45 research outputs found
Parametric resonant acceleration of particles by gravitational waves
We study the resonant interaction of charged particles with a gravitational
wave propagating in the non-empty interstellar space in the presence of a
uniform magnetic field. It is found that this interaction can be cast in the
form of a parametric resonance problem which, besides the main resonance,
allows for the existence of many secondary ones. Each of them is associated
with a non-zero resonant width, depending on the amplitude of the wave and the
energy density of the interstellar plasma. Numerical estimates of the
particles' energisation and the ensuing damping of the wave are given.Comment: LaTeX file, 16 page
Transverse Wave Propagation in Relativistic Two-fluid Plasmas around Schwarzschild-anti-de Sitter Black Hole
The 3+1 formalism of Thorne and Macdonald has been used to derive the linear
two-fluid equations for transverse waves in the plasma closed to the
Schwarzschild-anti-de Sitter (SAdS) black hole. We reformulate the relativistic
two-fluid equations to take account of gravitational effects due to the event
horizon and negative cosmological constant and describe the set of simultaneous
linear equations for the perturbations. Using a local approximation we
investigate the one-dimensional radial propagation of Alfven and high frequency
electromagnetic waves. We derive the dispersion relation for these waves and
solve it for the wave number k numerically.Comment: 11 pages. arXiv admin note: substantial text overlap with
arXiv:1008.4838, arXiv:0807.4595, arXiv:0902.3766, arXiv:0806.2740,
arXiv:0904.337
The Emission of Electromagnetic Radiation from Charges Accelerated by Gravitational Waves and its Astrophysical Implications
We provide calculations and theoretical arguments supporting the emission of
electromagnetic radiation from charged particles accelerated by gravitational
waves (GWs). These waves have significant indirect evidence to support their
existence, yet they interact weakly with ordinary matter. We show that the
induced oscillations of charged particles interacting with a GW, which lead to
the emission of electromagnetic radiation, will also result in wave
attenuation. These ideas are supported by a small body of literature, as well
as additional arguments for particle acceleration based on GW memory effects.
We derive order of magnitude power calculations for various initial charge
distributions accelerated by GWs. The resulting power emission is extremely
small for all but very strong GWs interacting with large quantities of charge.
If the results here are confirmed and supplemented, significant consequences
such as attenuation of early universe GWs could result. Additionally, this
effect could extend GW detection techniques into the electromagnetic regime.
These explorations are worthy of study to determine the presence of such
radiation, as it is extremely important to refine our theoretical framework in
an era of active GW astrophysics.Comment: Appears in Gravitational Wave Astrophysics, Editor C.F. Sopuerta,
Astrophysics and Space Science Proceedings, Volume 40. ISBN
978-3-319-10487-4. Springer International Publishing Switzerland, 2015, p.
30
Kinetic description of particle interaction with a gravitational wave
The interaction of charged particles, moving in a uniform magnetic field,
with a plane-polarized gravitational wave is considered using the
Fokker-Planck- Kolmogorov (FPK) approach. By using a stochasticity criterion,
we determine the exact locations in phase space, where resonance overlapping
occurs. We investigate the diffusion of orbits around each primary resonance of
order (m) by deriving general analytical expressions for an effective diffusion
coeficient. A solution to the corresponding diffusion equation (Fokker-Planck
equation) for the static case is found. Numerical integration of the full
equations of motion and subsequent calculation of the diffusion coefficient
verifies the analytical results.Comment: LaTeX file, 15 page
Anisotropic Null String Cosmologies
We study string propagation in an anisotropic, cosmological background. We
solve the equations of motion and the constraints by performing a perturbative
expansion of the string coordinates in powers of c^2, the world-sheet speed of
light. To zeroth order the string is approximated by a tensionless string
(since c is proportional to the string tension T). We obtain exact, analytical
expressions for the zeroth and the first order solutions and we discuss some
cosmological implications.Comment: 9 pages, plain Te
Photometry of GSC 762-110, a new triple-mode radially pulsating star
Stars pulsating in three radial modes are very rare; only three examples are
known in the Galaxy. These stars are very useful since their periods may be
measured very precisely, and this will constrain the global stellar parameters
and the models of the star's interior. The purpose of this paper is to present
a new example of the class of triple-mode radial pulsators. A search for
candidate multi-mode pulsators was carried out in public survey data.
