Ecole Normale Suprieure, 22 March 2011, LA-UR Images: Cassini; Marois et al. (2008) D. Saumon Los Alamos National Laboratory Clouds in brown dwarfs and hot young planets 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 Brown dwarfs and hot young planets Clouds and the L T transition Back to hot young planets The basics of brown dwarfs Main sequence stars Brown dwarfs Planets Substellar in mass ~ 12 to 77 M Jupiter Compact! R ~ 0.09 to 0.16 R sun (all ~ size of Jupiter) No stable source of nuclear energy Evolution = cooling: L bol and T eff decrease with time The basics of brown dwarfs Two new spectral classes cooler than dM: L (T eff ~ 2400 1400K) T (T eff ~ 1400 600K) and soon Y Very strong molecular bands H 2 O, CO, CH 4, NH 3, FeH, TiO Condensates form in the atmosphere for T eff 2000K M6.5 L5 T4.5 From Cushing et al. (2006) Spectral energy distributions: M, L and T dwarfs NIR color-magnitude diagrams: Field brown dwarfs Data from Knapp et al (2004), Burgasser et al. (2006), Liu & Leggett (2005) 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 Ts are brighter in J than late Ls!? Sample of local disk brown dwarfs Hot young planets HR 8799 b,c,d,e Star: A5 V 30 160Myr old Inner & outer dust disks (R ~ 8AU and R ~ 66AU) bcde a (AU) Mass (M J )* T eff (K)*~900~1100 ? Marois et al. (2008, 2010), Currie et al. (2011) * Masses and T eff are approximate Near IR color-magnitude diagrams: Young planets Planet data from Marois et al. (2008), Lafrenire et al. (2008) and Neuhuser (2008) In the near IR, hot young planets ~ consistent with the L dwarf sequence and its extension 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 T eff range (L~ K, 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 Brown dwarfs and hot young planets Clouds and the L T transition Back to hot young planets Color-magnitude diagrams: Limiting cloud models Cloudless models can explain late T dwarfs (>T4) A diffuse cloud model works best for optically thin clouds ( 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 Brown dwarfs and hot young planets Clouds and the L T transition Back to hot young planets HR 8799b, c, d photometry: Clouds All 3 planets: zJHKLM photometry can only be fitted with cloudy atmospheres models Marois et al. (2008) HR 8799b 2.2 m spectrum: Detection of CH 4 Bowler et al. (2010) When fitted with field BD spectra, this spectrum matches that of T1-T3 dwarfs. CH 4 is present in this spectrum 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, and ( 0.1) Age of the star: Myr Evolution models then give M, R, T eff, gravity Using a variety of brown dwarf atmosphere models, fits to the photometry give T eff for all 3 planets that are too high (or R too small). Bowler et al. (2010) planet b Trouble with HR 8799bcd Burrows, Sudarsky & Hubeny (2006) 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) Model E MJMJ J-K MJMJ A new class of objects? Madhusudhan, Burrows & Currie (2011) `T eff log gM/M J Age (Myr) b c d J-K s MJMJ model E model AE 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 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 T eff log gf sed M/M J Age b Myr c Myr d Gyr Data from Marois et al. (2008), Hinz et al. (2010), Currie et al. (2011) 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 T eff (< 1400K) The T eff of the L T cloud clearing appears to be rather sensitive to gravity (HD B, 25 M j, has T eff ~1150K, but is cloudy) 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 T eff > 1400K (all L), absent for T eff 100>54> >330 Mass (M J ) T eff (K) ~1400~1800 notes Too young for models Not bound to 2M1207A Brown dwarf? L data only Lafrenire et al (2008), Lagrange et al. (2010) and data compiled in Neuhuser (2008) T eff =800 K cloud = 2/3 T eff =1200 K cloud = 2/3 Clouds and photospheres All models: log g=5 f sed =3 T eff =1600 K cloud = 2/3 T eff =2000 K Fits of entire SED of brown dwarfs Stephens et al.(2009) Fits of entire SED of brown dwarfs Stephens et al.(2009) Brown dwarfs and hot young planets Clouds and the L/T transition Non-equilibrium chemistry Back to hot young planets Unexpected species in the atmosphere of Jupiter AsH 3 Noll, Larson & Geballe (1990) Bjoraker, Larson & Kunde (1986) CO GeH 4 Bzard et al. (2002 ) Chemistry and vertical transport in brown dwarf atmospheres Chemistry of carbon & nitrogen: slow CO + 3H 2 CH 4 + H 2 O fast slow N 2 + 3H 2 2NH 3 fast Transport: Convection ( mix ~ minutes) Radiative zone ( mix ~ hours to years?) e.g. meridional circulation Two characteristic mixing time scales in the atmosphere CO & N 2 : ms to > Hubble time! sun Effect of mixing on abundances Net effect: Excess of CO in the spectrum Depletion of CH 4, NH 3 