Exoplanetary Atmospheres: Temperature Structure of Irradiated Planets. PHY 688, Lecture 23 Mar 20, 2009

Transcription

1 Exoplanetary Atmospheres: Temperature Structure of Irradiated Planets PHY 688, Lecture 23 Mar 20, 2009

2 Outline Review of previous lecture hot Jupiters; transiting planets primary eclipses and atmospheric transmission spectroscopy secondary eclipses and direct flux measurements Properties of irradiated giant planets atmospheric temperature structure isothermal region temperature inversion Mar 20, 2009 PHY 688, Lecture 23 2

3 Previously in PHY 688 Mar 20, 2009 PHY 688, Lecture 23 3

4 > 300 Planets (c.a. 2005) Now Known vast majority discovered through radial velocity surveys 5 M Earth < M sin i < 15 M Jupiter 1 day < P < 15 years two dozen multiple planet systems known 55 Cnc: 5 planets! significant population of hot Jupiters completely unexpected before initial discovery wealth of information on orbital parameters, but exact masses are scarce Mar 20, 2009 PHY 688, Lecture 23 4 (exoplanets.org)

5 Geometry for Transit Probability Mar 20, 2009 PHY 688, Lecture 23 5 (kepler.nasa.gov)

6 First Extrasolar Planet Transit: HD b HD b was a known extrasolar planet in a = AU semi-major axis Mar 20, 2009 PHY 688, Lecture 23 6 (Charbonneau et al. 2000)

7 Accurate Mass and Radius Determination i is nearly 90º; edge-on dominant source of uncertainty is now stellar parameters mass, radius also need good model of limb darkening Mar 20, 2009 PHY 688, Lecture 23 7 (Charbonneau et al. 2000)

8 Anatomy of a Transit parameters: w, l depend on R * /R p, i, P d depends on R * /R p c depends on limb darkening (Brown et al. 2001) Mar 20, 2009 PHY 688, Lecture 23 8

9 HD b Transit Observed with the Hubble Space Telescope (Brown et al. 2001) Mar 20, 2009 PHY 688, Lecture 23 9

10 Sizes and Compositions of Hot Jupiters (Charbonneau et al. 2007) Mar 20, 2009 PHY 688, Lecture 23 10

11 Exoplanet Transit Spectroscopy From Star To Observer Planet X A ray may be wholly, partly, or negligibly absorbed, depending upon its impact parameter and its wavelength. Thus, the planet appears larger when observed at wavelengths that are strongly absorbed. Mar 20, 2009 PHY 688, Lecture 23 11

12 Differential Na I Absorption measure difference of transit depths in and out of Na I doublet at 589 nm gives increase in planet radius at 589 nm due to extra Na I opacity (Charbonneau et al. 2002) Wavelength (nm) Mar 20, 2009 PHY 688, Lecture 23 12

13 >60 Transiting Planets Now Known hot Jupiters and Neptunes P < 5 days e = 0 but also some unusual systems HD 80606b: P = 111 days!! e = 0.94 (most eccentric known planet!) announced end of February, 2009 T eff = K strong irradiation Mar 20, 2009 PHY 688, Lecture 23 13

14 Detecting Thermal Emission From Planet s Day Side: Secondary Eclipse Secondary Eclipse See thermal radiation from planet disappear and reappear Primary Eclipse See radiation from star transmitted Through the planet s atmosphere Mar 20, 2009 PHY 688, Lecture 23 14

15 Planet s Thermal Emission Best Detected in the Mid-Infrared 24-micron photometry with Spitzer of HD note: 0.015% primary eclipse, 0.004% secondary eclipse wavy nature of continuum: day-night variation (Deming et al. 2005) Mar 20, 2009 PHY 688, Lecture 23 15

16 Planet s Thermal Emission Best Detected in Mid-Infrared TrES-1b Spitzer photometry model (thick line) is not fit to data (solid diamonds) (Charbonneau et al. 2005) generally good agreement, although model over-predicts 4.5-micron emission Mar 20, 2009 PHY 688, Lecture 23 16

17 Current State of the Art: Emission Spectroscopy during Secondary Eclipse Spitzer Space Telescope: µm and 16, 24 µm photometry 8 15 µm spectra Hubble Space Telescope µm spectra models include: day-night side heat redistribution extra H 2 O and CO opacity in upper atmosphere, etc Relative Flux HD b (Swain et al & references therein) Mar 20, 2009 PHY 688, Lecture 23 17

18 Outline Review of previous lecture hot Jupiters; transiting planets primary eclipses and atmospheric transmission spectroscopy secondary eclipses and direct flux measurements Properties of irradiated giant planets atmospheric temperature structure isothermal region temperature inversion Mar 20, 2009 PHY 688, Lecture 23 18

19 From Lecture 17: H Phase Diagram temperature-pressure (T-P) diagram for isolated planets, temperature increases monotonically toward interior (Guillot 2006) Mar 20, 2009 PHY 688, Lecture 23 19

20 From Lecture 20: P-T Profile of a Brown Dwarf Atmosphere L dwarf T dwarf giant planet Mar 20, 2009 PHY 688, Lecture (Ackerman & Marley 2001)

21 Effect of Irradiation balance between internal flux and flux incident from star T eff 4 = T int 4 + W T * 4 W dimensionless dilution factor ~ 10 3 incident light penetrates to depth τ pen, such that # " pen = W T * % $ for τ < τ pen, T eff is governed by irradiation and is constant isothermal, radiative region for τ > τ pen, T eff T int, and rises monotonically with τ T int & ( ' 4 )1 Mar 20, 2009 PHY 688, Lecture 23 21

22 P-T Profiles of Hot Jupiters AU isothermal regions are radiative Mar 20, 2009 PHY 688, Lecture (Fortney et al. 2007)

23 Cloud-Free Hot Jupiters May Show Only Tenuous Spectral Features emission from isothermal region appears blackbodylike between 8 15 micron no H 2 O?! Spitzer IRS spectrum of HD b model from Burrows et al. (2006) H 2 O likely present, but not detectable Relative Flux note however, that these are extremely challenging observations! Mar 20, 2009 PHY 688, Lecture (Grillmair et al. 2007)

24 Other Planets Require Extra Opacity at High Altitudes extra opacity evident as excess >5 µm emission true for very hot Jupiters expected to cause a temperature inversion in the upper atmosphere κ extra additional opacity at high altitude P n fraction of incident flux redistributed to planet s night side Spitzer photometry of TReS 4b (Knutson et al. 2008) Mar 20, 2009 PHY 688, Lecture 23 24

25 Temperature Inversions in Very Hot Jupiters i.e., stratospheres gas-phase TiO / VO? tholins, polyacetylenes, etc, produced through photolysis of CH 4 and NH 3? (Fortney et al. 2008) Mar 20, 2009 PHY 688, Lecture 23 25

26 The Earth s Stratosphere stratospheric clouds Mar 20, 2009 PHY 688, Lecture 23 26

27 Hot and Very Hot Jupiters: pl vs. pm Planets distinction: based on lack or presence of high-level TiO/VO associated with a stratosphere cf. L vs. M stellar spectral types transition at around AU equivalent separation from the Sun note dependences on: observed planetary hemisphere orbital phase for planets on very eccentric orbits HD 17156b, HD 80606b, HD b (Fortney et al. 2008) Mar 20, 2009 PHY 688, Lecture 23 27