We present a final summary of all ROSAT X-ray observations nearby stars. All available with the PSPC, HRI and WFC have been matched CNS4 catalog stars results gathered in Nearby XUV-emitting Stars data base, via www from Home Page Hamburger Sternwarte at URL http://www.hs.uni-hamburg.de/DE/For/Gal/Xgroup/nexxus. New volume-limited samples F/G-stars ( pc), K-stars M-stars pc) are constructed within which detection rates more than 90% obtained; only one star (GJ 1002) remains undetected...

We systematically study the X-ray and ultraviolet emission of a subsample M dwarfs from recent proper-motion survey, selecting all within 10pc to obtain nearly volume-limited sample (~90% completeness). Archival ROSAT, XMM-Newton GALEX data are combined with published spectroscopic studies Halpha rotation broad picture stellar activity on dwarfs. make use synthetic model spectra determine relative contributions photospheric chromospheric flux. also analyse same diagnostics for comparison...

We present Chandra HETGS observations of the classical T Tauri star (CTTS) V4046 Sgr. The He-like triplets , and are clearly detected. Similar to CTTS TW Hya BP Tau, forbidden lines weak compared intercombination line, indicating high plasma densities in X-ray emitting regions. triplet, however, is within low-density limit, agreement with predictions accretion funnel infall model an additional stellar corona. Sgr first close binary exhibiting these features. Together previous high-resolution...

Classical T Tauri stars (CTTS) are surrounded by actively accreting disks. According to current models material falls along the magnetic field lines from disk with more or less free-fall velocity onto star, where plasma heats up and generates X-rays. We want quantitatively explain observed high energy emission measure infall parameters data. Absolute flux measurements allow calculate filling factor mass accretion rate.We use a numerical model of hot spot solve conservation equations. A...

Aims. Flares on dM stars contain plasmas at very different temperatures and thus affect a wide wavelength range in the electromagnetic spectrum. While coronal properties of flares are studied best X-rays, chromosphere star is observed optical ultraviolet ranges. Therefore, multiwavelength observations essential to study flare throughout atmosphere star.

Aims. We report simultaneous observations of the nearby flare star Proxima Centauri with VLT/UVES and XMM-Newton over three nights in March 2009. Our optical X-ray cover star’s quiescent state, as well its flaring activity allow us to probe stellar atmospheric conditions from photosphere into chromosphere, then corona during different stages.

Cool stars are known to produce flares probably as a result of the magnetic reconnection in their outer atmospheres. We present simultaneous XMM-Newton optical V band and X-ray observations M8 dwarf LP 412-31. During observation giant flare occurred, with an amplitude 6 mag total energy erg both soft X-rays. Both onset decay were completely covered wavebands temporal resolution 20 s, allowing determination time scales, well study temperature evolution flaring plasma. The data consistent...

We report the results of a 68 ks long X-ray observation M9V ultracool dwarf star LHS 2065 with ROSAT high resolution imager (HRI). During observations major flare occurred peak luminosity erg/s and total soft energy release erg. In addition, another smaller occurred. The were carried out half year apart. first no significant emission from could be detected, while in second addition to flares also quiescent at level was seen. belongs coolest hydrogen burning stars known. show that coronal may...

Context. The activity indicators of M dwarfs are distinctly different for early and late types. coronae display high X-ray luminosities temperatures, a pronounced inverse FIP effect, frequent flaring to the extent that no quiescent level can be defined in many cases. For dwarfs, fewer but more violent flares have been observed, luminosity is much lower.

We present simultaneous high-temporal and high-spectral resolution observations of the nearby flare star CN Leo at optical soft X-ray wavelengths. During our observing campaign a major occurred, raising star's instantaneous energy output by almost three orders magnitude. The shows often observed impulsive behavior, with rapid rise slow decay in broad maximum about 200 seconds after peak. In addition to this usually encountered phenomenology we find, however, an extremely short ( s) peak,...

Aims.We present simultaneous observations with VLT/UVES and XMM-Newton of the active M5.5 dwarf CN Leo (Gl 406). The data were gathered during three half nights in May 2004 December 2005, they cover quiescent states, as well flaring activity. Our main aim is to derive coronal properties from X-ray compare these results optical line.

<i>Context. <i/>Stellar flares affect all atmospheric layers from the photosphere over chromosphere and transition region up into corona. Simultaneous observations in different spectral bands allow to obtain a comprehensive picture of environmental conditions physical processes going on during phases flare.<i>Aims. <i/>We investigate properties coronal plasma giant flare active M dwarf CN Leo observed simultaneously with UVES spectrograph at VLT <i>XMM-Newton<i/>.<i>Methods. <i/>From X-ray...

Recent improvements in the modeling of solar convection and line formation led to downward revisions photospheric abundances lighter elements, which turn changes radiative opacity interior hence conflicts with zone depth as inferred from helioseismic oscillation frequencies. An increase Ne/O abundance values observed for nearby stars has been proposed a solution. Because absence strong neon lines optical, are difficult measure correct stellar currently hotly debated. Based on X-ray spectra...

We present UVES/VLT observations of the nearby flare star CN Leo covering Wing-Ford FeH band near 1 μm with high spectral resolution. Some absorption lines in this are magnetically sensitive and allow a measurement mean magnetic flux on Leo. Our observations, three nights separated by 48 hours each, clear detection field Bf ≈ 2.2 kG. The differential measurements show night-to-night variability extremely significance. Finally, our data strongly suggest time scales as low 6 line chromospheric...

We investigate the frequency and amplitude distribution of flares on actice M dwarf CN Leo observed simultaneously in coronal X‐rays, chromospheric line emission, photospheric optical continuum. find that most larger events are visible all atmospheric layers, these equivalent to solar white light flares. Several smaller only lines, which corresponds H‐alpha One event is very strong but weak lines invisible continuum, indicating a rather large scale height flaring loop. no obvious correlation...