scholarly journals Wave Activity and Prominence Eruption

1998 ◽  
Vol 167 ◽  
pp. 314-317 ◽  
Author(s):  
F. Baudin ◽  
K. Bocchialini ◽  
C. Delannee ◽  
S. Koutchmy ◽  
G. Stellmacher ◽  
...  
Keyword(s):  
Dissipation Rate ◽  
Wave Activity ◽  
Observational Evidence ◽  
Loop System ◽  
Mhd Waves ◽  
Plasma Instabilities ◽  
Important Ingredient ◽  
X Ray ◽  
Convective Structures ◽  
Energy And Momentum

AbstractObservational evidence of 3 and 5 min vertical oscillations of a filament on the disk are recorded. Wave activity was observed before, during and after a filament disappearance, inside and around the filament. Both an Hα brightening and, later, a blowing out of a faint soft X-ray (Yohkoh) loop system occuring in connection with a flare were noticed. The wave activity seems to be a dynamically important ingredient of this erupting prominence.Propagating MHD waves and convective structures bring their energy and momentum from the photosphere towards the chromosphere up to the coronal heights where they are partially reflected and/or dissipated. The transition from the laminar to the turbulent state of the whole prominence enhances the dissipation rate of the external waves inside this system, adding energy to produce the heating and lifting of the plasma. Internal plasma instabilities could trigger this transition in the framework of a prominence disappearance.

scholarly journals The Origin of Magnetic Fields in Elliptical Galaxies

2002 ◽  
Vol 12 ◽  
pp. 731-732
Author(s):  
Anvar Shukurov
Keyword(s):  
Magnetic Fields ◽  
Faraday Rotation ◽  
Dissipation Rate ◽  
Elliptical Galaxies ◽  
Observational Evidence ◽  
Turbulent Velocity ◽  
Dynamo Action ◽  
Interstellar Gas ◽  
X Ray ◽  
Upper Limit

AbstractWe argue that interstellar gas in elliptical galaxies can be turbulent, with turbulent scale and velocity of 400 pc and 20 km s−1respectively. An upper limit on turbulent velocity, ≃ 50 km s−1, follows from the requirement that the turbulence dissipation rate does not exceed the X-ray gas luminosity. The turbulence can generate random magnetic fields of 0.3 μG strength at the above scale via fluctuation dynamo action. The resulting Faraday rotation is random, with a typical value of 5-30 rad m−2, consistent with observational evidence available.

scholarly journals Motion of dust particles in dry snow under temperature gradient metamorphism

2019 ◽  
Vol 13 (9) ◽  
pp. 2345-2359 ◽  
Author(s):  
Pascal Hagenmuller ◽  
Frederic Flin ◽  
Marie Dumont ◽  
François Tuzet ◽  
Isabel Peinke ◽  
...  
Keyword(s):  
Time Series ◽  
Temperature Gradient ◽  
Pore Space ◽  
Observational Evidence ◽  
Climate Forcing ◽  
Dust Particles ◽  
Snow Surface ◽  
X Ray ◽  
Arctic Regions ◽  
Radiative Impact

Abstract. The deposition of light-absorbing particles (LAPs) such as mineral dust and black carbon on snow is responsible for a highly effective climate forcing, through darkening of the snow surface and associated feedbacks. The interplay between post-depositional snow transformation (metamorphism) and the dynamics of LAPs in snow remains largely unknown. We obtained time series of X-ray tomography images of dust-contaminated samples undergoing dry snow metamorphism at around −2 ∘C. They provide the first observational evidence that temperature gradient metamorphism induces dust particle motion in snow, while no movement is observed under isothermal conditions. Under temperature gradient metamorphism, dust particles can enter the ice matrix due to sublimation–condensation processes and spread down mainly by falling into the pore space. Overall, such motions might reduce the radiative impact of dust in snow, in particular in arctic regions where temperature gradient metamorphism prevails.

