11,149 research outputs found
Astrokit -- an Efficient Program for High-Precision Differential CCD Photometry and Search for Variable Stars
Having a need to perform differential photometry for tens of thousands stars
in a several square degrees field, we developed Astrokit program. The software
corrects the star brightness variations caused by variations of atmospheric
transparency: to this end, the program selects for each star an individual
ensemble of reference stars having similar magnitudes and positions in the
frame. With ten or more reference stars in the ensemble, the differences
between their spectral types and the spectral type of the object studied become
unimportant. Astrokit searches for variable stars using Robust Median
Statistics criterion, which allows candidate variables to be selected more
efficiently than by analyzing the standard deviation of star magnitudes. The
software allows very precise automatic analysis of long inhomogeneous sets of
photometric observations of a large number of objects to be performed, making
it possible to find "hot Jupiter" type exoplanet transits and low-amplitude
variables. We describe the algorithm of the program and the results of its
application to reduce the data of the photometric sky survey in Cygnus as well
as observations of the open cluster NGC188 and the transit of the exoplanet
WASP-11 b / HAT-P-10 b, performed with the MASTER-II-URAL telescope of the
Kourovka Astronomical Observatory of the Ural Federal University.Comment: to be published in Astrophysical Bulletin, Vol. 69, No.
Giant Pulses with Nanosecond Time Resolution detected from the Crab Pulsar at 8.5 and 15.1 GHz
We present a study of shape, spectra and polarization properties of giant
pulses (GPs) from the Crab pulsar at the very high frequencies of 8.5 and 15.1
GHz. Studies at 15.1 GHz were performed for the first time. Observations were
conducted with the 100-m radio telescope in Effelsberg in Oct-Nov 2007 at the
frequencies of 8.5 and 15.1 GHz as part of an extensive campaign of
multi-station multi-frequency observations of the Crab pulsar. A selection of
the strongest pulses was recorded with a new data acquisition system, based on
a fast digital oscilloscope, providing nanosecond time resolution in two
polarizations in a bandwidth of about 500 MHz. We analyzed the pulse shapes,
polarisation and dynamic spectra of GPs as well as the cross-correlations
between their LHC and RHC signals. No events were detected outside main pulse
and interpulse windows. GP properties were found to be very different for GPs
emitted at longitudes of the main pulse and the interpulse. Cross-correlations
of the LHC and RHC signals show regular patterns in the frequency domain for
the main pulse, but these are missing for the interpulse GPs. We consider
consequences of application of the rotating vector model to explain the
apparent smooth variation in the position angle of linear polarization for main
pulse GPs.
We also introduce a new scenario of GP generation as a direct consequence of
the polar cap discharge. We find further evidence for strong nano-shot
discharges in the magnetosphere of the Crab pulsar. The repetitive frequency
spectrum seen in GPs at the main pulse phase is interpreted as a diffraction
pattern of regular structures in the emission region. The interpulse GPs
however have a spectrum that resembles that of amplitude modulated noise.
Propagation effects may be the cause of the differences.Comment: Astronomy & Astrophysics (accepted
Enhanced four-wave mixing via elimination of inhomogeneous broadening by coherent driving of quantum transition with control fields
We show that atoms from wide velocity interval can be concurrently involved
in Doppler-free two-photon resonant far from frequency degenerate four-wave
mixing with the aid of auxiliary electromagnetic field. This gives rise to
substantial enhancement of the output radiation generated in optically thick
medium. Numerical illustrations addressed to typical experimental conditions
are given.Comment: LaTeX2e, hyperref, 7 pages, 5 figures, to appear in PRA 1 august 200
Linking of the BENSON graph-plotter with the Elektronika-1001 computer
A device, developed by the Institute of Space Research of the Academy of Sciences of the USSR, for linking the Elektronika-100I computer with the BENSON graph-plotter is described. Programs are compiled which provide display of graphic and alphanumeric information. Instructions for their utilization are given
Magnetoelectric response of multiferroic BiFeO3 and related materials
We present a first-principles scheme for computing the magnetoelectric
response of multiferroics. We apply our method to BiFeO3 (BFO) and related
compounds in which Fe is substituted by other magnetic species. We show that
under certain relevant conditions -- i.e., in absence of incommensurate spin
modulation, as in BFO thin films and some BFO-based solid solutions -- these
materials display a large linear magnetoelectric response. Our calculations
reveal the atomistic origin of the coupling and allow us to identify the most
promising strategies to enhance it.Comment: 4 pages with 1 figure embedded. More information at
http://www.icmab.es/dmmis/leem/jorg
A nontrivial bosonic representation of large spin systems at high temperatures
We report on a nontrivial bosonization scheme for spin operators. It is shown
that in the large limit, at infinite temperature, the operators
behave like the creation and annihilation
operators, and , corresponding to a harmonic oscillator in thermal
equilibrium, whose temperature and frequency are related by . The component is found to be equivalent to the position variable
of another harmonic oscillator occupying its ground Gaussian state at zero
temperature. The obtained results are applied to the Heisenberg XY Hamiltonian
at finite temperature.Comment: 12 pages, preprint, we have included a brief discussion of the
antiferromagnetic cas
New cantacaderid lace bugs from Dominician amber (Heteroptera: Tingidae, Catacaderiane)
New fossil tingids, representatives of the small subfamily Cantacaderinae (Tingidae) from the Oligocene Dominican amber, are described and discussed. The fossil species Eocader babyrussus n. sp. belongs to the recent neotropical genus Eocader of the tribe Phatnomini
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