The evolution of brown dwarf's infrared spectroscopic properties

IR and Sub-mm Spectroscopy - a New Tool for Studying Stellar EvolutionSpS1, 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)

= 3.5 106 K

= 1 106 K

= 2.4 106 K

MRR from planets to solar type stars

Chabrier et al. 2009, CS15 proceedings

• Binary work confirms model predictions (and theory)

• Missing brown dwarf constraints

• COROT-3b consistent with brown dwarf parameters or inflated planet with a massive core.

• HAT-P-2b must be enriched (5Z) with a core: 9Mjup

OGLE-TR-122(M=0.085 M)

Baraffe et al. 1998Chabrier & Baraffe, ARAA 2000

Eclipsing binaries: rapid rotators & activeSlower contraction due tomagnetically driven inhibition of convection and spot coverage?

Eclipsing brown dwarf: Teff reversal :Stassun et al. (2006)[H]a = 7 [H]b :Reiners et al. (2007)

layered or oscillatory convection?

5Z, 9 Mjup

Evolution of the surface temperature

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⊙).

Atmospheric composition across the MLT

2200K1800K

1000K

Teff from M ---> L -----> T dwarf

Baraffe et al. ‘1998,2003; Chabrier et al. 2000, Allard et al. 2001Marley et al. 2000, 2002; Burrows et al. 2003, 2006

Formation and settling of « dust » in brown dwarf atmospheres

Gravity vs surface temperature

Log g (cgs) vs Teff (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 106, 107, 108 and 5 x 109 yrs isochrones from bottom to top.

H2O temperature dependence

λ (μm)

1 2 3 4 5

log

κ

-24

-22

-20

-18

-16

-14

-12

-10

1000 K

2000 K

3000 K

500 K

0.1 Myr log10 g = 2.5log10 g = 3.0

H2!

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

Ruiz, Leggett & Allard (ApJ 491, L107, 1997)

Forsterite detected in BDs?

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 μm. This may be a result of a population of small silicate grains that are not predicted in current cloud models.

Cushing et al (2006)

Effects of grains on atmosphere profiles: « green house » effect whichheats up the outer layers

4) Non equilibrium chemistry

Common assumption of local chemical equilibrim (LCE).

But, if some chemical reactions are very slow -----> vertical transportvia convective motions can lead to departure from equilibrium

Mechanism suggested to operate in Jupiter in 1997 (Prinn & Barshay) andexpected as well in exoplanet atmospheres

• Non equilibrium carbon chemistry:

main reaction CO + 3H2 <-------> CH4 + H2O below ~ 2000 K, CH4 becomes the dominant form of C Transformation CO ----> CH4 much slower than inverse reaction if mix << CO CH4 abundance of CO much larger than LCE predictions

existence of this process confirmed by the detection of CO in the atmosphere of a cool brown dwarf GL 229b (Teff ~ 1000 K)

• Non equilibrium nitrogen chemistry:

same process expected for N: N2 + 3H2 <-------> 2NH3

reaction N2 ----> NH3 much slower than inverse reaction

DynamicalTransport

N2 and CO is transported from inner/warmer regions of the atmosphere, depleting NH3 (N2) and CH4 (CO)

Saumon et al. (2003)

2D RHD simulations of cloud formation

in brown dwarf atmospheres

CO5BOLD models (Bernd Freytag), gas and grains (Mg2SiO4) 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.

W350 x H80 km2 over 36 hours

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Gravity Waves !!!

3D Radiation HydrodynamicsFreytag & Allard 2009

3D radiation hydrodynamical simulation of a brown dwarf (Teff=1500K, logg=5, type L) atmosphere cube (340 x 340 x 113 km3). 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 (Mg2SiO4), 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!

• Offers synthetic spectra and thermal structures of published model grids and the relevant publications.

• Computes synthetic spectra, with/without irradiation by a parent star, and photometry for:

main sequence stars

brown dwarfs (1 Myrs - 10 Gyrs)

extrasolar giant planets

telluric exoplanets

• Computes isochrones and finds the parameters of a star by chi-square fitting of colors and/or mags to the isochrones.

• Rosseland/Planck as well as monochromatic opacity tables calculations

http://phoenix.ens-lyon.fr/simulator

NOW OPEN!

TVLM513-46546Hallinan 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

Maser cyclotron excited by Jupiter’s magnetic field fed of ionized particles ejected from

its moon io.

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