56,034 research outputs found
DIRBE Minus 2MASS: Confirming the Cosmic Infrared Background at 2.2 Microns
Stellar fluxes from the 2MASS catalog are used to remove the contribution due
to Galactic stars from the intensity measured by DIRBE in four regions in the
North and South Galactic polar caps. After subtracting the interplanetary and
galactic foregrounds, a consistent residual intensity of 14.8 +/- 4.6 kJy/sr or
20.2 +/- 6.3 nW/m^2/sr at 2.2 microns is found. At 1.25 microns the residuals
show more scatter and are a much smaller fraction of the foreground, leading to
a weak limit on the CIRB of 12.0 +/- 6.8 kJy/sr or 28.9 +/- 16.3 nW/m^2/sr (1
sigma).Comment: ApJ in press. 14 pages Latex with 7 included figures. accepted
version with 1 new figur
COBE Observations of the Cosmic Infrared Background
The Diffuse InfraRed Background Experiment on COBE measured the total
infrared signal seen from space at a distance of 1 astronomical unit from the
Sun. Using time variations as the Earth orbits the Sun, it is possible to
remove most of the foreground signal produced by the interplanetary dust cloud
[zodiacal light]. By correlating the DIRBE signal with the column density of
atomic hydrogen measured using the 21 cm line, it is possible to remove most of
the foreground signal produced by interstellar dust, although one must still be
concerned by dust associated with H_2 (molecular gas) and H II (the warm
ionized medium). DIRBE was not able to determine the CIRB in the 5-60 micron
wavelength range, but did detect both a far infrared background and a near
infrared background. The far infrared background has an integrated intensity of
about 34 nW/m^2/sr, while the near infrared and optical extragalactic
background has about 59 nW/m^2/sr. The Far InfraRed Absolute Spectrophotometer
(FIRAS) on COBE has been used to constrain the long wavelength tail of the far
infrared background but a wide range of intensities at 850 microns are
compatible with the FIRAS data. Thus the fraction of the CIRB produced by SCUBA
sources has large uncertainties in both the numerator and the denominator.Comment: Invited paper presented at the 2nd VERITAS Symposium on TeV
Astrophysics of Extragalactic Sources, April 24-26, 2003 at the Adler
Planetarium in Chicago. 8 pages LaTeX with 3 embedded figure
DIRBE Minus 2MASS: Confirming the CIRB in 40 New Regions at 2.2 and 3.5 Microns
With the release of the 2MASS All-Sky Point Source Catalog, stellar fluxes
from 2MASS are used to remove the contribution due to Galactic stars from the
intensity measured by DIRBE in 40 new regions in the North and South Galactic
polar caps. After subtracting the interplanetary and Galactic foregrounds, a
consistent residual intensity of 14.69 +/- 4.49 kJy/sr at 2.2 microns is found.
Allowing for a constant calibration factor between the DIRBE 3.5 microns and
the 2MASS 2.2 microns fluxes, a similar analysis leaves a residual intensity of
15.62 +/- 3.34 kJy/sr at 3.5 microns. The intercepts of the DIRBE minus 2MASS
correlation at 1.25 microns show more scatter and are a smaller fraction of the
foreground, leading to a still weak limit on the CIRB of 8.88 +/- 6.26 kJy/sr
(1 sigma).Comment: 25 pages LaTeX, 10 figures, 5 tables; Version accepted by the ApJ.
Includes minor changes to the text including further discussion of zodiacal
light issues and the allowance for variable stars in computing uncertainties
in the stellar contribution to the DIRBE intensitie
Approximate Coulomb distortion effects in (e,e'p) reactions
In this paper we apply a well-tested approximation of electron Coulomb
distortion effects to the exclusive reaction (e,e'p) in the quasielastic
region. We compare the approximate treatment of Coulomb distortion effects to
the exact distorted wave Born approximation evaluated by means of partial wave
analysis to gauge the quality of our approximate treatment. We show that the
approximate M\"oller potential has a plane-wave-like structure and hence
permits the separation of the cross section into five terms which depend on
bilinear products of transforms of the transition four current elements. These
transforms reduce to Fourier transforms when Coulomb distortion is not present,
but become modified with the inclusion of Coulomb distortion. We investigate
the application of the approximate formalism to a model of 208Pb(e,e'p) using
Dirac-Hartree single particle wave functions for the ground state and
relativistic optical model wave functions for the continuum proton. We show
that it is still possible to extract, albeit with some approximation, the
various structure functions from the experimentally measured data even for
heavy nuclei.Comment: 32 pages, 11 figures, 19 reference
Extraction of Structure Functions from Quasielastic Electron Scattering (e,e') from Medium and Heavy Nuclei
Using a relativistic mean-field single particle knock-out model for (e,e')
reactions on nuclei, we investigate approximate treatments of Coulomb
distortion effects and the extraction of longitudinal and transverse structure
functions. We show that an effective momentum approximation (EMA) when coupled
with a focusing factor provides a good description of the transverse
contributions to the (e,e') cross sections for electron energies above 300 MeV
on 208Pb. This approximation is not as good for the longitudinal contributions
even for incident electron eneriges above 1 GeV and if one requires very
precise extraction of longitudinal and transverse structure functions in the
quasielastic region it is necessary to utilize distortion factors based on a
nuclear model and a more accurate inclusion of Coulomb distortion effects.Comment: 5 pages, 7 figures, submitted to Phys. Rev.
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