A Stellar Flare during the Transit of the Extrasolar Planet OGLE-TR-10b (2009)
Bentley, Samuel, Hellier, Coel, Maxted, Pierre, Dhillon, Vik, Marsh, Tom, Copperwheat, Chris, ...
We report a stellar flare occurring during a transit of the exoplanet OGLE-TR-10b, an event not previously reported in the literature. This reduces the observed transit depth, particularly in the...
An orbital period of 0.94days for the hot-Jupiter planet WASP-18b (2009)
Hellier, Coel, Anderson, D R, Cameron, A Collier, Gillon, Michaël, Hebb, L, Maxted, P F L, ...
The `hot Jupiters' that abound in lists of known extrasolar planets are thought to have formed far from their host stars, but migrate inwards through interactions with the proto-planetary disk from...
The 0.5MJ transiting exoplanet WASP-13b (2009)
Skillen, I., Pollacco, D., Collier Cameron, A., Hebb, L., Simpson, E., Bouchy, François, ...
We report the discovery of WASP-13b, a low-mass $ M_{\rm p} = 0.46 ^_~M_J$ transiting exoplanet with an orbital period of 4.35298 $\pm$ 0.00004 days. The transit has a depth of 9 mmag, and although...
Wasp-7: A Bright Transiting-Exoplanet System in the Southern Hemisphere (2009)
Hellier, Coel, Anderson, D. R., Gillon, M., Lister, T. A., Maxted, P. F. L., Queloz, D., ...
We report that a Jupiter-mass planet, WASP-7b, transits the V = 9.5 star HD 197286 every 4.95 d. This is the brightest discovery from the WASP-South transit survey so far and is currently the...
Wasp-7: A Bright Transiting-Exoplanet System in the Southern Hemisphere (2009)
Hellier, Coel, Anderson, D R, Gillon, Michaël, Lister, T A, Maxted, P F L, Queloz, D, ...
We report that a Jupiter-mass planet, WASP-7b, transits the V = 9.5 star HD 197286 every 4.95 d. This is the brightest discovery from the WASP-South transit survey so far and is currently the...
WASP-7: The brightest transiting-exoplanet system in the Southern hemisphere (2008)
Hellier, Coel, Anderson, D. R., Gillon, M., Lister, T. A., Maxted, P. F. L., Queloz, D., ...
We report that a Jupiter-mass planet, WASP-7b, transits the V = 9.5 star HD197286 every 4.95 d. This is the brightest discovery from the WASP-South transit survey and the brightest...
Disc-Magnetosphere interactions in Cataclysmic Variable Stars (2007)
I review, from an observational perspective, the interactions of accretion discs with magnetic fields in cataclysmic variable stars. I start with systems where the accretion flows via a stream, and...
Disc-Overflow Accretion In Intermediate Polars (2007)
We have recently realised that intermediate polars accrete in a range of modes. While accretion is predominantly through an accretion disc, in some systems the accretion stream overflows the disc and...
Recent Results on Intermediate Polars (2007)
Koji Mukai, Coel Hellier, Coel Hellier
. I review recent activity in the field of intermediate polars, concentrating on: the mode of accretion (disc-fed, disc-overflow or discless) ; accretion curtains (the transition region and the...
A comparison of white dwarf mass estimators using the Intermediate Polar XY Ari (2007)
Gavin Ramsay, Mark Cropper, Coel Hellier, Kinwah Wu
We determine the mass of the white dwarf in the eclipsing intermediate polar XY Ari following the method given in Cropper, Ramsay & Wu using a multi-temperature bremsstrahlung model. By fitting...
The X-ray spectrum of the intermediate polar AO Piscium (2007)
Coel Hellier, Koji Mukai, Manabu Ishida, Ryuichi Fujimoto
An ASCA observation of AO Psc shows an X-ray lightcurve dominated by a sinusoidal spin-pulse. There are absorption dips recurring with the orbital cycle, but otherwise no other periodic variations in...
The Accretion Geometry of Intermediate Polars (2007)
. Intermediate polars range from systems which accrete entirely via discs (e.g. EX Hya) through systems which combine disc and disc-overflow accretion (e.g. FO Aqr) to discless accretors (e.g. RX...
XMM-Newton Observations of the Cataclysmic Variable GW Lib (2007)
Hilton, Eric J., Szkody, Paula, Mukadam, Anjum, Mukai, Koji, Hellier, Coel, Van Zyl, Liza, ...
XMM-Newton observations of the accreting, pulsating white dwarf in the quiescent dwarf nova GW Librae were conducted to determine if the non-radial pulsations present in previous UV and optical data...
Why do some intermediate polars show soft X-ray emission? A survey of XMM-Newton spectra (2007)
We make a systematic analysis of the XMM-Newton X-ray spectra of intermediate polars (IPs) and find that, contrary to the traditional picture, most show a soft blackbody component. We compare the...
XMM-Newton observations of the complex spin pulse of the intermediate polar PQ~Geminorum (2006)
Evans, P. A., Hellier, Coel, Ramsay, Gavin
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...
HT Camelopardalis: The simplest intermediate polar spin pulse (2005)
The intermediate polar HT Cam is unusual in that it shows no evidence for dense absorption in its spectrum. We analyse an XMM-Newton observation of this star, which confirms the absence of absorption...
