numerical plasma simulation, technical university of braunschweig, germany extrasolar planets...

Numerical Plasma Simulation, Technical University of Braunschweig, Germany

Extrasolar PlanetsGeneral Properties and Magnetospheric Aspects

Uwe Motschmann

Institute for Theoretical Physics, Technical University of Braunschweig, Germany

Co-workers:

J.M. Griessmeier, TU BraunschweigS. Preusse, MPS Katlenburg-Lindau

E. Kuehrt, DLR BerlinH. Rucker, IWF Graz

G. Mann, AIP PotsdamA. Lipatov, Moscow

Workshop Solar Terrestrial Interactions, Sinaia, September 2005


Outline

Discovery

Properties

Detection techniques

Magnetic interaction with the host star

Planetary radio emission


Known Extrasolar Planets (ESP)(24 August 2005)

163 planets

139 planetary systems[http://www.obspm.fr/encycl/encycl.html]

First ESP was detected in 1995[Mayor & Queloz, Nature ,1995]


Distribution of ESP

They are everywhere!

[http://capote.pharm.uky.edu/Skymap1.htm]


Definition of ESP

Spherical metal rich non-fusor

in an orbit around a fusor

outside the solar system

[Neuhäuser, http://www.astro.uni-jena.de]


Orbital Radii

[http://jilawww.colorado.edu/~pja/planets/extrasolar.html]

“Hot Jupiters”:~30 planets

with d<0.1 AU (2004)

Terrestrial planets: not (yet)

detectable

?


Detection Techniques

• direct imaging• radial velocity method (Doppler shift)• transit (dimming of star)• secondary transit (dimming of planet)• astrometry• microlensing


Detection by Doppler Shift(Radial Velocity Method)

Motion around center of mass → shift of spectral lines.

Detected ESP parameters: M sin(i), T, e


Detection by Transit

Transit of planet in front of the star

→ decrease of total intensity (1).

Detected ESP parameters: M, T, R


Detection by Secondary Transit

Second. transitPrimary transit

transit in front of star

decrease of total intensity (1)

transit behind star

decrease of IR intensity (0.25)

planetary emission

temperature of planet


Detection by Astrometry

motion around center of mass → observed motion of the star.

Detected parameters: M, T


Detection by Microlensing

Light from a distant star focussed by gravity

→ fine structure caused by planet.

Detected parameters: Mp/Ms, R, orbit


Direct Imaging

Infrared or vis imaging (adaptive optics)

→ optical separation of planet possible.

Detected parameters: R, spectrum

[Neuhäuser et al, A&A, 2005]


Summary: Detection Methods

1?

(2005) (GP Lupi)

Direct obs.

1

2002(Gl 876 b)

Astro-metry

28>100

2003 (O235/M53)

2000(HD

209458b)

1995(51 Peg b)

Micro-lensing

TransitDoppler

shiftSecond. Transit

2004 (HD

209458b)

2


Magnetic Interaction of ESP

• Interaction of ESP with stellar wind– Stellar wind– ESP (planetary magnetic field, …)

• Action of the stellar wind to ESP• Re-action of the ESP to star• Purpose of the study

– New phenomena compared with solar system– Observable consequences: superflares, planetary radio

emission


Stellar Wind Models

• Parker [1958]• hydrodynamic approach• spherical symmetry• no rotation• no selfconsistent magnetic field

• Weber & Davis [1967]• magnetohydrodynamic approach• axisymmetric• rotation• magnetic field


Parker’s Wind

0 1 2 3 4 5-3

-2

-1

0

1

2

3

0

1

2

Noz

zle

radi

us /

criti

cal r

adiu

s

distance / critical radius

Velocity / sound speed

Sonic point

Rcrit☼ = 8 ·106 km

= 0.05 AU


Weber and Davis’ Wind

→ 3 characteristic points: Alfven point,

supermagnetosonic point,

submagnetosonicsonic point.

