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Methods for the detection of exosolar planets

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?

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Methods for the detection of exosolar planets

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

  2. Overview • Introduction • Today‘s methods • Future prospects • Summary

  3. 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

  4. 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

  5. Introduction3 • 1992 first planet around pulsar found (OBS! Not using radial velocity method!) Pulsar timing: Systematic variation in arrival of pulsar pulses

  6. Introduction4 • 1995 first planet around Main Sequence(MS) Star (51 Peg) • Since then: More than 110 planets found!

  7. 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.

  8. Planetary Doppler Shift 1 Source: www.Extrasolar.net

  9. Planetary Doppler Shift 2

  10. Planetary Doppler Shift 3

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

  12. 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

  13. Planetary Doppler Shift 6

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

  15. 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

  16. Planetary Doppler Shift 9 Only determination of MP sin i

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

  18. Astrometry 1 • Star‘s apperent path due to planet is ellipse with major half axis a: • 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

  19. Astrometry 2

  20. Astrometry 3

  21. Astrometry 4 • Problem: milliarcsec precision only reached in radio • Hipparcos: ~1 milliarcsec • VLTI(not yet available): 10-100µarcsec

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

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

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

  25. Transits 2

  26. Transits 3

  27. Future prospects • Imaging of planets in IR and VIS • Problems:

  28. Interferometric imaging 1 • Ratio in IR (i.e. at lmaxPlanet) 105 better • Furthermore: interferometry to further reduce starlight • Nulling interferometry: destructive interference at star position but not at planet position

  29. 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 Summary

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