1,492 research outputs found
Influence of strong-coupling and retardation effects on superconducting state in compound
In the framework of strong-coupling formalism, we have calculated the
thermodynamic parameters of superconducting state in the
compound. The values of critical temperature () are ~K and ~K
for the Coulomb pseudopotential and , respectively. In
the paper, we have determined the low temperature values of order parameter
(), specific heat jump at the critical temperature (), and thermodynamic critical field (). The dimensionless
thermodynamic ratios: , , and
are equal to:
,
, and
. Due to the
significant strong-coupling and retardation effects () those values highly deviate from the predictions of BCS theory.Comment: 5 pages, 4 figure
The unbalanced phonon-induced superconducting state on a square lattice beyond the static boundary
The paper presents our verification of induction of the superconducting state
on a square lattice by the linear electron-phonon interaction for values of the
unbalance parameter () less than
. Symbols and denote the values
of the coupling constant in the diagonal and the non-diagonal channel of the
self-energy. Calculations were carried out using the Eliashberg equations, in
which the order parameter () and the
wave function renormalising factor () depend
explicitly on the Matsubara frequency () and the wave vector (). The value of in the static boundary (), equal to (), is significantly greater
than the obtained limit value of . Values of the thermodynamic functions
of the superconducting state determined for our assumptions are significantly
different from the values calculated in accordance with the BCS theory. The
results were obtained for the electron-phonon interaction function explicitly
dependent on the momentum transfer between electron states.Comment: 12 pages, 9 figure
Interaction of the hydrogen molecule with the environment: stability of the system
We study the stability of the hydrogen molecule interacting with the
environment according to the balanced gain and loss energy scheme. We
determined the properties of the molecule taking into account all electronic
interactions, where the parameters of the Hamiltonian have been computed by
using the variational method. The interaction of the hydrogen molecule with the
environment was modeled parametrically () with the help of the
non-hermitian operator. We have shown that the hydrogen molecule is dynamically
unstable. The dissociation time () decreases, if the parameter
increases (for , we get ). At
the dynamic instability of the hydrogen molecule overlaps its static
instability as the coupling constant increases. We observed the
decrease in the dissociation energy and the existence of the metastable state
of the molecule (~Ry). The hydrogen molecule is
statically unstable for ~Ry. One can also observed
the symmetry breaking effect for the electronic Hamiltonian
(~Ry). However, it does not affect the
properties of the hydrogen molecule, such as: the electronic Hamiltonian
parameters, the phonon and rotational energy, and the values of the
electron-phonon coupling constants.Comment: 16 pages, 8 figure
The Optical Gravitational Lensing Experiment. OGLE-III Long Term Monitoring of the Gravitational Lens QSO 2237+0305
We present results of the long term monitoring of the gravitational lens QSO
2237+0305 conducted during the OGLE survey. Light curves of all four components
of the lens obtained during the second phase of the OGLE project (OGLE-II;
1997-2000) are supplemented with the data collected in the OGLE-III phase in
the observing seasons 2001-2006. Calibration procedures to tie the new OGLE-III
data with already calibrated OGLE-II light curves are described. The resulting
homogeneous OGLE data set is the most extensive photometric coverage of the
gravitational lens QSO 2237+0305, spanning now one decade - the seasons from
1997 to 2006 - and revealing unique microlensing activity of this spectacular
object.
All photometric data of the gravitational lens QSO 2237+0305 collected by
OGLE are available to the astronomical community from the OGLE Internet
archive.Comment: 11 page
The Optical Gravitational Lensing Experiment. Triple-Mode and 1O/3O Double-Mode Cepheids in the Large Magellanic Cloud
We report the discovery of three new triple-mode classical Cepheids in the
Large Magellanic Cloud, two of them with the fundamental, first overtone and
second overtone excited, and one pulsating simultaneously in the first three
overtones. Thus, the number of triple-mode Cepheids in the LMC is increased to
five. We also present two objects belonging probably to a new type of
double-mode Cepheids having the first and third overtones excited. We measure
the rates of period change in these stars and detect decrease of periods in two
of them, what is in conflict with theoretical predictions.Comment: 10 pages, 5 figure
The Optical Gravitational Lensing Experiment. OGLE-III Photometric Maps of the Large Magellanic Cloud
We present the OGLE-III Photometric Maps of the Large Magellanic Cloud. They
cover about 40 square degrees of the LMC and contain mean, calibrated VI
photometry and astrometry of about 35 million stars observed during seven
observing seasons of the third phase of the Optical Gravitational Lensing
Experiment - OGLE-III.
