Observations of extrasolar planets
1Wednesday, November 9, 2011
Mercury
2Wednesday, November 9, 2011
Venusradar image from Magellan (vertical scale exaggerated 10 X)
3Wednesday, November 9, 2011
Mars4Wednesday, November 9, 2011
Jupiter
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Saturn
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Saturn
7Wednesday, November 9, 2011
Uranus and Neptune
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we need to look out about 10 parsecs
or 2 million astronomical units
to examine 100 stars for planets
9Wednesday, November 9, 2011
• the Earth is visible in reflected light from the Sun
• the total light reflected by Earth is about 10-9 of the light emitted by the Sun
• Jupiter is bigger but more distant so only about 4X brighter than Earth
These would be easy to see with modern telescopes at 10 parsecs if the star were not right beside them
(imagine looking at a lighthouse 1000 km away and trying to detect a firefly flying 1 meter from the light)
With current technology direct imaging requires one or more of:
• planet with a large orbital radius (e.g. 100 AU vs. 30 AU for Neptune)
• observations in the infrared (for a black body in thermal equilibrium at 100 AU around the Sun, emission peaks at 100 microns)
• young planet (Jupiter’s internal luminosity falls at 1/age)
why is finding planets hard?
10Wednesday, November 9, 2011
• star is at 7.7 parsecs• planet has 110 AU orbital radius, 900 yr orbital period• 100-300 Myr stellar age
11Wednesday, November 9, 2011
HR 8799
• star is at 39 parsecs • planets have masses of 7-10 Jupiter masses and projected separations of 14-68 AU• 30-160 Myr age
Marois et al. (2008, 2010)
12Wednesday, November 9, 2011
• current accuracy: velocity of 1 meter/sec (3 parts in 109)
• cross-correlation uses all lines in spectrum
• high S/N (bright stars, big telescopes)
• iodine absorption cell• old stars (less rotation, less activity)• G stars
• Jupiter: orbital period of 12 yr, reflex velocity of Sun 13 meter/sec
• Earth: orbital period of 1 yr, reflex velocity of Sun 0.1 meter/sec
13Wednesday, November 9, 2011
Given the star mass M (known from spectral type), radial-velocity observations yield:
• orbital period P• semi-major axis a• combination of planet mass m & inclination I, m sin I• orbit eccentricity e
14Wednesday, November 9, 2011
• the star is similar to the Sun and 11 parsecs away
• the planet orbits once every 15.8 days, has a mass 4 X that of Jupiter (if edge-on orbit), and is 0.11 AU from the star 100 meters/second
15Wednesday, November 9, 2011
HD 82943
planet 1:
m sin I = 1.84MJ
P = 435 de = 0.18 ± 0.04
planet 2:
m sin I = 1.85MJ
P = 219 de = 0.38 ± 0.01(Mayor et al. 2003)
16Wednesday, November 9, 2011
Timing
• works for pulsars, pulsating stars, eclipsing binaries
• observed period is P=P0(1+v/c) so
17Wednesday, November 9, 2011
Pulsar planets
• three planets discovered orbiting PSR B1257+12 by Wolszczan & Frail (1992)
• orbital parameters can be determined far more accurately than for radial-velocity measurements of nearby stars
• two planets near 3:2 resonance which enhances mutual perturbations, so these can be measured
• remarkably similar to the inner solar system
18Wednesday, November 9, 2011
Konacki & Wolszczan (2003)
(a) no planets
(b) three planets
(c) three planets + mutual interactions
19Wednesday, November 9, 2011
Konacki & Wolszczan (2003)
20Wednesday, November 9, 2011
Transit of Venus
• next June 6, 2012, 22:10 UTC at Tokyo
1769
Jupiter’s satellite Io
21Wednesday, November 9, 2011
22Wednesday, November 9, 2011
22Wednesday, November 9, 2011
Transit searches
Why are these so hard?
