Lecture 11: The Discovery of the World of Exoplanets
• What are exoplanets & where are they?• Indirect methods for planet detection
Planets Orbiting Other Stars
Number of planets discovered around other stars:
540 planets 58 multiple planet systems
Star-to-planet inequalities:
• In light: 1010 (optical) to 107 (infrared)
• In mass: 105 to 103
• In size: 102 to 10.
Four main methods of discovery:
1) Direct 2) Radial velocity or Doppler ‘wobble’3) Transits 4) Gravitational microlensing
51 Peg b & HD 209458b:
“Hot Jupiters”
Method of discovery: Radial velocity ‘wobble’
of the starRadial velocities seenin star HD 209458 -the variation is dueto a planet that is lessmassive than Jupiter.
(Mazeh et al. 1999;Marcy et al. 2000)
Ups And System vs. Solar System
Kepler-11 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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Kepler discoveries
Evidence for Planet OGLE-TR-56b
Light Dimming
Doppler Shift
Konacki, Torres, Sasselov,
Jha, 2003, Nature
Method of discovery: Radial velocity ‘wobble’
of the starRadial 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 after Latham et al.’10
Rad
ius
Kepler: New Planets on the Mass-Radius Diagram
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 & MEarth.
The HAT Network: FLWO Mt.Hopkins AZ
(Bakos et al. 2004)
… and at Mauna Kea Obs., Hawaii
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