Plasma diagnostics of a Plasma diagnostics of a giant stellar flare giant stellar flare

Carolin Liefke1

Birgit Fuhrmeister1

Ansgar Reiners1,2

Jürgen H.M.M. Schmitt1

1 Hamburger Sternwarte, 2 Georg-August Universität Göttingen

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OutlineOutline

• The active M dwarf CN Leo• XMM-Newton observations of a giant flare• EPIC spectra

– Evolution of flare plasma temperature and emission measure

– Loop modelling– Development of iron abundance in the course of the flare

• RGS spectra– Densities from the O VII triplet– Neon triplet and abundance

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The active M dwarf CN LeoThe active M dwarf CN Leo• Close-by mid-M dwarf (Teff = 2800 K, spectral type

M5.5), well-known flare star

• Shows persistent optical coronal Fe XIII line emission (Schmitt & Wichmann, 2001; Fuhrmeister & Schmitt 2003)

• Measured photospheric magnetic fields: Bf~2.2kG, with variations of ≈ 100 G observed (Reiners, Schmitt & Liefke, 2007)

• Six observations with XMM-Newton, simultaneous optical high-resolution spectroscopy with VLT/UVES

• Shows distinct periods of quiescence (at comparably low levels) and flaring in X-rays (Fuhrmeister, Liefke & Schmitt, 2007)

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• Flux increases by factors up to 500 in the optical and up to 100 in X-rays

The giant flareThe giant flare

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EPIC spectraEPIC spectra

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Temperature and Temperature and emission measure modellingemission measure modelling

• Time-resolved spectral fitting with a two-temperature component model of collisionally-ionized diffuse plasma (vapec)

Development of flare temperature (emission measure weighted average of the two components) and total emission measure of the flare plasma

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Loop lengthLoop lengthL = 1.7 · 109 cm according to the method of Reale et al. 1997

TMax = 5.6 · 107 K

= 0.70

= 237 s

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Fe abundanceFe abundance

• Quiescent iron abundance: 0.59 ± 0.07 (relative to Anders & Grevesse, 1989)

• Evaporated material shows strong enhancement of iron

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RGS spectraRGS spectraRGS 1 RGS 2

Flare

Quiescence

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Density variationsDensity variations

log ne ≈ 10, but consistent with low-density limit

log ne > 12

O VII triplet during quiescence and flare

fi=2 .88±1 .53

0.150.08 0.08

=i

f

20.8 ks 1.4 ks

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NeonNeon

• Neon triplet also consistent with density increase, but iron contamination prevents unambiguous conclusions

• Neon lines are weak in general, neon abundance is low: ANe/AO = 0.24 ± 0.03 (Sun: ANe/AO = 0.15, active stars: ANe/AO ≈ 0.42)

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ConclusionsConclusions• A giant flare with a flux increase of a factor of 100 has

been observed with XMM-Newton on the active M dwarf CN Leo

• Time-resolved X-ray spectroscopy with the EPIC instruments allows to investigate the development of temperature and emission measure of the flare plasma

• Loop length of 1.7 · 109 cm

• The iron abundance of the flare plasma is enhanced by a factor > 2

• In O VII, the density of the flare plasma is increased by a factor of > 100

• The neon abundance of CN Leo is comparably low in general