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Figure captions
Figure:
Run of the relative abundances of gas
phase (full lines) and crystallized species across a T
K model atmosphere typical of the young Pleiades brown
dwarfs Teide1 and Calar3. The condensation of perovskite (CaTiO3,
dashed line) is the principle cause of TiO depletion in the
atmospheres of dwarfs later than about M6. The abundance of the
condensate Ca2SiO4 is drawn at log10()=-5.0 but is not
labeled for sake of clarity.
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Figure:
Same as above for a T
K
model atmosphere typical of the reddest known field dwarfs GD165B,
Kelu1, and the DENIS objects.
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Figure:
The extinction cross-sections per particle
of dust grains. The mie formalism is used assuming a power-law
(
)
grain size distribution with diameters from 0.00625
and 0.24 m. Monoatomic grains such as Fe, Cu, and Ni contribute
scattering at optical wavelengths only, while corundum, magnesium
aluminium spinel, calcium titenide, hematite, magnetite, and
Ca2Al2SiO7 crystals show strong peaks of absortion, at
infrared wavelengths, that could compete with the local water vapor
``continuum'' in hot/young brown dwarfs. Note however that if the
grains were elliptical and randomly oriented, the sharp absorption
peaks shown here could be washed out.
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Figure:
The extinction profiles are compared for
grain size distributions with 1, 2, 10 and 100 times the ISM values
adopted for this work (full lines from bottom to top respectively,
where the two first curves are nearly undistinguishable). The
scattering and absorption contributions of the 100 ISM profile are
also shown (dotted lines). The conditions are those of the
photospheric layers (
,
i.e.
T
K) of our standard 1800K AMES-Dusty model atmosphere.
The structures seen in the profile at
m are due to
dust absorption (Mg2SiO4 at 10 and 16.5 m and MgAl2O4at 13 m). Scattering contributions dominate below m, and
remain modest at longer wavelengths for grain sizes
times
the adopted values. The absoption profile, on the other hand, is
only little sensitive to grain sizes.
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Figure:
Thermal structures of the AMES-Cond models
with T
ranging from 3000 to 100K by steps of 500K, with
two additional models at 700 and 400K, logg=5.0, and solar
metallicity. The convection zones are labeled with cross-symbols.
The approximate location of the photosphere is indicated with filled
circles and triangles marking the
and
1.0 optical depths. All models shown stop at
.
As
decreases, the photosphere becomes progressively more
isothermal.
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Figure:
Thermal structures of the fully dusty models
with T
ranging from 2400 to 1600K by steps of 200K, with
two additional models at 2500 and 1500K, logg=5.0. None of the curves
shown actually overcross. The radiative zones are marked by full
lines while the convective region is shown as dotted lines. The
location of the photosphere is also indicated, with full circles and
triangles marking the
and 1.0 optical
depths respectively. The strongest optical molecular bands and
resonance lines form near
.
All models
shown stop at
.
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Figure:
Thermal structures of models with T
K and 1800K, logg=5.0, and solar metallicity for three types of
models: (1) the standard NextGen models treated in gas phase only
(dotted line); (2) the AMES-Dusty models assuming a full distribution
of the dust (full line), and; (3) the AMES-Cond models including dust
in the CE but ignoring their opacities (dashed line). All models are
converged. Note that the NextGen models use a different source of
water vapor opacity (see text).
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Figure:
Spectral sequence of brown dwarfs to EGP
model atmospheres in the total settling (AMES-Cond) approximation.
From top to bottom: T
K, and
200K. The gravity is fixed to
.
These models (AMES-Cond)
assume complete settling of the grains (i.e. neglects all dust
opacity). The spectral resolution has been reduced from 2Å to
30Å by boxcar smoothing in order to make comparison of the spectra
easier. We observe that CH4 bands already develop at 2000K in
these extremely transparent and cool AMES-Cond atmospheres. They
gradually replace water vapor bands while H2O condenses to ice
below 300K.
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Figure:
To isolate atomic features we compare a
K AMES-Cond model (full line) with a spectrum obtained by
neglecting all molecular lines (dotted lines). The pseudo-continuum
is essentially formed by the van der Waals wings of the Na I D and K I
resonance doublets at 5891,5897Å and
7687,7701Å. Weaker lines of Rb I (7802 and
7949Å), Cs I (8523 and 8946Å), and K I
(11693,11776 and 12436,12525Å) are also seen.
The background flux (obtained by neglecting both atomic and molecular
lines, not shown) lies outside the plot! The spectral resolution is
reduced to 30Å for this illustration.
