732 research outputs found
Phobos and Deimos: Satellites of Mars
The physical characteristics of Phobos and Deimos, satellites of Mars, are discussed. Phobos and Deimos are used as an example to discuss the probable internal structure of objects of this type and the structural formations on their surfaces. The history of astronomical observations of Mars is also described
Spectroscopic signatures related to a sunquake
© 2015. The American Astronomical Society. All rights reserved.. The presence of flare-related acoustic emission (sunquakes (SQs)) in some flares, and only in specific locations within the flaring environment, represents a severe challenge to our current understanding of flare energy transport processes. In an attempt to contribute to understanding the origins of SQs we present a comparison of new spectral observations from Hinode's EUV imaging Spectrometer (EIS) and the Interface Region Imaging Spectrograph (IRIS) of the chromosphere, transition region, and corona above an SQ, and compare them to the spectra observed in a part of the flaring region with no acoustic signature. Evidence for the SQ is determined using both time-distance and acoustic holography methods, and we find that unlike many previous SQ detections, the signal is rather dispersed, but that the time-distance and 6 and 7 mHz sources converge at the same spatial location. We also see some evidence for different evolution at different frequencies, with an earlier peak at 7 mHz than at 6 mHz. Using EIS and IRIS spectroscopic measurements we find that in this location, at the time of the 7 mHz peak the spectral emission is significantly more intense, shows larger velocity shifts and substantially broader profiles than in the location with no SQ, and there is a good correlation between blueshifted, hot coronal, hard X-ray (HXR), and redshifted chromospheric emission, consistent with the idea of a strong downward motion driven by rapid heating by nonthermal electrons and the formation of chromospheric shocks. Exploiting the diagnostic potential of the Mg ii triplet lines, we also find evidence for a single large temperature increase deep in the atmosphere, which is consistent with this scenario. The time of the 6 mHz and time-distance peak signal coincides with a secondary peak in the energy release process, but in this case we find no evidence of HXR emission in the quake location, instead finding very broad spectral lines, strongly shifted to the red, indicating the possible presence of a significant flux of downward propagating Alfvén waves
Paramagnetic Meissner effect in superconductors from self-consistent solutions of Ginzburg-Landau equations
The paramagnetic Meissner effect (PME) is observed in small superconducting
samples, and a number of controversial explanations of this effect are
proposed, but there is as yet no clear understanding of its nature. In the
present paper PME is considered on the base of the Ginzburg-Landau theory (GL).
The one-dimensional solutions are obtained in a model case of a long
superconducting cylinder for different cylinder radii R, the GL-parameters
\kappa and vorticities m. Acording to GL-theory, PME is caused by the presence
of vortices inside the sample. The superconducting current flows around the
vortex to screeen the vortex own field from the bulk of the sample. Another
current flows at the boundary to screen the external field H from entering the
sample. These screening currents flow in opposite directions and contribute
with opposite signs to the total magnetic moment (or magnetization) of the
sample. Depending on H, the total magnetization M may be either negative
(diamagnetism), or positive (paramagnetism). A very complicated saw-like
dependence M(H) (and other characteristics), which are obtained on the base of
self-consistent solutions of the GL-equations, are discussed.Comment: 6 pages, 5 figures, RevTex, submitted to Phys. Rev.
Anomalies of Density, Stresses, and the Gravitational Field in the Interior of Mars
We determined the possible compensation depths for relief harmonics of
different degrees and orders. The relief is shown to be completely compensated
within the depth range of 0 to 1400 km. The lateral distributions of
compensation masses are determined at these depths and the maps are
constructed. The possible nonisostatic vertical stresses in the crust and
mantle of Mars are estimated to be 64 MPa in compression and 20 MPa in tension.
The relief anomalies of the Tharsis volcanic plateau and symmetric feature in
the eastern hemisphere could have arisen and been maintained dynamically due to
two plumes in the mantle substance that are enriched with fluids. The plumes
that originate at the core of Mars can arise and be maintained by the anomalies
of the inner gravitational field achieving +800 mGal in the region of plume
formation, - 1200 mGal above the lower mantle-core transition layer, and -1400
mGal at the crust.Comment: 9 pages, 5 figure
The 2013 February 17 sunquake in the context of the active region's magnetic field configuration
© 2017. The American Astronomical Society. All rights reserved. Sunquakes are created by the hydrodynamic response of the lower atmosphere to a sudden deposition of energy and momentum. In this study, we investigate a sunquake that occurred in NOAA active region 11675 on 2013 February 17. Observations of the corona, chromosphere, and photosphere are brought together for the first time with a nonlinear force-free model of the active region's magnetic field in order to probe the magnetic environment in which the sunquake was initiated. We find that the sunquake was associated with the destabilization of a flux rope and an associated M-class GOES flare. Active region 11675 was in its emergence phase at the time of the sunquake and photospheric motions caused by the emergence heavily modified the flux rope and its associated quasi-separatrix layers, eventually triggering the flux rope's instability. The flux rope was surrounded by an extended envelope of field lines rooted in a small area at the approximate position of the sunquake. We argue that the configuration of the envelope, by interacting with the expanding flux rope, created a “magnetic lens” that may have focussed energy on one particular location of the photosphere, creating the necessary conditions for the initiation of the sunquake
Curvature Radiation by Ultrarelativistic Protons
We study pion curvature radiation by a proton, i.e. pion emission by a proton
moving along a curved trajectory. We suggest an approximate semiclassical
solution and the exact solution for which we assume that a proton moves in a
fictitious magnetic field with the Larmor radius equal to the curvature radius
of the real trajectory. As possible application we consider the pion radiation
by ultrahigh energy protons moving along curved magnetic field lines. Such
situation can occur in the magnetosphere of a young pulsar, in the
magnetosphere of the accretion disk around a black hole, and in the vicinity of
a superconducting cosmic string. The decay products of these pions, such as
high energy photons or neutrinos, can give the observable consequences of the
considered mechanism.Comment: 5 pages, revtex, to appear in Physics Letters
Can we detect local helioseismic parameter shifts in coronal holes?
Changes in helioseismic mode parameters in active regions and across the solar disk are well documented, but local magnetic activity and geometric effects may not account for all of the scatter seen in the results. We use results from theHelioseismic and Magnetic Imagerring-diagram pipeline for Carrington rotation 2113 to look for differences in mode amplitude and frequency between coronal holes and other quiet-Sun regions. While we do not find a systematic difference, the results do suggest that the correlation between magnetic activity index and mode parameters shows less scatter in coronal hole regions than in general quiet Sun
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