Andrew Collier Cameron

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Andrew Collier Cameron University of St Andrews
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Are we alone in the Universe?The plurality of
worlds

• In some worlds there is no Sun and Moon, in
  others they are larger than in our world, and in
  others more numerous. In some parts there are
  more worlds, in others fewer (...) in some parts
  they are arising, in others failing. There are
  some worlds devoid of living creatures or plants
  or any moisture.
• Democritus (ca. 460-370 B.C.), after Hyppolytus
  (3rd cent. A.D.)
• There cannot be more worlds than one.
• Aristotle De Caelo

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How do galaxies, stars and planets form and
evolve?

• The worlds come into being as follows many
  bodies of all sorts and shapes move from the
  infinite into a great void they come together
  there and produce a single whirl, in which,
  colliding with one another and revolving in all
  manner of ways, they begin to separate like to
  like.
• Leucippus (480-420(?) B.C.), after Diogenes
  Laertios (3rd cent. A.D.)

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Dusty discs around young stars

• Roughly half of all new-born Sun-like stars are
  surrounded by solar system-sized dusty discs.
• Could this mean that half of all Sun-like stars
  have planetary systems?

Proto-planetary discs in the Orion Nebula
(NASA/STScI)
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Searching for extra-solar Jupiters

• A planet and its parent star orbit round their
  common centre of gravity.
• The star is much more massive than the planet, so
  the reflex orbital speed is small.
• A massive planet in a close orbit gives its star
  a reflex velocity of a few tens of ms1.
• This gives a small but measurable Doppler shift.

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51 Pegasi The first wobbling star
Discovered by Michel Mayor Didier Queloz in
mid-1995.
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Todays state of play

• 237 planets in 203 systems, Oct 1995 -
  20-Aug-2007 from Doppler wobble searches.
• 25 multiple systems
• 24 transiting systems, 19 from transit searches
• 4 microlensing planets (more distant!)

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Recipe for building Jupiters

• Ingredients
• 10 Earth masses of ice-coated dust particles
• Lots of gas (mostly hydrogen)
• Method
• Allow dust ice to coagulate
• Allow solid core to sweep up gas
• Leave to cool for 5 billion years
• Common problems
• Tidal gaps starve planet of gas.
• Gas accretion takes tens of millions of years,
  longer than lifetime of disc.
• Migrating planets spiral into star.

Numerical simulation by Pawel Artymowicz,
Stockholm.
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Tip of the iceberg?

• Left panel Core accretionmigration simulation
  by Ida Lin (2004), showing gas giants, ice
  giants, rocky planets.

• Right panel Radial-velocity discoveries so far.

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Iron abundance and planet formation
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Eccentric Orbits
Unclear why.
Planet-planet interactions Eccentricity
pumping Small planets ejected Tidal
circularisation
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Other planet-building recipes

• If disk cools efficiently by infrared radiation,
  fragments can collapse spontaneously to form
  instant planets.
• Several dozen planets form and interact.

Numerical simulation by Ken Rice, University of
St Andrews.
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Other planet-building recipes

• If disk cools efficiently by infrared radiation,
  fragments can collapse spontaneously to form
  instant planets.
• Several dozen planets form and interact.
• Smaller planets get ejected from system.
• One big fish survives in an eccentric orbit.
• Problems
• Hard to get multiple, smaller planets to survive
  in near circular orbits.

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Lessons from Doppler Wobbles

• gt 5 of Sun-like stars host a Jupiter
• Metallicity matters
• Orbits differ from Solar System
• wide range of orbit radii ( P gt 2d )
• wide range of eccentricities
• New processes
• Migration -- spiral-in
• eccentricity pumping
• ejection
• What sort of planets are the hot Jupiters ?

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1.6
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Transit Lightcurves
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SuperWASP hardware

• Pollacco et al 2006, PASP 118, 1407
• Lenses
• Canon 200mm f/1.8
• Aperture 11.1 cm
• CCD Detector
• 2048 x 2048 thinned e2v (Andor, Belfast)
• 13.5x13.5 micron pixels
• Field of View
• 7.8 x 7.8 degrees
• 13.7 arcsec/pixel
• Mount
• OMI/Torus robotic mount
• Operating Temperature
• 50 ºC
• 3-stage Peltier Cooling

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WASP data reduction pipeline
Flatfield
Bias
Pre-processed
Raw
Field recognition, astrometry, aperture
photometry, calibration/de-trending
Flux-RMS
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Current Observing fields
Data processed so far (stellar density plot)
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Substellar mass-radius relation
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Mass-radius relation for hot Jupiters

• WASP-1b,-2b Cameron et al 2007, MNRAS

( XO-2b, HAT-P-2b, HAT-P-3b, TrES-3, TrES-4,
CoRoT-EXO-1b, Gl 436b since 2007 May 1)
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Why we need many more

• How does planet radius scale with
• Planet mass? (Fortney et al 2007)
• Planet age? (Many!)
• Metallicity/opacity? (Burrows et al 2007, Guillot
  et al 2006)
• Existence/size of core? (Guillot et al 2006)
• Proximity to host star? (Fortney et al 2007)
• Migration history?
• ?

