3,775 research outputs found
Interpretation of Infrared Vibration-Rotation Spectra of Interstellar and Circumstellar Molecules
Infrared vibration-rotation lines can be valuable probes of interstellar and
circumstellar molecules, especially symmetric molecules, which have no pure
rotational transitions. But most such observations have been interpreted with
an isothermal absorbing slab model, which leaves out important radiative
transfer and molecular excitation effects. A more realistic non-LTE and
non-isothermal radiative transfer model has been constructed. The results of
this model are in much better agreement with the observations, including cases
where lines in one branch of a vibration-rotation band are in absorption and
another in emission. In general, conclusions based on the isothermal absorbing
slab model can be very misleading, but the assumption of LTE may not lead to
such large errors, particularly if the radiation field temperature is close to
the gas temperature.Comment: 10 pages, 5 figures, ApJ in pres
Absolute Properties of the Eclipsing Binary Star V501 Herculis
V501 Her is a well detached G3 eclipsing binary star with a period of
8.597687 days for which we have determined very accurate light and
radial-velocity curves by using robotic telescopes. Results of these data
indicate that the component stars have masses of 1.269 +/- 0.004 and 1.211 +/-
0.003 solar masses, radii of 2.001 +/- 0.003 and 1.511 +/- 0.003 solar radii,
and temperatures of 5683 +/- 100K and 5720 +/- 100K, respectively. Comparison
with the Yonsei-Yale series of evolutionary models results in good agreement at
an age of about 5.1 Gyr for a somewhat metal rich composition. Those models
indicate that the more massive, larger, slightly cooler star is just beyond
core hydrogen exhaustion while the less massive, smaller, slightly hotter star
has not quite reached core hydrogen exhaustion. The orbit is not yet
circularized, and the components are rotating at or near their
pseudosynchronous velocities. The distance to the system is 420 +/- 30 pc
The Infrared Nucleus of the Wolf-Rayet Galaxy Henize 2-10
We have obtained near-infrared images and mid-infrared spectra of the
starburst core of the dwarf Wolf-Rayet galaxy He 2-10. We find that the
infrared continuum and emission lines are concentrated in a flattened ellipse
3-4'' or 150 pc across which may show where a recent accretion event has
triggered intense star formation. The ionizing radiation from this cluster has
an effective temperature of 40,000 K, corresponding to stars, and
the starburst is years old.Comment: 17 pages Latex, 7 postscript figures, 1 postscript table, accepted to
A
Ionized Gas in the Galactic Center: New Observations and Interpretation
We present new observations of the [Ne II] emission from the ionized gas in
Sgr A West with improved resolution and sensitivity. About half of the emission
comes from gas with kinematics indicating it is orbiting in a plane tipped
about 25\degree\ from the Galactic plane. This plane is consistent with that
derived previously for the circumnuclear molecular disk and the northern arm
and western arc ionized features. However, unlike most previous studies, we
conclude that the ionized gas is not moving along the ionized features, but on
more nearly circular paths. The observed speeds are close to, but probably
somewhat less than expected for orbital motions in the potential of the central
black hole and stars and have a small inward component. The spatial
distribution of the emission is well fitted by a spiral pattern. We discuss
possible physical explanations for the spatial distribution and kinematics of
the ionized gas, and conclude that both may be best explained by a one-armed
spiral density wave, which also accounts for both the observed low velocities
and the inward velocity component. We suggest that a density wave may result
from the precession of elliptical orbits in the potential of the black hole and
stellar mass distribution.Comment: 28 pages, 13 figures, ApJ in pres
Artificial Pothole and Level Ditch Development as a Means of Increasing Waterfowl Production
The glaciated prairie pothole country of the Midwest forms a vital segment of the most important waterfowl breeding habitat in North America. Here are hatched three-quarters of all the ducks raised in the United States. During a recent seven-year period the three-state area of Minnesota and the Dakotas produced an average of 4 to 5 million ducks annually (Janzon, 1947). This wetland region which once comprised 115,000 square miles in five states had shrunk to about 56,000 square miles by 19.56 (Lynch, 1956). To maintain the pre,;ent rate of waterfowl production in the face of continued destruction of habitat through drainage and other land use practices detrimental to breeding ducks will require that remaining wet lands, particularly those in public ownership, be developed as much .as possible toward their maximum potential for waterfowl production.
In recent years the U. S. Fish and Wildlife Service has excavated several hundred experimental artificial potholes and level ditches on its refuges in the Dakotas and Minnesota. It was believed that these water areas would increase the number of ducks breeding on the refuge marshes by providing additional territorial sites. Before more funds are invested to expand this work it is important to determine the success of the existing development in meeting this objective.
This study, to evaluate the artificial pothole and level ditch development, was initiated. in 1957 by the U.S. Fish and Wildlife Service at Lower Souris National Wildlife Refuge in North Dakota. The project was carried out in collaboration with the Utah Cooperative wildlife Research Unit and the Department of Wildlife Management, Utah State University
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