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Figure:
Same as Figure 8 in the
optical to near-red spectral range. Here the spectra have been
arbitrarily scaled to facilitate the comparison. From top to bottom:
T
,
and 1500K. The spectral
resolution is 2Å.
|
Figure:
Same as Figure 10
for models from 1500K to 100K at 100K steps.
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Figure:
Same as Figure 10
where we zoom in on the CH3D band system at 4.55 m. From top
to bottom: T
,
and
400K. The CH3D band appears at 1000K at this gravity and for this
dust treatment limit. Note that
K dwarfs are dusty and
that, though they don't appear here, CO bands at 4.67 m easily
are detectable in these hotter atmospheres.
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Figure:
Same as Figure 10
where we zoom in on the NH3 band system at 11.012 m. The
ammonia band system appears at 1000K, along with several other
molecular lines essentially due to methane. The spectral resolution
is 5Å.
|
Figure:
Same as Figure 8 in the
full dusty (AMES-Dusty) limiting case. From top to bottom: T
K, and 1500K. The gravity is fixed at
.
Here the strong heating effects of dust opacities
prevent the formation of methane bands, and dissociate H2O while
producing a hotter water vapor opacity profile, much weaker and
transparent to radiation. From 1700K, the grain opacity profiles
rapidly dominate the UV to red spectral region, smoothing out the
emergent flux into a continuum where only the core of the strongest
atomic resonance lines (Na I D and K I doublets) are seen.
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Figure:
Two
K AMES-Cond models of
different surface gravity are compared: (1)
(full line),
(2)
(dotted line). The spectral resolution has been
reduced from 2Å to 10Å by boxcar smoothing in order to make
comparison of the spectra easier.
|
Figure:
Same as Figure 15 for
K AMES-Cond models, and (1)
(full line),
(2)
(dotted line). Here the spectral resolution has
been reduced to 30Å by boxcar smoothing. In the inset we show a
zoom of the optical to red spectral regime, were we distinguish water
vapor bands at 0.93, 0.95 and 1.12 m, Cs I resonance transitions
at 0.86 and 0.89 m, the K I resonance doublet at 0.77, 0.79
m, and the cores of a few other lines such as the Na I D doublet
bluewards of 0.75 m. While molecular bands are moderately
affected by the gravity change, the optical background opacity due to
the wings of the Na I D and K I doublets is reduced by nearly a factor
of 10 in the low gravity model. The latter model is more typical of
low mass brown dwarfs and jovian planets.
|
Figure:
Two
K AMES-Dusty models
of different surface gravity are compared: (1)
(full
line), (2)
(dotted line). The spectral resolution has
been reduced to 10Å by boxcar smoothing.
|
Figure:
Same as Figure 17 for
K AMES-Dusty models. While gravity effects are quasi
nonexistent redwards of 2.5 m, they are quite large in the
optical to red spectral region, mainly as a result of enhanced
efficiency of dust grain formation at the higher pressures and
densities of high gravity atmospheres. A -value of 5.5 is
typical of most field brown dwarfs discovered since 1996.
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Figure:
Two
K models with
are compared to illustrate the difference between our two limiting
cases: (1) AMES-Dusty with full dust opacity (full line), and (2)
AMES-Cond with full gravitational settling (no dust opacity, dotted
line).
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Figure:
Same as Figure 19 for
K
models with
.
A 1500K blackbody (dashed line) is
overplotted for comparison.
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Figure:
The AMES-Cond model for
K and
(full line) is compared to the corresponding
model (dotted line) used in their analysis of the Gl229B
spectrum. model (dotted line) used in their analysis of the Gl229B
spectrum.
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Figure:
The 10 Gyr NextGen isochrones (dotted), and the
locii of the Cond (short dashed) and Dusty (full) models
are compared to the photometric observations of field stars and brown
dwarfs, and to Pleiades objects including the brown dwarfs PPl15,
Teide1 and Calar3 (star and filled circle symbols). The field T
dwarfs Gliese 229B and SDSS1624 are also shown. Unresolved binarity
is reflected in this diagram by a red excess in J-K. Note that the
Cond and Dusty models have been shifted in J-K by +0.15 in order to
eliminate water opacity source effects in this comparison. The Cond
models are computed (i) with the line wings coverage value of 5000Å (long-dashed line), and (ii) with a maximum coverage of 15000Å (short-dashed line) to illustrate the impact of this parameter on the
Cond models.
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Next: About this document ...
Up: The Limiting Effects of
Previous: Discussion and Conclusions
Peter Hauschildt
2001-05-23