Multiwavelength observations of a giant flare on CN Leonis

Abstract

Context. Stellar flares affect all atmospheric layers from the photosphere over chromosphere and transition region up into the corona. Simultaneous observations in different spectral bands allow to obtain a comprehensive picture of the environmental conditions and the physical processes going on during different phases of the flare. Aims. We investigate the properties of the coronal plasma during a giant flare on the active M dwarf CN Leo observed simultaneously with the UVES spectrograph at the VLT and XMM-Newton. Methods. From the X-ray data, we analyze the temporal evolution of the coronal temperature and emission measure, and investigate variations in electron density and coronal abundances during the flare. Optical Fe xiii line emission traces the cooler quiescent corona.Results. Although of rather short duration (exponential decay time τ LC < 5 min), the X-ray flux at flare peak exceeds the quiescent level by a factor of ≈100. The electron density averaged over the whole flare is greater than 5 × 10 11 cm −3 . The flare plasma shows an enhancement of iron by a factor of ≈2 during the rise and peak phase of the flare. We derive a size of <9000 km for the flaring structure from the evolution of the the emitting plasma during flare rise, peak, and decay. Conclusions. The characteristics of the flare plasma suggest that the flare originates from a compact arcade instead of a single loop. The combined results from X-ray and optical data further confine the plasma properties and the geometry of the flaring structure in different atmospheric layers.

Multi-wavelength observations of a giant flare on CN Leonis

“…In this study of smaller flares, a tentative density increase has been measured, though the obtained density values are in agreement with the quiescent ones when accounting for the errors. For the present giant flare multi-wavelength data with XMM-Newton have also been obtained, and we determined coronal densities of at least 10 12 cm −3 (Liefke et al 2010). Therefore, the giant flare leads to very high electron densities in both the corona and the chromosphere.…”

“…An overview of the observed optical spectra can be found in Fuhrmeister et al (2008), including an emission line list. The X-ray data are presented in Liefke et al (2010). Here we use the optical high-resolution UVES spectra for comparison to a grid of flaring chromosphere models computed with the stellar atmosphere code PHOENIX.…”

A study of X-ray flares - II. RS CVn-type binaries

“…Using the RGS data of flares F2 from σ Gem, Nordon & Beher (2008) show that abundances enriched during the flare. A change of the metal abundance during a strong flare was detected for the RS CVn‐like stars II Peg (Mewe et al 1997), UX Ari (Güdel et al 1999) and σ 2 Crb (Osten et al 2003), Algol (Ottmann & Schmitt 1996; Favata & Schimtt 1999), dwarf stars EV Lac (Favata et al 1998, 2000a), CN Leo (Liefke, Fuhrmeister & Schmitt 2010) and AB Dor (Güdel et al 2001) and pre‐main‐sequence star V773 Tau (Tsuboi et al 1998). In these cases abundances vary with an initial rise from a quiescent state value of Z ≈ 0.3 Z ⊙ to Z = 1 Z ⊙ , and a subsequent decay to the pre‐flare value.…”

STELLAR CORONAE, SOLAR FLARES: A DETAILED COMPARISON OF Σ GEM, HR 1099, AND THE SUN IN HIGH-RESOLUTION X-Rays

“…Nordon & Behar (2008) found no strong or consistent correlation of abundance changes during stellar flares. From low-resolution, few-temperature-component models, Liefke, Fuhrmeister & Schmitt (2010) found a factor of three increase in Fe abundance over the quiescent value during a large flare on CN Leo; they could detect no effect in other elements. Wood & Linsky (2010) and Wood, Laming & Karovska (2012) examined the FIP effect in M-dwarfs and found that both high and low activity stars can have an inverse FIP effect.…”