Ecole Normale Supérieure, 22 March 2011, LA-UR-11-01402

1. Clouds in brown dwarfs and hot young planets D. Saumon Los Alamos National Laboratory Images: Cassini; Marois et al. (2008) Ecole Normale Supérieure, 22 March 2011, LA-UR-11-01402

2. Modeling • Mark Marley (NASA Ames) • Katharina Lodders (Washington U.) • Richard Freedman (NASA Ames) • Observations/Analysis • Michael Cushing (IPAC) • Sandy Leggett (Gemini Observatory) • Tom Geballe (Gemini Observatory) • Adam Burgasser (UCSD) • Denise Stephens (Brigham Young) • Spitzer/IRS Dim Suns Team: • Tom Roellig, Amy Mainzer, John Wilson, Greg Sloan, • Davy Kirkpatrick, Jeff Van Cleve

3. Brown dwarfs and hot young planets • Clouds and the LT transition • Back to hot young planets

4. Main sequence stars Brown dwarfs Planets The basics of brown dwarfs Substellar in mass ~ 12 to 77 MJupiter Compact! R ~ 0.09 to 0.16 Rsun (all ~ size of Jupiter) No stable source of nuclear energy Evolution = cooling: Lbol and Teff decreasewith time

5. The basics of brown dwarfs Two new spectral classes cooler than dM: L (Teff ~ 2400 1400K) T (Teff ~ 1400  600K) … and soon Y Very strong molecular bands H2O, CO, CH4, NH3, FeH, TiO Condensates form in the atmosphere for Teff 2000K

6. M6.5 L5 T4.5 Spectral energy distributions: M, L and T dwarfs From Cushing et al. (2006)

7. NIR color-magnitude diagrams: Field brown dwarfs Sample of local disk brown dwarfs L dwarfs naturally extend the dM sequence T dwarfs are “blue” in near-IR colours! Rapid shift in IR colours at the LT transition. Early T’s are brighter in J than late L’s!? Data from Knapp et al (2004), Burgasser et al. (2006), Liu & Leggett (2005)

8. Hot young planets HR 8799 b,c,d,e Star: A5 V 30160Myr old Inner & outer dust disks (R ~ 8AU and R ~ 66AU) * Masses and Teff are approximate Marois et al. (2008, 2010), Currie et al. (2011)

9. Near IR color-magnitude diagrams: Young planets In the near IR, hot young planets ~ consistent with the L dwarf sequence and its extension Planet data from Marois et al. (2008), Lafrenière et al. (2008) and Neuhäuser (2008)

10. Hot young planets compared to field brown dwarfs Similarities Young planets far from their star have effectively evolved in isolation Their NIR colours extend the brown dwarf sequence Teff range (L~ 2400-1400K, T~1400 – 600K) Differences Lower gravity (lower mass, younger) Possibly metal-rich if formed in a protoplanetary disk Hot young planets are more hip Atmospheric physics & chemistry should be very similar

11. Brown dwarfs and hot young planets • Clouds and the LT transition • Back to hot young planets

12. diffuse cloud cloud deck no cloud condensation level Color-magnitude diagrams: Limiting cloud models Cloudless models can explain late T dwarfs (>T4) A diffuse cloud model works best for optically thin clouds (<L4) A more sophisticated cloud model is required (cloud deck)

13. Teff 2000K 1600K 1200K 800K 400K } L } T photosphere Condensation and qualitative cloud behaviour Condensation: Fe (Teff ~ 2000K) Silicates (Teff ~ 1600K) H2O (Teff ~ 300K) Main chemical transitions: CO  CH4 (Teff ~ 1200K) N2 NH3 (Teff ~ 800K) A cloud layer will gradually disappear below the photosphere as Teff decreases  cloudless atmosphere!

14. A simple cloud model A minimalist 1-D cloud model results from a balance between: 1) Vertical transport of particles (e.g. turbulent diffusion) 2) Gravitational settling of the particles Kzz: coefficient of diffusive mixing fsed: dimensionless sedimentation parameter (as fsed increases, cloud deck becomes thinner) The location of the bottom of the cloud is determined by the condensation curve Ackerman & Marley (2001)

15. Color-magnitude diagrams: Models with clouds At constant fsed, the cloud layer gradually disappears below the photosphere For L dwarfs, fsed ~ 1-2 The LT transition occurs over Teff ~ 1400 1200K Transition can be accounted for by an increase of fsed

16. The L T transition as cloud clearing Transition from fsed=2 to cloudless models. The L T transition can also be explained as a gradual clearing of the cloud Marley, Saumon & Goldblatt (2010)