scholarly journals An Observational Evidence of the Common Envelope Phase

2004 ◽  
Vol 194 ◽  
pp. 37-38
Author(s):  
Marek J. Sarna ◽  
Jeremy J. Drake
Keyword(s):  
Abundance Ratio ◽  
Observational Evidence ◽  
Coronal Emission ◽  
X Ray ◽  
Common Envelope ◽  
Transmission Grating ◽  
Processed Material ◽  
The Common ◽  
Red Giant ◽  
First Time

AbstractChandra Low Energy Transmission Grating Spectrograph observations of the pre-cataclysmic binary V471 Tau have been used to estimate the C/N abundance ratio of the K dwarf component for the first time. While the white dwarf component dominates the spectrum longward of 50 Å, at shorter wavelengths the observed X-ray emission is entirely due to coronal emission from the K dwarf. The H-like 2p 2Р3/2, 1/2 → 1s 2S1/2 resonance lines of С and N yield an estimate of their logarithmic abundance ratio relative to the Sun of [C/N]= –0.38 ± 0.15—half of the currently accepted solar value. We interpret this result as the first clear observational evidence for the presumed common envelope phase of this system, during which the surface of the K dwarf was contaminated by CN-cycle processed material dredged up into the red giant envelope

scholarly journals The XXL Survey

2018 ◽  
Vol 620 ◽  
pp. A9 ◽  
Author(s):  
L. Faccioli ◽  
F. Pacaud ◽  
J.-L. Sauvageot ◽  
M. Pierre ◽  
L. Chiappetti ◽  
...  
Keyword(s):  
Galaxy Clusters ◽  
Selection Criteria ◽  
Important Ingredient ◽  
X Ray ◽  
Final Development ◽  
Validation Tests

Aims. A well characterised detection pipeline is an important ingredient for X-ray cluster surveys. Methods. We present the final development of the XXL Survey pipeline. The pipeline optimally uses X-ray information by combining many overlapping observations of a source when possible, both for its detection and its characterisation. It can robustly detect and characterise several types of X-ray sources: AGNs (point-like), galaxy clusters (extended), galaxy clusters contaminated by a central AGN, and pairs of AGNs close on the sky. We perform a thorough suite of validation tests via realistic simulations of XMM-Newton images and we introduce new selection criteria for various types of sources that will be detected by the survey. Results. We find that the use of overlapping observations allows new clusters to be securely identified that would be missed or less securely identified by using only one observation at a time. We also find that, with the new pipeline we can robustly identify clusters with a central AGN that would otherwise have been missed, and we can flag pairs of AGNs close on the sky that might have been mistaken for a cluster.

scholarly journals Observational evidence for intermediate-mass black holes

2017 ◽  
Vol 26 (11) ◽  
pp. 1730021 ◽  
Author(s):  
Mar Mezcua
Keyword(s):  
Black Holes ◽  
Galaxy Formation ◽  
Globular Clusters ◽  
High Redshift ◽  
Galactic Nuclei ◽  
Observational Evidence ◽  
Intermediate Mass ◽  
X Ray ◽  
Mass Scaling ◽  
Intermediate Mass Black Holes

Intermediate-mass black holes (IMBHs), with masses in the range [Formula: see text]–[Formula: see text][Formula: see text]M[Formula: see text], are the link between stellar-mass BHs and supermassive BHs (SMBHs). They are thought to be the seeds from which SMBHs grow, which would explain the existence of quasars with BH masses of up to 10[Formula: see text][Formula: see text]M[Formula: see text] when the Universe was only 0.8 Gyr old. The detection and study of IMBHs has thus strong implications for understanding how SMBHs form and grow, which is ultimately linked to galaxy formation and growth, as well as for studies of the universality of BH accretion or the epoch of reionization. Proving the existence of seed BHs in the early Universe is not yet feasible with the current instrumentation; however, those seeds that did not grow into SMBHs can be found as IMBHs in the nearby Universe. In this review, I summarize the different scenarios proposed for the formation of IMBHs and gather all the observational evidence for the few hundreds of nearby IMBH candidates found in dwarf galaxies, globular clusters, and ultraluminous X-ray sources, as well as the possible discovery of a few seed BHs at high redshift. I discuss some of their properties, such as X-ray weakness and location in the BH mass scaling relations, and the possibility to discover IMBHs through high velocity clouds, tidal disruption events, gravitational waves, or accretion disks in active galactic nuclei. I finalize with the prospects for the detection of IMBHs with up-coming observatories.

