Ge/Ay133

What can transit observations tell us about (exo)-planetary science?

Part II – “Spectroscopy” & Atmospheric Composition/Dynamics

Kudos to Heather Knutson, now at Caltech!

Rapid Progress: Transiting Planets, 1 May 2007

One year later (2008): 43 Systems And Counting

Ice/Rock Planets

Updates from exoplanets.org :

Hot Jupiter/Neptune atmospheres?

M L T

In the optical/near-IR, the spectra of M → T dwarfs (similar temp. as the hot Jupiters) show strong alkali metal lines:

Transit

Secondary EclipseSee thermal radiation

and reflected light from planet disappear and reappear

See radiation from star transmitted through the planet’s atmosphere

Orbital Phase Variations

See cyclical variations in brightness of planet

Transiting Planets as a Tool for Studying Exoplanet Atmospheres

Characterizing Atmospheres With Transmission Spectroscopy

• Probes composition of atmosphere at day-night terminator

• Can search for clouds, hazes, condensates

HST STIS transits of HD 209458b from 290-1030 nm (Knutson et al. 2007a)

Atmosphere

Star

Planet

First detection ofan extrasolar planetatmosphere:

Look for the transit depth in filters on and off the Na D-line with HST.

Charbonneau, D. et al. 2001, ApJ, 568, 377

Atmospheres Part II: Most atoms have their so called resonance lines in the UV. The H I depth is VERY large. EXOSPHERE?

Vidal-Madjar, A. et al. 2004, ApJ, 604, L69

Water and Haze on HD 189733b

Figure from Pont, Knutson et al. (2007) showing atmospheric transmission function derived from HST ACS measurements between 600-1000 nm

Figure from Swain et al (2008) showing infrared atmospheric transmission function derived from HST NICMOS spectra compared to models for the planet’s transmission spectrum with (orange) and without (blue) additional methane absorption (Tinetti et al. 2008).

Featureless visible light spectrum indicates hazes…

… which disappear in infrared, revealing water absorption features.

What about day/night chemistry? Need IR observations:

GL 229B (BD)

T dwarf IR opacities dominated by CH4, H2O.

Oppenheimer, B. et al. 1998, ApJ, 502, 932

A Broadband Emission Spectrum For HD 189733b

Charbonneau, Knutson et al. (2008), Barman (2008)

Use secondary eclipses to acquire dayside fluxes:

Can even collect R~50-100 spectra: IRS Data for HD 189733b

Grillmair et al., Nature 456, 767 (Dec. 11 2008)

Gillett, Low, & Stein (1969), “The 2.8-14 Micron Spectrum of Jupiter”

“Most of the features of the 2.8-14 μm spectrum of Jupiter can be accounted for on the basis of absorption by NH3, CH4, and H2.”

A Near-IR Emission Spectrum for HD 189733b

“Most of the features of the 2.8-14 μm spectrum of Jupiter can be accounted for on the basis of absorption by NH3, CH4, and H2.” Swain et al. (2009)

HST NICMOS observations of a secondary eclipse of HD 189733b

Even in space, these measurements are at the limits of current detectors:

HSTNICMOS

Spitzer

A Surprise: The Emission Spectrum of HD 209458b

Why would two hot Jupiters with similar masses, radii, compositions, and temperatures have such different pressure-temperature profiles?

Requires a model with a temperature inversion and water features in emission instead of absorption.

Knutson et al. (2008c), Burrows et al. (2007)

Gas Phase TiO/VO

Temperature Inversion?

Problem: Cold Trap

Figure from Fortney et al. (2008)

As described in Hubeny et al. (2003), Burrows et al. (2007, 2008), and Fortney et al. (2008)

TrES-4 is a great test case!

Teq = 1760 K

InvertedNon-Inverted

One alternative: photochemistry(tholins, polyacetylenes?)

Possible Explanation: UV Chromospheric Stellar Activity?

Figure from Knutson et al. 2010, ApJ, 720, 1569

Incr

easi

ng U

V

Ultimately want many objects/wavelengths;

Problem: Switch from inverted to non-inverted states can artificially increase day-night contrast

Observations of HD 209458b from Knutson et al. (2008a)

Model for HD 209458b from Showman et al. (2008)

Solution: Use 3.6 and 4.5 μm phase curves to map extent of inversion

Ultimately want many objects/wavelengths;

Observations of HD 209458b from Knutson et al. (2008a)

Solution: Use 3.6 and 4.5 μm phase curves to map extent of inversion

The warm Spitzer mission has done another 18 planets at 3.6/4.5 m (H. Knutson, P.I.).

Test of Spitzer color index with stellar UV activity Knutson et al. 2010, ApJ, 720, 1569

Ground? Line shape would give pressure at the photosphere,center/shift the wind profiles. Challenge is the Earth’s atmosphere!

Limits only just beginning to reach sufficient sensitivity…

CO Search

Terrestrial CH4

Deming, D. et al. 2005, ApJ, 622, 1149

First possible ground based high spectral resolution detection:

Gives orbital velocity and thus absolute mass of the planet & star (w/RV), is the blueshift due to strong winds across the terminator?

Snellen, I. et al. 2010, Nature, 465, 1049

A Diversity of Worlds

Super-Earths & Mini-Neptunes

Mass range:1-10 Earth masses

Prospects for Studies of Terrestrial Planets With the James Webb Space Telescope (launches 2018?)

Seager, Deming, & Valenti (2008)

Neptune-mass planets are observable with Spitzer and HST….

… but observations of earth-like planets orbiting M dwarfs will require JWST-level precision

Predicted transmission spectrum for a 0.5 Mearth, 1 Rearth, 300 K planet orbiting a M3V, J=8 star

Imaging extrasolar planetary systems?

Jovian-mass planets cool slowly, so few-few 10s of MYr old objects are fairly bright…

And have emission peaks in the near-IR atmospheric windows where AO systems perform well.

Marois et al. (2008), Science

Signatures of “young” planetary systems?

One group of systems to try are the so-called ‘debris disks’ that we’ll learn about later. These are young stars with “2nd generation dust” caused by planetesimal collisions.

Pictoris (VLT,proper motion now confirmed)

HR 8799 Marois et al. (2008), Science

Can also use coronography/PSF subtraction in space:

Too bright @ 600 nm? Circum- planetary disk?

If so, Mp?

Use dynamics!

Fomalhaut dynamical analysis of companion mass:

Kalas, P. et al. (2008), Science

Neptune-mass planets are observable with Spitzer and HST….

Modeling of the dust ring suggests an upper limit to the companion of ~3 MJ. Photometry-based mass estimate uncertainties are dominated by possible age(s).

Formation? (In situ/scattering?)