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Extrasolar Planets

Extrasolar Planets. Is there a twin of our Home Planet somewhere out there? Gero Rupprecht, ESO Brandys, 07.05.2004. Giordano Bruno 1548-1600 “On the Infinite Universe and the Worlds". Every major scientific truth passes through the following three stages:

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Extrasolar Planets

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  1. ExtrasolarPlanets Is there a twin of our Home Planet somewhere out there? Gero Rupprecht, ESO Brandys, 07.05.2004

  2. Giordano Bruno 1548-1600 “On the Infinite Universe and the Worlds" • Every major scientific truth passes through • the following three stages: • People say it contradicts the Bible • People say it is already known • People say they always knew it right away…

  3. Michel Mayor Didier Queloz (Obs. Geneva) 6.10.1995 Public announcement of the discovery of the first extrasolar planet: 51 Pegasi

  4. This was one of the most eagerly awaited • discoveries - Searches ongoing for decades: • many teams • many stars • different techniques • Without success! • Why? • Were the techniques not sensitive enough? • Perhaps there were no planets after all?

  5. The new planet: a mystery! • orbital period: 4.2 d • Mass: ~0.5 MJupiter • This is against all • that was expected!

  6. „Hot Jupiter" • circling its star inside the orbit of Mercury • Consequences: • Extreme temperatures • Extreme climate • IF it is a gas planet: very short lifetime!

  7. New discoveries followed suit • Today (May 2004): 123 Exoplanets known • in 108 systems • with 13 multiple planets • The most successful teams: • Geneva (Mayor, Queloz) • California/Carnegie (Marcy, Butler) • Anglo-Australian Telescope • Pennsylvania State University (Wolszczan) • More teams at different observatories

  8. Where are they located?

  9. How can Exoplanets be discovered? • Direct imaging • Observation of induced proper motion • Variation of the star‘s radial velocity • Variation of the star‘s brightness: • Gravitational lens effect • Transit!

  10. Ad 1: Direct imaging of the planet • VERY difficult due to • extreme contrast: about 1:10^9 • in the case of Jupiter/Sun at 5pc distance • very small angular separation: <1" • only from space: • “nulling interferometry” • GENIE (ESA/ESO VLTI 2008) • DARWIN (ESA) • TPF (NASA) 51 Pegasi

  11. Using the effects of gravity • Depending on our relative • Position we see either • a “wobble” in the • star’s position or • a “wobble” in the • star’s velocity Period = orbital period of the companion

  12. Ad 2: Observation of a star‘s proper motion • Superposition of space and orbital motion. • More difficult with increasing distance and • decreasing mass of the planet. • Requires at least observation of one full orbit. • So far no planet discovered but one confirmed by HST • ESO VLTI: 10^-4‘‘ – ok for Jupiter, not Uranus in 10pc • ESA mission GAIA to measure precise PM in 2012

  13. Ad 3: Variation of the star‘s radial velocity Geneva team • Dependent on the mass ratio star/planet • Independent of the distance from the observer • Jupiter causes 13m/s variation, Earth only 0.1m/s • Measurement limit 1m/s (HARPS at ESO 3.6m)

  14. HARPS: High Accuracy RV Planet Searcher on ESO/La Silla 3.6m All you need is … Stability! • Coude focus • fibre fed • image scrambler • no focusing mechanism • climatized room • vacuum vessel • heating blanket • special calibration method • long-term stability: 1m/s • short-term: ~30cm/s • good for Uranus-like planets

  15. HARPS: echelle spectrograph, RS=120000 CCD mosaic 4k*4k HARPS echelle grating Cross dispersed HARPS inside Echelle spectrum

  16. Ad 4a: Gravitational lens effect Very recent: published in April 2004 Observation Interpretation

  17. Ad 4b: Variation in brightness due to a transit One case known: HD 209458 – 1% dip Accessible even for amateurs: Nirölä Obs/Finland Sep. 2000 Meade 16’’ + Focal reducer SBIG ST7E CCD

  18. Transit method applied by HST Precise photometry Detection of a Na “atmosphere”

  19. Transit method: the future • only for a short fraction of the orbital period (hours) • only if Earth is nearly exactly in the orbital plane • Jupiter: 1% dimming, but Earth: 0.01% dimming! • Currently the only method to discover Earth sized planets: • only from space! • COROT (ESA, >2006; • 30cm telescope) • Kepler (NASA, • >2007; • 95cm telescope, • differential • photometer)

  20. Some examples for exoplanet systems

  21. All exoplanets known to date --- Jupiter --- Earth For comparison: Our solar system

  22. Exoplanets – what do we know about them? Obviously: they are clearly different from our own system! But who is typical: we or them?

  23. Multiple planets Radial velocity curve shows 2 periods Their orbits compared to Earth’s orbit

  24. A strange case: cannibal star – detected by VLT! • HD 82943 • 2 planets • Li in stellar spectrum! • explanation: cannibalism!

  25. Exoplanet summary • a new, “hot” field in astronomy • within reach of amateurs! • appealing for the general public • large potential for exciting • discoveries • >> Europe in the lead <<

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