Extreme-Ultraviolet Flux from the Virgo Cluster: Further Evidence for a 500,000-Kelvin Component

A surprising discovery in x-ray astronomy was that clusters of galaxies often contain vast quantities of hot (20 million kelvin) diffuse gas. Substantial diffuse extreme-ultraviolet (EUV) emission has recently been detected in the Virgo cluster of galaxies. Depending on the character of the interstellar medium in our galaxy, this emission could be either an aspect of the hot cluster gas or a previously undetected 500,000-kelvin component. Analysis of the observational data in combination with our current knowledge of the interstellar medium revealed that the EUV flux cannot be an effect of the interstellar medium. Hence, a warm cluster component appears likely.

The SERENDIP piggyback SETI project.

The SERENDIP project is an ongoing program of monitoring and processing broadband radio signals acquired by existing radio astronomy observatories. SERENDIP operates in a piggyback mode: it makes use of whatever observing plan (sequence of frequencies, sky coordinates, and polarizations) is under way at its host observatory. Moreover, the SERENDIP data acquisition system, once installed, operates autonomously. This approach makes it possible to obtain large amounts of high quality observing time in a manner that is economical and that does not adversely affect ongoing radio astronomy survey work. The SERENDIP II system has been installed at the NRAO 300-foot telescope at Green Bank, West Virginia, and has operated there for several thousand hours. In this report, we summarize our findings from these observations and describe the present status of the project. Two key elements of SERENDIP are the automated data acquisition system that uses adaptive thresholds and logs only statistically significant peaks in the real-time power spectra, and the subsequent off-line analysis programs that identify and reject a variety of interference signals. Several specific correlations have been identified that offer promise. At present, the development and testing of these interference rejection algorithms is the main thrust of our work.

Telescience at the University of California, Berkeley.

The University of California at Berkeley (UCB) is a member of a university consortium involved in telescience testbed activities under the sponsorship of NASA. Our Telescience Testbed Project consists of three experiments using flight hardware being developed for the Extreme Ultraviolet Explorer project at UCB's Space Sciences Laboratory. The first one is a teleoperation experiment investigating remote instrument control using a computer network such as the Internet. The second experiment is an effort to develop a system for operation of a network of remote workstations allowing coordinated software development, evaluation, and use by widely dispersed groups. The final experiment concerns simulation as a method to facilitate the concurrent development of instrument hardware and support software. We describe our progress in these areas.

Soft x-ray and extreme ultraviolet quantum detection efficiency of potassium bromide photocathode layers on microchannel plates.

The quantum detection efficiency (QDE) of potassium bromide, applied directly to the surface of a microchannel plate (MCP), has been measured over the wavelength range from 44 to 1216 A. We present the first measurements for the QDE of KBr between 44 and 256 A. These show that there is a high QDE peak (~70%) centered at ~70 A. The results at wavelengths above 256 A agree with our previous study. Investigation of the angular dependence of the QDE indicates that maximum efficiencies are achieved for graze angles

Soft x-ray and extreme ultraviolet quantum detection efficiency of potassium chloride photocathode layers on microchannel plates.

We present measurements of the quantum detectio efficiency (QDE) of potassium chloride, applied directly to the surface of a microchannel plate (MCP), over the 44-1460-A wavelength range. The contributions of the photocathode material in the channels, and on the interchannel web, to the QDE have been determined. Two broad peaks in the QDE centered at lambda congruent with 500 A and lambda congruent with 900 A are apparent, the former with ~40% peak QDE and the latter with ~30% peak QDE. The photoelectric threshold is observed at lambda ~1400 A, and there is a narrow QDE minimum at lambda~ 670 A, which correlates with 2xthe band gap energy for KC1. The angular variation of the QDE from 0 to 35 degrees to the channel axis has also been examined. We describe a simple QDE model and show that its predictions are in accord with our QDE measurements. Assessment of the stability of KC1 shows that there was no significant degradation of the QDE at wavelengths of

Ultraviolet quantum detection efficiency of potassium bromide as an opaque photocathode applied to microchannel plates.

We have measured the quantum detection efficiency (QDE) of potassium bromide as a photocathode applied directly to the surface of a microchannel plate over the 250-1600A wavelength range. The contributions of the photocathode material in the channels and on the interchannel web to the QDE have been determined. Two broad peaks in the QDE centered at ~450 and ~1050 A are apparent, the former with ~50% peak QDE and the latter with ~40% peak QDE. The photoelectric threshold is observed at ~1600 A, and there is a narrow QDE minimum at ~750 A which correlates with 2x the band gap energy for KBr. The angular variation of the QDE from 0 to 40 degrees to the channel axis has also been examined. The stability of KBr with time is shown to be good with no significant degradation of QDE at wavelengths below 1216 A over a 15-day period in air.

Astronomical observations with the FAUST telescope.

The far-ultraviolet space telescope (FAUST) was flown on Spacelab 1 to provide wide-field imaging in the wavelength range 1300 to 1800 angstroms. Most of the developed film showed high levels of background exposure. Frames with a lower background included exposures of the Cygnus Loop supernova remnant and an exposure in the direction of the galaxy cluster Abell 2634. Several exposures will be used in a search for hot white dwarf stars.

Continuous-readout extreme-ultraviolet airglow spectrometer.

A satellite-borne extreme-ultraviolet airglow spectrometer is described covering the 275-1420-A range with 8-A resolution. The spectrometer is of near normal incidence Rowland circle design and employs a holographically ruled concave grating. The detector is a microchannel plate with resistive anode providing a continuous readout of any 650-A ground-commandable subset of the total bandpass. This simultaneous wide spectral coverage results in a factor of 80 increase in sensitivity over a fixed exit slit design of equivalent resolution.

Low-distortion resistive anodes for two-dimensional position-sensitive MCP systems.

Microchannel plates (MCPs) are frequently employed with resistive anodes to detect charged particles or photons and yield analog signals from which event positions can be decoded. We discuss an anode geometry devised by C.W. Gear that offers theoretically distortionless encoding of Cartesian event positions into pulse charge ratios. Electron beam images taken with such an anode are shown, and confirm the usefulness of the approach.

Extreme ultraviolet photometer for observations of helium in interplanetary space.

A four-channel photometer sensitive to two solar EUV lines which are resonantly scattered by helium gas was developed for flight on the Apollo-Soyuz Test Project. Two channels observed the 58.4-nm line of He I and used helium gas resonant absorption cells to determine the intensities of the center and wings of that line. The other two channels observed the 30.4-nm line of He II. The instrument surveyed much of the celestial sphere during a series of slow rolling maneuvers by the Apollo spacecraft. The experiment operated properly, and usable data were obtained. Study of the distributions of flux seen, and of the ratio of 58.4-nm fluxes seen with gas cells full and empty, will refine current understanding of several poorly known properties of the local interstellar medium. Study of the 30.4-nm flux distribution will refine present knowledge of the structure of the earth's plasmasphere.

Extreme ultraviolet spectrometer for space research.

A normal incidence spectrometer for use in the wavelength region from 200 A to 1270 A has been developed. The design and calibration of the instrument are described in detail. The spectrometer can be employed to detect extreme uv radiation at a minimum flux level of 1 rayleigh with a spectral resolution of 40 A and a spatial resolution of 6 degrees . Data on the extreme uv night sky spectrum between 780 A and 1270 A obtained with this instrument on a recent rocket flight are presented.