224 research outputs found
The size of the accretion region in intermediate polars: eclipses of XY Arietis observed with RXTE
RXTE observed 20 eclipse egresses of the intermediate polar XY Ari in order
to study the size and structure of the X-ray emitting accretion regions. The
spin-phase averaged egress lasts 26 s, implying a white dwarf radius of 4.3-7.0
10^8 cm. The individual egresses occur later in orbital phase with later spin
phase, as expected if the white dwarf spins in the same sense as the orbital
motion. The eclipse times trace out the motion of the upper pole across the
white dwarf face; then, when the upper pole disappears over the white dwarf
limb and the lower pole appears, they trace the motion of the lower pole across
the face.
Aligning all the egresses shows that the majority of the X-ray flux emerges
in <2 s, implying accretion regions with area, f, < 0.002 as a fraction of the
white dwarf surface. Using only the spin-phase to align the egresses, however,
gives a longer (~5 s) time for the emergence of the majority of the flux,
implying that the accretion regions wander over an area of f < 0.01. There is
also evidence that a minority of the flux emerges from a much larger area, or
that we see accretion regions at both poles simultaneously at some spin phases.Comment: 11 pages, 10 figures, LaTeX, To appear in MNRAS. Also at
http://www.astro.keele.ac.uk/~ch
Stream-fed Accretion in Intermediate Polars
I review the observational evidence for stream-fed accretion in intermediate
polars. Recent work on the discless system V2400 Oph confirms the pole-flipping
model of stream-fed accretion, but this applies only to a minority of the flow.
The bulk of the flow is in the form of blobs circling the white dwarf, a state
which might have been a precursor to disc formation in other IPs. I also
discuss work on the systems with anomalously long spin periods, V1025 Cen and
EX Hya. There are arguments both for and against stream-fed accretion in V1025
Cen, and further work is necessary before reaching a conclusion about this
system.Comment: 10 pages, 6 figures, To appear in 'The Physics of Cataclysmic
Variables and Related Objects', Goettingen, August 5-10, 2001; includes
low-res figures to reduce siz
Some updates on the role of Magnetic Fields in Cataclysmic Variables
In this review talk I cover some recent developments in understanding the
role that magnetic fields play in cataclysmic variables. I discuss the recent
DNO--QPO unification models; the disk--magnetosphere boundary; some issues
concerning the soft blackbody component and the nature of the X-ray spectra in
MCVs; whether the SW Sex stars are magnetic, and finally I mention the weird
behavior of FS Aur and HS2331+3905.Comment: To appear in ``Compact Binaries in the Galaxy and Beyond'', RevMexA
An outburst of the magnetic cataclysmic variable XY Arietis observed with RXTE
We report the first observed outburst of the magnetic cataclysmic variable XY
Ari. X-ray observations show a flux increase by an order of magnitude the day
after the first signs of outburst. During the 5-d duration the X-ray spin pulse
is greatly enhanced and the X-ray spectrum far more absorbed. We suggest that
the inner disc pushes inwards during outburst, blocking the view to the lower
accreting pole, breaking the symmetry present in quiescence, and so producing a
large pulsation. The observations are consistent with a disc instability as the
cause of the outburst, although we can't rule out alternatives. We draw
parallels between our data and the UV delay and dwarf nova oscillations seen in
non-magnetic dwarf novae.Comment: 10 pages, 9 figures, LaTeX, also at http://www.astro.keele.ac.uk/~ch
XMM-Newton observations of the complex spin pulse of the intermediate polar PQ~Geminorum
The intermediate polar PQ Geminorum shows a complex pulsation, caused by a
spinning white dwarf, which varies markedly with wavelength. We report
XMM-Newton observations, including the soft and hard X-ray bands and the first
UV lightcurves of this star. We update the ephemeris for PQ Gem allowing us to
align these data with a compilation of lightcurves from the optical to the
X-ray. Building on work by previous authors, we show how a model in which
accretion flows along skewed field lines, viewed at the correct inclination,
can explain the major features of the lightcurves in all bands. We discuss how
the skew of the field lines relates to the spinning down of the white-dwarf
rotation.Comment: 7 pages, 7 figures, accepted for publication in MNRA
On the orbital period distribution of cataclysmic variables
Using the latest compilation of cataclysmic variable orbital periods by
Ritter & Kolb we argue against Verbunt's conclusion that the period gap is not
significant for nova-like variables. We also discuss the relation of the VY Scl
stars to the dwarf novae.Comment: 3 pages, 3 figures, LaTeX, To appear in MNRAS. Also at
http://www.astro.keele.ac.uk/~ch
TESS Hunt for Young and Maturing Exoplanets (THYME). IV. Three Small Planets Orbiting a 120 Myr Old Star in the Pisces-Eridanus Stream
Young exoplanets can offer insight into the evolution of planetary atmospheres, compositions, and architectures. We present the discovery of the young planetary system TOI 451 (TIC 257605131, Gaia DR2 4844691297067063424). TOI 451 is a member of the 120 Myr old Pisces–Eridanus stream (Psc–Eri). We confirm membership in the stream with its kinematics, its lithium abundance, and the rotation and UV excesses of both TOI 451 and its wide-binary companion, TOI 451 B (itself likely an M-dwarf binary). We identified three candidate planets transiting in the Transiting Exoplanet Survey Satellite data and followed up the signals with photometry from Spitzer and ground-based telescopes. The system comprises three validated planets at periods of 1.9, 9.2, and 16 days, with radii of 1.9, 3.1, and 4.1 R ?, respectively. The host star is near-solar mass with V = 11.0 and H = 9.3 and displays an infrared excess indicative of a debris disk. The planets offer excellent prospects for transmission spectroscopy with the Hubble Space Telescope and the James Webb Space Telescope, providing the opportunity to study planetary atmospheres that may still be in the process of evolving
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