375 research outputs found
On Chromospheric Variations Modeling for Main-Sequence Stars of G and K Spectral Classes
We present a method of chromospheric flux simulation for 13 late-type
main-sequence stars. These Sun-like stars have well-determined cyclic flux
variations similar to 11 yr solar activity cycle. Our flux prediction is based
on chromospheric HK emission time series measurements from Mount Wilson
Observatory and comparable solar data. We show that solar three - component
modeling explains well the stellar observations. We find that the 10 - 20% of K
- stars disc surfaces are occupied by bright active regions.Comment: 8 pages, 2 figure
Color Effects Associated with the 1999 Microlensing Brightness Peaks in Gravitationally Lensed Quasar Q2237+0305
Photometry of the Q2237+0305gravitational lens in VRI spectral bands with the
1.5-m telescope of the high-altitude Maidanak observatory in 1995-2000 is
presented. Monitoring of Q2237+0305 in July-October 2000, made at nearly daily
basis, did not reveal rapid (night-to-night and intranight) variations of
brightness of the components during this time period. Rather slow changes of
magnitudes of the components were observed, such as 0.08 mag fading of B and C
components and 0.05 mag brightening of D in R band during July 23 - October 7,
2000. By good luck three nights in 1999 were almost at the time of the strong
brightness peak of image C, and approximately in the middle of the ascending
slope of the image A brightness peak. The C component was the most blue one in
the system in 1998 and 1999, having changed its (V-I) color from 0.56 mag to
0.12 mag since August 1997, while its brightness increased almost 1.2 mag
during this time period. The A component behaved similarly between August 1998
and August 2000, having become 0.47 mag brighter in R, and at the same time,
0.15 mag bluer. A correlation between the color variations and variations of
magnitudes of the components is demonstrated to be significant and reaches
0.75, with a regression line slope of 0.33. A color (V-I) vrs color (V-R) plot
shows the components settled in a cluster, stretched along a line with a slope
of 1.31. Both slopes are noticeably smaller than those expected if a standard
galactic interstellar reddening law were responsible for the differences
between the colors of images and their variations over time. We attribute the
brightness and color changes to microlensing of the quasar's structure, which
we conclude is more compact at shorter wavelengths, as predicted by most quasar
models featuring an energizing central source.Comment: 14 pages, 7 figures, LaTeX, submitted to A&
Bogolyubov-Hartree-Fock approach to studying the QCD ground state
The quark's behaviour while influenced by a strong stochastic gluon field is
analyzed. An approximate procedure for calculating the effective Hamiltonian is
developed and the corresponding ground state within the Hartree-Fock-Bogolyubov
approach is found. The comparative analysis of various Hamiltonian models is
given and transition to the chiral limit in the Keldysh model is discussed in
detail.Comment: 18 pages, 4 figures, new version of the manuscrip
Image reconstruction technique and optical monitoring of the QSO2237+0305 from Maidanak Observatory in 2002 -- 2003
We have observed the gravitational lens system Q2237+0305 from the Maidanak
Observatory over the period from August 2002 to November 2003. Here we report
the results of our observations. We implemented a two-stage technique that has
been developed specifically for the purpose of gravitational lens image
reconstruction. The technique is based on the Tikhonov regularization approach
and allows one to obtain astrometric and photometric characteristics of the
gravitational lens system. Light curves with 78 data points for the four quasar
components are obtained. Slow brightness variations over the observational
period are found in all components. Images A, C, D have a tendency to decrease
in brightness. Image B does not vary more than 0.05mag. The observations did
not reveal evidence for large variations in brightness of the components due to
microlensing effects. To provide an overall picture of the photometry
behaviour, our data are combined with the Maidanak observations published for
1995 -- 2000.Comment: 9 pages, 4 figures, accepted by MNRA
Time delay between images of the lensed quasar UM673
We study brightness variations in the double lensed quasar UM673 (Q0142-100)
with the aim of measuring the time delay between its two images. In the paper