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Core mass and formation mechanism

• Recent example
• HD 149026b
• Transiting hot Saturn
• High density gt massive core
• Sato et al, ApJ, in press
• Test formation models
• Core accretionmigration
• Gravitational instability

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GJ 436 b
WASP-1b

• Gillon et al 2007 May 17, astro-ph/0705.2219
• Neptune-mass planet
• Neptune-like radius
• Radius depends strongly on composition (cf.
  Fortney et al 2007, astro-ph/0612671)
• Ice-giant structure.

WASP-2b
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Exoplanet Discovery Space
100 Doppler wobble planets
Cool Planets
Hot Planets
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Microlensing by a star

• Light from background stars is gravitationally
  bent around a foreground star.
• Light is amplified near the Einstein Ring.
• Misaligned objects produce 2 images, one inside
  and one outside the Einstein Ring

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Now if I had a REALLY big telescope...

• ...this is what a Sun-like star would do to the
  view of dust clouds in a nearby galaxy, 150,000
  ly away.
• The Einstein ring of the star is about the size
  of Jupiters orbit round the Sun.

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First definitive planetary lens event!
OGLE-2003-BLG-235/MOA-2003-BLG-53

• OGLE/PLANET/MOA collaboration
• 45 microlensing events monitored intensively over
  the last 5 years.
• No convincing Jupiter-like secondary peaks found
  until last week!
• Conclusion less than 30 of lensing stars have
  Jupiters.
• First definitive planet detection announced in
  NASA press release by D. Bennetts team, 2004
  April 15.

Courtesy Dave Bennett and OGLE/PLANET/MOA team
members
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Planetary Parameters

• Best-fitting model
• Planet mass 1.5 Jupiter
  masses
• Star mass 0.36 solar
  masses
• Planet-star distance 3 times
  Earth-Sun distance
• Distance from Earth 16000
  light-years!

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Space-based transit detection
HST
MOST
CoRoT
KEPLER
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Whats in their atmospheres?
1.5
Brown (2001)
transit depth
1.6
Na I
wavelength (microns)
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Na I absorption in HD 209458b

• Charbonneau et al (2002 ApJ 568, 377)
• Hubble Space telescope / STIS
• Weak detection of Na!
• Df/f 2x104

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The amazing evaporating planet

• Vidal-Madjar et al (2003) Nature 422, 123

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Star occults planet
Spitzer/IRAC 4.5, 8.0 micron
0.2
Direct detection of infrared light from planet -gt
effective temperature
TrES-1 Charbonneau et al. 2005 HD 209458
Deming et al. 2005
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Water in HD 189733b

• Planet silhouette size measured in SPITZER/IRAC
  3.6, 5.8, 8.0 mm bands during primary transit.
• Wavelength dependence matches water transmission
  spectrum, mixing ratio 5x104 .

Tinetti et al 2007, Nature 448, 163
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The continuously habitable zone
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The Darwin Mission 2018?

• Aim to discover Earth-like planets orbiting
  nearby stars and seek atmospheric biosignatures.
• Four interlinked collector mirrors flying 100m
  apart.
• Light waves from collectors interfere to cancel
  out glare of central star.

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Youd look pretty simple from 30 light-years away
too

• Nulling interferometry with infrared light from
  Darwins four collectors eliminates light from
  star.
• Simulated image of our own solar system seen from
  30 light-years away detects all inner planets
  except Mercury

Earth
Venus
(Sun)
Mars
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Mid-IR spectra of terrestrial planets
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History of the Earths atmosphere
Methane, Ammonia
Nitrogen
Water
Carbon Dioxide
Oxygen
Time before present (billions of years)
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Summary

• Transiting hot Jupiters probe
• Interior structure
• Formation history
• Atmospheric composition
• Albedo and energy budget
• Wide but shallow surveys (WASP, HAT, TrES, XO)
  yielding several planets/year bright enough for
  transit spectroscopy, Spitzer /JWST
  secondary-eclipse studies.
• Space-based transit studies capable of detecting
  hot (CoRoT) and warm (KEPLER) super-Earths and
  determing bulk composition.
• Efficient spectroscopic confirmation essential to
  eliminate impostors and determine planet masses.
• Long-term, high-precision transit timings may
  reveal lower-mass planets.
• DARWIN/TPF nulling interferometry will permit
  10-micron spectroscopy of terrestrial planet
  atmospheres.

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Postcards from Titan
Image Credit NASA/JPL/University of Arizona
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Transiting extrasolar giant planets

• 19 examples known.
• Stellar mass and period yield orbital separation
  a.
• Transit shape yields
• impact parameter
• stellar radius
• Transit depth yields ratio of radii
• Hence get direct measure of planetary density.