45 research outputs found
Optical considerations in infrared heterodyne spectrometer design
The optical design considerations for optimization of sensitivity, tunability, and versatility of an infrared heterodyne spectrometer are discussed using the GSFC CO2 laser heterodyne spectrometer optical front end as an example. Problems related to the coherent nature of the laser local oscillator beam (e.g., interference effects at edges of optical elements and at the beam combining beamsplitter) are described and proper beamsplitter design discussed. Optimum matching to the telescope is discussed. The severe effects of large central obscuration on the coherent telescope efficiency are described and steps to partially recover the lost system sensitivity are proposed. Measurements made with the GSFC 48 inch telescope (linear obscuration rate = 0.5) and the KPNO McMathe telescope (no obscuration) are given as examples
Light deflection by gravitational waves from localized sources
We study the deflection of light (and the redshift, or integrated time delay)
caused by the time-dependent gravitational field generated by a localized
material source lying close to the line of sight. Our calculation explicitly
takes into account the full, near-zone, plus intermediate-zone, plus wave-zone,
retarded gravitational field. Contrary to several recent claims in the
literature, we find that the deflections due to both the wave-zone 1/r
gravitational wave and the intermediate-zone 1/r^2 retarded fields vanish
exactly. The leading total time-dependent deflection caused by a localized
material source, such as a binary system, is proven to be given by the
quasi-static, near-zone quadrupolar piece of the gravitational field, and
therefore to fall off as the inverse cube of the impact parameter.Comment: 12 pages, REVTeX 3.0, no figur
Thermal bifurcation in the upper solar photosphere inferred from heterodyne spectroscopy of OH rotational lines
Low noise high spectral resolution observations of two pure rotation transitions of OH from the solar photosphere were obtained. The observations were obtained using the technique of optically null-balanced infrared heterodyne spectroscopy, and consist of center-to-limb line profiles of a v=1 and a v=0 transition near 12 microns. These lines should be formed in local thermodynamic equilibrium (LTE), and are diagnostics of the thermal structure of the upper photosphere. The v=0 R22 (24.5)e line strengthens at the solar limb, in contradiction to the predictions of current one dimensional photospheric models. Data for this line support a two dimensional model in which horizontal thermal fluctuations of order + or - 800K occur in the region Tau (sub 5000) approximately .001 to .01. This thermal bifurcation may be maintained by the presence of magnetic flux tubes, and may be related to the solar limb extensions observed in the 30 to 200 micron region
Is there any chlorine monoxide in the stratosphere?
A ground based search for the 856.50137/cm R(9.5) and for the 859.76765 R(12.5) transitions of stratospheric (Cl-35)O was made in the solar absorption mode using an infrared heterodyne spectrometer. Lines due to stratospheric HNO3 and tropospheric OCS were detected, at about 0.3% absorption levels. The expected lines of ClO in this same region were not detected, even though the optical depth of the ClO lines should be on the order of 0.2% using currently accepted ClO abundances. These infrared measurements suggest that stratospheric ClO is at least a factor of 7 less abundant than is indicated by indirect in situ fluorescence measurements, and the upper limit of 2.4x10 to the 13th power molecules/sq cm to the integrated column density of ClO is a factor of over 4 less than is indicted by microwave measurements. Results imply that the release of fluorocarbon precursors of ClO may be significantly less important for the destruction of stratospheric ozone than was previously thought
Ground based infrared measurements of the global distribution of ozone in the atmosphere of Mars
The global distribution of ozone in the atmosphere of Mars was determined from Doppler-limited infrared heterodyne spectroscopy measurements at the NASA Infrared Telescope Facility (IRTF) facility during June 3-7, 1988. Mars spectra near two O3 lines arising from the v sub 3 band near 1031.45 cm (-1) were used. The lines were Doppler shifted out of the strong terrestrial ozone absorption spectrum and its effect was removed. Ozone measurements were obtained at eight beam positions over a range of latitudes and local solar zenith angles. The beam size of the planet was 1.4 arcsec. A Martian CO2 line appeared in the spectra and was inverted to retrieve local temperature profiles. Using these temperature profiles, the total ozone column abundance at each position was retrieved by fitting the measured line with synthetic spectra generated by a radiative transfer program. The only previous measurement of ozone at this season was made above the South polar cap by Mariner 7 and revealed an abundance of 10 micron-atm. However, the retrieved O3 column abundances from this investigation are less than 2.2 micron-atm at all positions sampled. These results are consistent with mid-spring abundances predicted by photochemical models of Liu and Donahue, and Shimazaki and Shimizu
Discovery of natural gain amplification in the 10 muon m CO2 laser bands on Mars: The first definite natural laser
Fully resolved intensity profiles of various lines in the CO2 bands at 9.4 micrometers and 10.4 micrometers were measured on Mars using an infrared heterodyne spectrometer. Analysis of the line shapes shows that the Mars atmosphere exhibits positive gain on these lines, providing the first definite detection of natural optical gain amplification and enabling identification of these lines as the first definite natural laser ever discovered
Regular and Chaotic Motion in General Relativity: The Case of a Massive Magnetic Dipole
Circular motion of particles, dust grains and fluids in the vicinity of
compact objects has been investigated as a model for accretion of gaseous and
dusty environment. Here we further discuss, within the framework of general
relativity, figures of equilibrium of matter under the influence of combined
gravitational and large-scale magnetic fields, assuming that the accreted
material acquires a small electric charge due to interplay of plasma processes
and photoionization. In particular, we employ an exact solution describing the
massive magnetic dipole and we identify the regions of stable motion. We also
investigate situations when the particle dynamics exhibits the onset of chaos.
