5,525 research outputs found
Massive Variability Searches: The Past, Present and Future Massive Variability Searches
Many decades ago a search for variable stars was one of the main areas of
astrophysical research. Such searches, conducted with CCD detectors rather than
with photographic plates, became a by-product of several projects seeking
gravitational microlensing events towards the Magellanic Clouds and/or the
Galactic Bulge: EROS, MACHO, and OGLE. These searches demonstrated that is is
possible and practical to process in near real time photometry of tens of
millions of stars every night, and to discover hundreds of thousands of
variable stars. A limited subset of new variable star catalogs was published,
but no comprehensive database of all photometric results became public domain
so far. In the last few years a much broader, but shallower searches have been
undertaken, and many other are at various stages of implementation or planning.
There is a need to develop a system that would allow all these data to be
processed and to be posted on the Internet in real time. Full information
related to variability of point sources is made of a relatively few data types,
hence it may be relatively easy to handle. Yet, it may be diverse enough to be
interesting to a large number of users, professional as well as amateur, making
it possible to do real time virtual observing, as well as data mining.Comment: Published in the Proceedings of the MPA/ESO/MPE Workshop: `Mining the
Sky' held at Garching, Germany July 31 - August 4, 2000; Springer, Eds: A.J.
Banday, S. Zaroubi, and M. Bartelmann, p. 481; latex, 6 page
The Distance to Pleiades
The distance to Pleiades remains controversial. There is a simple way to
resolve the dispute definitely by measuring the distance to one of its
brightest members, Atlas, which is astrometric and spectroscopic binary.Comment: 3 pages, latex, 1 figure, submitted to Acta Astronomic
Metallicity of Red Clump Giants in Baade's Window
The red clump giants are potentially very useful as standard candles. There
is some controversy about the stability of their I-band absolute magnitude, but
it does not seem to be serious. No controversy was anticipated about their
colors, with metal rich giants expected to be redder and cooler than the metal
poor giants. The purpose of this paper is to point out that no such correlation
is apparent between [Fe/H] and effective temperature as determined with
Washington CCD photometry for the giants in Baade's Window. No explanation is
offered for this surprising result. It is also unknown why the galactic bulge
red clump giants are redder than the clump giants near the Sun by 0.2 mag in
the (V-I) color.Comment: 8 pages, self-contained latex, 5 postscript figures, submitted to
Acta Astronomic
Current Status of the Microlensing Surveys
The ongoing microlensing searches have generated more photometric
measurements of pulsating stars than all previous observing projects combined.
In particular, OGLE has made ~ 340,000 B, V, and I-band measurements of ~ 1,300
Cepheids in the Large Magellanic Clouds accessible over Internet.
Microlensing searches contributed to the development of very efficient image
subtraction software which works best in crowded fields. This suggests the use
of a period - flux amplitude rather than period - luminosity relation for the
Cepheids for distance determination, as the flux amplitude is directly
measurable with the image subtraction, and it is not biased by crowding.
Future projects will dramatically increase the data rate, will provide
all-sky coverage and a complete census of variables, including pulsating stars,
to the ever fainter limits. Time will show which approach, a small number of
large teams or a large number of small teams, will be more productive.Comment: 9 pages with 3 figures, latex, revised and extended on November 29,
1999, to be published in the ASP Conference Series Vol. XXX, 1999: ``The
Impact of Large Scale Surveys on Pulsating Star Research'', L. Szabados and
D. Kurtz, ed
To the concept of the elastic interaction
A general description of elastic matter and the long-range elastic
interaction is propose. The type of the far-field interaction is determined by
the way of breaking in the continuum distribution of the elastic field produced
by topological defects, which can present isolated inclusions. To provide an
adequate description of the inter-inclusion interaction. Thus we can determine
the size of inclusion as core topological defect in elastic field. In this
description the charge in electrodynamic and mass in gravity present
peculiarity of elastic filed and determined in term this field. The interaction
is a direct and immediate result of the field deformation. Exist two type
interaction. Interaction through change the ground state of elastic matter and
interaction with the help of the carrier of interaction, which can present as
small changing of deformations.Comment: 5 page
Gravitational Microlensing by the Globular Cluster Stars
The microlensing of background stars by compact objects in globular clusters
is analyzed. The main strength of the proposed search is the direct
relationship between the lens mass and the time scale of the microlensing
event. The main problem is the low overall rate of expected events which
implies that a ground based search should last for about a decade to generate a
non trivial number of events, like a few dozen. A space borne experiment could
increase the rate by a large factor by increasing the number of stars which
could be monitored thanks to the much better seeing. The clusters M22 with the
galactic bulge background, and 47 Tuc with the SMC background, are the two
examples of possible targets.Comment: 6 pages; plain TeX. Accepted for publication in Acta Astronomica 44/
Four-Fermi Effective Operators at e^+ e^- ---> \bar{t} t
The process of top quark pair production at Next Linear Collider (NLC) has
been considered adopting an effective Lagrangian approach and including all
operators of dim~6 which can be tree-level-generated within unknown underlying
theory. All contributing helicity amplitudes are presented. It has been found
that four-fermion operators can provide the leading non-standard contribution
to the total cross section. Expected statistical significance of the
non-standard signal for the total cross section and forward-backward asymmetry
have been calculated taking into account existing experimental constraints. It
has been shown that adopting realistic luminosity of NLC and conservative
efficiency for the top-quark pair detection, the total cross section may be
sensitive to non-standard physics of an energy scale around \Lambda=5\tev.Comment: LaTex, 10 pages, 4 PostScript figures (uuencoded
Cellular structure in system of interacting particles
The general description of formation the cellular structure in the system of
interacting particles is proposed. Interactions between particles are
presumably well-understood and the phase transition in which can be studied in
the scale of particle resolution. We presented analytical results of possible
cellular structures for suspension of colloidal particles, in system particles
immersed in liquid crystal and gravitational system. We have shown that
cellular structure formation can occur in system of interacting particles for
realistic values of temperature and particles concentration.Comment: 5 page
Genetic Optimization of Keywords Subset in the Classification Analysis of Texts Authorship
The genetic selection of keywords set, the text frequencies of which are
considered as attributes in text classification analysis, has been analyzed.
The genetic optimization was performed on a set of words, which is the fraction
of the frequency dictionary with given frequency limits. The frequency
dictionary was formed on the basis of analyzed text array of texts of English
fiction. As the fitness function which is minimized by the genetic algorithm,
the error of nearest k neighbors classifier was used. The obtained results show
high precision and recall of texts classification by authorship categories on
the basis of attributes of keywords set which were selected by the genetic
algorithm from the frequency dictionary
Type conditions of stable range for identification of qualitative generalized classes of rings
This article deals mostly with the following question: when is the classical
ring of quotients of a commutative ring a ring of stable range 1? We introduce
the concepts of a ring of (von Neumann) regular range 1, a ring of
semihereditary range 1, a ring of regular range 1, a semihereditary local ring,
a regular local ring. We find relationships between the introduced classes of
rings and known ones, in particular, it is established that a commutative
indecomposable almost clean ring is a regular local ring. A commutative any
ring of idempotent regular range 1 is an almost clean ring. It is shown that
any commutative indecomposable almost clean Bezout ring is an Hermite ring, any
commutative semihereditary ring is a ring of idempotent regular range 1. The
classical ring of quotients of a commutative Bezout ring is a (von Neumann)
regular local ring if and only if R is a commutative semihereditary local ring
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