247 research outputs found
Final data reduction and analysis of the AS and E OSO-4 grazing incidence X-ray telescope experiment
Final data analysis of grazing incidence of solar X ray telescope experiment of OSO- 4 satellit
Continuing data analysis of the AS/E grazing incidence X-ray telescope experiment on the OSO-4 satellite
The work to correct and extend the calculation of the theoretical solar X-ray spectrum produced during earlier OSO-4 data analysis is reported along with the work to formulate models of active regions, and compare these models with the experimental values. An atlas of solar X-ray photographs is included, and solar X-ray observations are correlated with the solar wind
A Contemporary View of Coronal Heating
Determining the heating mechanism (or mechanisms) that causes the outer
atmosphere of the Sun, and many other stars, to reach temperatures orders of
magnitude higher than their surface temperatures has long been a key problem.
For decades the problem has been known as the coronal heating problem, but it
is now clear that `coronal heating' cannot be treated or explained in isolation
and that the heating of the whole solar atmosphere must be studied as a highly
coupled system. The magnetic field of the star is known to play a key role,
but, despite significant advancements in solar telescopes, computing power and
much greater understanding of theoretical mechanisms, the question of which
mechanism or mechanisms are the dominant supplier of energy to the chromosphere
and corona is still open. Following substantial recent progress, we consider
the most likely contenders and discuss the key factors that have made, and
still make, determining the actual (coronal) heating mechanism (or mechanisms)
so difficult
Le Service Européen pour l’action Extérieure á l’heure de son épreuve : Une contribution tenforcée de l’UE au maintien de la paix ?
Cet article a pour objet de s’intéresser à l’impact que la mise en place d’un nouvel
organe comme le Service Européen pour l’Action Extérieure, extrêmement original et innovateur
du point de vue institutionnel, pourrait avoir à court et moyen terme sur la capacité de l’UE pour
décoller défnitivement en tant qu’acteur majeur et partenaire vraiment crédible dans le domaine du
maintien de la paix. Le moment semble opportun pour le faire dans la mesure où, après quelques
quatre ans d’existence et une fois surmontés un certain nombre de teething problems, un processus
de réflexion sur les faiblesses et potentialités du SEAE est en cours au sein du système institutionnel
de l’UE en vue d’une éventuelle révision de sa Décision de base.En este trabajo se propone un análisis del impacto que la creación y puesta en
funcionamiento de un nuevo órgano tan original e innovador desde el punto de vista institucional
como el Servicio Europeo de Acción Exterior podrÃa ejercer, a corto y medio plazo, sobre la
capacidad de la UE para afanzarse como actor realmente signifcativo y socio internacional creÃble
en el campo del mantenimiento de la paz. El momento parece oportuno para ello en la medida en
que, tras cuatro años de existencia y una vez superado un buen número de difcultades iniciales, se
ha abierto un proceso de reflexión sobre las defciencias y potencialidades del SEAE que podrÃa
conducir a una revisión de su Decisión fundacional.This paper aims to analyse the impact that the setup and functioning of a new body, as
original and innovative from an institutional point of view as the European External Action Service,
could have in the consolidation of the EU’s position as a signifcant and reliable international
partner in peacekeeping, both in the short and medium terms. This timing appears appropriate to
do so insofar as, after four years of existence and having overcome a signifcant number of teething
problems, a reflection process on the weaknesses and potentialities of the EEAS is currently in place
and could eventually lead to a review of its founding Decision
High resolution studies of the solar X-ray corona from Aerobee rockets
The research in high resolution solar X-ray astronomy is reported. The payload for the Aerobee 150 launch vehicle, which included a 23 cm diameter mirror whose polished surface was a nickel-phosphorus alloy is discussed along with the high resolution measurements, by Flight 13.028 CS, of the temperature and density structure of the lower corona. Flight 13.029 CS is also discussed
High Energy Properties of X-ray Sources observed with BeppoSAX
We report on highlight results on celestial sources observed in the high
energy band (>20 keV) with BeppoSAX. In particular we review the spectral
