Search results for "Flare"

X-ray flares on the UV Ceti-type star CC Eridani: a "peculiar" time-evolution of spectral parameters

2007

Context: Weak flares are supposed to be an important heating agent of the outer layers of stellar atmospheres. However, due to instrumental limitations, only large X-ray flares have been studied in detail until now. Aims: We used an XMM-Newton observation of the very active BY-Dra type binary star CC Eri in order to investigate the properties of two flares that are weaker than those typically studied in the literature. Methods: We performed time-resolved spectroscopy of the data taken with the EPIC-PN CCD camera. A multi-temperature model was used to fit the spectra. We inferred the size of the flaring loops using the density-temperature diagram. The loop scaling laws were applied for deriv…

Coronal loop hydrodynamics. The solar flare observedon November 12 1980 revisited: the UV line emission

2001

We revisit a well-studied solar flare whose X-ray emission originating from a simple loop structure was observed by most of the instruments on board SMM on November 12 1980. The X-ray emission of this flare, as observed with the XRP, was successfully modeled previously. Here we include a detailed modeling of the transition region and we compare the hydrodynamic results with the UVSP observations in two EUV lines, measured in areas smaller than the XRP rasters, covering only some portions of the flaring loop (the top and the foot-points). The single loop hydrodynamic model, which fits well the evolution of coronal lines (those observed with the XRP and the \FeXXI 1354.1 \AA line observed wit…

2015

Advanced Astronomy for Heliophysics Plus (ADAHELI+) is a project concept for a small solar and space weather mission with a budget compatible with an European Space Agency (ESA) S-class mission, including launch, and a fast development cycle. ADAHELI+ was submitted to the European Space Agency by a European-wide consortium of solar physics research institutes in response to the "Call for a small mission opportunity for a launch in 2017," of March 9, 2012. The ADAHELI+ project builds on the heritage of the former ADAHELI mission, which had successfully completed its phase-A study under the Italian Space Agency 2007 Small Mission Programme, thus proving the soundness and feasibility of its in…

The Sun as a benchmark of flaring activity in stellar coronae

2009

The solar corona is a template to study and understand stellar activity. However the solar corona differs from that of active stars: the Sun has lower X‐ray luminosity, and on average cooler plasma temperatures. Active stellar coronae have a hot peak in their emission measure distribution, EM (T), at 8–20 MK, while the non‐flaring solar corona has a peak at 1–2 MK. In the solar corona significant amounts of plasma at temperature ∼10 MK are observed only during flares.To investigate what is the time‐averaged effect of solar flares we measure the disk‐integrated time‐averaged emission measure, EMF (T), of an unbiased sample of solar flares. To this aim we analyze uninterrupted GOES/XRS light …

X-ray Flares in Orion Low Mass Stars

2007

Context. X-ray flares are common phenomena in pre-main sequence stars. Their analysis gives insights into the physics at work in young stellar coronae. The Orion Nebula Cluster offers a unique opportunity to study large samples of young low mass stars. This work is part of the Chandra Orion Ultradeep project (COUP), an ~10 day long X-ray observation of the Orion Nebula Cluster (ONC). Aims. Our main goal is to statistically characterize the flare-like variability of 165 low mass (0.1-0.3 M_sun) ONC members in order to test and constrain the physical scenario in which flares explain all the observed emission. Methods. We adopt a maximum likelihood piece-wise representation of the observed X-r…

A comparison between the X-ray variable Sun and solar-like main sequence stars

2003

We analyze the time variations of the solar X-ray luminosity observed with Yohkoh/SXT with the aim to compare the X-ray variability of the Sun with that of the other solar-like main sequence stars as function of the relevant time scales. Since the observational set-up and strategies used to observe the Sun dier from those used for the other stars, we have explored the solar X-ray variability properties starting from the available solar data, trying to reproduce the observational procedures adopted for the stars. We have quantified how the solar variability amplitude increases with the explored time scales and found that solar-cycle variability can contribute at most up to 60% to the spread …

BeppoSAX observation of a large long-duration X-ray flare from UX Arietis

2001

We present two X-ray observations of the RS CVn binary system UX Arietis performed with BeppoSAX in August 1997 and August 1998. A large flare lasting for about 1 day was detected during the rst observation, while the star was quiescent during the second one. Hard X-ray emission up to50 keV was detected in the PDS instrument during the rise and at the peak of the flare. Time-resolved spectroscopy of the flare with the LECS and MECS detectors shows that temperatures as high as 100 MK were reached at the flare peak; such high temperatures are responsible for the high-energy tail seen in the PDS. We conrm that the coronal abundance of UX Ari is strongly subsolar (Z=Z' 0:2 0:3); no signicant va…

On X-ray variability in ROSAT-PSPC observations of F7-K2 stars

2002

We have analyzed the X-ray variability of dF7-dK2 stars in the solar neighborhood detected with the pointed ROSAT-PSPC observations. Our data base is the sample of all stars listed in the CNS3 catalog (Gliese & Jahrei β 1991) having a $B-V$ color between 0.5 and 0.9; it includes 70 pointed observations of 40 distinct stars or multiple systems. We have applied the unbinned Kolmogorov-Smirnov test on all X-ray photon time series of our sample: only 10 observations relative to 8 distinct stars are variable at a confidence level greater than 99% and 4 of them belong to multiple systems. For the subsample of 9 stars observed both at the beginning and at the end of the mission, we can study the v…

Modeling the long duration rise phase of a flare detected on the M star TWA 11 B

2009

We present preliminary results from the analysis of a long duration flare that was observed in a serendipitous XMM-Newton detection of the M star CD-39 7717 B (TWA 11 B), member of the young stellar association TW Hya. Only the rise phase (with a duration of ~35 ks) and possibly the flare peak are present in the light-curve. The decay phase was not monitored. The fluorescent iron emission line at 6.4 keV was observed during this event. As far as we are concerned, since TWA 11 B seems to have no disk, this is only the third detection of Fe photospheric fluorescence. During the flare, the X-ray flux increased a factor of ~4. Taking the light curve and the evolution of the hardness ratio into …

Nonequilibrium of Ionization and the Detection of Hot Plasma in Nanoflare‐heated Coronal Loops

2008

Impulsive nanoflares are expected to transiently heat the plasma confined in coronal loops to temperatures of the order of 10 MK. Such hot plasma is hardly detected in quiet and active regions, outside flares. During rapid and short heat pulses in rarified loops the plasma can be highly out of equilibrium of ionization. Here we investigate the effects of the non-equilibrium of ionization (NEI) on the detection of hot plasma in coronal loops. Time-dependent loop hydrodynamic simulations are specifically devoted to this task, including saturated thermal conduction, and coupled to the detailed solution of the equations of ionization rate for several abundant elements. In our simulations, initi…