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The Big Questions Stellar Flares. particle acceleration in flares. chromospheric heating. coronal heating. irradiation of protoplanetary disk. outflow and wind acceleration. Questions. Are stellar flares different ? What can we learn from stellar flares? - PowerPoint PPT Presentation
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Zurich
FHNW, Windisch, Switzerland
Thermal and Non-thermal Emissions of Stellar Flares
Arnold O. Benz
Praha, 2014 J une 26
The Big Questions Stellar Flares
particle accelerationin flares
coronal heating
chromospheric heating
outflow and wind acceleration
irradiation ofprotoplanetary
disk
Are stellar flares different ?
What can we learn from stellar flares?
Flares in star and planet formation?
Role of flares in early solar system?
Questions
How Large Can a Flare Be?
Flare on EQ Peg (dM4e): 3·1033 erg in soft X-rays
Largest flare in stars: 2·1041 erg in soft X-rays(Grosso et al. 1997)
Largest flare in solar-type stars: 2·1038 erg in optical (Ashbrook 1959, Schaefer et al. 2000)
Largest flare in single solar-type stars: 6·1035 erg in
optical (Kepler data, Maehara et al. 2012; Candelaresi et al., poster)
How Large Can a Flare Be?
Energy in large solar active regionB = 2000 – 4000 G < nkT (photosphere)h= 2·109 cmr = 1010 cm
B2
8πr2 π h = 1035 erg
Free magnetic energy: 20%Released free energy: 50% → Max flare energy: 1034 erg
The maximum flare energy is dominated by
the size.
Large stellar flares must involve large active
regions.
Applications of Radio/X-ray Correlation
Prediction of radio flux from X-ray luminosity-> Discovery of radio emission of K, G, and F stars
Güdel 1994Güdel et al. 1994Güdel et al. 1995
Search for magnetic activity in embedded protostars (X-ray emission absorbed)
Summary L 1527
300σ peak deconvolved radius < 7 AUthermal free-free (corona+wind?)
No radio flare detected in 60 minutes
ΔFradio < 80 µJy (5σ)
radio/X-ray relation Lx = 1015.5 Lradio
→ Lx < 6 1030 erg/s
Very young protostars are less active than zero main sequence M stars, but need more observations
(Herschel Space Obs./HIFI, 1.1 THz)
12 deeply embedded young (< 105 y) stellar objects in OH+ absorption
Summary Herschel/HIFI
Enhanced irradiation in all protostars (low and high mass)
Irradiation increases from Class 0 to Class I (> 105 y)
The nature of the irradiation is not clearFUV, EUV, X-rays, particles?flares or shocks?
Conclusions
1. Flares make up the quiescent X-ray emission in active stars.
2. Huge stellar flares require larger volumes than solar flares.
3. Enhanced irradiation found in molecular abundances in early star and planet formation.
4. No evidence (yet) for X-rays and magnetic activity in Class 0 protostars
5. Flare (and CME) X-ray and energetic particles are relevantin early planet evolution.
Observations
G+B 1993B+G 1994
Theory
Gyro-synchrotron emissivity:
Conversion efficiencies: Dulk + Marsh 1982
X-ray Radio Correlation