34 research outputs found
Physical parameter eclipse mapping of the quiescent disc in V2051 Ophiuchi
We analyse simultaneous UBVR quiescent light curves of the cataclysmic variable V2051 Oph using the Physical Parameter Eclipse Mapping (PPEM) method in order to map the gas temperature and surface density of the disc for the first time. The disc appears optically thick in the central regions, and gradually becomes optically thin towards the disc edge or shows a more and more dominating temperature inversion in the disc chromosphere. The gas temperatures in the disc range from about 13 500 K near the white dwarf to about 6000 K at the disc edge. The intermediate part of the disc has temperatures of 9000 to 6500 K
The X-ray eclipse of the dwarf nova HT CAS observed by the XMM-Newton satellite: spectral and timing analysis
A cataclysmic variable is a binary system consisting of a white dwarf that
accretes material from a secondary object via the Roche-lobe mechanism. In the
case of long enough observation, a detailed temporal analysis can be performed,
allowing the physical properties of the binary system to be determined. We
present an XMM-Newton observation of the dwarf nova HT Cas acquired to resolve
the binary system eclipses and constrain the origin of the X-rays observed. We
also compare our results with previous ROSAT and ASCA data. After the spectral
analysis of the three EPIC camera signals, the observed X-ray light curve was
studied with well known techniques and the eclipse contact points obtained.
The X-ray spectrum can be described by thermal bremsstrahlung of temperature
keV plus a black-body component (upper limit) with
temperature eV. Neglecting the black-body, the bolometric
absorption corrected flux is erg
s cm, which, for a distance of HT Cas of 131 pc, corresponds to a
bolometric luminosity of erg s.
The study of the eclipse in the EPIC light curve permits us to constrain the
size and location of the X-ray emitting region, which turns out to be close to
the white dwarf radius. We measure an X-ray eclipse somewhat smaller (but only
at a level of ) than the corresponding optical one. If this
is the case, we have possibly identified the signature of either high latitude
emission or a layer of X-ray emitting material partially obscured by an
accretion disk.Comment: Accepted for publication on Astronomy and Astrophysics, 200
Is T Leonis a superoutbursting intermediate polar?
We present an XMM-Newton analysis of the cataclysmic variable T Leo. The
X-ray light curve shows sinusoidal variation on a period P_x equal to
0.89^{+0.14}_{-0.10} times the previously spectroscopically determined orbital
period. Furthermore, we find a signal in the power spectrum at 414 sec that
could be attributed to the spin period of the white dwarf. If true, T Leo would
be the first confirmed superoutbursting intermediate polar IP). The spin
profile is double-peaked with a peak separation of about 1/3 spin phases. This
appears to be a typical feature for IPs with a small magnetic field and fast
white dwarf rotation. An alternative explanation is that the 414 sec signal is
a Quasi-periodic Oscillation (QPO) that is caused by mass transfer variation
from the secondary, a bright region (``blob'') rotating in the disc at a radius
of approximately ~9 Rwd or - more likely - a travelling wave close to the inner
disc edge of a dwarf nova with a low field white dwarf. The XMM-Newton RGS
spectra reveal double peaked emission for the O VIII Ly alpha line. Scenarios
in the IP and dwarf nova model are discussed (an emitting ring in the disc,
bright X-ray spot on disc edge, or emitting accretion funnels), but the
intermediate polar model is favoured. Supported is this idea by the finding
that only the red peak appears to be shifted and the `blue' peak is compatible
with the rest wavelength. The red peak thus is caused by emission from the
northern accretion spot when it faces the observer. Instead, the peak at the
rest wavelength is caused when the southern accretion funnel is visible just on
the lower edge of the white dwarf - with the velocity of the accreting material
being perpendicular to the line of sight.Comment: 11 pages, 15 figures, accepted by A&
On the nature of the X-ray source in GK Per
We report XMM-Newton observations of the intermediate polar (IP) GK Per on
the rise to the 2002 outburst and compare them to Chandra observations during
quiescence. We find an asymmetric spin light curve implying an asymmetric shape
of a semi-transparent accretion curtain. A low Fe xvii (15.01/15.26 A) line
flux ratio confirms the need for an asymmetric geometry and significant effects
of resonant line scattering. Medium resolution spectra in outburst and
quiescence are both fitted with a leaky absorber model for the post shock hard
X-ray emission, a black body (outburst) for the thermalized X-ray emission from
the white dwarf and an optically thin spectrum. The difference between high and
low spin as well as QPO/flares states can be explained by a variation in the
absorbing column density. The Fe fluorescence at 6.4 keV (equivalent width of
447 eV) is not significantly variable during spin cycle or on QPO periods.
High-resolution RGS spectra reveal a number of emission lines from H-like and
He-like elements. The lines are broader than the instrumental response with a
roughly constant velocity dispersion for different lines, indicating identical
origin. He-like emission lines are used to give values for the electron
densities of log n_e ~ 12. We do not detect any variation in the emission lines
during the spin cycle, implying that the lines are not noticeably obscured or
absorbed. We conclude that they originate in the accretion curtains and propose
a model for their shape.Comment: 14 pages, 22 figures, accepted by A&A; text re quiescent data changed
slightly, references adde
Physical parameter eclipse mapping
We present a new Eclipse Mapping method for reconstructing the properties of accretion discs in eclipsing catatclysmic variables. Physical Parameter Eclipse Mapping reconstructs spatially resolved maps of physical parameters such as temperatures and surface densities by fitting observed eclipse light curves at several wavelengths with the aid of a model describing the dependence of the disc spectrum on the physical parameters. Physical Parameter Eclipse Mapping has clear advantages over a classical approach for many applications. Most importantly, all of the available spectrophotometric data can be fitted simultaneously. The only drawback is the assumption of a physical model prior to the reconstructions. However, the method is very flexible in the choice of the spectral model, since the method itself does not depend on the choice. Furthermore, physical considerations, observations and experience will help determine the model to be used.The analysis with synthetic data shows that reliable parameter distributions can be obtained if the reconstruction behaviour of the model used is well understood. This means that the reconstructions are only as good as the model allows. In ambiguous parameter regions the method can (by definition) not give us the correct answer. However, in ambiguous-free zones, we show that the method indeed gives us the correct answer.</p