Time-series photometry of one of the candidates, GSC 762-110, was performed.
GSC 762-110 was found to be a triple-mode radial pulsator, with a fundamental
period of 0.1945d and period ratios of 0.7641 and 0.8012. In addition two
non-radial modes were found, for which the amplitude has diminished
considerably over the last few years.Comment: Accepted for publication in Astronomy & Astrophysic
Gravito-magnetic instabilities in anisotropically expanding fluids
Gravitational instabilities in a magnetized Friedman - Robertson - Walker
(FRW) Universe, in which the magnetic field was assumed to be too weak to
destroy the isotropy of the model, are known and have been studied in the past.
Accordingly, it became evident that the external magnetic field disfavors the
perturbations' growth, suppressing the corresponding rate by an amount
proportional to its strength. However, the spatial isotropy of the FRW Universe
is not compatible with the presence of large-scale magnetic fields. Therefore,
in this article we use the general-relativistic (GR) version of the
(linearized) perturbed magnetohydrodynamic equations with and without
resistivity, to discuss a generalized Jeans criterion and the potential
formation of density condensations within a class of homogeneous and
anisotropically expanding, self-gravitating, magnetized fluids in curved
space-time. We find that, for a wide variety of anisotropic cosmological
models, gravito-magnetic instabilities can lead to sub-horizonal, magnetized
condensations. In the non-resistive case, the power spectrum of the unstable
cosmological perturbations suggests that most of the power is concentrated on
large scales (small k), very close to the horizon. On the other hand, in a
resistive medium, the critical wave-numbers so obtained, exhibit a delicate
dependence on resistivity, resulting in the reduction of the corresponding
Jeans lengths to smaller scales (well bellow the horizon) than the
non-resistive ones, while increasing the range of cosmological models which
admit such an instability.Comment: 10 pages RevTex, 4 figures, accepted for publication in the
International Journal of Modern Physics
Transverse Wave Propagation in Relativistic Two-fluid Plasmas in de Sitter Space
We investigate transverse electromagnetic waves propagating in a plasma in
the de Sitter space. Using the 3+1 formalism we derive the relativistic
two-fluid equations to take account of the effects due to the horizon and
describe the set of simultaneous linear equations for the perturbations. We use
a local approximation to investigate the one-dimensional radial propagation of
Alfv\'en and high frequency electromagnetic waves and solve the dispersion
relation for these waves numerically.Comment: 19 pages, 12 figure
Search for pulsation among suspected A-type binaries and the new multiperiodic Delta Scuti star HD217860
16 pages, 12 Postscript figures, 1 long table. Table 2 is only available in electronic form. Journal-ref: Astronomy and Astrophysics, in press (2007)We have explored a sample of suspected A-type binaries in a systematic way, both spectroscopically and photometrically. Due to their location in the H-R diagram, indications of pulsation and/or chemical peculiarities among these suspected binary (or multiple) systems may be found. High-resolution spectroscopy obtained with the ELODIE and MUSICOS spectrographs was used in combination with a few nights of differential CCD photometry in order to search for pulsation(s). Of the 32 investigated targets, eight are spectroscopic binaries, one of which is a close binary also showing eclipses, and three have been identified as Delta Scuti pulsators with rapid line-profile variations. Among the latter stars, HD 217860 reveals interesting multiperiodic photometric and spectroscopic variations, with up to eight frequencies common to two large photometric data sets. We suggest that at least one radial overtone mode is excited among the two most dominant frequencies. We furthermore found evidence for a strong modulation of the amplitude(s) and/or the (radial) frequency content of this intriguing Delta Scuti star
V371 Per - A Thick-Disk, Short-Period F/1O Cepheid
V371 Per was found to be a double-mode Cepheid with a fundamental mode period
of 1.738 days, the shortest among Galactic beat Cepheids, and an unusually high
period ratio of 0.731, while the other Galactic beat Cepheids have period
ratios between 0.697 and 0.713. The latter suggests that the star has a
metallicity [Fe/H] between -1 and -0.7. The derived distance from the Galactic
Plane places it in the Thick Disk or the Halo, while all other Galactic beat
Cepheids belong to the Thin Disk. There are indications from historical data
that both the fundamental and first overtone periods have lengthened.Comment: Accepted for publication in MNRA