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
QuickTime™ et undécompresseur codec YUV420
sont requis pour visionner cette image.
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.
QuickTime™ et undécompresseur Cinepak
sont requis pour visionner cette image.
Top Related