we combine our previously published observational data of UM673 obtained during
the 2003 - 2005 seasons at the Maidanak Observatory with archival and recently
observed Maidanak and CTIO UM673 data. We analyze the V, R and I-band light
curves of the A and B images of UM673, which cover ten observational seasons
from August 2001 to November 2010. We also analyze the time evolution of the
difference in magnitudes between images A and B of UM673 over more than ten
years. We find that the quasar exhibits both short-term (with amplitude of \sim
0.1 mag in the R band) and high-amplitude (\sim 0.3 mag) long-term variability
on timescales of about several months and several years, respectively. These
brightness variations are used to constrain the time delay between the images
of UM673. From cross-correlation analysis of the A and B quasar light curves
and error analysis we measure the mean time delay and its error of 89 \pm11
days. Given the input time delay of 88 days, the most probable value of the
delay that can be recovered from light curves with the same statistical
properties as the observed R-band light curves of UM673 is 95{+5/-16}{+14/-29}
days (68 and 95 % confidence intervals). Analysis of the V - I color variations
and V, R and I-band magnitude differences of the quasar images does not show
clear evidence of the microlensing variations between 1998 and 2010.Comment: Submitted to A&A, 11 pages, 9 figure
Time delays in PG1115+080: new estimates
We report new estimates of the time delays in the quadruple gravitationally
lensed quasar PG1115+080, obtained from the monitoring data in filter R with
the 1.5-m telescope at the Maidanak Mountain (Uzbekistan, Central Asia) in
2004-2006. The time delays are 16.4 days between images C and B, and 12 days
between C and A1+A2, with image C being leading for both pairs. The only known
estimates of the time delays in PG1115 are those based on observations by
Schechter et al. (1997) -- 23.7 and 9.4 days between images C and B, C and
A1+A2, respectively, as calculated by Schechter et al., and 25 and 13.3 days as
revised by Barkana (1997) for the same image components with the use of another
method. The new values of time delays in PG 1115+080 may be expected to provide
larger estimates of the Hubble constant thus decreasing a diversity between the
H_0 estimates taken from gravitationally lensed quasars and with other methods.Comment: 5 pages, 2 figures, Accepted for publication in MNRAS Letter
Spectrometric method to detect exoplanets as another test to verify the invariance of the velocity of light
Hypothetical influences of variability of light velocity due to the
parameters of the source of radiation, for the results of spectral measurements
of stars to search for exoplanets are considered. Accounting accelerations of
stars relative to the barycenter of the star - a planet (the planets) was
carried out. The dependence of the velocity of light from the barycentric
radial velocity and barycentric radial acceleration component of the star
should lead to a substantial increase (up to degree of magnitude) semi-major
axes of orbits detected candidate to extrasolar planets. Consequently, the
correct comparison of the results of spectral method with results of other
well-known modern methods of detecting extrasolar planets can regard the
results obtained in this paper as a reliable test for testing the invariance of
the velocity of light.Comment: 11 pages, 5 figure
Diagrammatic theory for Anderson Impurity Model. Stationary property of the thermodynamic potential
A diagrammatic theory around atomic limit is proposed for normal state of
Anderson Impurity Model. The new diagram method is based on the ordinary Wick's
theorem for conduction electrons and a generalized Wick's theorem for gtrongly
correlated impurity electrons. This last theorem coincides with the definition
of Kubo cumulants. For the mean value of the evolution operator a linked
cluster theorem is proved and a Dyson's type equations for one-particle
propagators are established. The main element of these equations is the
correlation function which contains the spin, charge and pairing fluctuations
of the system. The thermodynamic potential of the system is expressed through
one-particle renormalized Green's functions and the corelation function. The
stationary property of the thermodynamic potential is established with respect
to the changes of correlation function.Comment: 7 pages, 6 figures, Submitted to PR
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