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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
Planets Orbiting Other Stars
Number of planets discovered around other stars:
442 planets 44 multiple planet systems
UpsAnd System vs. Solar System
HD 209458b: a Hot Jupiter
Transits: A Method for Planet
Discovery
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
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 forsmall planets - RV amplitudeswill be less than 30 cm /sec.
Solution: build a clone to HARPS (South) and put it on a large telescopeUse 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: 1010 (optical) to 107 (infrared)
• In mass: 105 to 103
• In size: 102 to 10.
HD 209458b: a Hot Jupiter
Mass:
Radial velocities seenin star HD 209458 -the variation is dueto a planet that is lessmassive than Jupiter.
(Mazeh et al. 1999;Marcy et al. 2000)
Mass:
• For HD 209458b: Mp sin(i) = Ms vs P / 2 ap
= const. x (Ms
/1.1MSun) Mjup
+ 0.018 + 0.1• Transit light curve helps derive the orbit
inclination: i = 86o.7 + 0.2
• Both Mp and Rp determined to better than 5%!
What can we learn from transiting extrasolar
planetsHD 209458b: Dimming of light due to transit, observed with HST.
Brown, Charbonneau, Gilliland, Noyes, Burrows (2001)
Tells usDIRECTLY:Planet radius,
INDIRECTLY:Planet densityPlanet composition
Mass-RadiusDiagram:
Hot Jupiters
Super-Earths
Model: Seager & Sasselov 2000Detection: Charbonneau et al 2002
Atmosphere:What is special about atomic Na and the
alkali metals?
Seager & Sasselov (2000)
Atmosphere: Theoretical Transmission Spectra of HD 209458 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 EmissionInfrared Eclipses of Hot Jupiters:
Spitzer Space Telescope
First detection oflight from planetsorbiting other stars
D. Charbonneau, & D. Deming et al. March 2005
Infrared Eclipses
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Infrared Eclipses in HD 189733: Measuring the
Emitted Heat
Time (in fraction of day)
Orbital phaseRelative Intensity or Brightness
Eclipse detection (Feb. 20, 2006) by Deminget al. using the SpitzerSpace Telescope - in infrared light (heat)
SpectraObserved 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)
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Main points to take home:
1) Methods and parameters we can measure2) Mean density measurements: internal structure3) Measurements of surface temperature4) Atmospheric composition and temperatures5) Mapping of the surface