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 podría ejercer, a corto y medio plazo, sobre la capacidad de la UE para afanzarse como actor realmente signifcativo y socio internacional creíble 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 podría 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

The VAST Survey - I. Companions and the unexpected X-ray detection of B6-A7 stars

With an adaptive optics imaging survey of 148 B6-A7 stars, we have tested the hypothesis that unresolved lower-mass companions are the source of the unexpected X-ray detections of stars in this spectral type range. The sample is composed of 63 stars detected in X-rays within the ROSAT All-Sky Survey and 85 stars that form a control sample; both subsets have the same restricted distribution of spectral type, age, X-ray sensitivity and separation coverage. A total of 68 companion candidates are resolved with separations ranging from 0.3" to 26.2", with 23 new detections. The multiple star frequency of the X-ray sample based on companions resolved within the ROSAT error ellipse is found to be 43 (+6,-6)%. The corresponding control sample multiple star frequency is three times lower at 12 (+4,-3)% -- a difference of 31\pm7%. These results are presented in the first of a series of papers based on our Volume-limited A-Star (VAST) survey -- a comprehensive study of the multiplicity of A-type stars.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Societ