1,991 research outputs found
Helioseismic determination of the solar gravitational quadrupole moment
One of the most well-known tests of General Relativity (GR) results from
combining measurements of the anomalous precession of the orbit of Mercury with
a determination of the gravitational quadrupole moment of the Sun J_2. The
latter can be done by inference from an integral relation between J_2 and the
solar internal rotation. New observational data of high quality obtained from
the Solar Heliospheric Satellite (SoHO) and from the Global Oscillations
Network Group (GONG), allow the determination of the internal rotation velocity
of the Sun as a function of radius and latitude with unprecedented spatial
resolution and accuracy. As a consequence, a number of global properties of the
Sun can also be determined with much higher accuracy, notably the gravitational
quadrupole moment of the Sun. The anomalous precession of the orbit of Mercury
is primarily due to GR effects but there are classical corrections the largest
of which is that due to J_2. It is shown here that the data are currently
consistent with the predictions of GR.Comment: 5 pages, 1 figure, plain TeX uses epsf.tex, mn.tex, accepted for
MNRA
Unbiased image reconstruction as an inverse problem
An unbiased method for improving the resolution of astronomical images is
presented. The strategy at the core of this method is to establish a linear
transformation between the recorded image and an improved image at some
desirable resolution. In order to establish this transformation only the actual
point spread function and a desired point spread function need be known. Any
image actually recorded is not used in establishing the linear transformation
between the recorded and improved image. This method has a number of advantages
over other methods currently in use. It is not iterative which means it is not
necessary to impose any criteria, objective or otherwise, to stop the
iterations. The method does not require an artificial separation of the image
into ``smooth'' and ``point-like'' components, and thus is unbiased with
respect to the character of structures present in the image. The method
produces a linear transformation between the recorded image and the deconvolved
image and therefore the propagation of pixel-by-pixel flux error estimates into
the deconvolved image is trivial. It is explicitly constrained to preserve
photometry.Comment: 11 pages, TeX, uses mn.tex epsf.tex, accepted for publication in
MNRA
A procedure for the inversion of f-mode travel times for solar flows
We perform a two-dimensional inversion of f-mode travel times to determine
near-surface solar flows. The inversion is based on optimally localized
averaging of travel times. We use finite-wavelength travel-time sensitivity
functions and a realistic model of the data errors. We find that it is possible
to obtain a spatial resolution of 2 Mm. The error in the resulting flow
estimate ultimately depends on the observation time and the number of travel
distances used in the inversion.Comment: 8 pages, 9 figure
A modified R1 X R1 method for helioseismic rotation inversions
We present an efficient method for two dimensional inversions for the solar
rotation rate using the Subtractive Optimally Localized Averages (SOLA) method
and a modification of the R1 X R1 technique proposed by Sekii (1993). The SOLA
method is based on explicit construction of averaging kernels similar to the
Backus-Gilbert method. The versatility and reliability of the SOLA method in
reproducing a target form for the averaging kernel, in combination with the
idea of the R1 X R1 decomposition, results in a computationally very efficient
inversion algorithm. This is particularly important for full 2-D inversions of
helioseismic data in which the number of modes runs into at least tens of
thousands.Comment: 12 pages, Plain TeX + epsf.tex + mn.te
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