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?

Where should you look? Duquennoy & Mayor (1991) - Binaries

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 Young(ish) stars w/debris disks Planets at fairly large radii (24/38/68 & 115 AU) Planets at fairly large radii (24/38/68 & 115 AU) Both properties optimize detection potential. 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)

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  as, as of 2007) 200  as

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 (1952) 51 Peg announced in 1995 (PSR in 1992)..

Spectroscopy with Echelles: Photons have come a long way, don’t lose them! Echelle spectrometers in conjunction with large format arrays can provide R~30, ,000 spectra across the entire visible or near-IR range (  5  m, good for late type stars and brown dwarfs). Keck

Discovery space for indirect methods: Radial velocity Astrometry

Other distance independent tracers? TRANSITS Technique proposed in 1952, HD detected in ’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 M Earth 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, (26Jan2006)

Astrometry? Hard w/single apertures, but moving forward, ultimately to imaging. Artist’s conception, TPF-C (coronograph). Keck LGS-AO image, can now achieve ~200  as precision over short timescales. HST worse. ACS + Coronograph (HD )

Think about interferometry?

Aperture Diffraction Pattern

Radio arrays can give  as 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: Use the fringes to suppress the central star. First successful tests with Keck in 2007… Jupiter simulation at 10 pc.

Nulling can also be used with single apertures… Discovery image, 10.4m Keck telescope 10.4m Keck telescope Vortex coronograph image, using 1.5m section of the Hale telescope.