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

Thermal Flare Emission (soft X-rays)

Solar X-ray spectrumRHESSI

thermal

non-thermal

relativistic

XMM-NewtonChandra

Thermal soft X-rays of Orion sfrChandra, Feigelson & Getman

Ness, 2009

X-ray flare onAlgol

solar radii

sola

r ra

dii

Audard et al. 2003

dM0.UV Cet B (dM6.0Ve, zero main-sequence star)

Audard, 2000

Güdel, 2004

Quiescent thermal X-ray emission

Quiescent emission of binaries

YY Gem Güdel et al. 2001

AR Lac Siarkowski et al. 1996

Güdel, 2004Quiet and quiescent soft X-ray emissionWhen does magnetic activity start?

Non-thermal Flare Emission (hard X-rays and gyro-synchrotron radio)

Kosugiet al. 1988

Sun

non-thermal bremsstrahlung < 100 keV

no

n-t

her

mal

gyr

o-s

ynch

rotr

on

(>

100

keV

)

Sun

ROSAT/HRI 0.1 – 2.4 keV

Güdel et al. 1996

Radiogyro-synchrotron

UV Ceti BdM6e

Neupert effect

UV Cet B(dM6e)

VLBA3.6 cm

Güdel et al. 2002

Proxima Centauri

dM5.5e

Neupert effect

Radio - X-ray Correlation

Flare peak fluxes

L x =

1015.5 L r

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)

8 - 12 GHzEVLA L 1527, Class 0

protostar

8 - 12 GHzEVLA

Spectral index at peak flux: +0.82

8 - 12 GHzEVLA

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

age →abu

nd

ance

→

Observed:

Very high X-rax flux or FUV

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?

Flare Impact on Accretion Disks and Protoplanety Atmospheres

FUV

X-rays

energetic particles

Protostar Class 0

Armitage

Protostar Class I (105 – 106 y)

Shibata & Matsumoto1996

CME in planet andstar forming region

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.

Thank you !

Observations

G+B 1993B+G 1994

Theory

Gyro-synchrotron emissivity:

Conversion efficiencies: Dulk + Marsh 1982

X-ray Radio Correlation