# Presentation: 145087

## Molecular Opacities and Collisional Processes for   IR/Sub-mm Brown Dwarf and Extrasolar Planet Modeling

- Phillip C. Stancil
*Department of Physics and Astronomy *
*Center for Simulational Physics*
- The 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 depletion
- VO depletion
- FeH, Li, K, Na
- CrH
- Li  LiCl
- NaCl, 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 Li

- Li ?

- Wavelength (Å)

-  Stellar classifications based on optical/NIR spectra

## 104/T

- 1670 K

- 2000 K

- 2500 K

- 3330 K

- 1430 K

- Equilibrium abundances in a cool dwarf atmosphere (Lodders 1999)

- 104/T

- M

- L

- Log of abundance

## 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

- 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=2

- v=3

- LiCl T=1000 K

- 5

- 10

- 20

- 30

**H****2****0    CH****4****         NH****3**

- 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)

- 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 *T**e*ff=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

## NAH LTE spectra for rovibrational and electronic X-A transitions (Horvath et al. 2005, in prep.)

- v=1

- v=0

- X-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

- NaCl

- KCl

- KH

- KH?

## Non-LTE effects

- NLTE effects investigated for CO by:
- Ayres & Weidemann in the sun (1989)
- Schweitzer, Hauschildt, & Baron (2000) for M dwarfs
- NLTE effects might be expected for cool objects
- Non-Planckian radiation
- Strong irradiation from companion
- Slow collisional rates

- M8 model: Teff=2700 K

- CO v=1

## CO(v=1) + H  CO(v=0) + H

- M

- L

- T

- EGP

- 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 3s3p
- 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