Characterizing Extrasolar Planets from their Transit Lightcurves

Jason W. BarnesAssistant ProfessorDepartment of PhysicsUniversity of Idaho

ECE Seminar2008 December 11

Moscow, ID

Oblateness, Rings, Moons

Transit(if only they looked like this!)

Transit Lightcurves

Transit schematicTo first order (providing a surprisingly good description), lightcurve determines

l – transit durationd – transit depthw – ingress/egress duration – curvature from limb darkening

these 4 measurables determine 4 transit parameters:

Rp – planet radius

R* – star radius

b – transit impact parameterc

1 – stellar limb darkening

(Brown et al., 2001)

Transiting Planets Discovered So Far

The Kepler Mission:A Search for Habitable Planets

Kepler Field of View

Kepler Field of View

Kepler Focal Plane Assembly

Kepler Orbit and Quarterly Rolls

Kepler Focal Plane Assembly

Kepler Planet Discovery PipelineNew data arrive every 30 days.

1. Perform photometry2. De-trend time series3. Whiten4. Fold data at various test periods; hunt for transits using notched filter correlation5. Rule out false-positives (hard)

Characterizing Transit Lightcurves: Oblateness

Seager & Hui (2002); Barnes & Fortney (2003)

Time from Mid-Transit (hours)

Detectability of Non-Zero Obliquity Planet

Time from Mid-Transit (hours)

Detectability of Zero-Obliquity Planet

Barnes & Fortney (2003)

Deriving Rotation Rate from Oblateness

Barnes & Fortney (2003)

What Does Rotation Tell Us About Planets?

Bears fingerprints of formation

Reveals degree of tidal influence & Q

Could constrain tidal dissipation mechanismIncr

easi

ng s

emim

ajor

axi

s

Barnes & Fortney (2003)

Detectability of Large, Saturn-Like Ring Systems

Barnes & Fortney (2004)

Diffraction Can Reveal Ring Particle Size

Barnes & Fortney (2004)

Why Would Extrasolar Rings Matter?

Can help to constrain ring formation conditionsChemistry

Could empirically address age of ring systems in generalPossible Saturn implications

Will add to the ring menagerie; what ring architechtures are possible?

Are ring systems normal, or is Saturn special?

JupiterCassini / ISS

SaturnCassini / VIMS

UranusHST

NeptuneVoyager 2

Sartoretti & Schneider (1999)

Detecting Extrasolar Moons

2 methods:

Direct transit Transit timing

Brown, Charbonneau, Gilliland, Noyes, & Brown (2001) placed upper limitson moons of HD209458b from HST STIS photometry – 1.2 R⊕ and 3 M⊕

Algorithm Under Development

Simultaneous fit for timing, direct transitmaximum moon parameters to be fit:

M, , a, e, i,

Kepler Characterizing Transiting Planets Kepler will find Earth-sized planets. In doing so, Kepler will also incidentally discover ~100 transiting giant planets

Oblateness – result of planet's spin If nonzero obliquity, induces lightcurve asymmetry For zero obliquity, detectabilities are low If detected can allow inference of planet's rotation rate

Rings Induce evident transit signatures, for large Saturn-like systems Can help constrain the origin and evolution of all ring systems

Moons Revealed by both timing and direct moon transit Can find habitable moons and constrain planetary parameters