14470( 2) - 02-Dec-2015 12:44:33 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14470 Version: 2 Check-in Time: 02-Dec-2015 12:44:33 STScI Edit Number: 0 Title AR Sco: the first white dwarf pulsar? ------------------------------------------------------------------------------------ Type Cycle GO 23 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Boris T. Gaensicke The University of Warwick Y CoI: Prof. Thomas R. Marsh The University of Warwick N CoI: Dr. Steven G. Parsons Valparaiso University N CoI: Dr. Matthias R. Schreiber Valparaiso University N CoI: Dr. Danny Steeghs The University of Warwick N CoI: Dr. Elizabeth R. Stanway The University of Warwick N CoI: Ms. Odette Fabiola Toloza The University of Warwick N Castillo CoI: Dr. Peter J. Wheatley The University of Warwick N ------------------------------------------------------------------------------------ Abstract AR Sco was mis-classified in 1971 as a pulsating delta-Scuti star, and has received little attention until now. In May this year, we became aware of the truly unique nature of this object: besides a two-magnitude modulation on the 3.56h orbital period, we detected a coherent 2min variability from the optical into the radio, and a spectacular infrared excess across the WISE bands. Our optical spectroscopy reveals a late-type companion star, clearly identifying AR Sco as a compact binary. While most of its observational characteristics are reminiscent of neutron star or black hole binaries, the 2min modulation is archetypical of the spin period of a strongly magnetic white dwarf. We believe that AR Sco is the first white dwarf radio pulsar, where the combination of a large 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. The ultimate proof of our hypothesis relies on the unambiguous identification of the white dwarf, which will be achieved through the detection of Zeeman-split Ly alpha absorption in the requested COS/G140L observations. ------------------------------------------------------------------------------------ Observations Description ------------------------ We believe that AR Sco is the first white dwarf pulsar, and these COS FUV G140L observations are designed to detect the white dwarf photoshere, in particular Zeeman-split Ly alpha, to confirm our hypothesis. We have obtained detailed ground-based photometry (ULTRACAM u, g, i bands) as well as many SWIFT UVW1observations. The u-band and UVW1 flux have nearly identical flux levels, and the same orbital modulation amplitude, and we assume for the Phase II a flat spectrum (in Flambda). The target is acquired spectroscopically, assuming that HST hits the faintest (2e-14erg/cm2/s/AA) phase, any other phase will result in a S/N>40 in the target acq. 14470( 2) - 02-Dec-2015 12:44:33 - [ 2] We need to observe the target for five consecutive orbits to achieve nearly-complete orbital phase coverage (the orbital period is 3.55h), see Fig. 4 in the Phase I proposal. Because of the large orbital variability, we decided to split every single HST orbit into four FP-POS settings, so that we get an optimally wavelength-sampled spectrum at five different orbital phases. To minimise the overheads, we set the BUFFER-TIME to Texp-110sec (which is significantly shorter than the maximum buffer time given by our ETC simulation). The flux level at orbital maximum, 1.2e-14erg/cm2/s/AA (Fig. 1 in the Phase I proposal, middle panel), falls a factor ~30 below the maximum count rate of COS/G140L, so should pose no threat to the detector. We have a decade worth of optical monitoring of AR Sco (from the Catalina Real Time Survey), which shows no variability besides the orbital modulation, i.e. no flares, no outbursts. ------------------------------------------------------------------------------------ 14470( 2) - 02-Dec-2015 12:44:33 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 V-AR-SCO STAR, DA, PULSAR RA=16H21M47.2820S +/- 0.1", J2000 V = 16.5 DEC=-22D53'10.31" +/- 0.1" Reference Frame: ICRS Extended: NO Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 2000 0.0012301736882317392 -0.0316 0.0 ------------------------------------------------------------------------------------------------------------------------------------ 14470( 2) - 02-Dec-2015 12:44:33 - [ 4] Visit: 01 Visit Requirements: On Hold Comments: Additional Comments: Because of the substantial orbital phase variation, we split every single orbit into four FP-POS settings, so that we get five fully-sampled FUV spectra across the binary orbit. 