Engineering topics

Welsh, Barry Y.

Publications and source records attributed to Welsh, Barry Y..

13 records

NASA NTRS1993

Intense extreme ultraviolet emission from the B star Epsilon Canis Majoris

We report the discovery of the brightest nonsolar source of EUV emission: the B2 II star Epsilon Canis Majoris. This source has been detected by the Extreme Ultraviolet Explorer satellite's all-sky photometric survey. It is approximately 30 times brighter at 600 A than the predicted emission from the hot white dwarf star HZ 43, previously believed to be the brightest EUV source. We have fitted a simple B star photospheric model to the observed broadband EUV fluxes to explain this emission. Assuming a stellar temperature of 25,000 K and a gravity (log g) of 3.3, we derive an interstellar hydrogen column density of 1.05 +/- 0.05 x 10 exp 18/sq cm over the 187 pc to the star. This corresponds to a line-of-sight number density of hydrogen, of 0.002/cu cm, which is comparable to values found in the rarefied Local Bubble region which surrounds the sun.

Vallerga, John V.↗

NASA NTRS1992

NASA's Ultraviolet Astrophysics Branch: Present and future detector program

The various concepts in ultraviolet detector technology currently being funded by NASA's Astrophysics Division to carry out observations in the 100 to 3000 A region are reviewed. In order to match the science objectives of future space missions with new observational techniques, critical detector technology needs in the ultraviolet regime have been identified. The attempt by NASA's Astrophysics Division Advanced Programs Branch to formulate an integrated detector technology plan as part of the ongoing 'Astrotech 21' program in order to provide the technology base for these astrophysics missions of the 21st century is described.

Welsh, Barry Y.↗

NASA NTRS1992

NASA's ultraviolet astrophysics branch - The next decade

We review some of the mission concepts currently being considered by NASA's Astrophysics Division to carry out future observations in the 100-3000 Angstrom region. Examples of possible future missions include UV and visible interferometric experiments, a next generation Space Telescope and lunar-based UV instrumentation. In order to match the science objectives of these future missions with new observational techniques, critical technology needs in the ultraviolet regime have been identified. Here we describe how NASA's Astrophysics Division Advanced Programs Branch is attempting to formulate an integrated technology plan called the 'Astrotech 21' program in order to provide the technology base for these astrophysics missions of the 21st century.

Welsh, Barry Y.↗

NASA NTRS1992

Prospect of space-based interferometry at EUV and soft X-ray wavelengths

We review the current capabilities of high-resolution, spectroscopic, space-borne instrumentation available for both solar and stellar observations in the EUV and soft X-ray wavelength regimes, and describe the basic design of a compact, all-reflection interferometer based on the spatial heterodyne technique; this is capable of producing a resolving power (lambda/Delta-lambda) of about 20,000 in the 100-200 A region using presently available multilayer optical components. Such an instrument can be readily constructed with existing technology. Due to its small size and lack of moving parts, it is ideally suited to spaceborne applications. Based on best estimates of the efficiency of this instrument at soft X-ray wavelengths, we review the possible use of this high-resolution interferometer in obtaining high-resolution full-disk spectroscopy of the sun. We also discuss its possible use for observations of diffuse sources such as the EUV interstellar background radiation.

Welsh, Barry Y.↗

NASA NTRS1991

The interstellar tunnel of neutral-free gas toward Beta Canis Majoris

Using high-resolution sodium absorption observations of early-type stars to determine the distribution of neutral interstellar gas in the direction of the star Beta CMa, the contours of a large feature in the local interstellar medium, some 50 pc in diameter and 300 pc long, that appears to be virtually free of neutral gas have been mapped. This rarefied 'interstellar tunnel' is an extension of a region of very low gas density surrounding the sun called the Local Bubble, which may well have been formed by the interaction of expanding interstellar cavities produced by multiple supernova events. This large region of unusually low gas density will be a prime area for study in the soft X-ray and EUV spectral regions.

Welsh, Barry Y.↗

NASA NTRS1991

The Extreme Ultraviolet Explorer mission

The Extreme Ultraviolet Explorer (EUVE) is a NASA astronomy mission which will operate in the 70-760A spectral band. The science payload consists of three grazing incidence scanning telescopes and an EUV spectrometer/deep survey instrument. An overview of the planned mission profile is given, and the instrumentation which comprises the science payload is discussed. The EUVE is scheduled for launch in late August 1991.

