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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