J/AJ/156/150 High-time-resolution photometry of AR Scorpii (Stiller+, 2018)
High-time-resolution photometry of AR Scorpii: confirmation of the white dwarf's
spin-down.
Stiller R.A., Littlefield C., Garnavich P., Wood C., Hambsch F.-J., Myers G.
<Astron. J., 156, 150 (2018)>
=2018AJ....156..150S 2018AJ....156..150S (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, cataclysmic ; Stars, variable ; Stars, dwarfs ;
Photometry, CCD
Keywords: binaries: close - novae, cataclysmic variables -
stars: individual (AR Sco) - stars: magnetic field - white dwarfs
Abstract:
The unique binary AR Scorpii consists of an asynchronously rotating,
magnetized white dwarf (WD) that interacts with its red-dwarf companion
to produce a large-amplitude, highly coherent pulsation every 1.97 minutes.
Over the course of two years, we obtained 39 hours of time-resolved,
optical photometry of AR Sco at a typical cadence of 5 s to study this
pulsation. We find that it undergoes significant changes across the binary
orbital period and that its amplitude, phase, and waveform all vary as
a function of orbital phase. We show that these variations can be explained
by constructive and destructive interference between two periodic,
double-peaked signals: the spin-orbit beat pulse, and a weaker WD spin
pulse. Modeling of the light curve indicates that in the optical, the
amplitude of the primary spin pulse is 50% of the primary beat amplitude,
while the secondary maxima of the beat and spin pulses have similar
amplitudes. Finally, we use our timings of the beat pulses to confirm
the presence of the disputed spin-down of the WD. We measure a
beat-frequency derivative of ν=(-5.14±0.32)x10-17 Hz/s and show
that this is attributable to the spin-down of the WD. This value is
approximately twice as large as the estimate from Marsh et al. but is
nevertheless consistent with the constraints established in
Potter & Buckley (2018MNRAS.478L..78P 2018MNRAS.478L..78P). Our precise measurement of the
spin-down rate confirms that the decaying rotational energy of the
magnetized WD is sufficient to power the excess electromagnetic radiation
emitted by the binary.
Description:
We obtained 39 hr of high-time-resolution photometry of AR Sco using
the 80 cm Sarah L. Krizmanich Telescope (SLKT) and an unfiltered Santa
Barbara Instrument Group STL-1001 CCD camera at the University of
Notre Dame in 2016, 2017, and 2018. The exposure time was 2 s, and
factoring in the overhead between images, the typical cadence was 5-6 s,
and each time series usually spanned 1-3 hr.
We measured 1077 beat-pulse timings from our data set by fitting a
Gaussian to each well-observed beat pulse. The timings, which span two
years and three observing seasons, have a sufficiently long baseline
to search for ν.
Objects:
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RA (ICRS) DE Designation(s)
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16 21 47.28 -22 53 10.4 AR Scorpii = V* AR Sco
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig1.dat 26 27957 SLKT light curve of AR Sco
table3.dat 46 1077 Beat-pulse timings
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See also:
V/123 : Catalog of Cataclysmic Variables (Downes+ 2001-2006)
J/A+A/611/A66 : AR Sco VLA radio observations (Stanway+, 2018)
Byte-by-byte Description of file: fig1.dat
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Bytes Format Units Label Explanations
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1- 13 F13.5 d BJD Barycentric Julian Date; TDB
15- 20 F6.3 mag mag [-0.078/3.423] Differential, unfiltered magnitude
(1)
22- 26 F5.3 mag e_mag [0.012/0.541] 1σ uncertainty in mag
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Note (1): The comparison star was UCAC4 336-082341.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 7 I7 --- Epoch [-251505/234767] Beat cycle count (1)
9- 22 F14.6 d Tmax Time of pulse maximum (BJD_TDB) (2)
24- 37 F14.6 d Tmax-cor Corrected time of pulse maximum (BJD_TDB) (3)
39- 46 F8.6 d e_Tmax [7e-06/0.000212] 1σ uncertainty in Tmax
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Note (1): Per Eq. 2 from our paper.
Note (2): Uncorrected for the orbital variation of pulse-arrival times. See
our Section 3 for an explanation of the orbital-phase dependence.
Note (3): Corrected for the orbital variation of pulse-arrival times. The
correction is based on a fit to the pulse O-C as a function of orbital phase
(see our Fig. 6).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 15-Mar-2019