• probability that a given planet will transit is small, ~ rstar/a (only 0.5% at a = 1 AU)
• transit duration is short, ~(rstar/a)P/π
• transit depth is small, <1% *
• confusion from grazing eclipsing binary stars
• star spots, stellar pulsations, stellar flares
• incomplete sampling (daytime, weather, observing schedules, etc.)*
* much easier in space
23Wednesday, November 9, 2011
0.5%
24Wednesday, November 9, 2011
Kepler (NASA)• launch March 6 2009
• stare 24/7 for five years at a single patch of sky
• monitor 200,000 stars for transits
• ppm precision
25Wednesday, November 9, 2011
transit: planet moves in front of the star; U-shape because of limb darkening in staroccultation: planet moves behind the star; square shape
26Wednesday, November 9, 2011
transit: planet moves in front of the star; U-shape because of limb darkening in staroccultation: planet moves behind the star; square shape
26Wednesday, November 9, 2011
• orbital period P = 5.2 days• two curious features:
• sinusoidal brightness variations at fundamental and first harmonic • transit (U shape) is shallower than occultation (square well)
van Kerkwijk et al. (2010)
27Wednesday, November 9, 2011
• orbital period P = 5.2 days• two curious features:
• sinusoidal brightness variations at fundamental and first harmonic • transit (U shape) is shallower than occultation (square well)
• both can be explained if the companion is a white dwarf rather than a planet:
• occultation is deeper because the white dwarf is hotter than the primary (T=13,000 K vs. 9,400 K) • first harmonic due to tidal distortion of the primary by the white dwarf• fundamental due to Doppler boosting • white dwarf has mass 0.22±0.03 M⊙; radius 0.043±0.004 R⊙
• P/2 variations due to tidal distortion of the primary star by the white dwarf• P variations due to Doppler boosting orbital velocity to 1 km/s
van Kerkwijk et al. (2010)
28Wednesday, November 9, 2011
Struve (1952)
29Wednesday, November 9, 2011
Gravitational lensing
• a particle traveling at high speed v past a mass M with impact parameter b suffers angular deflection α =2GM/v2b
• in general relativity, deflection of a photon is obtained by replacing v by c and multiplying by 2:
• three effects: position shift, image splitting, image magnification
30Wednesday, November 9, 2011
Gravitational lensing
the gravitational field from the lensing star:
- splits image into two- magnifies one image and demagnifies the other- if source, lens and observer are exactly in line the image appears as an Einstein ring
lensing massEinstein ring
source track
31Wednesday, November 9, 2011
Gravitational microlensing
Consider a source star near the center of the Galaxy, lensed by an intervening star at half that distance. Then θE=0.001 arcsec ~ 4 AU.
• image splitting or shift is impossible to see
• image magnification is easy to see
• time required to transit Einstein ring ~DLθE/v~0.2 yr, for v~100 km/s
• substantial magnification if and only if impact parameter less than Einstein radius
• chance that any given star is microlensed is only ~10-6
32Wednesday, November 9, 2011
Mao et al. (2002)33Wednesday, November 9, 2011
Gravitational microlensing of planets
• Einstein radius scales as M1/2 so cross-section and expected duration scale as M1/2~ 0.03 for Jupiter, i.e. duration ~ 1 day for Jupiter, ~1 hour for Earth
• image magnification is the same
• Einstein ring radius ~ typical planet orbital radius
34Wednesday, November 9, 2011
Beaulieu et al. (2006): 5.5 (+5.5/-2.7) MEarth, 2.6(+1.5/-0.6) AU orbit, 0.22(+0.21/-0.11) MSun, DL=6.6±1.1 kpc
35Wednesday, November 9, 2011
fa
ctor
of
ten
daysGaudi et al. (2008)
xxx
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Gaudi et al. (2008)
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1% of Einstein radius or 15 µas
star path
source size
38Wednesday, November 9, 2011
• two planets, b and c• can detect orbital motion of Earth and planet c• mb = 0.71 ± 0.08 MJupiter, mc = 0.27 ± 0.03 MJupiter
