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Lecture III: Gas Giant Planets

Lecture III: Gas Giant Planets. From Lecture II: Phase separation Albedos and temperatures Observed transmission spectra Observed thermal spectra Observations of reflected light. Mass-Radius Plot for Hot Jupiters. H + He. H + He + rocky core. A Problem with Saturn ?.

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Lecture III: Gas Giant Planets

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  1. Lecture III: Gas Giant Planets From Lecture II: Phase separation Albedos and temperatures Observed transmission spectra Observed thermal spectra Observations of reflected light

  2. Mass-Radius Plot for Hot Jupiters H + He H + He + rocky core

  3. A Problem with Saturn ?... Its current luminosity is ~50% greater than predicted by models that work for Jupiter: If modelled like Jupiter, Saturn reaches its current Teff (luminosity) in only 2 Gyr ! Fortney & Hubbard (2004)

  4. A Problem with Saturn ?… • One idea for resolving the discrepancy - phase separation of neutral He from liquid metallic H(Stevenson & Salpeter 1977): for a saturation number fraction of the solute (He), phase separation will occur when the temperature drops below T : x = exp (B - A/kT) where x=0.085 (solar comp., Y=0.27), B=const.(~0), A~1-2 eV (pressure- dependent const.), therefore T = 5,000 - 10,000 K

  5. A Problem with Saturn ?... Phase diagram for H & He: Fortney & Hubbard (2004) Model results: Stevenson (‘75) vs. Pfaffenzeller et al. (‘95) - different sign for dA/dP !

  6. A Problem with Saturn ?... New models: Fortney & Hubbard (2004) Model results: The modified Pfaffenzeller et al. (‘95) phase diagram resolves the discrepancy. Good match to observed helium depletions in the atmospheres of Jupiter (Y=0.234) & Saturn (Y~0.2).

  7. Evolution Models of Exo-planets: Cooling curves: Fortney & Hubbard (2004) Models: All planets have 10 ME cores & no irradiation. The models with He separation have ~2 x higher luminosities.

  8. Mass-Radius Plot for Hot Jupiters H + He H + He + rocky core

  9. Atmosphere: • In general - outer boundary for planet’s thermal evolution - the extrasolar planets have introduced conditions which had never been modeled. • Clouds & (photo)chemistry • Evaporation (very hot & hot Jupiters) Transits make easier the spectroscopic studies of a planet’s atmosphere.

  10. Albedos Rowe et al.(2006)

  11. HD 209458b Albedos New upper limit on Ag (Rowe et al. 2008) Rowe et al.(2006)

  12. Models Constraints Different atmospheres blackbody model Equilibrium Temperature Spitzer Limit best fit 2004 1 sigma limit – or - ~2005 3 sigma limit Rowe et al. 2006 Rowe et al. (in prep)

  13. The Close-in Extrasolar Giant Planets Seager & Sasselov 2000 • Type and size of condensate is important • Possibly large reflected light in the optical • Thermal emission in the infrared

  14. Atmosphere: What is special about atomic Na and the alkali metals? Seager & Sasselov (2000)

  15. Atmosphere: Theoretical Transmission Spectra of HD 209458 b Occulted Area (%) Wavelength (nm) Seager & Sasselov (2000)

  16. Atmosphere: The tricks of transmission spectroscopy: Brown (2001)

  17. The actual detection (with the HST): • a 5s signal • 2x weaker than model expected, but within errors • Might indicate high clouds above terminator, but … Charbonneau et al. (2002)

  18. Direct Detection of Thermal Emission

  19. Model Constraints Different atmospheres blackbody model Equilibrium Temperature HD 209458b Spitzer Limit Tb = 1130 K Deming et al. 2005

  20. Spectra Four observed data points vs. models Burrows, Sudarsky, & Hubeny (2006)

  21. Infrared Eclipses in HD 189733: Measuring the Emitted Heat Time (in fraction of day) Detection (Feb. 20, 2006) by Deming et al. using the Spitzer Space Telescope Relative Intensity or Brightness Orbital phase

  22. Variability in IR Eclipse Depths Temperature map of a partially eclipsed face of HD209458b in a model with 400 m/s winds. Rauscher et al. (2006)

  23. Variability in IR Eclipse Depths Temperature map of a partially eclipsed face of HD209458b in a model with 400 m/s winds. Rauscher et al. (2006)

  24. uAnd b The Spitzer IR photometry at 24 micron: A) Raw data B) Corrected for zodiacal foreground Harrington, et al. (2006)

  25. uAnd b The Spitzer IR photometry at 24 micron fit to a model Harrington, et al. (2006)

  26. Lecture II: Observed Spectra of EGPs Albedos and temperatures Observed transmission spectra Observed thermal spectra Observations of reflected light

  27. Observations for Reflected Light • Sudarsky Planet types • I : Ammonia Clouds • II : Water Clouds • III : Clear • IV : Alkali Metal • V : Silicate Clouds • Predicted Albedos: • IV : 0.03 • V : 0.50 Picture of class IV planet generated using Celestia Software Sudarsky et al. 2000

  28. Micromagnitude variability from planet phase changes • Space-based: MOST(~2005), COROT (~2007), Kepler (~2008) Photometric Light Curves • D m=2.5 (Rp/D)22/3/p(sin(a) + (p-a)cos(a))

  29. Scattered Light • Need to consider: • phase function • multiple scattering

  30. Scattering Phase Functions and Polar Plots MgSiO3 (solid), Al2O3 (dashed), and Fe(s) Forward throwing & “glory” Seager, Whitney, & Sasselov 2000

  31. Scattered Light Changes with Phase Seager, Whitney, & Sasselov 2000 51 Peg @ 550 nm

  32. MOST at a glance Mission • Microvariability and Oscillations of STars / Microvariabilité et Oscillations STellaire • First space satellite dedicated to stellar seismology • Small optical telescope & ultraprecise photometer • goal: ~ few ppm = few micromag Canadian Space Agency (CSA)

  33. MOST at a glance MOST CVZ = Continuous Viewing Zone orbit normal vector to Sun Orbit • circular polar orbit • altitudeh = 820 km • periodP = 101 min • inclinationi = 98.6º • Sun-synchronous • stays over terminator • CVZ ~ 54° wide • -18º < Decl. < +36º • stars visible for up to 8 wks • Ground station network • Toronto, Vancouver, Vienna

  34. Lightcurve Model for HD 209458b • Relative depths • transit: 2% • eclipse: 0.005% • Duration • 3 hours • Phase changes of planet Relative Flux Eclipse Transit Phase

  35. The Lightcurve from MOST 2005 observations, 40 minute binned data 0.03 mag 45 days • 2004 data : 14 days, 4 orbital cycles • 2005 data : 45 days, 12 orbital cycles • duty cycle : ~90% • 473 896 observations • 3 mmag point-to-point precision

  36. 0.1 mag 0.02 mag 0.8 mmag

  37. Albedo Results • Best fit parameters: • Albedo : 0.07 ± 0.05 • stellar radius : 1.346 ± 0.005 RJup • Other Parameters: • stellar mass: 1.101 Msun • inclination: 86.929 • period : 3.52... days see Knutson et al. 2006 1,2,3 sigma error contours Radius (Jupiter) Geometric Albedo Rowe et al. (in prep)

  38. Atmospheres MOST bandpass • HD 209458b is darker than Jupiter • Rule out class V planet with bright reflection silicon clouds Geometric Albedo Marley et al. 1999

  39. HD 209458b Albedos New upper limit on Ag (Rowe et al. 2007) Rowe et al.(2006)

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