Detection of Extrasolar Planets

ASTR 4: Life in the Universe

Outline• Spectral Types• Basic Geometry• In-direct Methods

– Astrometric Method– Radial Velocity (Doppler Spectroscopy) Method– Transit Method– Planetary Atmosphere Method– Pulsar Timing Method– Gravitational Microlensing Method

• Direct Methods– Direct Imaging– Interferometric Method– Coronagraphic Method

Spectral Types

Basic Geometry

Astrometric Method

Radial Velocity Method

Radial Velocity Method"A Jupiter-Mass Companion to a Solar-Type Star", M. Mayor & D. Queloz, 1995, Nature 378, 355

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• TransitsPlanet crosses line of sight between observer and star and blocks a small amount of light from the star

• Different from occultation or eclipseOccult means to cover over or to hide

• PhotometryMethod of measuring the amount of lightA light meter on a camera is a photometer

Transit of Mercuryin 2003

Transit Method

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• The relative change in brightness (L/L) is equal to the relative areas (Aplanet/Astar)

• To measure 0.01% must get above the Earth’s atmosphere

• Method is robust but you must be patient:Require at least 3 transits, preferably 4 with same

brightness change, duration and temporal separation(the first two establish a possible period, the third confirms it)

Jupiter: 1% area of the Sun (1/100)

Earth or Venus0.01% area of the Sun (1/10,000)

Transit Method - An Example

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• Not all planetary orbits are aligned along our line of sight to a star

• Diameter of Sun d* is about 0.01 AU. Diameter of Earth orbit D is 2 AU

• Random probability of detecting a Sun-Earth analog is about 0.5%

• So one needs to look at thousands of stars IF all have an Earth

2) Solid angle of d*/D for all possible pole positions for any given LOS

3) Geometric Transit Probability = d*/D

22d*/D

1) Range of Pole Positions = d*

D/2

D/2 Orbital radius

d*

Stellar Diameter

Geometry For Transit Probability

Transit Method – Light Curve

Transit Method - Light Curve Depth

Planetary Atmosphere Method

Planetary Atmosphere Method

Gravitational Microlensing Method

Gravitational Microlensing Method

The best fit light curve of the MACHO-97-BLG-41 microlensing event. The data consists of 356 MPS R-band observations from the Mt. Stromlo 1.9m telescope, 197 MACHO-R and 194 MACHO-V band observations from the Mt. Stromlo 1.3m telescope, 35 R-band observations from the CTIO 0.9m telescope, and 17 R-band observations from the Wise 1.0m telescope. The MACHO-R, MACHO-V, Wise-R, CTIO-R, and MPS data are plotted in red, blue, green, cyan, and magenta respectively. The tick interval for the inset figures is 1 day. 

http://www.nd.edu/~srhie/MPS/97-BLG-41/97blg41.html

Direct Imaging Method - Photometric Precision

Direct imaging of exo-planets is Hard:Direct imaging of exo-planets is Hard:

10 10 Sun

Earth

Differential Photometric Direct Imaging of a brown dwarf in infrared wavelength.

Other Direct Methods• Interferometry

– Infrared Interferometry– SIM (Space Interferometry Mission)

• Coronagraph– Visible Light Coronagraph– TPF (Terrestrial Planet Finder)

Infrared Interferometeric Image

SIM & TPF

Coronagraphic Imaging

Coronagraphic image of the Sun

Coronagraphic image of a brown dwarf; an object about 60 to 80 times the mass of Jupiter, orbiting less than 20 AU from its parent star. The star is removed by image processing to reveal the brown dwarf. (Keck and Gemini images)

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SummaryMethod Yield Mass Limit Status

Pulsar Timing m/M ; Lunar Successful (3)

Radial Velocity m sini ; Uranus Successful (~100)

Astrometry m ; Ds ; aGround: Telescope Jupiter OngoingGround: Interferometer <Jupiter In developmentSpace: Interferometer Uranus Being studied

Transit Photometry A ; sini=1Ground Jupiter HD209458, OGLE TR-

56?Space Venus Planned Kepler,

Edd.

Reflection Photometry: albedo*A ; Space Saturn Planned Kepler, Edd.

Microlensing: f(m,M,r,Ds,DL )Ground sub-Uranus On-going

Direct Imaging albedo*A ; Ds ; a ; MGround Saturn Being studiedSpace Earth Being studied