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Transiting Extrasolar Planets
Recent Progress, XO Survey, and the Future
Christopher J. Burke
Solar System
Has Predominately
Circular Orbits
Top View
Side View
Planet Formation
NASA/JPL-Caltech/R. Hurt (SSC)
Courtesy of Windows to the Universe,
~200 Extrasolar Planets
>7% stars have Jupiter mass planets within 5 AU
● 1.2% stars have Hot Jupiter planets
● Most planets have a>1 AU
Metallicity Correlation
Fischer & Valenti 2005
Multi-planet systems common (>30%)
Wright et al. (2006)
Low mass planets more common
than high mass planets.
NASA/JPL-Caltech/T. Pyle (SSC)
5.5 Earth mass planet Beaulieu et al. (2006)
How do you detect planets?
Radial Velocity Technique
Doppler Shifted Light
Only Measure Planet Mass
©Think Quest
Extrasolar Planet Detection
Transit Technique
Δf = (Rp/R*)2 ~1%
Charbonneau et al. 2006, Brown et al. 2001
70 Mearth core
Core Dominated
Sato et al. (2005) & Fortney et al. (2005)
Difficult to explain
Charbonneau et al.
Inflated Radius
What do we learn from
Transiting Planets?
Highly accurate radii
Stellar limb darkening
Dan Bruton
HD 209458b
Knutson et al. (2006)
What do we learn from
Transiting Planets?
Highly accurate planet radii
Stellar limb darkening
Characterize planet atmosphere
Transmission spectroscopy
Na, H, C, O detection HD 209458
Charbonneau et al. (2002), Vidal-Madjar (2003, 2004)
Out of Transit
In Transit
Compare Spectra
Vidal-Madjar (2003)
Vidal-Madjar (2003)
What do we learn from
Transiting Planets?
Highly accurate planet radii
Stellar limb darkening
Characterize planet atmosphere
Phased light curve – optical
Reflected Light
Albedo <0.25 Rowe et al. (2006)
will soon reach ~0.1 limits
Hot Jupiter planets are dark!
What do we learn from
Transiting Planets?
Highly accurate planet radii
Stellar limb darkening
Characterize planet atmosphere
Secondary Eclipse – IR
Test planet atmosphere models
NASA/JPL-Caltech/R. Hurt (SSC)
Constrain atmosphere
metallicity, clouds,
redistribution of heat, perhaps
CO & H2O
Disentagling these effects may be difficult
Burrows et al. (2006)
Motivated to find bright
transiting planets
XO Transit Survey
PI Peter McCullough
Jeff Valenti
Ken Janes, Boston U
Jim Heasley, U of Hawaii
Chris Johns-Krull, Rice U
Extended Team Professionals & “Amateurs”
Ron Bissinger, CA
Mike Fleenor, TN
Cindy Foote, UT
Enrique Garcia, Spain
Bruce Gary, AZ
Paul Howell, ME
Franco Malia, Italy
Gianluca Masi, Italy
Tonny Vanmunster, Belgium
Haleakala, Maui
Baker Nunn Observatory 1957
Built to track satellites
in particular Sputnik
Today houses XO
10 cm aperture
Every 10 min
7.2o x 63o strip
Why have so few transits been found?
Only 1.2% stars have Hot Jupiter planets
The probability for a Hot Jupiter to transit ~10%
Most stars are too big (sub-giant or giant)
In magnitude limited survey only 10%
of stars are dwarfs Gould & Morgan (2003)
There are many objects that mimic
a transit signal
Transit Imposters
Transit surveys yield 10/1 false positives
Dwarf star eclipsing a subgiant/giant
Grazing eclipsing binary
Triple star / blend diluted deep eclipse
Brown dwarfs
Transit Imposters
Brown dwarf same radius
as planet!
96 MJup
Radial Velocity Followup Required!
How does XO deal with imposters
Stellar spectral type estimate
Photometric catalogs - Tycho, 2MASS, TASS
Transit duration, depth, and period
consistent with a planet orbiting the
estimated stellar spectral type
Discriminate dwarfs from giants
Closer stars
Higher Proper Motion
NASA/IPAC Infrared Science Archive
XO's Extended Team
Triple Stars
XO has time
on the
for precision
as a bona fide
Future of Extrasolar Planets
HARPS now achieves 20 cm/s
RV stability over several days
Pont priv. comm. (2006)
ESO La Silla 3.6m
Space Based Transit Searches
COROT – Launched Dec. 26
27cm primary
2.5 year duration
150 day continuous
Space Based Transit Searches
KEPLER – Nov. 2008
1.4m primary
4 year duration fully continuous
42 CCDs to fill 1.2o diameter FOV
100,000 stars V<15.0
Precision Transit Timing
Sensitive to moons, rings,
stellar spots
Can detect Earth mass
planets in resonance
XO Future
XO-2b, XO-3b, XO-4b,...
Expansion to 3+ mounts in 2007