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Extrasolar Planets

This article explores the exciting field of exoplanet discovery, discussing the different techniques used and the discoveries made so far. It also highlights the importance of these findings and their potential for exciting future discoveries.

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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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