861 research outputs found
Conductivity, weak ferromagnetism and charge instability in single crystal
The temperature dependence of resistivity, magnetization and electron-spin
resonance of the single crystal were measured in temperature
range of . Magnetization hysteresis in applied magnetic field
up to 0.7 T at , irreversible temperature behavior of
magnetization and resistivity were found . The obtained data were explained in
terms of degenerate tight binding model using random phase approximation. The
contribution of holes in and bands of manganese ions to the
conductivity, optical absorbtion spectra and charge instability in were studied. Charge susceptibility maxima resulted from the competition of
the on-site Coulomb interaction between the holes in different orbitals and
small hybridization of sub-bands were calculated at .Comment: 6 pages, 12 figure
Accretion dynamics in the classical T Tauri star V2129 Oph
We analyze the photometric and spectroscopic variability of the classical T
Tauri star V2129 Oph over several rotational cycles to test the dynamical
predictions of magnetospheric accretion models. The photometric variability and
the radial velocity variations in the photospheric lines can be explained by
rotational modulation due to cold spots, while the radial velocity variations
of the He I (5876 \AA) line and the veiling variability are due to hot spot
rotational modulation. The hot and cold spots are located at high latitudes and
about the same phase, but the hot spot is expected to sit at the chromospheric
level, while the cold spot is at the photospheric level. Using the
dipole+octupole magnetic-field configuration previously proposed in the
literature for the system, we compute 3D MHD magnetospheric simulations of the
star-disk system. We use the simulation's density, velocity and scaled
temperature structures as input to a radiative transfer code, from which we
calculate theoretical line profiles at all rotational phases. The theoretical
profiles tend to be narrower than the observed ones, but the qualitative
behavior and the observed rotational modulation of the H\alpha and H\beta
emission lines are well reproduced by the theoretical profiles. The
spectroscopic and photometric variability observed in V2129 Oph support the
general predictions of complex magnetospheric accretion models with
non-axisymmetric, multipolar fields.Comment: Accepted by Astronomy and Astrophysic
The Use of Contact Heat Generators of the New Generation for Heat Production
We substantiated the need for searching for, and realization of, fundamentally new approaches, using more efficient physical, heat-mass-exchanging and aerodynamic processes, which will make it possible to improve energy effectiveness and ecological cleanliness of heat generation in the systems for individual and decentralized heat supply.For the heat supply to large cities and industrial regions, we examined the advantages of using highly efficient contact heat-generators of different types, which include compactness due to low metal consumption and, as a result, attractive price.It is proposed to use a heat-generator of contact type of the new generation, with the aid of which it was possible to solve a set of problems on the qualitative combustion of fuel and effective heat exchange of gases with the heated water. The use of tubular technology for the combustion of gas is its special feature. Due to it, quality heat exchanging characteristics are provided.In view of further studies, we presented the relevance of creating heat-generators with the use of highly effective hydrogen technologies, which will make it possible to devise the new energy paradigm of heat supply for residential areas and industrial zones through the possibility of accumulation of electrical energy and accumulation of hydrogen
Relativistic Jets from Accretion Disks
The jets observed to emanate from many compact accreting objects may arise
from the twisting of a magnetic field threading a differentially rotating
accretion disk which acts to magnetically extract angular momentum and energy
from the disk. Two main regimes have been discussed, hydromagnetic jets, which
have a significant mass flux and have energy and angular momentum carried by
both matter and electromagnetic field and, Poynting jets, where the mass flux
is small and energy and angular momentum are carried predominantly by the
electromagnetic field. Here, we describe recent theoretical work on the
formation of relativistic Poynting jets from magnetized accretion disks.
Further, we describe new relativistic, fully-electromagnetic, particle-in-cell
simulations of the formation of jets from accretion disks. Analog Z-pinch
experiments may help to understand the origin of astrophysical jets.Comment: 7 pages, 3 figures, Proc. of High Energy Density Astrophysics Conf.,
200
Magnetometry of the classical T Tauri star GQ Lup: non-stationary dynamos & spin evolution of young Suns
We report here results of spectropolarimetric observations of the classical T
Tauri star (cTTS) GQ Lup carried out with ESPaDOnS at the Canada-France-Hawaii
Telescope (CFHT) in the framework of the "Magnetic Protostars and Planets"
(MaPP) programme, and obtained at 2 different epochs (2009 July & 2011 June).
From these observations, we first infer that GQ Lup has a photospheric
temperature of 4,300+-50\^A K and a rotation period of 8.4+-0.3 d; it implies
that it is a 1.05+-0.07 Msun star viewed at an inclination of ~30deg, with an
age of 2-5 Myr, a radius of 1.7+-0.2 Rsun, and has just started to develop a
radiative core.
Large Zeeman signatures are clearly detected at all times, both in
photospheric lines & in accretion-powered emission lines, probing longitudinal
fields of up to 6 kG and hence making GQ Lup the cTTS with the strongest
large-scale fields known as of today. Rotational modulation of Zeeman
signatures is clearly different between our 2 runs, demonstrating that
large-scale fields of cTTSs are evolving with time and are likely produced by
non-stationary dynamo processes.
Using tomographic imaging, we reconstruct maps of the large-scale field, of
the photospheric brightness & of the accretion-powered emission of GQ Lup. We
find that the magnetic topology is mostly poloidal & axisymmetric; moreover,
the octupolar component of the large-scale field (of strength 2.4 & 1.6 kG in
2009 & 2011) dominates the dipolar component (of strength ~1 kG) by a factor of
~2, consistent with the fact that GQ Lup is no longer fully-convective.
GQ Lup also features dominantly poleward magnetospheric accretion at both
epochs. The large-scale dipole of GQ Lup is however not strong enough to
disrupt the surrounding accretion disc further than about half-way to the
corotation radius, suggesting that GQ Lup should rapidly spin up like other
similar partly-convective cTTSs (abridged).Comment: MNRAS, in press (17 pages, 10 figures, 1 table
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