11,742 research outputs found
Radio and near-infrared observations of the steep spectrum Galactic plane radio source WKB 0314+57.8
Radio and near-infared observations towards the steep spectrum Galactic plane
radio source WKB 0314+57.8 are presented, in order to clarify the nature of
this source. The radio observations include archival and survey data, together
with new Giant Metrewave Radio Telescope observations at 617 MHz. The
near-infrared observations are in the J and K bands, from the Gemini instrument
on the Shane 3-m telescope. The radio observations show that WKB 0314+57.8 is
extended, with an very steep spectrum (with flux density proportional to
frequency to -2.5 power between 40 MHz and 1.5 GHz). The colour--magnitude
diagram constructed from near-infrared observations of the field suggests the
presence of a z approx 0.08 galaxy cluster behind the Galactic plane, reddened
by about 6 magnitudes of visual extinction. Although the steep spectrum source
has no obvious identification, two other radio sources in the field covered by
the near-infrared observations have tentative identifications with galaxies.
These observations indicate that WKB 0314+57.8 is a relic source in a cluster
of galaxies, not a pulsar.Comment: 6 pages, to appear in MNRAS, typos correcte
Critical fluctuations and random-anisotropy glass transition in nematic elastomers
We carry out a detailed deuterium NMR study of local nematic ordering in
polydomain nematic elastomers. This system has a close analogy to the
random-anisotropy spin glass. We find that, in spite of the quadrupolar nematic
symmetry in 3-dimensions requiring a first-order transition, the order
parameter in the quenched ``nematic glass'' emerges via a continuous phase
transition. In addition, by a careful analysis of the NMR line shape, we deduce
that the local director fluctuations grow in a critical manner around the
transition point. This could be the experimental evidence for the Aizenman-Wehr
theorem about the quenched impurities changing the order of discontinuous
transition
Photonic gaps in cholesteric elastomers under deformation
Cholesteric liquid crystal elastomers have interesting and potentially very
useful photonic properties. In an ideal monodomain configuration of these
materials, one finds a Bragg-reflection of light in a narrow wavelength range
and a particular circular polarization. This is due to the periodic structure
of the material along one dimension. In many practical cases, the cholesteric
rubber possesses a sufficient degree of quenched disorder, which makes the
selective reflection broadband. We investigate experimentally the problem of
how the transmittance of light is affected by mechanical deformation of the
elastomer, and the relation to changes in liquid crystalline structure. We
explore a series of samples which have been synthesized with photonic stop-gaps
across the visible range. This allows us to compare results with detailed
theoretical predictions regarding the evolution of stop-gaps in cholesteric
elastomers
Double precision trajectory program /DPTRAJ 2.2C/
Four part program computes trajectory of space probe moving in solar system and subject to variety of forces
Dwarf Nova Oscillations and Quasi-Periodic Oscillations in Cataclysmic Variables - VIII. VW Hyi in outburst observed with the Southern African Large Telescope
We analyse four light curves obtained at high time resolution (~ 0.1 s) with
the 11-m Southern African Large Telescope, at the ends of two normal outbursts
and one superoutburst of the dwarf nova VW Hyi. All of these contain at least
some Dwarf Nova Oscillations (DNOs), which, when at their highest amplitudes,
are seen in unprecedented detail. In addition to the expected DNOs with periods
> 20 s we find a previously unknown modulation at 13.39 s, but none at shorter
periods. The various DNOs and their interaction with the longer period
Quasi-periodic Oscillations are interpreted in terms of the model of
magnetically controlled flow from an accretion disc proposed earlier in this
series of papers. Our observations include rare DNOs very late in outburst; we
find that the fundamental period does not increase beyond ~ 90 s, which is the
same value that the independent ``longer period DNOs'' converge on.Comment: Accepted for publication in MNRAS. 7 pages, 10 figures, 2 table
High Speed Photometry of SDSS J013701.06-091234.9
We present high speed photometry of the Sloan Digital Sky Survey cataclysmic
variable SDSS J013701.06-091234.9 in quiescence and during its 2003 December
superoutburst. The orbital modulation at 79.71\pm0.01 min is double humped; the
superhump period is 81.702\pm0.007 min. Towards the end of the outburst late
superhumps with a period of 81.29\pm0.01 min were observed. We argue that this
is a system of very low mass transfer rate, and that it probably has a long
outburst interval.Comment: 5 pages, 8 figures. Accepted for publication in MNRA
Three-dimensional Simulations of Accretion to Stars with Complex Magnetic Fields
Disk accretion to rotating stars with complex magnetic fields is investigated
using full three-dimensional magnetohydrodynamic (MHD) simulations. The studied
magnetic configurations include superpositions of misaligned dipole and
quadrupole fields and off-centre dipoles. The simulations show that when the
quadrupole component is comparable to the dipole component, the magnetic field
has a complex structure with three major magnetic poles on the surface of the
star and three sets of loops of field lines connecting them. A significant
amount of matter flows to the quadrupole "belt", forming a ring-like hot spot
on the star. If the maximum strength of the magnetic field on the star is
fixed, then we observe that the mass accretion rate, the torque on the star,
and the area covered by hot spots are several times smaller in the
quadrupole-dominant cases than in the pure dipole cases. The influence of the
quadrupole component on the shape of the hot spots becomes noticeable when the
ratio of the quadrupole and dipole field strengths , and
becomes dominant when . In the case of an off-centre dipole
field, most of the matter flows through a one-armed accretion stream, forming a
large hot spot on the surface, with a second much smaller secondary spot. The
light curves may have simple, sinusoidal shapes, thus mimicking stars with pure
dipole fields. Or, they may be complex and unusual. In some cases the light
curves may be indicators of a complex field, in particular if the inclination
angle is known independently. We also note that in the case of complex fields,
magnetospheric gaps are often not empty, and this may be important for the
survival of close-in exosolar planets.Comment: 13 pages, 21 figures, accepted for publication in MNRA
Photonic band structure of highly deformable, self-assembling systems
We calculate the photonic band structure at normal incidence of highly
deformable, self-assembling systems - cholesteric elastomers subjected to
external stress. Cholesterics display brilliant reflection and lasing owing to
gaps in their photonic band structure. The band structure of cholesteric
elastomers varies sensitively with strain, showing new gaps opening up and
shifting in frequency. A novel prediction of a total band gap is made, and is
expected to occur in the vicinity of the previously observed de Vries bandgap,
which is only for one polarisation
The white dwarf in dwarf nova SDSS J080434.20+510349.2: Entering the instability strip?
SDSS J080434.20+510349.2 is the WZ type binary that displayed rare outburst
in 2006 (Pavlenko et al., 2007). During the long-lasting tail of the late stage
of the outburst binary shown the two-humped or four-humped profile of the
orbital light modulation. The amplitude of orbital light curve decreased while
the mean brightness decreased, more over that occurred 10 times faster
during the fast outburst decline in respect to the late quiet state of slow
outburst fading. There were no white dwarf pulsations detected neither 1 - 1.5
months prior to the outburst nor in 1.5 - 2 months after the 2006 outburst in
this system. However the strong non-radial pulsations with period 12.6 minutes
and mean amplitude of 0.05^m were first detected in V band with 2.6-m Shajn
mirror telescope of the Crimean astrophysical observatory in ~ 8 months after
the outburst. The evolution of pulsations over two years in 2006 - 2008 is
considered. It is supposed that pulsations first appeared when the cooling
white dwarf (after the outburst) entered the instability strip although the
possibility of temporary lack of pulsations at some occasions also could not be
excluded.Comment: Submitted to Proceedings of 16th European White Dwarf Workshop
(EUROWD08
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