plasma diagnostics of a giant stellar flare carolin liefke 1 birgit fuhrmeister 1 ansgar reiners 1,2...
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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