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-AR-SCO COS/FUV ACQ/PEA PSA G140L 1105 1 60 S (60 KXD S) Comments: We have good orbital phase coverage with Swift UVW1 (2600A) and SDSS u (3650A), amplitude and flux in the two bands are identical, so we adopt a flat spectrum in Flambda. At orbital minimum, the flux in Swift UVW1 is 2e-15 erg/cm2/s/AA, and we set up the target acquisition to achieve a S/N of 40 at that faintest phase. At orbital maximum, the system reaches 1.2e-14 erg/cm2/s/AA. This is a factor ~30 below the COS bright limit for the chosen setup. ------------------------------------------------------------------------------------------------------------------------------------ 2 V-AR-SCO COS/FUV ACQ/PEA PSA G140L 1105 STEP-SIZE=0.9, CENTER=DEF, 1 60 S (60 KD NUM-POS=5 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=335, FP-POS=1 1 445 S (445 G S) Comments: We have good orbital phase coverage with Swift UVW1 (2600A) and SDSS u (3650A), amplitude and flux in the two bands are identical, so we adopt a flat spectrum in Flambda. At orbital minimum, the flux in Swift UVW1 is 2e-15 erg/cm2/s/AA, at orbital maximum 1.2e-14 erg/cm2/s/AA. We adopt the max. flux for the ETC run given above. The bright phase is a factor ~30 below the COS maximum count rate. ------------------------------------------------------------------------------------------------------------------------------------ 4 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=335, FP-POS=2 1 445 S (445 G S) ------------------------------------------------------------------------------------------------------------------------------------ 5 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=335, FP-POS=3 1 445 S (445 G S) ------------------------------------------------------------------------------------------------------------------------------------ 6 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=334, FP-POS=4 1 444 S (444 G S) ------------------------------------------------------------------------------------------------------------------------------------ 14470( 2) - 02-Dec-2015 12:44:33 - [ 5] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 7 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=1 1 647 S (647 G S) Comments: We have good orbital phase coverage with Swift UVW1 (2600A) and SDSS u (3650A), amplitude and flux in the two bands are identical, so we adopt a flat spectrum in Flambda. At orbital minimum, the flux in Swift UVW1 is 2e-15 erg/cm2/s/AA, at orbital maximum 1.2e-14 erg/cm2/s/AA. We adopt the max. flux for the ETC run given above. The bright phase is a factor ~30 below the COS maximum count rate. ------------------------------------------------------------------------------------------------------------------------------------ 8 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=2 1 647 S (647 G S) ------------------------------------------------------------------------------------------------------------------------------------ 9 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=3 1 647 S (647 G S) ------------------------------------------------------------------------------------------------------------------------------------ 10 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=4 1 650 S (650 G S) ------------------------------------------------------------------------------------------------------------------------------------ 11 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=1 1 647 S (647 G S) Comments: We have good orbital phase coverage with Swift UVW1 (2600A) and SDSS u (3650A), amplitude and flux in the two bands are identical, so we adopt a flat spectrum in Flambda. At orbital minimum, the flux in Swift UVW1 is 2e-15 erg/cm2/s/AA, at orbital maximum 1.2e-14 erg/cm2/s/AA. We adopt the max. flux for the ETC run given above. The bright phase is a factor ~30 below the COS maximum count rate. ------------------------------------------------------------------------------------------------------------------------------------ 12 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=2 1 647 S (647 G S) ------------------------------------------------------------------------------------------------------------------------------------ 13 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=3 1 647 S (647 G S) ------------------------------------------------------------------------------------------------------------------------------------ 14 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=4 1 650 S (650 G S) ------------------------------------------------------------------------------------------------------------------------------------ 14470( 2) - 02-Dec-2015 12:44:33 - [ 6] Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 15 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=1 1 647 S (647 G S) Comments: We have good orbital phase coverage with Swift UVW1 (2600A) and SDSS u (3650A), amplitude and flux in the two bands are identical, so we adopt a flat spectrum in Flambda. At orbital minimum, the flux in Swift UVW1 is 2e-15 erg/cm2/s/AA, at orbital maximum 1.2e-14 erg/cm2/s/AA. We adopt the max. flux for the ETC run given above. The bright phase