methods for the detection of exosolar planets astronomical seminar january 2004 erik butz
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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:
c
v
Through shift in spectral lines, velocity of an object can be determined
Introduction 3
1992 first planet around pulsar found (OBS! Not using radial velocity method!)
Pulsar timing: Systematic variation in arrival of pulsar pulses
Introduction 4
1995 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: www.Extrasolar.net
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 ~MP => easier to find
larger planets and smaller periods =>shorter observation times
Due to orbital inclination no direct determination of MP
Planetary Doppler Shift 9
Only determination of MP 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 :
d
a
M
M P *
Effect is larger for nearby stars
If M*, a and d known: Determination of MP
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): 10-100µarcsec
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 improbableEffect is small:
Sun/Jupiter in 10 pc: ~2% (0.02m)
Transits 1 Advantages:
Feasible with low effortCan be done with many stars in short time
Transits 2
Transits 3
Future prospects
Imaging of planets in IR and VIS
Problems:
!!10~ 9
*
L
LP
Interferometric imaging 1
Ratio in IR (i.e. at maxPlanet) 105 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
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