1,040 research outputs found
Filtering Interpolators for Image Comparison Algorithms
Comparing two or more images, either by differencing or ratioing, is important to many remote sensing problems. Because the pixel sample points for the images are (almost) always separated by some nonzero shift, a resampling, or interpolation, process must be performed if one image is to be accurately compared to another. Considered in Fourier space, an interpolator acts as a filter that attenuates some frequencies (usually high) of the image. Thus, when the shifted and unshifted images are compared, the former has been filtered, while the latter has not; the effect of this difference is called interpolation error. The key idea of this paper is to apply a filter to the unshifted image that matches the filtering effect of applying the interpolator to the shifted image, thereby drastically reducing interpolation error. The resulting interpolators, called filtering interpolators, are derived and discussed in detail elsewhere. Basic results will be given in this presentation
New Constraints on the Energetics, Progenitor Mass, and Age of the Supernova Remnant G292.0+1.8 Containing PSR J1124-5916
We present spatially resolved spectroscopy of the supernova remnant (SNR)
G292.0+1.8 with the Chandra X-ray observatory. This SNR contains the 135 ms
pulsar, J1124-5916. We apply non-equilibrium ionization (NEI) models to the
data. By comparing the derived abundances with those predicted from
nucleosynthesis models, we estimate a progenitor mass of 30-40 solar masses. We
also derive the intrinsic parameters of the supernova explosion such as its
energy, the age of the SNR, the blast wave velocity, and the swept-up mass. In
the Sedov interpretation, our estimated SNR age of 2,600 years is close to the
pulsar's characteristic age of 2,900 years. This confirms the pulsar/SNR
association and relaxes the need for the pulsar to have a non-canonical value
for the braking index, a large period at birth or a large transverse velocity.
We discuss the properties of the pulsar wind nebula (PWN) in the light of the
Kennel and Coroniti model and estimate the pulsar wind magnetization parameter.
We also report the first evidence for steepening of the power law spectral
index with increasing radius from the pulsar.Comment: 5 pages, 3 figures. To appear in ApJL, Feb 1 2003 (submitted Oct 9
2002, accepted Dec 19 2002
Precision and accuracy of the orbital parameters derived from 2D & 1D space observations of visual or astrometric binaries
Recent investigations (e.g. Han et al. 2001) have shown that fitting the
Hipparcos observations with an orbital model when the astrometric wobble caused
by the companion is below the noise level can have rather unexpected
consequences. With new astrometric missions coming out within the next ten
years, it is worth investigating the orbit reconstruction capabilities of such
instruments at low signal-to-noise ratio. This is especially important because
some of them will have no input catalogue thus meaning that all the orbital
parameters will have to be derived from scratch. The puzzling case of almost
parabolic orbits is also investigated.Comment: 6 pages, 7 figures, accepted by A&
X-ray Observation and Analysis of The Composite Supernova Remnant G327.1-1.1
Based on the data from the observation of the SNR G327.1-1.1 by ASCA and
ROSAT, we find that G327.1-1.1 is a composite remnant with both a nonthermal
emission component and a diffuse thermal emission component. The nonthermal
component is well fitted by a power-law model with photon index about 2.2. This
component is attributed to the emission from the synchrotron nebula powered by
an undiscovered central pulsar. The thermal component has a temperature of
about 0.4 keV. We attribute it to the emission from the shock-heat swept-up
ISM. Its age, explosion energy and density of ambient medium are derived from
the observed thermal component. Some charactistics about the synchrotron nebula
are also derived. We search for the pulsed signal, but has not found it. The
soft X-ray(0.4 - 2 keV) and hard X-ray(2 - 10 keV) images are different, but
they both elongate in the SE-NW direction. And this X-ray SE-NW elongation is
in positional coincidence with the radio ridge in MOST 843MHz radio map. We
present a possibility that the X-ray nonthermal emission mainly come from the
trail produced by a quickly moving undiscoverd pulsar, and the long radio ridge
is formed when the pulsar is moving out of the boundary of the plerionic
structure.Comment: 20 pages, 4 Postscript figures, aasms4.sty and psfig.sty, to be
published in Astrophysical Journal, January 20, 1999, Vol. 51
Climate Suite Study for the National Polar-Orbiting Operational Environmental Satellite System Internal Concepts Study
Our recommendations to NPOESS for the sensors it should adopt to meet threshold requirements for global monitoring of ozone and, to some extent, of aerosols and of atmospheric temperature, pressure, and water vapor content are summarized in this report. The degree to which these sensors fulfill other NPOESS requirements than ozone is also summarized. The number of sensors that should be in the constellation is discussed in terms of desired reliability, continuity of coverage, and the ability to cross-calibrate successive sensors. Our recommendations for specific ozone measurement requirements, IORD item 4.1.6.2.28, are given. We make the case that the monitoring of three minor constituents in the upper atmosphere (N20, ClO or ClONO2, and HNO3) should be added to the list of NPOESS requirements because of their importance to long-term ozone studies and the small additional cost required (ozone sensors are already designed to measure them). Specific measurement requirements, which should be regarded as supplementary to the ozone requirement, are given here. The necessity of using two types of sensors, nadir-viewers and limb-scanners, for atmospheric studies is discussed
Resolving the compact HII regions in N160A with HST
Using high-resolution imaging with the Hubble Space Telescope, we study the
Large Magellanic Cloud HII region N160A and uncover several striking features
of this complex massive star-forming site. The two compact high excitation HII
blobs (HEBs) A1 and A2 are for the first time resolved and their stellar
content and morphology is revealed. A1, being of higher excitation, is powered
by a single massive star whose strong wind has created a surrounding bubble. A2
harbors several exciting stars enshrouded inside large quantities of dust. The
whole N160A nebula is energized by three star clusters for which we obtain
photometry and study their color-magnitude diagram. The HII region is
particularly dusty, with extinction values reaching an A_v~2.5 mag in the
visible, and it is separated from the molecular cloud by an outstanding
ionization front. A previously detected infrared young stellar object is also
accurately located with respect to the HII region.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy &
Astrophysics. A version of the paper with higher quality images is available
at http://wwwusr.obspm.fr/~heydari/projects/N16
Lung Cancer Metastasis Presenting as a Solitary Skull Mass
Lung cancer has been well documented to spread to bone and the axial skeleton after metastasis to adjacent organs. Bony metastasis is not, however, the typical presenting manifestation. The differential diagnosis for a tissue mass on the skull should warrant a workup for metastatic disease. Bony metastasis plays an important role in treatment and disease management. We report an exceptionally rare case of stage IV lung adenocarcinoma that presented with a solitary skull metastasis and a significant soft-tissue component. The lesion was treated by excision via craniotomy and subsequent medical management of the adenocarcinoma. This case illustrates a very rare presentation of lung adenocarcinoma and also represents what the authors believe to be the first report of a solitary skull mass originating from a lung primary. We also present a review of the literature surrounding bony metastasis to the skull and implications for patient care
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