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