5,608 research outputs found
Spectroscopic observations of the eclipsing Polar MN Hya (RX J0929--24)
We present low--medium resolution optical spectroscopy of the eclipsing AM
Her system MN Hya (RX J0929--24). We determine the magnetic field strength at
the primary accretion region of the white dwarf to be 42MG from the spacing of
cyclotron features visible during ~0.4--0.7. From spectra taken during the
eclipse we find that the secondary has a M3--4 spectral type. Combined with the
eclipse photometry of Sekiguchi, Nakada & Bassett and an estimate of the
interstellar extinction we find a distance of ~300--700pc. We find unusual line
variations at phase ~0.9: Halpha is seen in absorption and emission. This is at
the same point in the orbital phase that a prominent absorption dip is seen in
soft X-rays.Comment: accepted by MNRAS, 7 pages, 5 fig
Economic geology of the Avoca mineralized belt S.E. Ireland and Parys Mountain, Anglesey
Imperial Users onl
The X-ray eclipse of OY Car resolved with XMM-Newton: X-ray emission from the polar regions of the white dwarf
We present the XMM-Newton X-ray eclipse lightcurve of the dwarf nova OY Car.
The eclipse ingress and egress are well resolved for the first time in any
dwarf nova placing strong constraints on the size and location of the X-ray
emitting region. We find good fits to a simple linear eclipse model, giving
ingress/egress durations of 30+/-3 sec. Remarkably this is shorter than the
ingress/egress duration of the sharp eclipse in the optical as measured by Wood
et al. (1989) and ascribed to the white dwarf (43+/-2 sec). We also find that
the X-ray eclipse is narrower than the optical eclipse by 14+/-2 sec, which is
precisely the difference required to align the second and third contact points
of the X-ray and optical eclipses. We discuss these results and conclude that
X-ray emission in OY Car most likely arises from the polar regions of the white
dwarf.
Our data were originally reported by Ramsay et al (2001), but they did not
make a quantitative measurement of eclipse parameters. We have also corrected
important timing anomalies present in the data available at that time.Comment: 6 pages, 5 figures; accepted for publication in MNRA
Disorder effect in low dimensional superconductors
The quasiparticle density of states (DOS), the energy gap, the superfluid
density , and the localization effect in the s- and d-wave
superconductors with non-magnetic impurity in two dimensions (2D) are studied
numerically. For strong (unitary) scatters, we find that it is the range of the
scattering potential rather than the symmetry of the superconducting pairing
which is more important in explaining the impurity dependences of the specific
heat and the superconducting transition temperature in Zn doped YBCO. The
localization length is longer in the d-wave superconducting state than in the
normal state, even in the vicinity of the Fermi energy.Comment: 2 pages, uuencoded compressed postscript file, IRC-940610
ROSAT observations of V471 Tauri, showing that stellar activity is determined by rotation, not age
I present pointed ROSAT PSPC observations of the pre-cataclysmic binary V471
Tauri. The hard X-ray emission (>0.4keV) is not eclipsed by the K star,
demonstrating conclusively that this component cannot be emitted by the white
dwarf. Instead I show that its spectrum and luminosity are consistent with
coronal emission from the tidally spun-up K star. The star is more active than
other K stars in the Hyades, but equally active as K stars in the Pleiades with
the same rotation periods, demonstrating that rotation--and not age--is the key
parameter in determining the level of stellar activity.
The soft X-ray emission (<0.4keV) is emitted predominately by the white dwarf
and is modulated on its spin period. I find that the pulse-profile is stable on
timescales of hours and years, supporting the idea that it is caused by opacity
of accreted material. The profile itself shows that the magnetic field
configuration of the white dwarf is dipolar and that the magnetic axis passes
through the centre of the star.
There is an absorption feature in the lightcurve of the white dwarf, which
occurs at a time when our line-of-sight passes within a stellar radius of the K
star. The column density and duration of this feature imply a volume and mass
for the absorber which are similiar to those of coronal mass ejections of the
Sun.Comment: 7 pages, 7 figures, accepted for publication in MNRAS. Also available
at http://www.star.le.ac.uk/~pjw
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