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