The evolution of an X2.7 solar flare, that occurred in a complex βγδ magnetic configuration region on 2003 November 3, is discussed utilizing a multiwavelength data set. The Hα images taken from the solar tower telescope at ARIES, Nainital, reveal well-defined footpoint (FP) and loop-top (LT) sources. As the flare evolves, the LT source moves upward and the separation between the two FP sources...

Abstract In coronal loop modeling, it is commonly assumed that the loops are semicircular with a uniform cross-sectional area. However, observed rarely semicircular, and extrapolations of magnetic field show strength decreases height, implying area expands height. We examine these two assumptions directly, to understand how they affect hydrodynamic radiative response short, hot strong, impulsiv...

A solar flare was observed on 1997 April 7 with the Soft X-ray Telescope (SXT) on Yohkoh. The flare was associated with a “halo” coronal mass ejection (CME). The flaring region showed areas of reduced soft X-ray (SXR) brightness—“dimmings”—that developed prior to the CME observed in white light and persisted for several hours following the CME. The most prominent dimming regions were located ne...

Direct comparison of high-resolution X-ray spectra of the active dMe star AD Leo, observed three times with Chandra, shows variability of key density-sensitive lines, possibly due to flaring activity. In particular, a significant long-duration enhancement of the coronal density is indicated by the Ne IX and Si XIII He-like triplets, and possibly also by density-sensitive Fe XXI line ratios. Sub...

The " current wisdom " regarding the structuring of the X-ray emitting corona in active stars (i.e. a corona dominated by extended coronal structures) is briefly reviewed, followed by a review of a new approach to flare analysis and the analysis of a significant number of newly observed and previously published large flares, all leading to a much more compactly structured corona. Recent observa...

Long period longitudinal oscillations of a flaring coronal loop are studied numerically. In the recent work of Nakariakov et al. (2004) it has been shown that the time dependence of density and velocity in a flaring loop contain pronounced quasi-harmonic oscillations associated with the 2nd harmonic of a standing slow magnetoacoustic wave. In this work we investigate the physical nature of thes...

The Sun is the late-type star we can study with the highest level of detail. In the interpretation of stellar data, therefore, it is often assumed that the physical processes of the coronae of late-type stars are similar to those of the solar corona, i.e. the “solar-stellar analogy”. In order to investigate the validity of this assumption, we have started a program to study systematically the S...

Aims. To understand the contribution of active region and flare plasmas to the λ195 channels of SOHO/EIT (Extreme-ultraviolet Imaging Telescope) and TRACE (Transition Region and Coronal Explorer). Methods. We have analysed an M8 flare simultaneously observed by the Coronal Diagnostic Spectrometer (CDS), EIT, TRACE and RHESSI. We obtained synthetic spectra for the flaring region and an outer reg...

Evolution of a coronal loop in response to an impulsive energy release is numerically modelled. It is shown that the loop density evolution curves exhibit quasi-periodic perturbations with the periods given approximately by the ratio of the loop length to the average sound speed, associated with the second standing harmonics of an acoustic wave. The density perturbations have a maximum near the...