Methods for the detection of exosolar planets Astronomical Seminar January 2004 Erik Butz

Overview Introduction Today‘s methods Future prospects Summary

Introduction Big question of mankind: Are we alone in the universe? Many speculations: Mars, Venus and other planets in the solar system Search for exosolar planets was hopeless for several centuries because of insufficient sensitivity of instrumentation and because of enormous distances

Introduction 2 Key technique for first discoveries developed by Christian Doppler in 1842: Through shift in spectral lines, velocity of an object can be determined

Introduction first planet around pulsar found (OBS! Not using radial velocity method!) Pulsar timing: Systematic variation in arrival of pulsar pulses

Introduction first planet around Main Sequence(MS) Star (51 Peg) Since then: More than 110 planets found!

Today‘s methods Several searches ongoing using Radial Veclocity technique Measurement of Doppler shift in the spectrum of the star due to gravitational influence of the planet.

Planetary Doppler Shift 1 Source:

Planetary Doppler Shift 2

Planetary Doppler Shift 3

Planetary Doppler Shift 4 Long struggle to reach sufficient sensitivities Jupiter causes shift of 15 m/s Compare to line-width ~km/s

Planetary Doppler Shift 5 Breakthrough hoped for at 10 m/s First groups were unlucky:  Did not find planet with sensitivity of 10 m/s  51 Peg: 50 m/s => would not have been a problem

Planetary Doppler Shift 6

Planetary Doppler Shift 7 Todays precision:~2 m/s Compare to:  Earth:0.1 m/s  No Earth finder with present doppler methods!

Planetary Doppler Shift 8 Advantages:  Enables finding of planet with comparably low effort  Can be used on smaller telescopes as well Disadvantages:  Deviation is ~M P => easier to find larger planets and smaller periods =>shorter observation times  Due to orbital inclination no direct determination of M P

Planetary Doppler Shift 9 Only determination of M P sin i

Todays methods 2 Complementary searches using astrometric measurements Measurement of systematic variations of star position also because of gravitational influence of planet

Astrometry 1 Star‘s apperent path due to planet is ellipse with major half axis  :  Effect is larger for nearby stars  If M *, a and d known: Determination of M P Deviation for Jupiter in d ~ 10 pc is of order of milliarcsec or lower

Astrometry 2

Astrometry 3

Astrometry 4 Problem: milliarcsec precision only reached in radio Hipparcos: ~1 milliarcsec VLTI(not yet available): µarcsec

Astrometry 5 Future: µarcsec astrometry possible, but: Earth moves sun about 500 km  0,03 % Sunspots and other dynamic instabilities  0.5 %

Today‘s methods 3 Luminosity variation during Transits of planets Problems:  Situation is highly improbable  Effect is small: Sun/Jupiter in 10 pc: ~2% (0.02 m )

Transits 1 Advantages:  Feasible with low effort  Can be done with many stars in short time

Transits 2

Transits 3

Future prospects Imaging of planets in IR and VIS Problems:

Interferometric imaging 1 Ratio in IR (i.e. at max Planet ) 10 5 better Furthermore: interferometry to further reduce starlight Nulling interferometry: destructive interference at star position but not at planet position

Summary Several methods for discovery of exosolar planets More then 110 planets found Future methods will enable more discoveries and deeper investigation With Transits: Atmosphere‘s =>signatures of life With extremely large(150 mirrors of 1 m 150 km baseline) space telescope imaging on exosolar planets