3,284 research outputs found
X-Ray Spectra of Z Sources
A simple, physically consistent model has been proposed that seeks to explain
in a unified way the X-ray spectra and rapid X-ray variability of the so-called
Z sources and other accreting neutron stars in low-mass systems. Here we
summarize the results of detailed numerical calculations of the X-ray spectra
of the Z sources predicted by this model. Our computations show that in the Z
sources, photons are produced primarily by electron cyclotron emission in the
neutron star magnetosphere. Comptonization of these photons by the hot central
corona and radial inflow produces X-ray spectra, color-color tracks, and
countrate variations like those observed in the Z sources.Comment: 6 pages, 2 Postscript figures in 4 files, uses aas2pp4.sty, submitted
to ApJ (Letters) 1995 May 3
A combinatorial identity for studying Sato-Tate type problems
We derive a combinatorial identity which is useful in studying the
distribution of Fourier coefficients of L-functions by allowing us to pass from
knowledge of moments of the coefficients to the distribution of the
coefficients.Comment: This paper contains the proof of a combinatorial identity used to
study effective equidistribution laws for the Fourier coefficients of
elliptic curve L-functions investigated by the first two authors in
http://arxiv.org/abs/1004.275
Bounds on the Compactness of Neutron Stars from Brightness Oscillations
The discovery of high-amplitude brightness oscillations at the spin frequency
or its first overtone in six neutron stars in low-mass X-ray binaries during
type~1 X-ray bursts provides a powerful new way to constrain the compactness of
these stars, and hence to constrain the equation of state of the dense matter
in all neutron stars. Here we present the results of general relativistic
calculations of the maximum fractional rms amplitudes that can be observed
during bursts. In particular, we determine the dependence of the amplitude on
the compactness of the star, the angular dependence of the emission from the
surface, the rotational velocity at the stellar surface, and whether there are
one or two emitting poles. We show that if two poles are emitting, as is
strongly indicated by independent evidence in 4U 1636-536 and KS 1731-26, the
resulting limits on the compactness of the star can be extremely restrictive.
We also discuss the expected amplitudes of X-ray color oscillations and the
observational signatures necessary to derive convincing constraints on neutron
star compactness from the amplitudes of burst oscillations.Comment: 8 pages plus one figure, AASTeX v. 4.0, submitted to The
Astrophysical Journal Letter
The Feasibility of Using Thermography to Detect Subsurface Voids in Painted Wooden Panels
Thermography is a technique whereby the structure or condition of an object is studied by means of precisely measuring temperature variations over the surfaces of the object. The research which is described in this thesis was undertaken to determine whether thermographic techniques could be applied to the field of art conservation to detect subsurface voids within painted wooden panels. It must be stressed, however, that this research was carried out as a feasibility study with no attempt being made to establish or refine a technique that could be immediately applied to the examination of works of art.
The text of this thesis is divided into four sections. The first of these sections, the Introduction, is an attempt to establish a need for a technique capable of detecting subsurface voids within panel paintings. The second section entitled The Theoretical Basis for Thermographic Analyses of Subsurface Voids explains why voids can be detected through the measurement of surface temperatures, and the equipment necessary to make these temperature measurements is explained. The section entitled Experimental Procedures and Results describes the research carried out for this thesis and contains a number of photographs which illustrate the effectiveness of thermography in detecting subsurface voids. The final section of the text entitled Conclusions summarizes the findings of the research and relates these findings to the possible future application of thermography to the analysis of actual works of art
- …