Stream-field interactions in the magnetic accretor AO Piscium (2005)
UV spectra of the magnetic accretor AO Psc show absorption features for half the binary orbit. The absorption is unlike the wind-formed features often seen in similar stars. Instead, we attribute it...
What can XMM-Newton tell us about the spin periods of Intermediate Polars? (2004)
XMM-Newton's unprecedented combination of spectral resolution and high throughput allows us to perform the best phase-resolved X-ray analysis of intermediate polars to date. The Optical Monitor gives...
Why does the intermediate polar V405 Aurigae show a double-peaked spin pulse? (2004)
V405 Aurigae is an intermediate polar showing a double-peaked pulsation in soft X-rays and a single-peaked pulsation in harder X-rays. From XMM-Newton observations we find that the soft band is...
On the iron Kalpha complex in magnetic cataclysmic variables (2004)
We present a compilation of spectra of the iron Kalpha region in magnetic cataclysmic variables, using data from the Chandra-HETG. The H-like, He-like and fluorescent components are clearly resolved,...
Some updates on the role of Magnetic Fields in Cataclysmic Variables (2004)
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...
Some updates on the role of magnetic fields in Cataclysmic variables (2004)
En este resumen se cubren algunos aspectos de los recientes desarrollos en la comprensión del papel que juegan los campos magneticos en variables cataclísmicas: presento una discusión sobre los...
On the magnetic accretor GK Persei in outburst (2003)
Hellier, Coel, Harmer, Sean, Beardmore, A. P.
RXTE made 5 X-ray observations of the magnetic accretor GK Per during its 1996 outburst, recording a count rate of ten times the quiescent level. The 351-s spin pulse shows a deep, nearly sinusoidal...
Twisted accretion curtains in the intermediate polar FO Aquarii (2003)
Evans, P. A., Hellier, Coel, Ramsay, Gavin, Cropper, Mark
We report on a ~37-ks XMM-Newton observation of the intermediate polar FO Aquarii, presenting X-ray and UV data from the EPIC and OM cameras. We find that the system has changed from its previously...
The accretion flow in the discless intermediate polar V2400 Ophiuchi (2002)
Hellier, Coel, Beardmore, A. P.
RXTE observations confirm that the X-ray lightcurve of V2400 Oph is pulsed at the beat cycle, as expected in a discless intermediate polar. There are no X-ray modulations at the orbital or spin...
On the accretion mode of the intermediate polar V1025 Centauri (2002)
Hellier, Coel, Wynn, Graham, Buckley, David
The long white-dwarf spin periods in the magnetic cataclysmic variables EX Hya and V1025 Cen imply that if the systems possess accretion discs then they cannot be in equilibrium. It has been...
Stream-fed Accretion in Intermediate Polars (2002)
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...
On Echo Outbursts and ER UMa Supercycles in SU UMa-type Cataclysmic Variables (2001)
I present a variation on Osaki's tidal-thermal-instability model for SU UMa behavior. I suggest that in systems with the lowest mass ratios, the angular-momentum dissipation in an eccentric disk is...
Outbursts of EX Hydrae: mass-transfer events or disc instabilities? (2000)
Hellier, Coel, Kemp, Jonathan, Naylor, T., Bateson, Frank M., Jones, Albert, Overbeek, Danie, ...
We present the 45-yr record of EX Hya's lightcurve and discuss the characteristics of its 15 observed outbursts. We then concentrate on the 1998 outburst, reporting the first outburst X-ray...
I review the observational properties of SW Sex stars. I show that they can be explained by an accretion stream overflowing the disc, combined with an accretion disc wind. I suggest that SW Sex...
Doppler tomography of intermediate polar spin cycles (1999)
I collect emission line profiles for seven intermediate polars, phase-resolved over the spin cycles. I then present the first systematic application of Doppler tomography to the spin cycles, with the...
Recent results on intermediate polars (1999)
I review recent activity in the field of intermediate polars, concentrating on: the mode of accretion (disc-fed, disc-overflow or discless); accretion curtains (the transition region and the...
YY Draconis and V709 Cassiopeiae: two intermediate polars with weak magnetic fields (1998)
Norton, A. J., Beardmore, A. P., Allan, Alasdair, Hellier, Coel
We present data from long ROSAT HRI observations of the intermediate polars YY Dra and V709 Cas which show that V709 Cas, like YY Dra, exhibits a double-peaked X-ray pulse profile. Neither system...
Iron Kalpha line widths in magnetic cataclysmic variables (1998)
Hellier, Coel, Mukai, Koji, Osborne, J. P.
Following a recent report that AO Psc has broad iron Kalpha emission lines we have looked at the ASCA spectra of 15 magnetic cataclysmic variables. We find that half of the systems have Kalpha lines...
On the orbital period distribution of cataclysmic variables (1998)
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...
The phase 0.5 absorption in SW Sextantis-type cataclysmic variables (1998)
The SW Sextantis stars are a group of cataclysmic variables with distinctive observational characteristics, including absorption features in the emission line cores at phases 0.2-0.6. Hellier and...
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,...
An outburst of the magnetic cataclysmic variable XY Arietis observed with RXTE (1997)
Hellier, Coel, Mukai, Koji, Beardmore, A. P.
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...