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Detection of Extrasolar Planets
ASTR 4: Life in the Universe
Outline
• Spectral Types
• Basic Geometry
• In-direct Methods
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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
Transit Method
•
Transits
Planet crosses line of sight between
observer and star and blocks
a small amount of light from the star
•
Different from occultation or eclipse
Occult means to cover over or to hide
•
Photometry
Method of measuring the amount of light
A light meter on a camera is a photometer
Transit of Mercury
in 2003
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Transit Method - An Example
•
The relative change in brightness (DL/L) is equal to the relative areas
(Aplanet/Astar)
Jupiter:
1% area of the Sun (1/100)
Earth or Venus
0.01% area of the Sun (1/10,000)
•
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)
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Geometry For Transit Probability
•
Not all planetary orbits are aligned along our line of sight to a star
D/2
Stellar
Diameter
Orbital radius
d*
1) Range of Pole Positions =
d*
D/2
2d*/D
2
2) Solid angle of d*/D
for all possible pole positions
for any given LOS
3) Geometric Transit Probability = d*/D
•
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
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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 Rband 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-BLG41/97blg41.html
Direct Imaging Method - Photometric
Precision
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)
Summary
Method
Yield
Mass Limit
Pulsar Timing
m/M ; t
Lunar
Radial Velocity
m sini ; t Uranus
Astrometry
m ; t ; Ds ; a
Ground: Telescope Jupiter
Ongoing
Ground: Interferometer
<Jupiter
Space: Interferometer
Uranus
Transit Photometry
Ground
Space
Status
Successful (3)
Successful (~100)
In development
Being studied
A ; t ; sini=1
Jupiter HD209458, OGLE TR-56?
Venus
Planned Kepler, Edd.
Reflection Photometry: albedo*A ; t
Space
Saturn
Planned Kepler, Edd.
Microlensing:
Ground
f(m,M,r,Ds,DL )
sub-Uranus On-going
Direct Imaging
Ground
Space
albedo*A ; t ; Ds ; a ; M
Saturn
Being studied
Earth
Being studied
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