and H 2 O For CO, CH 4 and H 2 O, 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! } A case study: Gl 570D (T8) T eff =820K log g=5.23 [M/H]=0 Equilibrium model Model with mixing Model fluxes are computed at Earth Saumon et al. (2006) Gl 570D: 3-5 m spectrum and photometry T eff = 820K log g=5.23 [M/H]=0 Equilibrium (no CO) With mixing (excess CO) Absolute fluxes CH 4 CO Geballe et al. (2009) Departure from chemical equilibrium: Summary The consequence of very basic considerations (universality) Important at low T eff : late L dwarfs and T dwarfs Affects CO ( ), CH 4 ( ), H 2 O ( ) and NH 3 ( ), all important sources of opacity CO excess observed in all 6 T dwarfs subjected to detailed analysis (e.g. Gl 570D) NH 3 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? Chemistry and vertical transport Temperature surface CO < mix CH4 < mix CO > CH 4 (equilibrium) CH 4 > CO (excess CO) CO > mix CH4 < mix slow CO CH 4 fast CH 4 CO Cloudless model T eff =1000K log g=5 equilibrium Non-equilibrium abundances in brown dwarfs Cloudless model T eff =1000K log g=5 log K zz (cm 2 /s) =2 Non-equilibrium abundances in brown dwarfs Cloudless model T eff =1000K log g=5 log K zz (cm 2 /s) =4 Non-equilibrium abundances in brown dwarfs Cloudless model T eff =1000K log g=5 log K zz (cm 2 /s) =6 Ground-based photometry: K, L & M 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 T dwarfs L dwarfs M dwarfs Adapted from Leggett et al. (2007) Effect on 4.6 m CO band T eff =1000K log g=5 K zz =0, 10 2, 10 4, 10 6 cm 2 /s K zz =0, 10 4 cm 2 /s M 4-5 m M flux Can affect searches for exoplanets Effect on CO bands T eff =1000K log g=5 K zz =0, 10 2, 10 4, 10 6 cm 2 /s K zz =0, 10 4 cm 2 /s M K band 4-5 m M flux Can affect searches for exoplanets Effect on NH 3 bands T eff =1000K log g=5 K zz =0, 10 2, 10 6 cm 2 /s K zz =0, 10 4 cm 2 /s & no NH 3 log g=5 H bandK band 10 m Gl 570D: M band spectrum T eff =820K log g=5.23 [M/H]=0 Equilibrium model (no CO) With mixing: mix =14d With mixing: mix =6.7h Model fluxes normalized to data 6.5h of integration on Gemini CO is present in the spectrum (4.4 detection) Geballe et al. (2009) Other examples of non-equilibrium abundances in brown dwarfs Object Spectral Type T eff (K) log g (cm/s 2 ) [M/H] log K zz (cm 2 /s) Under abund of NH 3 ? Excess of CO? 2MASS 0415 T > 4 Gl 570DT 0.7 2MASS 1217 T > 2 Data too noisy Gl 229BT7p to Marginal data 2MASS 0937 T6p 0.3 Ind Ba T ~ ? No data HR 8799c spectroscopy: Non-equilibrium? Models in chemical equilibrium (with or without clouds) cannot reproduce the shape of the 4 m spectrum Janson et al. (2010) Cloudy model T eff =1100K, log g=4 HR 8799b, c, d photometry: Excess CO? Models in chemical equilibrium are inconsistent with the M band upper limits Hinz et al. (2010) ( K) ( K) Burrows, Sudarsky & Hubeny (2006) clouds Model E Brown dwarfs and hot young planets Clouds and the L T transition Evolution of brown dwarfs Back to hot young planets Evolution of brown dwarfs end of the main sequence time BD evolution is primarily: Cooling, contraction and a phase of deuterium fusion Controlled by surface boundary condition Opacity of the atmosphere! (clear vs cloudy) Brown dwarf evolution: a hybrid model The L-T transition can be reproduced by increasing f sed Toy model of the evolution: Boundary Condition: cloudy (T eff > 1400K) to clear (T eff < 1200K) Interpolate atmospheric B.C. (not the evolution) in between Synthetic disk population IMF: dN/dM ~ M -1 SFR: Constant (0-10Gyr) Monte Carlo sampling Let evolve and cloudyclear evolution 10 Gyr envelope Reproduces CMD fairly well Brown dwarf evolution: a hybrid model clear cloudy hybrid Observations: An apparent dearth of brown dwarfs in the transition! A more complete sample should reveal a pile up at the transition Pile up of brown dwarfs in the L-T transition A direct consequence of changes in the atmosphere Synthetic galactic clusters Synthetic clusters Hybrid evolution IMF: dN/dM ~ M -0.6 Constant SFR over age 1Myr (~ isochrone) A distinctive feature due to deuterium fusion (50-100Myr) In principle, detectable with deep enough surveys Evolution of brown dwarfs: Summary Brown dwarf evolution is relatively simple Two new features: Cloudy to clear atmosphere transition will cause an accumulation of brown dwarfs in the L-T transition region Deuterium burning phase should be detectable in the CMD of galactic clusters (50-100Myr) Both are potentially observable predictions (e.g. Pan-STARRS) Synthetic disk population of brown dwarfs Assume IMF: dN/dM ~ M -1 Constant SFR (0-10Gyr) Single BDs only Monte Carlo sampling Let evolve and evolution 10 Gyr envelope Brown dwarf evolution: variations on hybrid model