is a factor ~30 below the COS maximum count rate. ------------------------------------------------------------------------------------------------------------------------------------ 16 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=2 1 647 S (647 G S) ------------------------------------------------------------------------------------------------------------------------------------ 17 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=3 1 647 S (647 G S) ------------------------------------------------------------------------------------------------------------------------------------ 18 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=4 1 650 S (650 G S) ------------------------------------------------------------------------------------------------------------------------------------ 19 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=1 1 647 S (647 G S) Comments: We have good orbital phase coverage with Swift UVW1 (2600A) and SDSS u (3650A), amplitude and flux in the two bands are identical, so we adopt a flat spectrum in Flambda. At orbital minimum, the flux in Swift UVW1 is 2e-15 erg/cm2/s/AA, at orbital maximum 1.2e-14 erg/cm2/s/AA. We adopt the max. flux for the ETC run given above. The bright phase is a factor ~30 below the COS maximum count rate. ------------------------------------------------------------------------------------------------------------------------------------ 20 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=2 1 647 S (647 G S) ------------------------------------------------------------------------------------------------------------------------------------ 21 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=3 1 647 S (647 G S) ------------------------------------------------------------------------------------------------------------------------------------ 22 V-AR-SCO COS/FUV TIME-TA PSA G140L 1105 BUFFER-TIME=537, FP-POS=4 1 650 S (650 G S) ------------------------------------------------------------------------------------------------------------------------------------ 14470( 2) - 02-Dec-2015 12:44:33 - [ 7] 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 | ------------------------------------------------------------------------------------------------------------------------------------ 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-AR-SCO 1 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KXD V-AR-SCO 2 COS/FUV ACQ/PEA PSA G140L 1105 none none none none 1 N/A KD V-AR-SCO 3 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G V-AR-SCO 4 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G V-AR-SCO 5 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G V-AR-SCO 6 COS/FUV TIME-TA PSA G140L 1105 none none none none 1 N/A G V-AR-SCO 7 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G V-AR-SCO 8 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G V-AR-SCO 9 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G V-AR-SCO 10 COS/FUV TIME-TA PSA G140L 1105 none none none none 2 N/A G V-AR-SCO 11 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G V-AR-SCO 12 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G V-AR-SCO 13 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G V-AR-SCO 14 COS/FUV TIME-TA PSA G140L 1105 none none none none 3 N/A G V-AR-SCO 15 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G V-AR-SCO 16 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G V-AR-SCO 17 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G V-AR-SCO 18 COS/FUV TIME-TA PSA G140L 1105 none none none none 4 N/A G V-AR-SCO 19 COS/FUV TIME-TA PSA G140L 1105 none none none none 5 N/A G V-AR-SCO 20 COS/FUV TIME-TA PSA G140L 1105 none none none none 5 N/A G V-AR-SCO 21 COS/FUV TIME-TA PSA G140L 1105 none none none none 5 N/A G 14470( 2) - 02-Dec-2015 12:44:33 - [ 8] 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-AR-SCO 22 COS/FUV TIME-TA PSA G140L 1105 none none none none 5 N/A G 14470( 2) - 02-Dec-2015 12:44:33 - [ 9] Summary Form for Proposal 14470 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures PSA ------------------------------------------------------------------------------------------------------------------------------------ Configurations COS/FUV ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAKD, ACQ/PEAKXD, TIME-TAG ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters BUFFER-TIME=334, BUFFER-TIME=335, BUFFER-TIME=537, CENTER=DEF, FP-POS=1, FP-POS=2, FP-POS=3, FP-POS=4, NUM-POS=5, STEP-SIZE=0.9 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements G140L ------------------------------------------------------------------------------------------------------------------------------------ Target Names V-AR-SCO ------------------------------------------------------------------------------------------------------------------------------------