Molecular Opacities and Collisional Processes for
IR/Sub-mm Brown Dwarf and Extrasolar Planet Modeling
Phillip C. StancilDepartment of Physics and Astronomy
Center for Simulational PhysicsThe University of Georgia
Lexington, KY; May 3, 2005
Collaborators
N. Balakrishnan Adrienne
Horvath Andy Osburn Stephen Skory Philippe Weck Benhui Yang
Peter Hauschildt Andy Schweitzer
Funding: NASA
Atomic/molecular: Astrophysics:
Kate Kirby Brian Taylor T. Leininger F. X. Gadéa
Chemistry:
Outline
Introduction Opacities for LTE spectral models Electronic transitions Rovibrational transitions Collisional excitation for non-LTE Summary
Effective Temperatures and Spectral Classifications
TiO, VO, CaH, MgH
TiO depletionVO depletionFeH, Li, K, NaCrHLi LiClNaCl, RbCl,
CsCl
H2O condenses
CO
CH4
N2
NH3
Burrows et al. (2001)
M - dwarfs
EGP?
0.2 M
0.3MJ
73 MJ
15 MJ
MgH in the Visible
A-X: 10,091 transitions B-X: 10,649 transitions X, A, B levels: 313, 435,
847
4000 K
3000 K
2000 K
2000 K dusty
A-X
Weck et al. (2003), Skory et al. (2003)
Wavelength (Å)
PHOENIX models
CaH in the Visible A-X: 26,888
transitions Also, B-X, C-
X, D-X, E-X transitions
Weck, Stancil, & Kirby (2003)
Problem: with new CaH line data, models are a factor of 10 smaller than M dwarf observations
Substellar objects (brown dwarfs) have insufficient mass to maintain nuclear burning (~0.08 M ~80 MJ)
Lithium test for substellarity: presence of Li 6708 Å line
Keck II spectrum of an L5 dwarf (Reid et al. 2000)
No LiLi ?
Wavelength (Å)
Stellar classifications based on optical/NIR spectra
1670
K
2000
K
2500
K
3330
K
1430
K Equilibrium abundances in a cool dwarf atmosphere (Lodders 1999)
104/T
M L
Log o
f abu
nd
an
ce
However, for T<1600 K, Li is converted to LiCl (LiOH)
Li test not useful for the coolest L dwarfs or T dwarfs
Lodders (1999) and Burrows et al. (2001) suggested that the LiCl fundamental vibrational band at 15.8 m should be looked for; total Li elemental abundance could be obtained
Problem I. LiCl feature at 15.8 m previously inaccessible from ground or space
• Problem II. Current spectral models lack alkali-molecule opacities due to lack of molecular line lists
• Solution I. Space-based IR observatories: Spitzer, JWST, Herschel, TPF
• Solution II. Line lists are being calculated in our group: LiCl, NaH, …, and incorporated into the stellar atmosphere code PHOENIX
25 MJ (800 K, 10 pc, T dwarf) theoretical spectra by Burrows et al. (2003)
Weck et al. (2004)Wavelength (m)
v=1
v=2v=3
LiCl T=1000 K
5 10 20
30
H20 CH4 NH3
SIRTF
JWST
LTE spectra with 3,357,811 lines between 29,370 levels
Inclusion of LiCl in PHOENIX models gave no distinct features
The maximum flux difference is 20%
Spectrum is dominated by H2O opacity
It will be hard to detect LiCl with SIRTF or JWST
NaCl or KCl may be more promising
Also, alkali-hydrides (NaH, KH)
Models constructed for Teff=900, 1200, and 1500 K and log(g)=3.0 (young), 4.0, and 5.0 (old, > 1 Gyr)
Solar metallicity
L
T T
T
New Spitzer IR Observations
Roellig et al. (2004)
TrES-1: Charbonneou et al. (2005)
HD 209458B: Deming et al. (2005)
M3.5
L8
T1/T6
EGP
EGP
v=1
v=0X-A
NAH LTE spectra for rovibrational and electronic X-A transitions (Horvath et al. 2005, in prep.)
Future mid- to far-IR observations of L/T dwarfs (and maybe extrasolar giant planets) may be able to detect NaH, NaCl, KCl, and other molecular alkali species
Burrows et al. (2001)
LiCl
NaH
NaClKCl
KH
KH?
Non-LTE effects
NLTE effects investigated for CO by:
1) Ayres & Weidemann in the sun (1989)
2) Schweitzer, Hauschildt, & Baron (2000) for M dwarfs
NLTE effects might be expected for cool objects
i. Non-Planckian radiationii. Strong irradiation from
companioniii. Slow collisional rates
M8 model: Teff=2700 K
CO v=1
CO(v=1) + H CO(v=0) + H
MLTEGP
Orion Peak 1 and 2
Dense cores
CO(v=1,j=0) + H CO(v’=0,j’=0-25) + H
Summary Advances in brown dwarf (BD) and extrasolar giant
planet (EGP) spectra modeling requires line lists of ``new’’ molecules, e.g. hydrides (CrH, FeH), alkalis (NaCl, KH, KCl, …), …
Non-LTE (NLTE) effects may play a role in the coolest objects, e.g. H2O, NH3, CH4
NLTE effects are likely for atomic lines, e.g. Na 3s3p
• Non-local chemical equilibrium (NLCE) may need consideration: ionization, dissociation, recombination, association CO is overabundant by a factor of 100 in the T dwarf Gl 229B
