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Exoplanet Atmospheres ­
Learning from the Physics of Substellar Objects
Derek Homeier1

France Allard1 Bernd Freytag3
PEPS
1C

Isabelle Baraffe2,1

Gilles Chabrier1,2

RAL/ècole Normale SupÈrieure de Lyon
2 3

University of Exeter Uppsala Universitet


Ultracool atmospheres (M dwarfs, brown dwarfs) are complex -- planetary atmospheres are more complex

· · · ·

Irradiation & heat redistribution, rotation Greater compositional diversity Transmission spectroscopy only sensitive to highest part of atmosphere O-en few data points to constrain multiparameter models NASA

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


(Sub-) stellar atmosphere modelling


independent Variables (minimal):
effective temperature surface gravity
L = 4 R2 Teff4 Teff
ITERATION

INPUT
line opacity

· · · · · · · ·

Pressure Stratification

continuum opacity molecular band opacity

g(r) = GM/r2

mass M or radius R or luminosity composition ("metallicity") convection (micro-) turbulence & mixing rotation chemical peculiarities magnetic fields etc....

Radiation Field

OUTPUT

Converged? NO Temperature Correction

YES

END SYNTHETIC SPECTRUM

PHOENIX workflow (P. Hauschildt)

adding more dimensions to the modelling problem
Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


Molecular Bands -- Methane
ARTICLE IN PRESS
L.S. Rothman et al. / Journal of Quantitative Spectroscopy & Radiative Transfer 110 (2009) 533 ­572

108 lines 105 lines STDS

1010 lines
Yurchenko et al. 2014

Fig. 2. Polyad energy-level structure for

12

CH4.

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014

Boudon et al. 2006

HITRAN

ExoMol


Molecular line blanketing: Methane · 30 Mio. lines computed with the STDS program

· ·

(UniversitÈ de Bourgogne) -- 2013 update: 80 Mio.

-1 Vibrational and rotational states up to ~ 8000 cm

Completeness: ~50% (mid-IR) - 10% (H-band) - 0% ( Y/J)
GEISA/HITRAN STDS GS only STDS GS+Dyad STDS all

3.5e+11

3e+11

2.5e+11
F[erg/s/cm2/cm]

2e+11

1.5e+11

1e+11

5e+10

0 3 3.2 3.4 3.6 [µm] 3.8 4 4.2

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


Mixing and Diffusion - a closer Look
mt10g50mm00n03
9 8

log(D/[cm2/s])

7 6 5 4 3 3
D Vrms*Hp Vrms2*timeac Vrms2*timeac*Ma

convective overshoot and gravity wave excitation dominant in brown dwarfs

4

5 6 7 8 9 log(P/[dyn/cm2]) Freytag et al. 2010

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


Mixing and Diffusion - a closer Look
mt10g50mm00n03
9 8

7 6 5 4 3 3
D Vrms*Hp Vrms2*timeac Vrms2*timeac*Ma

convective overshoot and gravity wave excitation dominant in brown dwarfs -- but in planets too inefficient (Schwarzschild boundary @ 100 global circulation important!

log(D/[cm2/s])

4

5 6 7 8 9 log(P/[dyn/cm2]) Freytag et al. 2010

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


T dwarfs -- more clouds
e Astrophysical Journal, 756:172 (17pp), 2012 September 10 Morley et al.

Morley et al. 2012

gure 9. Color­magnitude diagrams for M, L, and T dwarfs. As in Figure 1, observed ultracool dwarf color is plotted against the absolute magnitude for all known own dwarfs with measured parallax. In the top three plots, J - K color is plotted against absolute J magnitude; in the bottom three plots, J - H color is plotted ainst absolute H magnitude. All photometry is in the MKO system. M dwarfs are plotted as black circles, L dwarfs as red circles, and T dwarfs as blue circles. bservational data are from Dupuy & Liu (2012) and Faherty et al. (2012). The locations of the brown dwarfs Ross 458C and UGPS 0722­05, the objects to which e compare model spectra to observations in Figures 11 and 12, are shown with a purple star and square symbol, respectively. Models: models are plotted as lines. ch labeled temperature Derek Homeiermarks topapproximate mospheres odel m a substvelltemperature.pectirepresentative gravplanetlottedCfrom bridloteo Ex he lanet at locations of the m frowith that effecti e ar pers Three ve UK Exo ities are ps - : am left p g t ,

·

Separate cloud setup for low-temperature condensates
1 3 /0 4 /1 4 2 0 1 4


Clouds from L to Y dwarfs in a single model
10

12

log g = 5.0 log g = 4.0 M dwarfs L dwarfs T dwarfs HR 8799

PHOENIX-Settl 2014

M

J

14

16

18 1 0 J 1 K 2
s

3

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


Clouds in Brown Dwarfs and Planets
10 10
1 16

10

15

10

14

10

13

10

12

10

11

10

10

Pi /P 10 9 10

8

10

7

10

6

10

5

10

4

10

3

10

2

10

0


10
1

water ice, ammonium hydrosulphide clouds

10

2

Jupiter
3

10

CH4 CO H2 O NH3
0 1000 2000 3000 T (K) / grain size (µm) 4000



deep silicate clouds

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


Atmospheric composition

· · · ·

Metal abundances in general, and carbon and oxygen in particular, can differ from host star various degrees of oxygen and carbon depletion can occur depending on location and accretion history in the protoplanetary disk "non-solar " C/O, additional impact of cloud condensation e.g. Ch. Helling with I. Kamp et al. 2014 (Life, in press)

?

try arXiv:1403.4420

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


Clouds affect carbon/oxygen chemistry
10 04000 . 0.001 0.002 0.003 Pi /P 0.004 0.005 0.006 0.007 0.008 10
3

H2 O CO

10

2

­0.1 dex O

10

1

P (bar)

10

0

10

1

WASP 43b 1­10 x solar

10

2

10

3


1500 2000 T (K) 2500 3000

sequestration of oxygen in deep silicate clouds!

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


Clouds in hot Neptunes and super-Earths
10 10 10 10 10 10 10 10 10 10 10 10
8

10

10

10

9

10

8

10

7

Pi /P 10 6

10

5

10

4

10

3

10

2

10

1

7

6

5

CH4 CO2 CO Na2 S, NaCl KCl Mgn Mnm Sil O

k

4

3

2

1

0

1

2

GJ 436b 100 x solar

3

0

500

1000

1500

2000

2500

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


Clouds in hot Neptunes and super-Earths
GJ 436b transit models and WFC3 observations (Knutson et al. 2014)

7100

Transit depth (ppm)

7000

6900

6800

[Fe/H] = +1.0 [Fe/H] = +1.5 [Fe/H] = +2.0
6700 1. 1 1. 2 1. 3 1. 4 (µm) 1. 5 1. 6 1. 7

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014


Conclusions

· · · ·

Cloud modelling successful in brown dwarfs Impact also on measured gas phase composition and thermal structure (evolution boundary!) Peculiarities of planetary atmospheres (mixing, nucleation processes) yet to be understood For mature, irradiated planets connection to circulation models essential
NASA

Derek Homeier Exoplanet atmospheres from a substellar perspective UK Exoplanets - Cambridge, 13/04/14 2014