1,946 research outputs found
Optimization of exposure time division for wide field observations
The optical observations of wide fields of view encounter the problem of
selection of best exposure time. As there are usually plenty of objects
observed simultaneously, the quality of photometry of the brightest ones is
always better than of the dimmer ones. Frequently all of them are equally
interesting for the astronomers and thus it is desired to have all of them
measured with the highest possible accuracy.
In this paper we present a novel optimization algorithm dedicated for the
division of exposure time into sub-exposures, which allows to perform
photometry with more balanced noise budget. Thanks to the proposed technique,
the photometric precision of dimmer objects is increased at the expense of the
measurement fidelity of the brightest ones. We tested the method on real
observations using two telescope setups demonstrating its usefulness and good
agreement with the theoretical expectations. The main application of our
approach is a wide range of sky surveys, including the ones performed by the
space telescopes. The method can be applied for planning virtually any
photometric observations, in which the objects of interest show a wide range of
magnitudes.Comment: 18 pages, 5 figure
Bad pixel modified interpolation for astronomical images
We present a new method of interpolation for the pixel brightness estimation
in astronomical images. Our new method is simple and easily implementable. We
show the comparison of this method with the widely used linear interpolation
and other interpolation algorithms using one thousand astronomical images
obtained from the Sloan Digital Sky Survey. The comparison shows that our
method improves bad pixels brightness estimation with four times lower mean
error than the presently most popular linear interpolation and has a better
performance than any other examined method. The presented idea is flexible and
can be also applied to presently used and future interpolation methods. The
proposed method is especially useful for large sky surveys image reduction but
can be also applied to single image correction.Comment: 16 pages, 10 figures. Printed in PASP, September 201
The usability of the optical parametric amplification of light for high-angular-resolution imaging and fast astrometry
High-angular-resolution imaging is crucial for many applications in modern
astronomy and astrophysics. The fundamental diffraction limit constrains the
resolving power of both ground-based and spaceborne telescopes. The recent idea
of a quantum telescope based on the optical parametric amplification (OPA) of
light aims to bypass this limit for the imaging of extended sources by an order
of magnitude or more. We present an updated scheme of an OPA-based device and a
more accurate model of the signal amplification by such a device. The
semiclassical model that we present predicts that the noise in such a system
will form so-called light speckles as a result of light interference in the
optical path. Based on this model, we analysed the efficiency of OPA in
increasing the angular resolution of the imaging of extended targets and the
precise localization of a distant point source. According to our new model, OPA
offers a gain in resolved imaging in comparison to classical optics. For a
given time-span, we found that OPA can be more efficient in localizing a single
distant point source than classical telescopes.Comment: Received: 11 November 2017, revision received: 31 January 2018,
accepted: 31 January 201
Beyond the current noise limit in imaging through turbulent medium
Shift-and-add is an approach employed to mitigate the phenomenon of
resolution degradation in images acquired through a turbulent medium. Using
this technique, a large number of consecutive short exposures is registered
below the coherence time of the atmosphere or other blurring medium. The
acquired images are shifted to the position of the brightest speckle and
stacked together to obtain high-resolution and high signal-to-noise frame. In
this paper we present a highly efficient method for determination of frames
shifts, even if in a single frame the object cannot be distinguished from the
background noise. The technique utilizes our custom genetic algorithm, which
iteratively evolves a set of image shifts. We used the maximal energy of
stacked images as an objective function for shifts estimation and validate the
efficiency of the method on simulated and real images of simple and complex
sources. Obtained results confirmed, that our proposed method allows for the
recovery of spatial distribution of objects even only 2% brighter than their
background. The presented approach extends significantly current limits of
image reconstruction with the use of shift-and-add method. The applications of
our algorithm include both the optical and the infrared imaging. Our method may
be also employed as a digital image stabilizer in extremely low light level
conditions in professional and consumer applications.Comment: 8 pages, 4 figure
Quantum Telescopes: feasibility and constrains
Quantum Telescope is a recent idea aimed at beating the diffraction limit of
spaceborne telescopes and possibly also other distant target imaging systems.
