Showing papers by "Edward L. Wright published in 2000"

Tentative Detection of the Cosmic Infrared Background at 2.2 and 3.5 Microns Using Ground-based and Space-based Observations

Abstract: The cosmic infrared background (CIRB) is the sum total of the redshifted and reprocessed short-wavelength radiation from the era of galaxy formation, and hence contains vital information about the history of galactic evolution. One of the main problems associated with estimating an isotropic CIRB in the near-infrared (1-5 μm) is the unknown contribution from stars within our own Galaxy. The optimal observational window to search for a background in the near-IR is at 3.5 μm since that is the wavelength region where the other main foreground, the zodiacal dust emission, is the least. It is not possible to map out the entire 3.5 μm sky at a resolution that will accurately estimate the flux from stars. However, since the CIRB is presumably isotropic, it can potentially be detected by selecting a smaller field and imaging it at good resolution to estimate the stellar intensity. We selected a 2° × 2° "dark spot" near the north Galactic pole which had the least intensity at 3.5 μm after a zodiacal light model was subtracted from the all-sky maps generated by the Diffuse Infrared Background Experiment (DIRBE). Still, the large area of the field made it very difficult to mosaic at 3.5 μm using the available arrays. Thus, the field was mosaicked at 2.2 μm, then the bright stars were selected and reimaged at 2.2 and 3.5 μm. The resulting total intensity of the bright stars was combined with a model for the contribution from dimmer stars and subtracted from the zodi-subtracted DIRBE map. The contribution from the interstellar medium was also subtracted, leaving a residual intensity at 2.2 μm of 16.4 ± 4.4 kJy sr-1 or 22.4 ± 6.0 nW m-2 sr-1, and at 3.5 μm of 12.8 ± 3.8 kJy sr-1 or 11.0 ± 3.3 nW m-2 sr-1. The nature of our analysis suggests that this excess emission is probably a detection of the cosmic background in the near-infrared.

Detection of the Cosmic Infrared Background at 2.2 and 3.5 Microns Using DIRBE Observations

Abstract: We compare data from the Diffuse Infrared Background Experiment (DIRBE) on COBE to the model of the infrared sky provided by Wainscoat and colleagues in 1992. The model is first compared with broadband K (2.2 ?m) star counts. Its success at K band lends credence to its physical approach, which is extrapolated to the L band (3.5 ?m). We have analyzed the histograms of the pixel-by-pixel intensities in the 2.2 and 3.5 ?m maps from DIRBE after subtracting the zodiacal light. The shape of these histograms agrees quite well with the histogram shape predicted using the Wainscoat model of the infrared sky, but the predicted histograms must be displaced by a constant intensity in order to match the data. This shift is the cosmic infrared background, which is 16.9 ? 4.4 kJy sr-1 or 23.1 ? 5.9 nW m-2 sr-1 at 2.2 ?m and 14.4 ? 3.7 kJy sr-1 or 12.4 ? 3.2 nW m-2 sr-1 at 3.5 ?m. Combining our near-IR results with the far-IR background detected by Hauser and colleagues in 1998 suggests that roughly half of the radiation produced by galaxies is absorbed by dust and reradiated in the far-IR.

DIRBE Minus 2MASS: Confirming the Cosmic Infrared Background at 2.2 Microns

Abstract: 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).

Permanent magnet focused, multi-stage depressed collector klystron amplifiers for satellite communications

Abstract: A new line of high-efficiency multi-stage depressed collector (MSDC) klystron amplifiers has been developed by Communications and Power Industries Microwave Power Products (CPI/MPP) for use in satellite communications and scientific applications market. These klystrons are air-cooled with permanent magnet focusing. The first products are designed to service the satellite uplink and terrestrial repeater markets. MSDC technology for these applications can reduce power consumption by as much as 60%. A general discussion about the benefits of MSDC technology for these applications, as well as two examples of their use, are presented. CPI/MPP has developed the VKU-8891M series klystrons which provide 2.4 kW CW tunable in the frequency range from 17.3 to 18.4 GHz with instantaneous bandwidths up to 85 MHz. The klystron is designed with a 4-stage MSDC which has increased the saturated efficiency of the device from 24% to 40% A detailed discussion of the design, as well as a comparison between simulation and experiment, is presented. CPI/MPP is also developing the VKS-7964M klystron in the frequency range from 2.1 to 2.4 GHz, with instantaneous bandwidths up to 8 MHz. This klystron has a 4-stage MSDC. The simulated efficiency of this klystron approaches 60%. We predict the measured efficiency. A detailed discussion of the design, as well as a comparison between simulation and experiment, is presented.

Gun-only magnet used for a multi-stage depressed collector klystron

Abstract: A klystron tube for amplifying signals at microwave radio frequencies utilizes an electron source for emitting electrons through a field focused by a high energy magnet in the RF section of the tube. After the electrons have passed through the active area of the tube, the electrons strike the collector which, in this case, is a multistage depressed collector. The multiple stages of the depressed collector are connected to high energy voltage sources of different potentials. The magnet used for focusing the electron beam is closed (no open pole pieces) at the multistage depressed collector so that no magnetic flux reversals are present to affect the beam dispersal, due to electrostatic space charge forces, onto the multistage depressed collector.