17. Clouds in brown dwarfs: Summary Condensates (Fe & silicates) are present throughout the L spectral class (Teff > 1400K) The condensates gravitationally settle into cloud decks Mid- to late-T dwarfs appear to be free of clouds Clearing of clouds at the LT transition indicated by CMDs Physical mechanism: unknown An increase of sedimentation efficiency? A break up of the cloud layer? There are hints that the LT transition is gravity sensitive The LT transition must also occur in hot young planets

18. Brown dwarfs and hot young planets • Clouds and the LT transition • Back to hot young planets

19. HR 8799b, c, d photometry: Clouds All 3 planets: zJHKL’M photometry can only be fitted with cloudy atmospheres models Marois et al. (2008)

20. HR 8799b 2.2m spectrum: Detection of CH4 When fitted with field BD spectra, this spectrum matches that of T1-T3 dwarfs. CH4 is present in this spectrum Bowler et al. (2010)

21. planet b planet b Trouble with HR 8799bcd 9 photometric channels spanning 1.03 to 5m d=39.4  1.0 pc Luminosities of log L/L= - 5.1, - 4.7 and - 4.7 (0.1) Age of the star: 30-160Myr Evolution models then give M, R, Teff, gravity Using a variety of brown dwarf atmosphere models, fits to the photometry give Teff for all 3 planets that are too high (or R too small). Bowler et al. (2010)

22. Model E MJ MJ J-K J-K Trouble with HR 8799bcd Brown dwarf models used by Bowler et al (2010) & Currie et al (2011) The model E sequences do not enter the mag-color space of the L8-L9 dwarfs  Can fit the color but not the magnitude (radius) of the planet Model A cloud extends to the top of the atmosphere (much thicker than E)  more promising (as found by Currie et al 2011) Burrows, Sudarsky & Hubeny (2006)

23. 12 14 16 model E model AE MJ -1 0 1 2 3 J-Ks A new class of objects? Madhusudhan, Burrows & Currie (2011) A new, intermediate, “AE” cloud model Good fits for all 3 planets Consistent with evolution and age of the system (30-160Myr) Claim: The hot young planets occupy a different NIR color space than BDs Require models with very thick clouds to explain their colors

24. Our fits of HR 8799 bcd (work in progress) These best fitting model spectra for c & d are too old and too massive! BUT: within 1.5, models agree with the upper age limit of 160Myr Data from Marois et al. (2008), Hinz et al. (2010), Currie et al. (2011)

25. A different view of clouds in hot young planets These planets look like very late L dwarfs only colder Need only to delay the cloud clearing to lower Teff (< 1400K) The Teff of the L T cloud clearing appears to be rather sensitive to gravity (HD 203030 B, 25 Mj, has Teff ~1150K, but is cloudy)

26. Exoplanets: What have we learned from brown dwarfs? Hot young planets have much in common with field brown dwarfs and can be modelled with the same tools and physics The study of clouds in field brown dwarf is highly relevant to hot young planets: Cloud decks of iron and silicate particles Clouds present for Teff > 1400K (all L), absent for Teff<1200K (late T) in field brown dwarfs Clouds disappear over only 200K of cooling in Teff Apparently gravity dependent (e.g. HD 203030 B, 2MASS 1207B?) Mechanism presently unknown

27. Exoplanets: What have we learned from brown dwarfs? HR 8799 planets: NIR colors similar to those of the latest L dwarfs but b & d are fainter Their NIR colors extend the cloudy L dwarf sequence Good fits of the 1 – 4.7m photometry can be obtained with cloudy models Claims that they have much thicker clouds than field brown dwarfs are not justified The same cloud model (and same fsed range) as for BDs is adequate Understanding these planets only requires that the cloud clearing of the L  T transition occurs at lower Teff for lower gravities Independent evidence of the latter has been accumulating

28. Backup slides

29. FeH TiO TiO TiO TiO VO VO CrH K I FeH Rb I K I Cs I H2O Cs I New spectral class: L dwarfs TiO and VO bands peak at dM9 then weaken through L sequence Strong CrH and FeH FeH peaks at mid-L Lines of alkali metals appear CO at 2.3m Strong H2O J-K increases steadily Teff ~ 2400 – 1400K L dwarfs are nearly all brown dwarfs Adapted from Kirkpatrick et al. (1999)

