Search results for "Superflare"
showing 9 items of 9 documents
The Mouse That Roared: A Superflare from the dMe Flare Star EV Lac Detected by Swift and Konus-Wind
2010
We report on a large stellar flare from the nearby dMe flare star EV Lac observed by the Swift and Konus-Wind satellites and the Liverpool Telescope. It is the first large stellar flare from a dMe flare star to result in a Swift trigger based on its hard X-ray intensity. Its peak f_X from 0.3--100 keV of 5.3x10^-8 erg/cm2/s is nearly 7000 times larger than the star's quiescent coronal flux, and the change in magnitude in the white filter is >4.7. This flare also caused a transient increase in EV Lac's bolometric luminosity (L_bol) during the early stages of the flare, with a peak estimated L_X/L_bol ~3.1. We apply flare loop hydrodynamic modeling to the plasma parameter temporal changes …
Viewing the Sun as an X-ray star
2003
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 Sun as an X-ray star. Our program aims to explore how far the solar model can be applied to other stars. In this paper we review the results obtained from these studies and, in particular, we discuss the variability of a star identical to the Sun during its cycle, the contribution of different coronal …
Simultaneous Kepler/K2 and XMM‐Newton observations of superflares in the Pleiades
2019
Proceeding of a contributed talk given at the meeting: "TIME-DOMAIN ASTRONOMY: A HIGH ENERGY VIEW" held at ESAC, Madrid, 13 - 15 JUNE 2018 Together with coronal mass ejection, flares are the most energetic stellar magnetic events, ignited by a sudden release of magnetic energy, which triggers a cascade of interconnected phenomena, each resulting in emission in different bands. For this reason, flares are intrinsic multiwavelength phenomena. In particular, optical and soft X-ray emission probes two different events occurring during flares: the heating of plasma in the upper photosphere at the footpoints of the magnetic loops and the heating and cooling of the plasma confined in the loops in …
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 …
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…
High-resolution spectroscopy of two carbon stars with long-term obscuration events
2012
In this paper, we provide an analysis of the high-resolution optical spectra of two carbon variables, V1983 Cyg and V2074 Cyg, which are presumed to be cool R Corona Borealis (RCB) stars, according to their photometric behaviour. The stars show irregular long-term visual light variations of relatively large amplitude, similar to those exhibited by RCB variables. Based on the comparison of our high-resolution spectra with those of various carbon stars, we conclude that both variables have spectral properties typical for cool N-type carbon stars. However, two major differences from the spectra of normal carbon stars have been noted: the presence of high-velocity (∼−60 km s−1) components in th…
X-ray variability of Pleiades late-type stars as observed with the ROSAT-PSPC
2003
We present a comprehensive analysis of X-ray variability of the late-type (dF7-dM) Pleiades stars, detected in all ROSAT-PSPC observations; X-ray variations on short (hours) and medium (months) time scales have been explored. We have grouped the stars in two samples: 89 observations of 42 distinct dF7-dK2 stars and 108 observations of 61 dK3-dM stars. The Kolmogorov-Smirnov test applied on all X-ray photon time series show that the percentage of cases of significant vari- ability is quite similar on both samples, suggesting that the presence of variability does not depend on mass for the time scales and mass range explored. The comparison between the Time X-ray Amplitude Distribution functi…
Discussion – Periodic variations and asteroseismology of active OB stars
2010
AbstractWe summarize the discussion held after the session on periodic variations and asteroseismology. The session not only included seven talks, but as well thirty excellent posters were shown. It was impossible to summarize all these in the available frame of a discussion, and so this work focuses on very few sub-topics only mentioned in the actual discussion session. These topics were the relation of pulsation and turbulence, pulsation in close binaries, the observed photometric variability, the connection of pulsations and outburst, and bipolar flows.
Simultaneous Kepler/K2 and XMM-Newton observations of superflares in the Pleiades
2019
Flares are powerful events ignited by a sudden release of magnetic energy. With the aim of studying flares in the 125-Myr-old stars in the Pleiades observed simultaneously in optical and X-ray light, we obtained new XMM-Newton observations of this cluster during the observations of Kepler K2 Campaign 4. Our objective is to characterize the most powerful flares observed in both bands and to constrain the energy released in the optical and X-ray, the geometry of the loops, and their time evolution. We aim to compare our results to existing studies of flares occurring in the Sun and stars at different ages. We selected bright X-ray/optical flares occurred in 12 known members of the Pleiades fr…