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Lecture 14: The Discovery of the World of Exoplanets Indirect methods for planet detection The Astrometric method The Doppler shift method The Transit method
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Planets Orbiting Other Stars Number of planets discovered around other stars: 442 planets 44 multiple planet systems
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UpsAnd System vs. Solar System
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HD 209458b: a Hot Jupiter
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Transits: A Method for Planet Discovery
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Venus in Front of the Sun
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Transit Measurements
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Evidence for Planet OGLE-TR-56b Light Dimming Doppler Shift Konacki, Torres, Sasselov, Jha, 2003, Nature
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OGLE-TR-113b Transit Light Curve Doppler Shift Konacki, Torres, Sasselov, Jha (2004)
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Transiting Planets - the search is on! Transits occur due to chance alignments, therefore one has to observe millions of stars in order to ‘catch’ a few transiting planets; Here at Harvard we have 2 automated networks of small telescopes searching: HAT & TrES.
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The HAT Network: FLWO Mt.Hopkins AZ (Bakos et al. 2004)
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… and at Mauna Kea Obs., Hawaii
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KEPLER: Search for Earth Twins GOAL: discover ~30 Earths in habitable zones; also - thousands of giant planets like Jupiter and Super-Earths. NASA Mission - launched 3/2009 Transit Search: ~120,000 stars in a North field (in Cygnus); Can detect planets like our Earth
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New Earths Facility The “PROBLEM” with KEPLER: not able to get data on masses for small planets - RV amplitudes will be less than 30 cm /sec. Solution: build a clone to HARPS (South) and put it on a large telescope Use it to measure masses, and hence mean densities for KEPLER’s best candidate Earths.
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Main points to take home: 1) Four main methods of discovery: direct, Doppler wobble, transits, microlensing. 2) Doppler effect: deriving planet mass. 3)Transits: (1) detection probability; (2) deriving the radius. 4) NASA Kepler Mission
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Lecture 15: The Exploration of the World of Exoplanets Methods and parameters we can measure Mean density measurements: internal structure Measurements of surface temperature Atmospheric composition and temperatures Mapping of the surface
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Star-to-planet inequalities: In light: 10 10 (optical) to 10 7 (infrared) In mass: 10 5 to 10 3 In size: 10 2 to 10.
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HD 209458b: a Hot Jupiter
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Mass: Radial velocities seen in star HD 209458 - the variation is due to a planet that is less massive than Jupiter. (Mazeh et al. 1999; Marcy et al. 2000)
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Mass: For HD 209458b: M p sin(i) = M s v s P / 2 a p = const. x ( M s / 1.1M Sun ) M jup + 0.018 + 0.1 Transit light curve helps derive the orbit inclination: i = 86 o.7 + 0.2 Both M p and R p determined to better than 5%!
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What can we learn from transiting extrasolar planets HD 209458b: Dimming of light due to transit, observed with HST. Brown, Charbonneau, Gilliland, Noyes, Burrows (2001) Tells us DIRECTLY: Planet radius, INDIRECTLY: Planet density Planet composition
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Mass-Radius Diagram: Hot Jupiters Super-Earths
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Model: Seager & Sasselov 2000 Detection: Charbonneau et al 2002
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Atmosphere: What is special about atomic Na and the alkali metals? Seager & Sasselov (2000)
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Atmosphere: Theoretical Transmission Spectra of HD 209458 b Wavelength (nm) Occulted Area (%) Seager & Sasselov (2000)
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Atmosphere: The tricks of transmission spectroscopy: Brown (2001)
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A star and its planet in infrared light (Artist conception)
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Direct Detection of Thermal Emission Infrared Eclipses of Hot Jupiters: Spitzer Space Telescope
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First detection of light from planets orbiting other stars D. Charbonneau, & D. Deming et al. March 2005
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Infrared Eclipses
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Infrared Eclipses in HD 189733: Measuring the Emitted Heat Time (in fraction of day) Orbital phase Relative Intensity or Brightness Eclipse detection (Feb. 20, 2006) by Deming et al. using the Spitzer Space Telescope - in infrared light (heat)
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Spectra Observed IR data points vs. models Knutson, Charbonneau, et al. (2007)
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A study of an extrasolar planet Heather Knutson & Dave Charbonneau (2007)
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A map of an extrasolar planet Heather Knutson & Dave Charbonneau (2007)
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Main points to take home: 1) Methods and parameters we can measure 2) Mean density measurements: internal structure 3) Measurements of surface temperature 4) Atmospheric composition and temperatures 5) Mapping of the surface
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