72 research outputs found
Searching for Space Debris Elements with the “Pi of the Sky” System
The main purpose of the “Pi of the Sky” system is to investigate short timescale astrophysical phenomena (particularly gamma-ray bursts, optical transients and variable stars). Wide field, short exposures and full automation of the system, together with effective algorithms, give good prospects for effective identification of space debris elements. These objects can be a great danger for current and future space missions, and should be continuously monitored and cataloged. Algorithms for identifying optical transients (OT), designed for the “Pi of the Sky” experiment enable moving objects like planes, satellites and space debris elements to be identified. The algorithm verifies each OT candidate against a database of known satellites and is also able to automatically self-identify moving objects not present in this database. The data collected by the prototype in the Las Campanas Observatory enabled us to obtain a large sample of observations of moving objects. Some of these objects were identified as high-orbit geostationary (GEO) satellites, which shows that it is possible to observe even distant satellites with small aperture photo lenses. The analysis of the sample is still going on. The preliminary results and algorithms for automatic identification of moving objects will be described here
Analysis of White Dwarfs with Strange-Matter Cores
We summarize masses and radii for a number of white dwarfs as deduced from a
combination of proper motion studies, Hipparcos parallax distances, effective
temperatures, and binary or spectroscopic masses. A puzzling feature of these
data is that some stars appear to have radii which are significantly smaller
than that expected for a standard electron-degenerate white-dwarf equations of
state. We construct a projection of white-dwarf radii for fixed effective mass
and conclude that there is at least marginal evidence for bimodality in the
radius distribution forwhite dwarfs. We argue that if such compact white dwarfs
exist it is unlikely that they contain an iron core. We propose an alternative
of strange-quark matter within the white-dwarf core. We also discuss the impact
of the so-called color-flavor locked (CFL) state in strange-matter core
associated with color superconductivity. We show that the data exhibit several
features consistent with the expected mass-radius relation of strange dwarfs.
We identify eight nearby white dwarfs which are possible candidates for strange
matter cores and suggest observational tests of this hypothesis.Comment: 11 pages, 6 figures, accepted for publication in J. Phys. G: Nucl.
Part. Phy
Theoretical UBVRI colors of iron core white dwarfs
We explore photometric properties of hypothetical iron core white dwarfs and
compute their expected colors in UBVRI Johnson broadband system. Atmospheres of
iron core WDs in this paper consist of pure iron covered by a pure hydrogen
layer of an arbitrary column mass. LTE model atmospheres and theoretical
spectra are calculated on the basis of Los Alamos TOPS opacities and the
equation of state from the OPAL project, suitable for nonideal Fe and H gases.
We have also computed UBVRI colors of the models and determined an area on the
B-V vs. U-B and U-B vs. V-I planes, occupied by both pure Fe, and pure H model
atmospheres of WD stars. Finally, we search for iron core white dwarf
candidates in the available literature.Comment: 13 pages, 12 figures, Astronomy & Astrophysics (2003) in prin
The catalog of short periods stars from the ''Pi of the Sky'' data
Based on the data from the ''Pi of the Sky'' project we made a catalog of the
variable stars with periods from 0.1 to 10 days. We used data collected during
a period of two years (2004 and 2005) and classified 725 variable stars. Most
of the stars in our catalog are eclipsing binaries - 464 (about 64%), while the
number of pulsating stars is 125 (about 17%). Our classification is based on
the shape of the light curve, as in the GCVS catalog. However, some stars in
our catalog were classified as of different type than in the GCVS catalog. We
have found periods for 15 stars present in the GCVS catalog with previously
unknown period.Comment: New Astronomy in prin
Simultaneous solution of Kompaneets equation and Radiative Transfer equation in the photon energy range 1 - 125 KeV
Radiative transfer equation in plane parallel geometry and Kompaneets
equation is solved simultaneously to obtain theoretical spectrum of 1-125 KeV
photon energy range. Diffuse radiation field is calculated using
time-independent radiative transfer equation in plane parallel geometry, which
is developed using discrete space theory (DST) of radiative transfer in a
homogeneous medium for different optical depths. We assumed free-free emission
and absorption and emission due to electron gas to be operating in the medium.
The three terms and where is photon phase density and , in Kompaneets equation and those due to
free-free emission are utilized to calculate the change in the photon phase
density in a hot electron gas. Two types of incident radiation are considered:
(1) isotropic radiation with the modified black body radiation [1] and
(2) anisotropic radiation which is angle dependent. The emergent radiation at
and reflected radiation are calculated by using the
diffuse radiation from the medium. The emergent and reflected radiation contain
the free-free emission and emission from the hot electron gas. Kompaneets
equation gives the changes in photon phase densities in different types of
media. Although the initial spectrum is angle dependent, the Kompaneets
equation gives a spectrum which is angle independent after several Compton
scattering times.Comment: 31 pages, 8 figures, Accepte
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