Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Millihertz Optical/UV Oscillations in 4U 1626-67: Evidence for a Warped
  Accretion Disk   We have detected large-amplitude 0.3-1.2 mHz quasi-periodic oscillations
(QPOs) from the low-mass X-ray binary pulsar 4U 1626-67/KZ TrA, using UV
photometry from HST and ground-based optical photometry. These 1 mHz QPOs,
which have coherence (Nu/DeltaNu)=8, are entirely distinct from the 130 mHz
pulsar spin frequency, a previously known 48 mHz QPO, and the 42 min binary
period (independently confirmed here). Unlike the 48 mHz and 130 mHz
oscillations which are present in both the optical/UV and the X-ray emission,
the 1 mHz QPOs are not detected in simultaneous observations with RXTE. The rms
amplitude of the mHz QPO decreases from 15% in the far UV to 3% in the optical,
while the upper limit on a corresponding X-ray QPO is as low as 0.8%. We
suggest that the mHz oscillations are due to warping of the inner accretion
disk. We also report the detection of coherent upper and lower sidebands of the
130 mHz optical pulsations, with unequal amplitude and a spacing of 1.93 mHz
around the main pulsation. The origin of these sidebands remains unclear.

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The categories of this paper are: mtrl-th
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The categories of this paper are: quant-ph
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The categories of this paper are: q-alg
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The categories of this paper are: eess
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The categories of this paper are: funct-an
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The categories of this paper are: stat
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The categories of this paper are: bayes-an
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The categories of this paper are: cs
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The categories of this paper are: hep-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org
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The categories of this paper are: cmp-lg
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The categories of this paper are: solv-int
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The categories of this paper are: physics
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The categories of this paper are: plasm-ph
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The categories of this paper are: acc-phys