scholarly journals Post-noon two-minute period pulsating aurora and their relationship to the dayside convection pattern

1999 ◽  
Vol 17 (7) ◽  
pp. 877-891 ◽  
Author(s):  
S. E. Milan ◽  
T. K. Yeoman ◽  
M. Lester ◽  
J. Moen ◽  
P. E. Sandholt
Keyword(s):  
Current System ◽  
Wave Activity ◽  
Mhd Waves ◽  
Magnetohydrodynamic Wave ◽  
Auroral Emission ◽  
Minute Period ◽  
Optical Signature ◽  
Short Period ◽  
Auroral Emissions ◽  
Auroral Phenomena

Abstract. Poleward-moving auroral forms, as observed by meridian-scanning photometers, in the vicinity of the cusp region are generally assumed to be the optical signature of flux transfer events. Another class of quasi-continuous, short period (1-2 min) wave-like auroral emission has been identified, closely co-located with the convection reversal boundary in the post-noon sector, which is similar in appearance to such cusp aurora. It is suggested that these short period wave-like auroral emissions, the optical signature of boundary plasma sheet precipitation in the region 1 field-aligned current system, are associated with ULF magnetohydrodynamic wave activity, which is observed simultaneously by ground magnetometer stations. This association with ULF wave activity is strengthened by the observation of several harmonic frequencies in the pulsation spectrum, each an overtone of the fundamental standing wave resonance frequency.Key words. Magnetospheric physics (auroral phenomena; magnetopause · cusp · and boundary layers; MHD waves and instabilities)

scholarly journals Observational Evidence for the Origin of X-ray Sources in Globular Clusters

2007 ◽  
Vol 3 (S246) ◽  
pp. 301-310 ◽  
Author(s):  
Frank Verbunt ◽  
Dave Pooley ◽  
Cees Bassa
Keyword(s):  
Statistical Method ◽  
Globular Clusters ◽  
Cataclysmic Variables ◽  
Observational Evidence ◽  
X Ray ◽  
Cluster Mass ◽  
Low Mass ◽  
Optical Identifications ◽  
X Ray Binaries

AbstractLow-mass X-ray binaries, recycled pulsars, cataclysmic variables and magnetically active binaries are observed as X-ray sources in globular clusters. We discuss the classification of these systems, and find that some presumed active binaries are brighter than expected. We discuss a new statistical method to determine from observations how the formation of X-ray sources depends on the number of stellar encounters and/or on the cluster mass. We show that cluster mass is not a proxy for the encounter number, and that optical identifications are essential in proving the presence of primordial binaries among the low-luminosity X-ray sources.

scholarly journals Observational evidence for stellar-mass black holes

2006 ◽  
Vol 2 (S238) ◽  
pp. 3-12 ◽  
Author(s):  
Jorge Casares
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Mass Spectrum ◽  
Radial Velocity ◽  
Stellar Mass ◽  
Observational Evidence ◽  
X Ray ◽  
History Of ◽  
X Ray Binaries ◽  
Dynamical Masses

AbstractRadial velocity studies of X-ray binaries provide the most solid evidence for the existence of stellar-mass black holes. We currently have 20 confirmed cases, with dynamical masses in excess of 3 M⊙. Accurate masses have been obtained for a subset of systems which gives us a hint at the mass spectrum of the black hole population. This review summarizes the history of black hole discoveries and presents the latest results in the field.

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