, which provides flux-calibrated coverage between 1118 and 2150 A. This configuration provides us with good coverage of Lyman-alpha, where Zeeman splitting would be most evident, and of the H2 quasi-molecular absorption at 1600 A, which is particularly sensitive to temperature (Allard et al., 2004). We used white dwarf models with the temperature estimate for AR Sco to calculate the required exposure time for our observations. To confirm the white dwarf, we require signal-to-noise ratio (SNR) of ~5 in the vicinity of the Lyman-alpha line, which according to the ETC requires ~34, 800 sec. Overheads consist of guide star acquisition (6 min in the first orbit, 4 min for subsequent orbits), target acquisition (4 min in the first orbit only), and instrument overheads (5 min for the first orbit, 2 min for subsequent orbits). Our target has an orbital visibility of 55 min, so accounting for these overheads we require 12 orbits to reach the required SNR in the FUV. Our request can be broken into separate smaller visits if necessary. J1912 is the brightest object in a 25 arcsec radius, and even during the strongest detected flares its brightness does not surpass V~16, well below the brightness limit of the COS. ------------------------------------------------------------------------------------ 17276( 5) - 04-Aug-2023 15:54:54 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 J191213.72-4 STAR, INTERACTING RA=19H12M13.7198S +/- J2000 V = 16.86 +/- 0.92 41045.1 BINARY, INTERMEDIATE 0.00007802636", POLAR, REGULAR VARIABLE DEC=-44D10'45.08" +/- 0.000079562016" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 -0.0015440452438078712 -0.011009999999999999 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 17276( 5) - 04-Aug-2023 15:54:54 - [ 4] Visit: 01 (First visit) Visit Requirements: 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 J191213.72- COS/NUV ACQ/IMA PSA MIRRORA 1 5 S (5 S) 441045.1 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2508, FP-POS=1 1 2508 S 441045.1 G (2508 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2782, FP-POS=2 1 2782 S 441045.1 G (2782 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2782, FP-POS=3 1 2782 S 441045.1 G (2782 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2782, FP-POS=4 1 2782 S 441045.1 G (2782 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 | ------------------------------------------------------------------------------------------------------------------------------------ J191213.72-441045.1 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J191213.72-441045.1 2 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G J191213.72-441045.1 3 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G J191213.72-441045.1 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G J191213.72-441045.1 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G 17276( 5) - 04-Aug-2023 15:54:54 - [ 5] Visit: 02 (Second visit) Visit Requirements: 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 J191213.72- COS/NUV ACQ/IMA PSA MIRRORA 1 5 S (5 S) 441045.1 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2508, FP-POS=1 1 2508 S 441045.1 G (2508 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2782, FP-POS=2 1 2782 S 441045.1 G (2782 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2782, FP-POS=3 1 2782 S 441045.1 G (2782 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2782, FP-POS=4 1 2782 S 441045.1 G (2782 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 | ------------------------------------------------------------------------------------------------------------------------------------ J191213.72-441045.1 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J191213.72-441045.1 2 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G J191213.72-441045.1 3 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G J191213.72-441045.1 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G J191213.72-441045.1 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G 17276( 5) - 04-Aug-2023 15:54:54 - [ 6] Visit: 03 (Third visit) Visit Requirements: 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 J191213.72- COS/NUV ACQ/IMA PSA MIRRORA 1 5 S (5 S) 441045.1 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2508, FP-POS=1 1 2508 S 441045.1 G (2508 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2782, FP-POS=2 1 2782 S 441045.1 G (2782 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2782, FP-POS=3 1 2782 S 441045.1 G (2782 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2782, FP-POS=4 1 2782 S 441045.1 G (2782 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 | ------------------------------------------------------------------------------------------------------------------------------------ J191213.72-441045.1 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J191213.72-441045.1 2 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G J191213.72-441045.1 3 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G J191213.72-441045.1 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G J191213.72-441045.1 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G 17276( 5) - 04-Aug-2023 15:54:54 - [ 7] Visit: 04 (Second visit repeat) Visit Requirements: Period 0.16811989 D AND ZERO-PHASE HJD2459784.98230 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 J191213.72- COS/NUV ACQ/IMA PSA MIRRORA 1 5 S (5 S) 441045.1 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2508, FP-POS=1 1 2508 S PHASE 0.45 TO 0.7 441045.1 G see below (2148 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 | ------------------------------------------------------------------------------------------------------------------------------------ J191213.72-441045.1 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J191213.72-441045.1 2 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 2148.0 S G 17276( 5) - 04-Aug-2023 15:54:54 - [ 8] Visit: 05 (Third visit repeat) Visit Requirements: Period 0.16811989 D AND ZERO-PHASE HJD2459784.98230 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 J191213.72- COS/NUV ACQ/IMA PSA MIRRORA 1 5 S (5 S) 441045.1 GE ------------------------------------------------------------------------------------------------------------------------------------ 2 J191213.72- COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=2508, FP-POS=1 1 2508 S PHASE 0.45 TO 0.7 441045.1 G see below (2148 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 | ------------------------------------------------------------------------------------------------------------------------------------ J191213.72-441045.1 1 COS/NUV ACQ/IMA PSA MIRRORA none none none none 1 N/A GE J191213.72-441045.1 2 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 2148.0 S G 17276( 5) - 04-Aug-2023 15:54:54 - [ 9] Summary Form for Proposal 17276 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV, COS/NUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/IMAGE, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=2508, BUFFER-TIME=2782, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PHASE 0.45 TO 0.7, Period 0.16811989 D AND ZERO-PHASE HJD2459784.98230 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L, MIRRORA ------------------------------------------------------------------------------------------------------------------------------------ Target Names J191213.72-441045.1 ------------------------------------------------------------------------------------------------------------------------------------