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Extrasolar planet detection:
Methods and limits
Ge/Ay133
How do you find a planet?
• Look for it? Hard (as we’ll see)!
Only planets imaged
are very young and
far from their stars.
Are such objects
common or rare?
Duquennoy & Mayor (1991) - Binaries
•Where should you look?
Eccentricities very different than the solar system:
Secondary masses & planets?
Spectral Energy Distributions
(or, Blinded by the light!...)
How do you find a planet?
• Look for it? Hard!
• Where should you look? Few AU?
Further out easier…
• Look for its affect on the star? (Indirect)
Direct imaging of extrasolar planets:
Marois et al. (2008)
Kalas et al. (2008)
Initial systems consistent w/discovery space:
• Young(ish) stars w/debris disks
• Planets at fairly large radii (24/38/68 & 115 AU)
Both properties optimize detection potential.
How do you find a planet?
• Look for it? Hard!
• Where should you look? Few AU?
Further out easier…
• Look for its affect on the star? (Indirect)
200 mas
Astrometric displacement of the Sun due to Jupiter
as seen from a distance of 10 pc
(Current state of the art w/Keck AO = 200 mas, as of 2007)
Discovery space for
indirect methods:
Radial velocity
Astrometry
(r=distance to the star)
Radial
velocity
signature
is distance
independent
(S/N is not!)
First (written)
proposal by
Otto Struve, The
Observatory 72,
p. 199-200 (1952)
51 Peg announced
in 1995 (PSR 1257+12
in 1992).
Spectroscopy with Echelles:
Keck
Photons have come a long
way, don’t lose them!
Echelle spectrometers in
conjunction with large
format arrays can provide
R~30,000-100,000 spectra
across the entire visible or
near-IR range (l<5 mm,
good for late type stars
and brown dwarfs).
Discovery space for
indirect methods:
Radial velocity
Astrometry
Other distance independent tracers? TRANSITS
Technique proposed in 1952, HD 209458 detected in 2000.
100’s now with the first CoRoT and Kepler results.
Transit photometry from space: Kepler!
Routes to Earth-like planets?
Microlensing II: Best geometry uses stars at a
few kpc against the Galactic Bulge.
5.5 MEarth planet at 2.6 AU
around a M-dwarf (0.22 M)
primary at 6.6 ± 1.0 kpc.
J.-P. Beaulieu et al. Nature 439, 437-440 (26Jan2006)
Astrometry? Hard w/single apertures, but
moving forward, ultimately to imaging.
Keck LGS-AO image, can now
achieve ~200 mas precision over
short timescales. HST worse.
ACS +
Coronograph
(HD 141569)
Artist’s conception,
TPF-C (coronograph).
Think about interferometry?
Aperture
Diffraction Pattern
Radio arrays can give mas precision (non-thermal):
In the optical, difficult to
maintain strict instrument
stability, so use “dual star”
astrometry. Large apertures
are needed to get enough
background stars nearby.
Nulling:
Jupiter simulation at 10 pc.
Use the
fringes to
suppress
the central
star. First
successful
tests with
Keck in
2007…
Nulling can also be used with
single apertures…
Vortex coronograph
image, using 1.5m section
of the Hale telescope.
Discovery image,
10.4m Keck telescope