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

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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

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Collaborators
Atomic/molecular
Astrophysics
Chemistry

• Kate Kirby
• Brian Taylor
• T. Leininger
• F. X. Gadéa

• N. Balakrishnan
• Adrienne Horvath
• Andy Osburn
• Stephen Skory
• Philippe Weck
• Benhui Yang

• Peter Hauschildt
• Andy Schweitzer

Funding NASA
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Outline

• Introduction
• Opacities for LTE spectral models
• Electronic transitions
• Rovibrational transitions
• Collisional excitation for non-LTE
• Summary

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Effective Temperatures and Spectral
Classifications
0.2 M?

• TiO, VO, CaH, MgH
• TiO depletion
• VO depletion
• FeH, Li, K, Na
• CrH
• Li ? LiCl
• NaCl, RbCl, CsCl
• H2O condenses

M - dwarfs
CO
15 MJ
N2
73 MJ
CH4
EGP?
0.3MJ
NH3
Burrows et al. (2001)
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MgH in the Visible
4000 K
A-X
3000 K
2000 K

• A-X 10,091 transitions
• B-X 10,649 transitions
• X, A, B levels 313, 435, 847

2000 K dusty
Wavelength (Å)
Weck et al. (2003), Skory et al. (2003)
PHOENIX models
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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

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Keck II spectrum of an L5 dwarf (Reid et al. 2000)

• Stellar classifications based on optical/NIR
  spectra

Li ?
No Li
Wavelength (Å)

• 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

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2000 K
3330 K
1670 K
2500 K
Equilibrium abundances in a cool dwarf atmosphere
(Lodders 1999)
1430 K
Log of abundance
M
L
104/T
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• However, for Tlt1600 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

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25 MJ (800 K, 10 pc, T dwarf) theoretical spectra
by Burrows et al. (2003)
H20 CH4 NH3
SIRTF
JWST
LiCl T1000 K
LTE spectra with 3,357,811 lines between 29,370
levels
?v1
?v2
?v3
5
10
20
30
Weck et al. (2004)
Wavelength (?m)
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• 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)

T
T
L
T

• Models constructed for Teff900, 1200, and 1500 K
  and log(g)3.0 (young), 4.0, and 5.0 (old, gt 1
  Gyr)
• Solar metallicity

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New Spitzer IR Observations
M3.5
L8
EGP
T1/T6
EGP
Roellig et al. (2004) TrES-1 Charbonneou et al.
(2005) HD 209458B Deming et al. (2005)
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NAH LTE spectra for rovibrational and electronic
X-A transitions (Horvath et al. 2005, in prep.)
?v0
X-A
?v1

• 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

NaH
LiCl
NaCl
KCl
KH?
KH
Burrows et al. (2001)
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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 Teff2700 K
CO ?v1
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CO(v1) H ? CO(v0) H
M
L
T
EGP
Dense cores
Orion Peak 1 and 2
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CO(v1,j0) H ? CO(v0,j0-25) H
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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