Welsh, Barry Y.↗

NASA NTRS1991

Results from the calibration of the Extreme Ultraviolet Explorer instruments

The paper describes the main features and selected results of the calibration of the scientific instruments to be flown on the Extreme Ultraviolet Explorer in 1991. The instrument payload includes three grazing incidence scanning telescopes and an EUV spectrometer/deep survey instrument covering the spectral region 70-800 A. The measured imaging characteristics, the effective areas, and the details of spectral responses of the instruments are presented. Diagrams of the cross-sectional views of the scanning telescope and the deep-survey/spectrometer telescope are included.

Welsh, Barry Y.↗

NASA NTRS1990

High-resolution sodium absorption-line observations of the local interstellar medium

High-resolution observations of the sodium D1 and D2 interstellar absorption lines have been made toward 19 stars in the local ISM at distances ranging from 20 to 220 pc. A least-squares absorption line-fitting analysis is carried out on 10 of the stars that show detectable sodium. The velocity structure, velocity dispersions, and column densities of the various interstellar cloud components are derived. For the majority of stars, the best-fit dispersion parameter is about 2 km/s, corresponding to an upper limit for the kinetic temperature of the interstellar gas of about 5500 K. No sodium is detected toward stars with distances less than 42 pc, placing an upper limit 2.5 x 10 to the 18th/sq cm to the hydrogen column density in these lines of sight.

Welsh, Barry Y.↗

NASA NTRS1990

The Extreme Ultraviolet Explorer - Overview and calibration

The Extreme Ultraviolet Explorer (EUVE) is a NASA-funded astronomy mission that will operate in the 70 to 760 A band. The science payload, which has been designed and built by the Space Sciences Laboratory at the University of California, Berkeley, consists of three grazing incidence scanning telescopes and an EUV spectrometer/deep survey instrument. This paper gives details of the planned mission profile and an overview of the instrumentation that the science payload comprises. Topics such as the thermal design, contamination control, and details of the electronics system are discussed. Finally, the results of the calibration of the various subsystems that make up the EUVE instrumentation are reviewed, and the calibration plan for the integrated EUVE instruments is discussed.

Welsh, Barry Y.↗

NASA NTRS1990

Contamination control program results from three years of ground operations on the Extreme Ultraviolet Explorer instruments

A stringent contamination-control plan has been developed for the optical components of the Extreme Ultraviolet Explorer instruments, whose performance in the 80-900 A wavelength range is highly sensitive to particulate and molecular contamination. The contamination-control program has been implemented over the last three years during assembly, test and calibration phases of the instrument. These phases have now been completed and the optics cavities of the instruments have been sealed until deployment in space. Various approaches are discussed which have been used during ground operations to meet optics' contamination goals within the project schedule and budget. The measured optical properties of EUV witness mirrors are also presented which remained with the flight mirrors during ground operations. These were used to track optical degradation due to contamination from the cleanroom and high-vacuum test-chamber environments.

Ray, David C.↗

NASA NTRS1989

Small blaze angle gratings with various surface treatments for use in the extreme ultraviolet

Three replica gratings made from a single master, including two epoxy-overcoated gratings with different thicknesses of gold and one grating replicated directly in gold, were studied by measuring and comparing the performances of the gratings in EUV light at grazing incidence angles. The results show that, in situations which require a very low grazing angle, high-quality, mechanically ruled straight groove gratings provide good efficiency and uniform blaze independent of coating thickness up to 1000 A. However, the technique of direct replication in the surface material seems to result in substantially more light scattering and does not seem to have other obvious advantages.

Miller, Anne↗

NASA NTRS1989

Contamination control program for the Extreme Ultraviolet Explorer instruments

A contamination-control program has been instituted for the optical components of the EUV Explorer satellite, whose 80-900 A range performance is easily degraded by particulate and molecular contamination. Cleanliness requirements have been formulated for the design, fabrication, and test phases of these instruments; in addition, contamination-control steps have been taken which prominently include the isolation of sensitive components in a sealed optics cavity. Prelaunch monitoring systems encompass the use of quartz crystal microbalances, particle witness plates, direct flight hardware sampling, and optical witness sampling of EUV scattering and reflectivity.

Ray, David C.↗

NASA NTRS1988

The Berkeley extreme ultraviolet calibration facility

The vacuum calibration facilities of the Space Sciences Laboratory, University of California at Berkeley are designed for the calibration and testing of EUV and FUV spaceborne instrumentation (spectral range 44-2500 A). The facility includes one large cylindrical vacuum chamber (3 x 5 m) containing two EUV collimators, and it is equipped with a 4-axis manipulator of angular-control resolution 1 arcsec for payloads weighing up to 500 kg. In addition, two smaller cylindrical chambers, each 0.9 x 1.2 m, are available for vacuum and thermal testing of UV detectors, filters, and space electronics hardware. All three chambers open into class-10,000 clean rooms, and all calibrations are referred to NBS secondary standards.

Welsh, Barry Y.↗