30. New spectral class: T dwarfs CH4 appears in H and K bands CO (2.3m) disappears by T2 Very strong H2O No TiO or VO, weakening FeH and CrH Lines of alkali metals J-K decreases steadily Teff ~ 1400 – 600K T dwarfs are all brown dwarfs Spectra from Geballe et al. (2002) 2.5 1

31. Star: A3 V 300500Myr old dust disk (R=133-160AU) Planet: a ~ 115 AU Mass* ~ 1 3 MJupiter Teff *~ 400K Hot young planets Fomalhaut b * Mass and Teff are early estimates Kalas et al., Science, 322, 1345 (2008)

32. Other hot young planets? Lafrenière et al (2008), Lagrange et al. (2010) and data compiled in Neuhäuser (2008)

33. Teff=1200 K Teff=2000 K cloud= 2/3 Teff=1600 K Teff=800 K cloud= 2/3 cloud= 2/3 Clouds and photospheres All models: log g=5 fsed=3

34. Fits of entire SED of brown dwarfs Stephens et al.(2009)

35. Fits of entire SED of brown dwarfs Stephens et al.(2009)

36. Brown dwarfs and hot young planets • Clouds and the L/T transition • Non-equilibrium chemistry • Back to hot young planets

37. CO AsH3 GeH4 Unexpected species in the atmosphere of Jupiter Bézard et al. (2002) Noll, Larson & Geballe (1990) Bjoraker, Larson & Kunde (1986)

38. slow  CO + 3H2CH4 + H2O  fast slow  N2 + 3H22NH3  fast sun Chemistry and vertical transport in brown dwarf atmospheres Chemistry of carbon & nitrogen: CO &N2: ms to > Hubble time! Transport: Convection (mix ~ minutes) Radiative zone (mix~ hours to years?) e.g. meridional circulation Two characteristic mixing time scales in the atmosphere

39. Effect of mixing on abundances Net effect: Excess of CO in the spectrum Depletion of CH4, NH3 and H2O For CO, CH4 and H2O, the faster the mixing in the radiative zone, the larger the effect (up to saturation) A way to measure the mixing time scale in the atmosphere! } The most important opacity sources!

40. A case study: Gl 570D (T8) Model fluxes are computed at Earth Teff=820K log g=5.23 [M/H]=0 Equilibrium model Model with mixing Saumon et al. (2006)

41. Absolute fluxes CO CH4 Gl 570D: 3-5m spectrum and photometry Teff= 820K log g=5.23 [M/H]=0 Equilibrium (no CO)With mixing (excess CO) Geballe et al. (2009)

42. Departure from chemical equilibrium: Summary The consequence of very basic considerations (“universality”) Important at low Teff: late L dwarfs and T dwarfs Affects CO (), CH4 (), H2O () and NH3 (), all important sources of opacity CO excess observed in all 6 T dwarfs subjected to detailed analysis (e.g. Gl 570D) NH3 depleted in the IRS spectra of 3 T dwarfs analyzed so far Additional evidence shows that departures from equilibrium chemistry (i.e. vertical mixing) are common in brown dwarfs An opportunity to measure the mixing time scale in the atmosphere Mixing mechanism: turbulent break up of gravity waves?

43. surface CH4 > CO (excess CO) CO > mix CH4 < mix fast CH4 CO Temperature slow CO  CH4 CO > CH4 (equilibrium) CO < mix CH4 < mix Chemistry and vertical transport

44. Non-equilibrium abundances in brown dwarfs Cloudless model Teff=1000K log g=5 equilibrium

45. Non-equilibrium abundances in brown dwarfs Cloudless model Teff=1000K log g=5 log Kzz (cm2/s)=2

46. Non-equilibrium abundances in brown dwarfs Cloudless model Teff=1000K log g=5 log Kzz (cm2/s)=4

47. Non-equilibrium abundances in brown dwarfs Cloudless model Teff=1000K log g=5 log Kzz (cm2/s)=6

48. Ground-based photometry: K, L’ & M’ T dwarfs L dwarfs M dwarfs Adapted from Leggett et al. (2007) The K L’ M’ color-color diagram provides strong evidence that non-equilibrium chemistry (i.e. enhanced CO) is a common feature of T dwarfs

49. 4-5m M’ flux M’ Effect on 4.6m CO band Teff=1000K log g=5 Kzz=0, 102, 104, 106cm2/s Kzz=0, 104 cm2/s Can affect searches for exoplanets

50. M’ Effect on CO bands K band 4-5m M’ flux Kzz=0, 104 cm2/s Teff=1000K log g=5 Kzz=0, 102, 104, 106cm2/s Can affect searches for exoplanets