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