647 research outputs found
On the eclipsing cataclysmic variable star HBHA 4705-03
We present observations and analysis of a new eclipsing binary HBHA 4705-03.
Using decomposition of the light curve into accretion disk and hot spot
components, we estimated photometrically the mass ratio of the studied system
to be q=0.62 +-0.07. Other fundamental parameters was found with modeling. This
approach gave: white dwarf mass M_1 = (0.8 +- 0.2) M_sun, secondary mass
M_2=(0.497 +- 0.05) M_sun, orbital radius a=1.418 R_sun, orbital inclination i
= (81.58 +- 0.5) deg, accretion disk radius r_d/a = 0.366 +- 0.002, and
accretion rate dot{M} = (2.5 +- 2) * 10^{18}[g/s], (3*10^{-8} [M_sun/yr]).
Power spectrum analysis revealed ambiguous low-period Quasi Periodic
Oscillations centered at the frequencies f_{1}=0.00076 Hz, f_2=0.00048 Hz and
f_3=0.00036 Hz. The B-V=0.04 [mag] color corresponds to a dwarf novae during an
outburst. The examined light curves suggest that HBHA 4705-03 is a nova-like
variable star.Comment: 7 figures and 2 tables, accepted for publication in Acta Astronomic
Spatial distribution and galactic model parameters of cataclysmic variables
The spatial distribution, galactic model parameters and luminosity function
of cataclysmic variables (CVs) in the solar neighbourhood have been determined
from a carefully established sample of 459 CVs. The sample contains all of the
CVs with distances computed from the Period-Luminosity-Colours (PLCs) relation
of CVs which has been recently derived and calibrated with {\em 2MASS}
photometric data. It has been found that an exponential function fits best to
the observational z-distributions of all of the CVs in the sample, non-magnetic
CVs and dwarf novae, while the sech^{2} function is more appropriate for
nova-like stars and polars. The vertical scaleheight of CVs is 15814 pc
for the {\em 2MASS} J-band limiting apparent magnitude of 15.8. On the other
hand, the vertical scaleheights are 12820 and 1605 pc for dwarf novae
and nova-like stars, respectively. The local space density of CVs is found to
be pc^{-3} which is in agreement with the lower limit of
the theoretical predictions. The luminosity function of CVs shows an increasing
trend toward higher space densities at low luminosities, implying that the
number of short-period systems should be high. The discrepancies between the
theoretical and observational population studies of CVs will almost disappear
if for the z-dependence of the space density the sech^{2} density function is
used.Comment: 29 pages, 9 figures and 5 tables, accepted for publication in New
Astronom
The Spectroscopic Orbits of Three Double-lined Eclipsing Binaries: I. BG Ind, IM Mon, RS Sgr
We present the spectroscopic orbit solutions of three double-lines eclipsing
binaries, BG Ind, IM Mon and RS Sgr. The first precise radial velocities (RVs)
of the components were determined using high resolution echelle spectra
obtained at Mt. John University Observatory in New Zealand. The RVs of the
components of BG Ind and RS Sgr were measured using Gaussian fittings to the
selected spectral lines, whereas two-dimensional cross-correlation technique
was preferred to determine the RVs of IM Mon since it has relatively short
orbital period among the other targets and so blending of the lines is more
effective. For all systems, the Keplerian orbital solution was used during the
analysis and also circular orbit was adopted because the eccentricities for all
targets were found to be negligible. The first precise orbit analysis of these
systems gives the mass ratios of the systems as 0.894, 0.606 and 0.325,
respectively for BG Ind, IM Mon and RS Sgr. Comparison of the mass ratio
values, orbital sizes and minimum masses of the components of the systems
indicates that all systems should have different physical, dynamical and
probable evolutionary status.Comment: 17 pages, 6 figures and 4 tables, accepted for publication in New
Astronom
Quantifying the optical properties and chromophore concentrations of turbid media by chemometric analysis of hyperspectral diffuse reflectance data collected using a fourier interferometric imaging system
A non-contact Fourier transform interferometric imaging system was used to collect hyperspectral images of the steady-state diffuse reflectance from a point source in turbid media for the spectral range of 550-850 nm. Steady-state diffuse reflectance profiles were generated from the hyperspectral images, and partial least-squares (PLS) regression was performed on the diffuse reflectance profiles to quantify absorption (mu (alpha)) and reduced scattering (mu (s)') properties of turbid media. The feasibility of using PLS regression to predict optical properties was examined for two different sets of spatially-resolved diffuse reflectance data. One set of data was collected from 40 turbid phantoms, while the second set was generated by convolving Monte Carlo simulations with the instrument response of the imaging system. Study results show that PLS prediction of mu (alpha) and mu (s)' was accurate to within +/-8% and +/-5%, respectively, when the model was trained on turbid phantom data. Moreover, PLS prediction of optical properties was considerably faster and more efficient than direct least-squares fitting of spatially-resolved profiles. When the PLS model was trained on Monte Carlo simulated data and subsequently used to predict mu (alpha) and mu (s)' from the diffuse reflectance of turbid phantom, the percent accuracies degraded to +/-12% and +/-5%, respectively. These accuracy values are applicable to homogenous, semi-infinite turbid phantoms with optical property ranges comparable to tissues
State space c-reductions for concurrent systems in rewriting logic
We present c-reductions, a state space reduction technique.
The rough idea is to exploit some equivalence relation on states (possibly capturing system regularities) that preserves behavioral properties, and explore the induced quotient system. This is done by means of a canonizer
function, which maps each state into a (non necessarily unique) canonical representative of its equivalence class. The approach exploits the expressiveness of rewriting logic and its realization in Maude to enjoy several advantages over similar approaches: exibility and simplicity in
the definition of the reductions (supporting not only traditional symmetry reductions, but also name reuse and name abstraction); reasoning support for checking and proving correctness of the reductions; and automatization
of the reduction infrastructure via Maude's meta-programming
features. The approach has been validated over a set of representative case studies, exhibiting comparable results with respect to other tools
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