We discuss the quality of data and present color-magnitude diagrams of
selected fields. The OGLE-III Photometric Maps of the LMC are available to the
astronomical community from the OGLE Internet archive.Comment: 8 pages, 9 figure
The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. II. Type II Cepheids and Anomalous Cepheids in the Large Magellanic Cloud
In the second part of the OGLE-III Catalog of Variable Stars (OIII-CVS) we
present 197 type II Cepheids and 83 anomalous Cepheids in the Large Magellanic
Cloud (LMC). The sample of type II Cepheids consists of 64 BL Her stars, 96 W
Vir stars and 37 RV Tau stars. Anomalous Cepheids are divided into 62
fundamental-mode and 21 first-overtone pulsators. These are the largest samples
of such types of variable stars detected anywhere outside the Galaxy.
We present the period-luminosity and color-magnitude diagrams of stars in the
sample. If the boundary period between BL Her and W Vir stars is adopted at 4
days, both groups differ significantly in (V-I) colors. We identify a group of
16 peculiar W Vir stars with different appearance of the light curves, brighter
and bluer than ordinary stars of that type. Four of these peculiar W Vir stars
show additional eclipsing modulation superimposed on the pulsation light
curves. Four other stars of that type show long-period secondary variations
which may be ellipsoidal modulations. It suggests that peculiar W Vir subgroup
may be related to binarity. In total, we identified seven type II Cepheids
simultaneously exhibiting eclipsing variations which is a very large fraction
compared to classical Cepheids in the LMC. We discuss diagrams showing Fourier
parameters of the light curve decomposition against periods. Three sharp
features interpreted as an effect of resonances between radial modes are
detectable in these diagrams for type II Cepheids.Comment: 20 pages, 9 figure
The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. V. R Coronae Borealis Stars in the Large Magellanic Cloud
The fifth part of the OGLE-III Catalog of Variable Stars presents 23 R CrB
(RCB) stars in the Large Magellanic Cloud (LMC). 17 of these objects have been
spectroscopically confirmed by previous studies, while 6 stars are new
candidates for RCB variables. We publish the VI multi-epoch OGLE photometry for
all objects.
We use the sample of carbon-rich long-period variables released in the
previous part of this catalog to select objects with severe drops in
luminosity, i.e. with the DY-Per-like light curves. DY Per stars are often
related to R CrB variables. We detect at least 600 candidates for DY Per stars,
mostly among dust enshrouded giants. We notice that our candidate DY Per stars
form a continuity with other carbon-rich long-period variables, so it seems
that DY Per stars do not constitute a separate group of variable stars.Comment: 13 pages, 5 color figure
The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. VII. Classical Cepheids in the Small Magellanic Cloud
The seventh part of the OGLE-III Catalog of Variable Stars (OIII-CVS)
consists of 4630 classical Cepheids in the Small Magellanic Cloud (SMC). The
sample includes 2626 fundamental-mode (F), 1644 first-overtone (1O), 83
second-overtone (2O), 59 double-mode F/1O, 215 double-mode 1O/2O, and three
triple-mode classical Cepheids. For each object basic parameters, multi-epoch
VI photometry collected within 8 or 13 years of observations, and finding
charts are provided in the OGLE Internet archive. We present objects of
particular interest: exceptionally numerous sample of single-mode
second-overtone pulsators, five double Cepheids, two Cepheids with eclipsing
variations superimposed on the pulsation light curves. At least 139
first-overtone Cepheids exhibit low-amplitude secondary variations with periods
in the range 0.60-0.65 of the primary ones. These stars populate three distinct
sequences in the Petersen diagram. The origin of this secondary modulation is
still unknown. Contrary to the Large Magellanic Cloud (LMC) we found only a few
candidates for anomalous Cepheids in the SMC. This fact may be a clue for the
explanation of the origin of the anomalous Cepheids. The period and luminosity
distributions of Cepheids in both Magellanic Clouds suggest that there are two
or three populations of classical Cepheids in each of the galaxies. The main
difference between the LMC and SMC lays in different numbers of Cepheids in
each group. We fit the period-luminosity (PL) relations of SMC Cepheids and
compare them with the LMC PL laws.Comment: 23 pages, 11 (color) figure
The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. VI. Delta Scuti Stars in the Large Magellanic Cloud
The sixth part of the OGLE-III catalog of Variable Stars presents \delta Sct
pulsators in the Large Magellanic Cloud. Altogether 2786 variable stars were
found and amongst them 92 are multi-mode objects, including 67 stars pulsating
in the fundamental mode and the first overtone (F/1O), nine double-mode
pulsators with various combinations of the first three overtones excited
(1O/2O, 2O/3O and 1O/3O pulsators), and two triple mode (F/1O/2O) \delta Sct
stars. In total 1490 of stars are marked as uncertain, due to scattered
photometry and small amplitudes. For single-mode objects it was not possible to
unambiguously identify pulsation mode, however we suggest the most of the
single-mode variable stars pulsate in the first overtone.Comment: 16 pages, 7 figure
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