88 research outputs found
The Near-Infrared and Optical Spectra of Methane Dwarfs and Brown Dwarfs
We identify the pressure--broadened red wings of the saturated potassium
resonance lines at 7700 \AA as the source of anomalous absorption seen in the
near-infrared spectra of Gliese 229B and, by extension, of methane dwarfs in
general. This conclusion is supported by the recent work of Tsuji {\it et al.}
1999, though unlike them we find that dust need not be invoked to explain the
spectra of methane dwarfs shortward of 1 micron. We find that a combination of
enhanced alkali abundances due to rainout and a more realistic non-Lorentzian
theory of resonant line shapes may be all that is needed to properly account
for these spectra from 0.5 to 1.0 microns. The WFPC2 measurement of Gliese
229B is also consistent with this theory. Furthermore, a combination of the
blue wings of this K I resonance doublet, the red wings of the Na D lines at
5890 \AA, and, perhaps, the Li I line at 6708 \AA can explain in a natural way
the observed WFPC2 band flux of Gliese 229B. Hence, we conclude that the
neutral alkali metals play a central role in the near-infrared and optical
spectra of methane dwarfs and that their lines have the potential to provide
crucial diagnostics of brown dwarfs. We speculate on the systematics of the
near-infrared and optical spectra of methane dwarfs, for a given mass and
composition, that stems from the progressive burial with decreasing \teff of
the alkali metal atoms to larger pressures and depths.Comment: Revised and accepted to Ap.J. volume 531, March 1, 2000, also
available at http://jupiter.as.arizona.edu/~burrows/papers/BMS.p
Shift and broadening of hyperfine components of the first doublet of cesium perturbed by foreign gases
Estereotipia e plasticidade na seqüência predatória de Theridion evexum keyserling 1884 (Araneae: Theridiidae)
The Theory of Brown Dwarfs and Extrasolar Giant Planets
Straddling the traditional realms of the planets and the stars, objects below
the edge of the main sequence have such unique properties, and are being
discovered in such quantities, that one can rightly claim that a new field at
the interface of planetary science and and astronomy is being born. In this
review, we explore the essential elements of the theory of brown dwarfs and
giant planets, as well as of the new spectroscopic classes L and T. To this
end, we describe their evolution, spectra, atmospheric compositions, chemistry,
physics, and nuclear phases and explain the basic systematics of
substellar-mass objects across three orders of magnitude in both mass and age
and a factor of 30 in effective temperature. Moreover, we discuss the
distinctive features of those extrasolar giant planets that are irradiated by a
central primary, in particular their reflection spectra, albedos, and transits.
Aspects of the latest theory of Jupiter and Saturn are also presented.
Throughout, we highlight the effects of condensates, clouds, molecular
abundances, and molecular/atomic opacities in brown dwarf and giant planet
atmospheres and summarize the resulting spectral diagnostics. Where possible,
the theory is put in its current observational context.Comment: 67 pages (including 36 figures), RMP RevTeX LaTeX, accepted for
publication in the Reviews of Modern Physics. 30 figures are color. Most of
the figures are in GIF format to reduce the overall size. The full version
with figures can also be found at:
http://jupiter.as.arizona.edu/~burrows/papers/rm
TEXTURE OF SALT STOCK WHOLE CUCUMBER PICKLES: CORRELATION OF INSTRUMENTAL AND SENSORY MEASUREMENTS
THEORETICAL RESPONSES OF DIFFERENT RHEOLOGICAL MODELS TO A SINUSOIDAL COMPRESSION IN A TRANSIENT STATE
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