There is no agreement yet on the best setup of such devices, but some
configurations have been already proposed. In this Letter we characterize the
predicted performance of Quantum Telescopes and their possible limitations. Our
extensive simulations confirm that the presented model of such instruments is
feasible and the device can provide considerable gains in the angular
resolution of imaging in the UV, optical and infrared bands. We argue that it
is generally possible to construct and manufacture such instruments using the
latest or soon to be available technology. We refer to the latest literature to
discuss the feasibility of the proposed QT system design.Comment: Optics Letters - published after major revisio
Observational Constraints on the Generalized Chaplygin Gas
In this paper we study a quintessence cosmological model in which the dark
energy component is considered to be the Generalized Chaplygin Gas and the
curvature of the three-geometry is taken into account. Two parameters
characterize this sort of fluid, the and the parameters. We use
different astronomical data for restricting these parameters. It is shown that
the constraint agrees enough well with the astronomical
observations.Comment: Accepted by IJMPD; 18 pages; 10 Figure
Dark energy FRW cosmology - dynamical system reconstruction
We develop a simple method of dark energy reconstruction using a geometrical
form of the luminosity-distance relation. In this method the FRW dynamical
system with dark energy is reconstructed instead of the equation of state
parameter. We give several examples which illustrate the usefulness of our
method in fitting the redshift transition from the decelerating to accelerating
phase as the value of the Hubble function at the transition.Comment: Talk presented at Spanish Relativity Meeting 2007, Puerto de la Cruz,
Tenerife, Spain, 10-14 September 200
Dusty Universe viewed by AKARI far infrared detector
We present the results of the analysis of multiwavelength Spectral Energy
Distributions (SEDs) of far-infrared galaxies detected in the AKARI Deep
Field-South (ADF--S) Survey. The analysis uses a carefully selected sample of
186 sources detected at the 90 m AKARI band, identified as galaxies with
cross-identification in public catalogues. For sources without known
spectroscopic redshifts, we estimate photometric redshifts after a test of two
independent methods: one based on using mainly the optical -- mid infrared
range, and one based on the whole range of ultraviolet -- far infrared data. We
observe a vast improvement in the estimation of photometric redshifts when far
infrared data are included, compared with an approach based mainly on the
optical -- mid infrared range. We discuss the physical properties of our
far-infrared-selected sample. We conclude that this sample consists mostly of
rich in dust and young stars nearby galaxies, and, furthermore, that almost 25%
of these sources are (Ultra)Luminous Infrared Galaxies. Average SEDs normalized
at 90 m for normal galaxies (138 sources), LIRGs (30 sources), and ULIRGs
(18 galaxies) a the significant shift in the peak wavelength of the dust
emission, and an increasing ratio between their bolometric and dust
luminosities which varies from 0.39 to 0.73.Comment: 8 pages, 7 figures, published in Earth, Planets and Spac
Cosmic acceleration from modified gravity with Palatini formalism
We study new FRW type cosmological models of modified gravity treated on the
background of Palatini approach. These models are generalization of Einstein
gravity by the presence of a scalar field non-minimally coupled to the
curvature. The models employ Starobinsky's term in the Lagrangian and dust
matter. Therefore, as a by-product, an exhausted cosmological analysis of
general relativity amended by quadratic term is presented. We investigate
dynamics of our models, confront them with the currently available
astrophysical data as well as against LCDM model. We have used the dynamical
system methods in order to investigate dynamics of the models. It reveals the
presence of a final sudden singularity. Fitting free parameters we have
demonstrated by statistical analysis that this class of models is in a very
good agreement with the data (including CMB measurements) as well as with the
standard LCDM model predictions. One has to use statefinder diagnostic in order
to discriminate among them. Therefore Bayesian methods of model selection have
been employed in order to indicate preferred model. Only in the light of CMB
data the concordance model remains invincible.Comment: 32 pages, jcappub style, 28 figures, final improved version, to be
published in JCA
Fatigue cracking of aluminium alloy AlZn6Mg0.8Zr subjected to thermomechanical treatment
The paper presents the results of experimental test of the fatigue of aluminium alloy type AlZn6Mg0,8Zr exposed to various low temperature thermomechanical treatment. Basquin’s characteristics of fatigue have been determined in mechanical test on smooth specimens at a simple state of loading in conditions of alternating bending. The tests were carried out on a fatigue test stand constructed by the authors – MZGS 100. The development of fatigue cracking has been described based on metallographic and fractographic investigations of the fractured samples making use of a scanning electron microscope (SEM). The results of qualitative microfractography of the tested samples in the low-cycle temporal range of fatigue strength revealed fractures of the transcrystalline quasi-cleavage type. It has also been found that local effects of intercrystalline brittle cracking of this type do occur
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