Detection of Extrasolar Giant Planets

Hwihyun Kim03/30/06

PAPER

• G. W. Marcy & R. P. Butler, “Detection of Extrasolar Giant Planets”, ARAA, 1998, 36:57-97

HISTORY OF DETECTION• 4th century : Aristotle and Epicurus argued about t

he uniqueness of the Earth

• Late 1500s : Copernicus(con), G. Bruno(pro)

• Early-1900s : – some “spiral nebulae” such as M51 misinterpreted as

planetary systems– Jeans-Jeffreys’ model for planet formation – Aitken(1938) : direct detection or by the wobble

HISTORY OF DETECTION• Wolszczan & Frail (1992) : 1st planetary system, PSR125

7+12 (post-SN recapture of material) by pulsar-timing method

• Mayor & Queloz (1995) : 51 Pegasi by Doppler periodicity

• Butler & Marcy (1996) : 1st detections of Jupiter-mass planets to solar-type star, 47 UMa and 70 Vir

• 2000s : HST-NICMOS, Spitzer, Kepler Space Mission(2007 ?), Space Interferometry Mission(SIM), Terrestrial Planet Finder(TPF) and so on....

DETECTION TECHNIQUES• Direct Detections

• Astrometric Detections

• Photometric Technique

• Doppler Technique

• Pulsar Timing

• Gravitational Microlensing

DIRECT DETECTIONS• Direct Imaging

– Small fluxes from the planets– Competing wings of the stellar PSF

• Solar-type star with MJ-planet at 5AU (Benchmark model)– Visible : ~10-9 (Vs = 5 and Vp = 27, 0.5”)– IR : improved to ~10-4 but low-resolution(>1”)

• Noise in PSF wings : seeing, microroughness of the mirror, and diffraction

DIRECT DETECTIONS• Minimum aperture D (diffraction alone)

• Remedy– Adaptive optics, Dark-speckle camera(JWST ?)– Ground-based interferometry, Keck, VLT, Spitzer....

50.41 10

D:aperture, λ:wavelength used, d:distance, r:orbital separation

d AUD meterspc r

ASTROMETRIC DETECTIONS• Stellar (proper) motion by its companion

– Determine Mp and i of a planet– Detect sub-MJ planets with future precision below 0.1 milliarcsec (mas)– Confirm planets detected by other means

• Angular wobble – Proportional to Mp and r– Inversely proportional to d

• Benchmark model : 0.5 mas

• Palomar 5-m (~250 μas, 1997), Keck (20 μas), & SIM (4 μas)

PHOTOMETRIC TECHNIQUE• Transit method : reduction in light

– aligned from astronomers’ vantage point

– 1% dimming by the Jupiter size planet

– Probability :

*

*

tan

i:inclination, a:semi-major axis, R :stellar radius

aiR

( ' 90 ) cos 'P i i i

PHOTOMETRIC TECHNIQUE• Marcy & Butler(1997) : 0.19% of

solar-type star exhibit transits

• Determination of – existence rate– occurrence rate – Planet radius

DOPPLER TECHNIQUE• Our Sun

– wobbles around the barycenter with ~13m/s by Jupiter(12.5 m/s) and Saturn(2.7m/s)

• Semi-amplitude K of the stellar radial velocity 1/3

2/3 2

2 32

*

sin2 1( * ) 1

4 (Kepler's third law)( )

p

p

p

m iGKp M m e

apG M m

DOPPLER TECHNIQUE

• Detectability of companions by the reflex velocity

• Intrinsic velocity scatter(σ) vs. rotational period(P) for F( ), G(∆ ⊙) and K(■) dwarfs (Saar et al, 1997)

OBSERVATIONS OF EXTRASOLAR PLANETS

• Walker et al (1995) : 21 dwarfs for 12 yrs with 13m/s

• Mayor & Queloz (1995) : 140 MS stars for 3 yrs

• Cochran & Hatzes (1994) : 33 stars for 10 yrs

• Marcy & Butler (1997) : 107 FGKM dwarfs with ~10m/s (8yrs) and 3m/s (4yrs)

DISTRIBUTION OF PLANETARY MASSES

• Histogram of M sini for all companions known around solar-type stars

• Tallest peak is at the lowest, least detectable masses(0-10 MJ)

47 Ursae Majoris• By Butler & Marcy (1996) with Doppler

measurement

• P = 3.0 yrs, e = 0.09 ± 0.04, a = 2.1 ± 0.1 AU and companion mass = (2.4 ± 0.1)/sini

55 Cancri and ρ Corona Borealis

• Mp ~ 1.0 MJ/sini (true masses < 3MJ)

• Orbital radii : 0.11 AU (55 Cnc) and 0.24 AU (ρ CrB) placing them inward of the ice-condensation point (~3AU)

• Low eccentricities (e= 0.04 and 0.11) – ρ CrB : too large orbit for tidal effects to cause low-e– 55 Cnc : tidal circulation and period of 14.7 days

• a) 55 Cnc

• b) ρ CrB by Noyes et al (1997)

• Both appear to have MJ-companions in nearly circular orbits.

70 Vir & 16 Cygni B : non-sinusoidal velocities

• Very eccentric Keplerian curves – e = 0.4 (70 Vir) and 0.687 (16 Cygni B)– Well fit by a simple Keplerian model

70 Vir ( Mp = 6.7 MJ/sini ) 16 Cygni - Lick( ) & McDonald(x)∆ - Mp = 1.67 ± 0.1 MJ/sini

GIANTS PLANETS ORBITING WITHIN 0.1AU

• MJ-companions with the orbital radii <0.1 AU

• Proximity to the star enhances the detectability (Fig. 1)

• 51 Peg : active corona and high X-ray flux

• Tau Boo : higher mass companion (3.7 MJ/sini )

• Upsilon And : short-term scatter (25m/s) by the rapid rotation of the star

SUMMARY• 8 extrasolar planet candidates have been i

dentified by Keplerian Doppler shifts(1998).

• Masses are between 0.5-7 MJ and semi-major axes are less than 2.1 AU.

• Detections imply that ~6% of solar-type stars have giant planets within 2 AU.