10,860 research outputs found
A comparison of operational and LANDSAT-aided snow water content estimation systems
How LANDSAT imagery can be cost effectively employed to augment an operational hydrologic model is described. Attention is directed toward the estimation of snow water content, a major predictor variable in the volumetric runoff forecasting model. A stratified double sampling scheme is supplemented with qualitative and quantitative analyses of existing operations to develop a comparison between the existing and satellite-aided approaches to snow water content estimation. Results show a decided advantage for the LANDSAT-aided approach
Chemical Equilibrium Abundances in Brown Dwarf and Extrasolar Giant Planet Atmospheres
We calculate detailed chemical abundance profiles for a variety of brown
dwarf and extrasolar giant planet atmosphere models, focusing in particular on
Gliese 229B, and derive the systematics of the changes in the dominant
reservoirs of the major elements with altitude and temperature. We assume an
Anders and Grevesse (1989) solar composition of 27 chemical elements and track
330 gas--phase species, including the monatomic forms of the elements, as well
as about 120 condensates. We address the issue of the formation and composition
of clouds in the cool atmospheres of substellar objects and explore the rain
out and depletion of refractories. We conclude that the opacity of clouds of
low--temperature (900 K), small--radius condensibles (specific chlorides
and sulfides), may be responsible for the steep spectrum of Gliese 229B
observed in the near infrared below 1 \mic. Furthermore, we assemble a
temperature sequence of chemical transitions in substellar atmospheres that may
be used to anchor and define a sequence of spectral types for substellar
objects with Ts from 2200 K to 100 K.Comment: 57 pages total, LaTeX, 14 figures, 5 tables, also available in
uuencoded, gzipped, and tarred form via anonymous ftp at
www.astrophysics.arizona.edu (cd to pub/burrows/chem), submitted to Ap.
Spectroscopic Constants, Abundances, and Opacities of the TiH Molecule
Using previous measurements and quantum chemical calculations to derive the
molecular properties of the TiH molecule, we obtain new values for its
ro-vibrational constants, thermochemical data, spectral line lists, line
strengths, and absorption opacities. Furthermore, we calculate the abundance of
TiH in M and L dwarf atmospheres and conclude that it is much higher than
previously thought. We find that the TiH/TiO ratio increases strongly with
decreasing metallicity, and at high temperatures can exceed unity. We suggest
that, particularly for subdwarf L and M dwarfs, spectral features of TiH near
0.52 \mic, 0.94 \mic, and in the band may be more easily measureable
than heretofore thought. The recent possible identification in the L subdwarf
2MASS J0532 of the 0.94 \mic feature of TiH is in keeping with this
expectation. We speculate that looking for TiH in other dwarfs and subdwarfs
will shed light on the distinctive titanium chemistry of the atmospheres of
substellar-mass objects and the dimmest stars.Comment: 37 pages, including 4 figures and 13 tables, accepted to the
Astrophysical Journa
Line Intensities and Molecular Opacities of the FeH Transition
We calculate new line lists and opacities for the
transition of FeH. The 0-0 band of this transition is responsible for the
Wing-Ford band seen in M-type stars, sunspots and brown dwarfs. The new
Einstein A values for each line are based on a high level ab initio calculation
of the electronic transition dipole moment. The necessary rotational line
strength factors (H\"onl-London factors) are derived for both the Hund's case
(a) and (b) coupling limits. A new set of spectroscopic constants were derived
from the existing FeH term values for v=0, 1 and 2 levels of the and
states. Using these constants extrapolated term values were generated for v=3
and 4 and for values up to 50.5. The line lists (including Einstein A
values) for the 25 vibrational bands with v4 were generated using a
merged list of experimental and extrapolated term values. The FeH line lists
were use to compute the molecular opacities for a range of temperatures and
pressures encountered in L and M dwarf atmospheres. Good agreement was found
between the computed and observed spectral energy distribution of the L5 dwarf
2MASS-1507.Comment: 52 pages, 3 figures, many tables, accepted for publication in the
Astrophysical Journal Supplement
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