Lecture 14: The Discovery of the World of Exoplanets Indirect methods for planet detection The Astrometric method The Doppler shift method The Transit method
Planets Orbiting Other Stars Number of planets discovered around other stars: 442 planets 44 multiple planet systems
UpsAnd System vs. Solar System
HD b: a Hot Jupiter
Transits: A Method for Planet Discovery
Venus in Front of the Sun
Transit Measurements
Evidence for Planet OGLE-TR-56b Light Dimming Doppler Shift Konacki, Torres, Sasselov, Jha, 2003, Nature
OGLE-TR-113b Transit Light Curve Doppler Shift Konacki, Torres, Sasselov, Jha (2004)
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.
The HAT Network: FLWO Mt.Hopkins AZ (Bakos et al. 2004)
… and at Mauna Kea Obs., Hawaii
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
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.
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
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
Star-to-planet inequalities: In light: (optical) to 10 7 (infrared) In mass: 10 5 to 10 3 In size: 10 2 to 10.
HD b: a Hot Jupiter
Mass: Radial velocities seen in star HD the variation is due to a planet that is less massive than Jupiter. (Mazeh et al. 1999; Marcy et al. 2000)
Mass: For HD b: M p sin(i) = M s v s P / 2 a p = const. x ( M s / 1.1M Sun ) M jup Transit light curve helps derive the orbit inclination: i = 86 o Both M p and R p determined to better than 5%!
What can we learn from transiting extrasolar planets HD b: 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
Mass-Radius Diagram: Hot Jupiters Super-Earths
Model: Seager & Sasselov 2000 Detection: Charbonneau et al 2002
Atmosphere: What is special about atomic Na and the alkali metals? Seager & Sasselov (2000)
Atmosphere: Theoretical Transmission Spectra of HD b Wavelength (nm) Occulted Area (%) Seager & Sasselov (2000)
Atmosphere: The tricks of transmission spectroscopy: Brown (2001)
A star and its planet in infrared light (Artist conception)
Direct Detection of Thermal Emission Infrared Eclipses of Hot Jupiters: Spitzer Space Telescope
First detection of light from planets orbiting other stars D. Charbonneau, & D. Deming et al. March 2005
Infrared Eclipses
Infrared Eclipses in HD : 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)
Spectra Observed IR data points vs. models Knutson, Charbonneau, et al. (2007)
A study of an extrasolar planet Heather Knutson & Dave Charbonneau (2007)
A map of an extrasolar planet Heather Knutson & Dave Charbonneau (2007)
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