properties of sources that belong to different classes of objects, i.e. stellar
coronae (Algol), supernova remnants (Cas A), low mass X-ray binaries (Cygnus
X-2 and the X-ray burster GS1826-238), black hole candidates (Cygnus X-1) and
Active Galactic Nuclei (Mkn 3). We detect, for the first time, the broad-band
spectrum of a stellar corona up to 100 keV; for Cas A we report upper limits to
the ^44Ti line intensities that are lower than those available to date; for Cyg
X-2 we report the evidence of a high energy component; we report a clear
detection of a broad Fe K line feature from Cygnus X-1 in soft state and during
its transition to hard state; Mkn 3 is one of several Seyfert 2 galaxies
detected with BeppoSAX at high energies, for which Compton scattering process
is important.Comment: To appear in the Proceedings of the 1997 Conference on 'The Active
X-ray Sky: Results from BeppoSAX and Rossi-XTE' eds. L. Scarsi, F. Fiore and
P. Giomm
Intensity oscillations in coronal XBPs from Hinode/XRT observations
Our aim is to investigate the intensity oscillations in coronal X-ray Bright
Points (XBPs). We analysed a 7-hours long time sequence of the soft X-ray
images obtained on April 14, 2007 with 2-min cadence using X-Ray Telescope
(XRT) on-board the Hinode mission. We use SSW in IDL to derive the time series
of 14 XBPs and 2 background regions. For the first time, we have tried to use
power spectrum analysis on XBPs data to determine the periods of intensity
oscillations. coronal X-ray Bright Points (XBPs). The power spectra of XBPs
show several significant peaks at different frequencies corresponding to a wide
variety of time scales which range from a few minutes to hours. The light
curves of all the XBPs give the impression that the XBPs can be grouped into
three classes depending on emission levels: (i) weak XBPs; (ii) bright XBPs;
and (iii) very strong XBPs. The periods of intensity oscillation are consistent
in all the XBPs and are independent of their brightness level, suggesting that
the heating mechanisms in all the three groups of XBPs are similar. The
different classes of XBPs may be related to the different strengths of the
magnetic field with which they have been associated.Comment: 7 pages, 3 figure
Solar-type dynamo behaviour in fully convective stars without a tachocline
In solar-type stars (with radiative cores and convective envelopes), the
magnetic field powers star spots, flares and other solar phenomena, as well as
chromospheric and coronal emission at ultraviolet to X-ray wavelengths. The
dynamo responsible for generating the field depends on the shearing of internal
magnetic fields by differential rotation. The shearing has long been thought to
take place in a boundary layer known as the tachocline between the radiative
core and the convective envelope. Fully convective stars do not have a
tachocline and their dynamo mechanism is expected to be very different,
although its exact form and physical dependencies are not known. Here we report
observations of four fully convective stars whose X-ray emission correlates
with their rotation periods in the same way as in Sun-like stars. As the X-ray
activity - rotation relationship is a well-established proxy for the behaviour
of the magnetic dynamo, these results imply that fully convective stars also
operate a solar-type dynamo. The lack of a tachocline in fully convective stars
therefore suggests that this is not a critical ingredient in the solar dynamo
and supports models in which the dynamo originates throughout the convection
zone.Comment: 6 pages, 1 figure. Accepted for publication in Nature (28 July 2016).
Author's version, including Method
Coronal Temperature Diagnostic Capability of the Hinode/X-Ray Telescope Based on Self-Consistent Calibration
The X-Ray Telescope (XRT) onboard the Hinode satellite is an X-ray imager
that observes the solar corona with unprecedentedly high angular resolution
(consistent with its 1" pixel size). XRT has nine X-ray analysis filters with
different temperature responses. One of the most significant scientific
features of this telescope is its capability of diagnosing coronal temperatures
from less than 1 MK to more than 10 MK, which has never been accomplished
before. To make full use of this capability, accurate calibration of the
coronal temperature response of XRT is indispensable and is presented in this
article. The effect of on-orbit contamination is also taken into account in the
calibration. On the basis of our calibration results, we review the
coronal-temperature-diagnostic capability of XRT
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