The evolution of brown dwarf's infrared spectroscopic properties IR and Sub-mm Spectroscopy - a New Tool for Studying Stellar Evolution SpS1, Session 8, Thursday Aug 6th, 9h-9h35 France Allard & Isabelle Barrafe Directrices de Recherche, CNRS Centre de Recherche Astrophysique de Lyon
Burning: from VLM stars to planets stars brown dwarfs Planemos (planetary mass objects) = 3.5 10 6 K = 1 10 6 K = 2.4 10 6 K
MRR from planets to solar type stars Chabrier et al. 2009, CS15 proceedings <ul><li>Binary work confirms model predictions (and theory) </li></ul><ul><li>Missing brown dwarf constraints </li></ul><ul><li>COROT-3b consistent with brown dwarf parameters or inflated planet with a massive core. </li></ul><ul><li>HAT-P-2b must be enriched (5Z ) with a core: 9M jup </li></ul>OGLE-TR-122 (M=0.085 M ) Baraffe et al. 1998 Chabrier & Baraffe, ARAA 2000 Eclipsing binaries : rapid rotators & active Slower contraction due to magnetically driven inhibition of convection and spot coverage? Eclipsing brown dwarf: T eff reversal : Stassun et al. (2006) [ H ]a = 7 [ H ]b : Reiners et al. (2007) layered or oscillatory convection? 5Z , 9 M jup
Evolution of the surface temperature <ul><li>Effective temperature vs time (yrs) for objects from 1 M ⊙ to 10 -3 M ⊙ (masses are indicated in M ⊙ ). Solid lines: Z = Z ⊙ , no dust opacity; dotted lines: Z= Z ⊙ , dust opacity included, shown for 0.01, 0.04 and 0.07 M ⊙ ; dashed line: Z = 10 -2 × Z ⊙ (only for 0.3 M ⊙ ). </li></ul>
2200K 1800K 1000K Teff from M ---> L -----> T dwarf Baraffe et al. ‘1998,2003; Chabrier et al. 2000 , Allard et al. 2001 Marley et al. 2000, 2002; Burrows et al. 2003, 2006 Formation and settling of « dust » in brown dwarf atmospheres
Gravity vs surface temperature <ul><li>Log g (cgs) vs T eff (K) for LMS (solid) and SSOs (dashed) from 1 M ⊙ to 0.001 M ⊙ (masses in M ⊙ are indicated on the curves). Dotted lines represent 10 6 , 10 7 , 10 8 and 5 x 10 9 yrs isochrones from bottom to top. </li></ul>
0.1 Myr log 10 g = 2.5 log 10 g = 3.0 H 2 ! Uncertainties at young ages!
Clouds in brown dwarfs Fergley & Lodders, Astrophysics Update 2, edited by John W. Mason. ISBN 3-540-30312-X. Published by Springer Verlag, Heidelberg, Germany, 2006, p.1 http://arxiv.org/abs/ astro-ph/0601381
Forsterite detected in BDs? <ul><li>Mid-type L dwarfs, observed with the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope, show an unexpected flattening from roughly 9 to 11 μ m. This may be a result of a population of small silicate grains that are not predicted in current cloud models. </li></ul>Cushing et al (2006)
Effects of grains on atmosphere profiles: « green house » effect which heats up the outer layers
<ul><li>4) Non equilibrium chemistry </li></ul><ul><li>Common assumption of local chemical equilibrim (LCE). </li></ul><ul><li>But, if some chemical reactions are very slow -----> vertical transport </li></ul><ul><li>via convective motions can lead to departure from equilibrium </li></ul><ul><li>Mechanism suggested to operate in Jupiter in 1997 (Prinn & Barshay) and </li></ul><ul><li>expected as well in exoplanet atmospheres </li></ul><ul><li>Non equilibrium carbon chemistry : </li></ul><ul><li>main reaction CO + 3H 2 <-------> CH 4 + H 2 O </li></ul><ul><li>below ~ 2000 K, CH 4 becomes the dominant form of C </li></ul><ul><li>Transformation CO ----> CH 4 much slower than inverse reaction </li></ul><ul><li> if mix << CO CH4 abundance of CO much larger than LCE predictions </li></ul>
<ul><li>existence of this process confirmed by the detection of CO in the </li></ul><ul><li>atmosphere of a cool brown dwarf GL 229b (T eff ~ 1000 K) </li></ul><ul><li>Non equilibrium nitrogen chemistry : </li></ul><ul><li>same process expected for N: N 2 + 3H 2 <-------> 2NH 3 </li></ul><ul><li>reaction N 2 ----> NH 3 much slower than inverse reaction </li></ul>
Dynamical Transport N 2 and CO is transported from inner/warmer regions of the atmosphere, depleting NH 3 (N 2 ) and CH 4 (CO) Saumon et al. (2003)
2D RHD simulations of cloud formation in brown dwarf atmospheres <ul><li>CO 5 BOLD models (Bernd Freytag), gas and grains (Mg 2 SiO 4 ) opacities from Phoenix, cloud model (dust size-bin distribution), nucleation, condensation, coagulation rates, and sedimentation velocity according to Rossow (1978). In red the dust mass density is indicated, while in green the entropy is shown to indicate the convection zone. </li></ul>W350 x H80 km 2 over 36 hours Gravity Waves !!!
3D Radiation Hydrodynamics Freytag & Allard 2009 3D radiation hydrodynamical simulation of a brown dwarf (T eff =1500K, logg=5, type L) atmosphere cube (340 x 340 x 113 km 3 ). Runtime: 1.8 hours stellar time (about 3 months on 6 processors). Time step: 0.18 sec (6 hydro steps, 1 viscosity step, 1 source step, 1 radiation step). Color coded (right) is the dust concentration (Mg 2 SiO 4 ), and (left) the entropy of the convective zone. The model does not include rotation effects (next step when the model is relaxed). Awaits financial support.
Web Simulator ONLINE ! <ul><li>Offers synthetic spectra and thermal structures of published model grids and the relevant publications. </li></ul><ul><li>Computes synthetic spectra, with/without irradiation by a parent star , and photometry for: </li></ul><ul><li>main sequence stars </li></ul><ul><li>brown dwarfs (1 Myrs - 10 Gyrs) </li></ul><ul><li>extrasolar giant planets </li></ul><ul><li>telluric exoplanets </li></ul><ul><li>Computes isochrones and finds the parameters of a star by chi-square fitting of colors and/or mags to the isochrones. </li></ul><ul><li>Rosseland/Planck as well as monochromatic opacity tables calculations </li></ul>http://phoenix. ens-lyon . fr/simulator NOW OPEN!
TVLM513-46546 Hallinan et al. (ApJ 663, L25, 2007) Time series of the radio emission detected with the VLA from the M9 dwarf TVLM 513-46546. Every 1.958 hrs a periodic pulse is detected when extremely bright beams of radiation originating at the poles sweep Earth when the dwarf rotates. This dim dwarf is producing radio emission which is thousands of times brighter than any ever detected from the Sun. CREDIT: Hallinan et al., NRAO/AUI/NSF Animated gif of the radio emission from the M9 dwarf TVLM 513-46546 detected with the VLA at 8.44 GHz . The time between each bright pulse corresponds to 1.958 hrs , which is the period of rotation of the dwarf . CREDIT: Hallinan et al., NRAO/AUI/NSF
Maser radio emission of Jupiter <ul><li>Maser cyclotron excited by Jupiter’s magnetic field fed of ionized particles ejected from </li></ul><ul><li>its moon io. </li></ul>