6,509 research outputs found
MM Observations of IRAS Galaxies: Dust Properties, Luminosity Functions and Contributions to the Sub-MM Background
We have studied the FIR/{\it mm} spectrum of IR galaxies by combining IRAS
photometry with new {\it mm} data on a complete southern IRAS galaxy sample.
The observed spectra and a dust model emphasize a dicothomy in the galaxy
population: half of the objects with a lot of warm dust are characterized by
higher values of the bolometric (UV-FIR) luminosity, of the dust-to-gas mass
ratio, of the dust optical depths and extinction, while those dominated by cold
({\it cirrus}) dust show opposite trends. From these data we derive the {\it
mm} luminosity function of galaxies and estimate their contribution to the
sub-{\it mm} background (BKG).Comment: 4 pg Latex file (using included crckapb.sty) gzip'd tar'd file
including 3 ps figures. Proceedings of 'Cold dust Morphology Conference',
Johannesburg, South Africa, January 21-26 1996 A wrong figure is replace
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Study of the dynamic tear film aberrations using a curvature sensing setup
The advancement in adaptive optics in recent years has increased the interest in the dynamic aberrations of the eye, including those introduced by the first optical surface provided by the tear film. A curvature sensing system to measure the dynamic topography of the tear film is described. This optical system was used to measure the aberrations of the tear film on 14 eyes. The evolution of this surface is monitored through videos of the tear film topography. The effect on optical quality is studied from the time-evolution of the RMS wavefront error showing non-negligible aberration variations attributed to the tear film layer; the effect of tear film break-up on the ocular optical quality is also discussed. Furthermore, the aberration maps are decomposed into their constituent Zernike components showing stronger contributions from 4th order terms, and also from those components with vertical symmetry which can be attributed to the effect of the eye lids on the tear film. Finally, the power spectra of the RMS wavefront error evolution show that the strongest contributions of the tear film aberrations are to be found at low frequencies, typically below 2Hz
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Curvature sensor for the measurement of the static corneal topography and the dynamic tear film topography in the human eye
A system to measure the topography of the first optical surface of the human eye noninvasively by using a curvature sensor is described. The static corneal topography and the dynamic topography of the tear film can both be measured, and the topographies obtained are presented. The system makes possible the study of the dynamic aberrations introduced by the tear film to determine their contribution to the overall ocular aberrations in healthy eyes, eyes with corneal pathologies, and eyes wearing contact lenses
The COBRAS/SAMBA CMB Project
COBRAS/SAMBA is a second generation satelitte dedicated to mapping at high
resolution and sensitivity the anisotropies of the Cosmic Microwave Background
(CMB). This mission is in the assessment study phase (A) at ESA, with a
decision expected mid 1996, for a launch around 2003.Comment: PostScript, 4 pages, 4 figures in text, to appear in the Proceedings
of the 1995 Moriond Meeting on ``Clustering in the Universe'
The origin of the diffuse background gamma-radiation
Recent observations have now provided evidence for diffuse background gamma radiation extending to energies beyond 100 MeV. There is some evidence of isotropy and implied cosmological origin. Significant features in the spectrum of this background radiation have been observed which provide evidence for its origin in nuclear processes in the early stages of the big-band cosmology and tie in these processes with galaxy fromation theory. A crucial test of the theory may lie in future observations of the background radiation in the 100 MeV to 100 GeV energy range which may be made with large orbiting spark-chamber satellite detectors. A discussion of the theoretical interpretations of present data, their connection with baryon symmetric cosmology and galaxy formation theory, and the need for future observations are given
Anisotropy Studies of the Unresolved Far-infrared Background
Dusty, starforming galaxies and active galactic nuclei that contribute to the
integrated background intensity at far-infrared wavelengths trace the
large-scale structure. Below the point source detection limit, correlations in
the large-scale structure lead to clustered anisotropies in the unresolved
component of the far-infrared background (FIRB). The angular power spectrum of
the FIRB anisotropies could be measured in large-area surveys with the Spectral
and Photometric Imaging Receiver (SPIRE) on the upcoming Herschel observatory.
To study statistical properties of these anisotropies, the confusion from
foreground Galactic dust emission needs to be reduced even in the ``cleanest''
regions of the sky.The multi-frequency coverage of SPIRE allows the foreground
dust to be partly separated from the extragalactic background composed of dusty
starforming galaxies as well as faint normal galaxies. The separation improves
for fields with sizes greater than a few hundred square degrees and when
combined with Planck data. We show that an area of about 400 degrees
observed for about 1000 hours with Herschel-SPIRE and complemented by Planck
provides maximal information on the anisotropy power spectrum. We discuss the
scientific studies that can be done with measurements of the unresolved FIRB
anisotropies including a determination of the large scale bias and the
small-scale halo occupation distribution of FIRB sources with fluxes below the
point-source detection level.Comment: 10 pages, 8 figures, replaced to match the extended version, accepted
by Ap
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