• assuming coplanar, circular orbits ab = 2.3 ± 0.2 AU, ac = 4.6 ± 0.5 AU• distance 1.49 ± 0.13 kpc• M*=0.50 ± 0.05 M⊙
Gaudi et al. (2008)
39Wednesday, November 9, 2011
Astrometry
the Sun’s motion as seen from
10 pc
why this is hard:
• typical motions << 0.001 arcsec ~ 10-8 radians
• not many nearby stars
• confusion from outer planets: maximum radial velocity is (m/M)(GM/a)1/2 but maximum wobble is (m/M)a
space missions:
• GAIA (ESA) • launch 2013 • every Jupiter analog within 50 pc• 104 - 5 × 104 planets•also transits via photometry
40Wednesday, November 9, 2011
the current track record:
• imaging: 26• radial velocity: 644• transits: 185
• gravitational lensing: 13• timing: 12
• astrometry: 0
see http://www.exoplanet.eu, http://exoplanets.org/
figure from Seager (2011)
41Wednesday, November 9, 2011
Current record-holders (RV surveys)
• smallest semi-major axis a = 0.0143 AU = 3.06 RSun
• largest semi-major axis a=11.6 AU (Jupiter = 5.2 AU)
• biggest eccentricity e = 0.94
• smallest eccentricity e = 0
• smallest mass 0.0061 MJupiter = 1.9 MEarth
42Wednesday, November 9, 2011
Mercury Venus Earth Mars Jupitersolar radius 0.00465 AU
43Wednesday, November 9, 2011
Mercury Venus Earth Mars Jupitersolar radius 0.00465 AU
GJ 1214 b, a=0.0143 AU
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undercounted because of selection effects
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45Wednesday, November 9, 2011
“hot Jupiters”
45Wednesday, November 9, 2011
Grether & Lineweaver (2006)
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Grether & Lineweaver (2006)
hydrogen burning limit
deuterium burning limit
46Wednesday, November 9, 2011
tidal circularization
47Wednesday, November 9, 2011
Ribas & Miralda-Escudé (2007)
binary stars
massive planets (M > 4 Jupiter masses)
planets (M < 4 Jupiter masses)
eccentricity distribution of massive planets is similar to that of binary stars
48Wednesday, November 9, 2011
Johnson (2007)
high-mass stars are more likely to host planets
49Wednesday, November 9, 2011
(from J. Winn)50Wednesday, November 9, 2011
(from J. Winn)
obliquity = angle between spin angular momentum of star and orbital angular momentum of planetRossiter-McLaughlin measures angle between projection of spin angular momentum of star and orbital angular momentum of planet on the sky plane
50Wednesday, November 9, 2011
51Wednesday, November 9, 2011
HAT-P-30b 7
−40
−20
0
20
40
RV [m
s−1]
−2 0 2Time from midtransit [hr]
−10
0
10
O−C
[m s
−1]
50 60 70 80 90 100! [deg]
2.5
3.0
3.5
4.0v
sin i
[km
s−1]
Fig. 4.— Rossiter-McLaughlin effect for HAT-P-30 Left.—Apparent radial velocity variation on the night of 2011 Feb 21, spanninga transit. The top panel shows the observed RVs. The bottom panel shows the residuals between the data and the best-fitting model.Right.—Joint constraints on λ and v sin i!. The contours represent 68.3%, 95.4%, and 99.73% confidence limits. The marginalized posteriorprobability distributions are shown on the sides of the contour plot.
HATNet operations have been funded by NASA grantsNNG04GN74G, NNX08AF23G and SAO IR&D grants.GT acknowledges partial support from NASA grantNNX09AF59G. We acknowledge partial support alsofrom the Kepler Mission under NASA CooperativeAgreement NCC2-1390 (D.W.L., PI). G.K. thanks the
Hungarian Scientific Research Foundation (OTKA) forsupport through grant K-81373. This research hasmade use of Keck telescope time granted through NASA(N167Hr). Based in part on data collected at SubaruTelescope, which is operated by the National Astronom-ical Observatory of Japan.
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HAT P-7bλ = 183±9°Winn et al. (2009)HAT P-30b
λ = 74 ± 9°Winn et al. (2009)
HAT P-14bλ = 189 ± 5°Winn et al. (2011)
52Wednesday, November 9, 2011
53Wednesday, November 9, 2011
Seager & Deming (2010)
detection of CH4, H2O, Na, CO, CO2
54Wednesday, November 9, 2011
55Wednesday, November 9, 2011