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)Marois et al. (2008) Kalas et al. (2008)Kalas et al. (2008)

Initial systems consistent w/discovery space:Initial systems consistent w/discovery space:• Young(ish) stars w/debris disksYoung(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 Jupiteras 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)

Radialvelocitysignatureis distanceindependent(S/N is not!)

First (written) proposal by Otto Struve, The Observatory 72, p. 199-200 (1952)

51 Peg announcedin 1995 (PSR 1257+12in 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~30,000-100,000 spectra across the entire visible or near-IR range (5 m,good for late type starsand brown dwarfs).

Keck

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!Transit photometry from space: Kepler!

Routes to Earth-like planets? 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 J.-P. Beaulieu et al. Nature 439439, 437-440 (26Jan2006), 437-440 (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 +ACS +CoronographCoronograph(HD 141569)(HD 141569)

Think about interferometry?

Aperture Diffraction Pattern

Radio arrays can give as precision (non-thermal):

In the optical, difficult tomaintain strict instrumentstability, so use “dual star”astrometry. Large aperturesare needed to get enoughbackground stars nearby.

Nulling:

Use thefringes tosuppressthe centralstar. Firstsuccessfultests withKeck in2007…Jupiter simulation at 10 pc.Jupiter simulation at 10 pc.

Nulling can also be used with single apertures…

Discovery image,Discovery image, 10.4m Keck telescope10.4m Keck telescope

Vortex coronograph Vortex coronograph image, using 1.5m section image, using 1.5m section of the Hale telescope.of the Hale telescope.