Download lec03_05oct2009

Extrasolar planet detection:
Methods and limits
Ge/Ay133
Spectral Energy Distributions
(or, Blinded by the light!...)
How do you find a planet?
• Look for it? Hard (as we’ve seen)!
Only planets imaged
are very young and
far from their stars.
Are such objects
common or rare?
How do you find a planet?
• Look for it? Hard!
• Where should you look? Few AU?
• 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
Routes to Earth-like planets?
Other distance independent tracers? TRANSITS
Technique proposed in 1952, HD 209458 detected in 2000.
Transit photometry from space: Kepler
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):
Palomar Testbed Interferometer (PTI)
In the optical, difficult to
maintain strict instrument
stability, so use “dual star”
astrometry. Large apertures
are needed to get enough
background stars nearby.
Space
Interferometry
Mission
(SIM)
Nulling:
Use the
fringes to
suppress
the central
star. First
tests w/
Keck in
2007.