237 research outputs found
Vlasov equation and collisionless hydrodynamics adapted to curved spacetime
The modification of the Vlasov equation, in its standard form describing a
charged particle distribution in the six-dimensional phase space, is derived
explicitly within a formal Hamiltonian approach for arbitrarily curved
spacetime. The equation accounts simultaneously for the Lorentz force and the
effects of general relativity, with the latter appearing as the gravity force
and an additional force due to the extrinsic curvature of spatial
hypersurfaces. For an arbitrary spatial metric, the equations of collisionless
hydrodynamics are also obtained in the usual three-vector form
Adiabatic nonlinear waves with trapped particles: II. Wave dispersion
A general nonlinear dispersion relation is derived in a nondifferential form
for an adiabatic sinusoidal Langmuir wave in collisionless plasma, allowing for
an arbitrary distribution of trapped electrons. The linear dielectric function
is generalized, and the nonlinear kinetic frequency shift is
found analytically as a function of the wave amplitude . Smooth
distributions yield , as usual. However,
beam-like distributions of trapped electrons result in different power laws, or
even a logarithmic nonlinearity, which are derived as asymptotic limits of the
same dispersion relation. Such beams are formed whenever the phase velocity
changes, because the trapped distribution is in autoresonance and thus evolves
differently from the passing distribution. Hence, even adiabatic is generally nonlocal.Comment: submitted together with Papers I and II
Interpretation of the Veiling of the Photospheric Spectrum for T Tauri Stars in Terms of an Accretion Model
The problem on heating the atmospheres of T Tauri stars by radiation from an
accretion shock has been solved. The structure and radiation spectrum of the
emerging so-called hot spot have been calculated in the LTE approximation. The
emission not only in continuum but also in lines has been taken into account
for the first time when calculating the spot spectrum. Comparison with
observations has shown that the strongest of these lines manifest themselves as
narrow components of helium and metal emission lines, while the weaker ones
decrease significantly the depth of photospheric absorption lines, although
until now, this effect has been thought to be due to the emission continuum
alone. The veiling by lines changes the depth of different photospheric lines
to a very different degree even within a narrow spectral range. Therefore, the
nonmonotonic wavelength dependence of the degree of veiling r found for some
CTTS does not suggest a nontrivial spectral energy distribution of the veiling
continuum. In general, it makes sense to specify the degree of veiling r only
by providing the set of photospheric lines from which this quantity was
determined. We show that taking into account the contribution of lines to the
veiling of the photospheric spectrum can cause the existing estimates of the
accretion rate onto T Tauri stars to decrease by several times, with this being
also true for stars with a comparatively weakly veiled spectrum. Neglecting the
contribution of lines to the veiling can also lead to appreciable errors in
determining the effective temperature, interstellar extinction, radial
velocity, and vsin(i)
Noise suppression and enhanced focusability in plasma Raman amplifier with multi-frequency pump
Laser pulse compression/amplification through Raman backscattering in plasmas can be facilitated by using multi-frequency pump laser beams. The efficiency of amplification is increased by suppressing the Raman instability of thermal fluctuations and seed precursors. Also the focusability of the amplified radiation is enhanced due to the suppression of large-scale longitudinal speckles in the pump wave structure
The Post-AGB Star IRAS 07253-2001: Pulsations, Long-Term Brightness Variability and Spectral Peculiarities
The observations and comprehensive study of intermediate initial mass stars
at the late stages of evolution, and after the asymptotic giant branch (AGB) in
particular, are of crucial importance to identify the common properties for the
stars of given group and to reveal binaries among them. This work aims to
investigate photometric and spectral peculiarities of a poorly studied post-AGB
candidate and infrared source IRAS 07253-2001. We present the new multicolour
photometry obtained with the telescopes of the Caucasian
mountain observatory and analyse it together with the data acquired by the All
Sky Automated Survey for SuperNovae. We report on the detection of multiperiod
brightness variability caused by pulsations. A beating of close periods, the
main one of 73 days and additional ones of 68 and 70 days, leads to amplitude
variations. We have also detected a long-term sine trend in brightness with a
period of nearly 1800 days. We suppose it to be orbital and IRAS 07253-2001 to
be binary. Based on new low-resolution spectroscopic data obtained with the
2.5-m telescope of the Caucasian mountain observatory in 2020 and 2023 in the
3500-7500 wavelength range we have identified spectral lines and
compiled a spectral atlas. We have found the [N II], [Ni II] and [S II]
forbidden emission lines in the spectrum and discuss their origin. The
H line has a variable double-peaked emission component. We have derived
preliminary estimates of the star's parameters and detected a variation of
radial velocity with a peak-to-peak amplitude of about 30 km s.Comment: 19 pages, 11 figures, 6 tables, Table 2 is only available in
electronic form, accepted to Astrophysical Bulleti
Recurrent Symbiotic Nova T Coronae Borealis Before Outburst
The results of photometric and spectral observations of T CrB obtained in a
wide range of wavelengths in 2011-2023 are presented. We use the near-IR light
curves to determine a new ephemeris for
the times of light minima when the red giant is located between the observer
and the hot component. The flux ratio H/H varied from ~3 to ~8
in 2020-2023, which may be due to a change in the flux ratio between the X-ray
and optical ranges. It is shown that the value of H/H depends on
the rate of accretion onto the hot component of the system. Based on high-speed
follow-up observations obtained on June 8, 2023, we detected a variability of
the HeII line with a characteristic time-scale of ~25 min, the
amplitude of variability in the band was ~0.07. Simulations of the
near-IR light curves accounting for the ellipsoidal effect allowed us to obtain
the parameters of the binary system: the Roche lobe filling factor of the cool
component , the mass ratio , the orbit
inclination . A comparison of the light curve obtained in
2005-2023 with the 1946 outburst template made it possible to predict the date
of the upcoming outburst - January 2024.Comment: 15 pages, 3 tables, 8 figures, submitted to Astronomy Letter
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