→ comparison with ESP position


0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.080

50

100

150

200

250

300

350

400

450

500

distance in AU

velo

city

in k

ms-1

Hot Jupiter orbits

T=2.0 106 K

T=0.5 106 K

Velocities much lower with respect to 1 AU

ESP may be located within Alfvén point![Preusse et al, A&A, 2005][Lipatov et al, PSS, 2005 ]

Weber and Davis’ Wind

Prot = 3dBsurf = 1…10G


Magnetic Communication

Close-in ESP Solar System

stellar wind velocityAlfvén velocity

Planetary disturbance is carried away by stellar wind

Planetary disturbance can reach the star

*

ESP


Superflares

• Stellar flare– catastrophic release of magnetic energy with particle

acceleration and emission of elm radiation

• Superflare– flare at solar like star with total energy release >100 x

energy of most intensive solar flares (>3000 x vis, >1000 x in X-ray)

• Superflare rate– ~101…102y [Schaefer et al, 2000]

• No solar superflare in last 2000y


Triggering of Superflares

• Reconnection in double star system [Simon et al, 1980]

• Reconnection of the stellar magnetic field with a close-in magnetized planetary companion [Rubenstein & Schaefer, 2000]


Internal Magnetic Field of ESP

Theoretical models scaling laws for magnetic moment

[Sano, 1993]e.g.

Conditions for large magnetic moment:

high density: possible fast rotation: limited by tidal locking

large planet: possible


Scaling Laws for Magnetic Moment

2/72/1

2/132/12/1

4/12/74/32/1

6/12/72/13/1

42/1

c

c

c

c

c

rM

rM

rM

ErM

rM

Busse 1976

Curtis and Ness 1986

Mizutani et al. 1992

Mizutani et al. 1992

Sano 1993


Tidal Locking of Close-in ESP

Tidal force bulge on planet

Fast rotation bulge displaced relative to star

Gravitation acts on tidal bulge spin-down

After some time: rotation=revolution


Timescale for Locked Rotation

tidally locke

d

not tidally locked

10 Gyr0.1 Gyr [Griessmeier et al, A&A, 2004]


Magnetic Moment and Tidal Locking

strongly reduced magnetic moment

Tidal locking

[Griessmeier et al, A&A, 2004]


Size of Magnetosphere

Dipole field:

Distance

magnetopause – planet:

m n v2 Bp2/2μ0

Bp M/RM3

Magnetopause size:

Pressure equilibrium at substellar point:

RM M1/3 (n v2)-1/6 d1/3


Stellar Wind Evolution

5.2 Gyr

Strong time dependence of stellar wind

velocity and density

Influences size of the magnetosphere


Size of Magnetosphere


Planetary Radio Emission in the Solar System

Flux density normalized to 1 AU

[Bastian et al, APJ. 545, 2000]

Strongly magnetized planets are nonthermal radio emitters!

ionospheric cutoff


Cyclotron Maser Instability (CMI)

vd

vk

bJv

v

fvk

v

fn

parparc

perp

parperppar

perpc

p 3

2'100

2

22 )(

1

2

222

kc

n

c

perpperpvkb

2

1

2

2

1

c

v

refraction index

argument of Besselfunction

Lorentz factor

- resonant wave particle interaction- dispersion relation for X mode [Wu & Lee, 1979]


Power input (stellar wind):

Magnetosphere:

Empirical scaling:

[Zarka et al, Astrophys. Space Sci., 277, 293, 2001]

Prad PSW

PSW (RM /d)2

RM (M, d)

Planetary Radio Emission


Tau Bootes b as Radio Candidate

Radio Flux normalized to 1AU [Griessmeier et al, 2005]


Radio Contrast Jupiter/Sun

ΦJ / ΦQS 103 [Griessmeier et al, A&A, 2005]


Contrast ESP/Star

Vis 10-8 [Burrows et al, APJ, 2004]IR 10-4 ...10-3 [Burrows et al, APJ, 2004]Radio >1 (>>1) [Griessmeier et al, A&A, 2005]

Contrast: Poynting flux of ESP / Poynting flux of star


Radio Flux Reaching Earth

Robin 2: sensitivity 100 mJyat 8-80 MHzready ca. 2005?

LOFAR: sensitivity 0.3-1.0 mJyat 10-240 MHzready 2006/08?

[http://www.lofar.org]


Outlook• Missions with defined launch time

– COROT (F, Europe, Nov 2005)

– KEPLER (NASA, Oct 2006)

– [EDDINGTON (ESA, 2008+)]

– Space Interferometry Mission (NASA, 2009)

– James Webb Space Telescope (ESA, NASA, 2009+)

– GAIA (ESA, 2008-2012)

• Planned missions– Big Occulting Steerable Satellite

– UMBRAS

– DARWIN (ESA)

– Galactic Exoplanet Survey Telescope

– Planet Imager (NASA)

– Terrestrial Planet Finder (NASA)

numerical plasma simulation, technical university of braunschweig, germany extrasolar planets...

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