In order to characterize the measure of chaoticness we employ techniques of
Poincar\'e surfaces of section and of recurrence plots.Comment: 11 pages, 6 figures, published in the proceedings of the conference
"Relativity and Gravitation: 100 Years after Einstein in Prague" (25. - 29.
6. 2012, Prague
On the stability of general relativistic geometric thin disks
The stability of general relativistic thin disks is investigated under a
general first order perturbation of the energy momentum tensor. In particular,
we consider temporal, radial and azimuthal "test matter" perturbations of the
quantities involved on the plane . We study the thin disks generated by
applying the "displace, cut and reflect" method, usually known as the image
method, to the Schwarzschild metric in isotropic coordinates and to the
Chazy-Curzon metric and the Zipoy-Voorhees metric (-metric) in Weyl
coordinates. In the case of the isotropic Schwarzschild thin disk, where a
radial pressure is present to support the gravitational attraction, the disk is
stable and the perturbation favors the formation of rings. Also, we found the
expected result that the thin disk models generated by the Chazy-Curzon and
Zipoy-Voorhees metric with only azimuthal pressure are not stable under a
general first order perturbationComment: 11 pages, RevTex. Phys Rev D (in press
Bending of Light by Gravity Waves
We describe the statistical properties of light rays propagating though a
random sea of gravity waves and compare with the case for scalar metric
perturbations from density inhomogeneities. For scalar fluctuations the
deflection angle grows as the square-root of the path length in the manner
of a random walk, and the rms displacement of a ray from the unperturbed
trajectory grows as . For gravity waves the situation is very
different. The mean square deflection angle remains finite and is dominated by
the effect of the metric fluctuations at the ends of the ray, and the mean
square displacement grows only as the logarithm of the path length. In terms of
power spectra, the displacement for scalar perturbations has while for gravity waves the trajectories of photons have which is a scale-invariant or `flicker-noise' process, and departures from
rectilinear motion are suppressed, relative to the scalar case, by a factor
where is the characteristic scale of the
metric fluctuations and is the path length. This result casts doubt on the
viability of some recent proposals for detecting or constraining the gravity
wave background by astronomical measurements.Comment: 14 pages, aastex, submitted to Astrophysical Journa
Stationary and Axisymmetric Solutions of Higher-Dimensional General Relativity
We study stationary and axisymmetric solutions of General Relativity, i.e.
pure gravity, in four or higher dimensions. D-dimensional stationary and
axisymmetric solutions are defined as having D-2 commuting Killing vector
fields. We derive a canonical form of the metric for such solutions that
effectively reduces the Einstein equations to a differential equation on an
axisymmetric D-2 by D-2 matrix field living in three-dimensional flat space
(apart from a subclass of solutions that instead reduce to a set of equations
on a D-2 by D-2 matrix field living in two-dimensional flat space). This
generalizes the Papapetrou form of the metric for stationary and axisymmetric
solutions in four dimensions, and furthermore generalizes the work on Weyl
solutions in four and higher dimensions. We analyze then the sources for the
solutions, which are in the form of thin rods along a line in the
three-dimensional flat space that the matrix field can be seen to live in. As
examples of stationary and axisymmetric solutions, we study the
five-dimensional rotating black hole and the rotating black ring, write the
metrics in the canonical form and analyze the structure of the rods for each
solution.Comment: 43 pages, v2: typos fixed, refs adde