52,708 research outputs found
X-ray inverse Compton emission from the radio halo of M87
M87 has been observed in the 0.2-4 KeV X-ray band using the High Resolution Imager on the Einstein Observatory, and at 1.452 GHz using the Very Large Array. The radio map showed that the halo contained prominent asymmetries to the east and southwest. The X-ray map indicated similar asymmetries, but they were imbedded in the diffuse hot gas that surrounds the core out to a radius of several arcminutes. The hot X-ray emitting gas was assumed to be spherically symmetric and could, therefore, be subtracted from the image. The resultant image was asymmetric with major lobes to the east and southwest that coincide approximately with the asymmetries in the radio halo. The data indicates that inverse Compton emission is a plausible model for the X-rays coming from the asymmetric component
Strange pulsation modes in luminous red giants
We show that the spectrum of radial pulsation modes in luminous red giants
consists of both normal modes and a second set of modes with periods similar to
those of the normal modes. These additional modes are the red giant analogues
of the strange modes found in classical Cepheids and RR Lyrae variables. Here,
we describe the behaviour of strange and normal modes in luminous red giants
and discuss the dependence of both the strange and normal modes on the outer
boundary conditions. The strange modes always appear to be damped, much more so
than the normal modes. They should never be observed as self-excited modes in
real red giants but they may be detected in the spectrum of solar-like
oscillations. A strange mode with a period close to that of a normal mode can
influence both the period and growth rate of the normal mode.Comment: 6 pages, 5 figures, accepted by MNRA
Plasma accelerator Patent
Crossed-field plasma accelerator for laboratory simulation of atmospheric reentry condition
A Coronal Hole's Effects on CME Shock Morphology in the Inner Heliosphere
We use STEREO imagery to study the morphology of a shock driven by a fast
coronal mass ejection (CME) launched from the Sun on 2011 March 7. The source
region of the CME is located just to the east of a coronal hole. The CME ejecta
is deflected away from the hole, in contrast with the shock, which readily
expands into the fast outflow from the coronal hole. The result is a CME with
ejecta not well centered within the shock surrounding it. The shock shape
inferred from the imaging is compared with in situ data at 1 AU, where the
shock is observed near Earth by the Wind spacecraft, and at STEREO-A. Shock
normals computed from the in situ data are consistent with the shock morphology
inferred from imaging.Comment: to appear in The Astrophysical Journa
Optical and near-infrared spectrophotometric properties of Long Period Variables and other luminous red stars
Based on a new and large sample of optical and near-infrared spectra obtained
at the Mount Stromlo and Siding Spring Observatories (Lancon & Wood 1998;
Lancon & Wood, in preparation), spectrophotometric properties of cool oxygen-
and carbon-rich Long Period Variables and supergiants are presented.
Temperatures of oxygen-rich stars are assigned by comparison with synthetic
spectra computed from up-to-date oxygen-rich model atmosphere grids. The
existence of reliable optical and near-infrared temperature indicators is
investigated. A narrow relation between the bolometric correction BC(I) and the
broad-band colour I-J is obtained for oxygen-rich cool stars. The ability of
specific near-infrared indices to separate luminosity classes, atmospheric
chemistry or variability subtypes is discussed. Some comments are also given on
extinction effects, water band strengths in Long Period Variables and the
evaluation of 12CO/13CO ratio in red giants.Comment: 14 pages, 21 figures, Latex, accepted for publication in Astronomy
and Astrophysics main journal. Also available at
http://www-astro.ulb.ac.be/~ralvarez
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Making hurricane track data accessible
Our interactive tool allows the exploration, validation and presentation of hundreds of years of dynamically simulated storm tracks. The tracks were generated as part of a research project to improve the risk assessment of tropical storm damage by the insurance industry. The main impact of the tool is that exploratory interactive visualisation is now being used by the storm track modellers to (a) validate and improve model outputs, (b) discuss outputs with their peers (c) obtain a better understanding of the formation and development of tropical storms and (d) present examples of the behaviour of storms under different conditions to the insurance industry and others. Insights into tropical storm behaviour have been obtained and these insights are being articulated
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