Chet B. Opal

New ultraviolet spectroscopic features found in comet Brorsen-Metcalf (1989o)

Spectrophotometric observations of Comet Brorsen-Metcalf from 300 to 360 nm with a resolution of about 0.1 nm are reported. The strongest features are OH 0-0(A-X) and 1-1 bands and the NH 0-0(A-X) bands. The CN 2-1 and 3-2(B-X) bands are verified and measured, and the OH 0-1 band is clearly found for the first time. A feature is measured at 325.8 nm is suggested to be the NH 0-0(c-a) transition. The CO2(+) features at 337.8, 350.4, and 351.2 nm are firmly identified for the first time. A weak feature at 354.7 nm is proposed as the fundamental transition of H2CO, which would make this the first optical spectrum cometary detection of this molecule that is very abundance in giant molecular clouds. 28 refs.

Evaluation Of Large Format Electron Bombarded Virtual Phase CCDs As Ultraviolet Imaging Detectors

An electron-bombarded Charge Coupled Device (EBCCD), when used with an external ultraviolet sensitive cathode, can be used as photon-counting UV detector with high quantum efficiency and wide dynamic range. We report on results obtained with the Texas Instruments VP1M 1024x1024 (18 micron square pixel) virtual phase CCD used with an electromagnetically focussed f/2 Schmidt camera. Excellent single photoevent discrimination and counting efficiency has been achieved with this device.

Rocket ultraviolet imagery of the Andromeda galaxy

Far-UV electrographic imagery of M31 is presented which was obtained during a sounding-rocket flight with an electrographic Schmidt camera sensitive in the wavelength range from 1230 to 2000 A. The resolution in the imagery is such that 50% of the energy from a point source is confined within a circle 40 arcsec in radius. Two conspicuous features are observed in the UV image of M31: one corresponding to a bright association (NGC 206) in the SW region of the disk and one centered on the galactic nucleus. Indications of the general spiral-arm structure are also evident. Absolute photometry and brightness distributions are obtained for the observed features, and both the central region and NGC 206 are shown to be diffuse sources. It is found that the brightness distribution of the central region is a flat ellipse with its major axis closely aligned with the major axis of the galaxy, which favors a source model consisting of young early-type stars close to the galactic plane and constitutes strong evidence against a nonthermal point source at the galactic center.

Far-ultraviolet spectra and flux distributions of some Orion stars

Far-ultraviolet (950--1800 A) spectra with about 2 A resolution were obtained of a number of stars in Orion during a sounding-rocket flight 1975 December 6. These spectra have been reduced to absolute flux distributions with the aid of preflight calibrations. The derived fluxes are in good agreement with model-atmosphere predictions and previous observations down to about 1200 A. In the 1200--1080 A range, the present results are in good agreement with model predictions but fall above the rocket measurements of Brune, Mount, and Feldman. Below 1080 A, our measurements fall below the model predictions, reaching a deviation of a factor of 2 near 1010 A and a factor of 4 near 950 A. The present results are compared with those of Brune et al. via Copernicus U2 observations in this spectral range, and possible sources of discrepancies between the various observations and model-atmosphere predictions are discussed. Other aspects of the spectra, particularly with regard to spectral classification, are briefly discussed.

Development of EBCCD Cameras for the Far Ultraviolet

Publisher Summary This chapter discusses development of electron-bombarded charge-coupled device (EBCCD) cameras for the far ultraviolet. Princeton University and the Naval Research Laboratory have ongoing programmes to develop imaging detectors with high quantum efficiency and photon-counting capability. The electron-bombarded CCD arrays were operated in Schmidt imaging systems with opaque KBr photocathodes. These were compared with a chevron micro channel plate detector (MCP) operated in pulse-counting mode, or a collecting electrode for direct photocurrent measurement, placed interchangeably at the Schmidt camera electron focus, with simultaneous light-source monitoring by calibrated photomultipliers. The EBCCD read-out electronics were operated in analogue read-out mode, with signal levels per pixel digitized and recorded on tape. A liquid nitrogen cooling system maintained the CCDs at –80oC or less during operations. Theoretically, the single-photoelectron responses of the two types of CCD differ in that in the thinned back surface bombarded CCD there is likely to be significant lateral spread of the generated secondary charge before collection at the front-side electrodes.

Focal reducer/CCD detector system for the McDonald 2.1-m telescope

A focal reducer which converts the f/13.5 primary Cassegrain beam of the McDonald 2.1 m telescope to f/3.0 is described. The resulting plate scale is 30 microns/arcsec, which is a good match to the resolution of typical CCDs for seeing conditions of about 1 arcsec. The present system uses a SID501 RCA CCD with 30-micron pixels; however, a TI 800 x 800 CCD with 15-micron pixels and other low-noise, small pixel devices will be used eventually. The focal reducer uses primarily reflective optics to provide good sensitivity down to the atmospheric cutoff at 3100A.

Performance Of The Rca C81020E Intensified CCD Device

The C81020E is an electrostatically-focused image tube with a fiber-optic window which uses a thinned SID504 CCD operated in electronombarded mode to detect accelerated photo-electrons. To evaluate this device, a system was assembled using a commercially available camera electronic chain, a frame grabber, and a microcomputer data acquisition system. Preliminary data on geometric and electronic linearity, dynamic range, and lifetime under electron bombardment indicate that the device could be useful in astronomical applications. It can be used at low light levels in lieu of conventional CCDs, and probably will be satisfactory as a photon counter in the event centroiding mode. The charge cloud produced by the primary appears to spread out over more than one pixel, precluding use of the device as a simple digicon.

Evaluation of the Texas Instruments' TC215-31 CCD for astronomical imaging

The characterization and low light level performance of the TC215-31 CCD is presented. This device has 12 by 12 micron pixels in a 1024 x 1024 format, with an active image area of 1000 x 1018 pixels. The device is evaluated in terms of its linearity, dark current, charge transfer efficiency, and spectral response. The spectral response of this device in the range of 300 nm to 1000 nm is discussed. The structure of the virtual phase pixel is such that half of the area is covered by a clocking electrode, with the uncovered half remaining sensitive to UV light. Thus this device can be useful in the UV provided that special consideration of the sampling is taken into account. Noise characteristics of this device were measured as a function of clock levels, amplifier bias, readout speed, and temperature. The output of this device is unique in that there are two output amplifiers, one for every other pixel. The mean noise of the two output amplifiers is about 20 electrons, with a dark current of 0.016 electrons/sec at -130 C. This device was used as an astronomical imager at the prime focus of a small Schmidt telescope.

Far Ultraviolet Wide Field Imaging And Photometry: Spartan-202 Mark II Far Ultraviolet Camera

The Spartan-202 space shuttle mission will include, as its primary scientific instrument, the Naval Research Laboratorys Mark II Far Ultraviolet Camera. The primary scientific objectives of this mission are imaging and photometry, over large areas of the sky, of hot stars, diffuse nebulae, and nearby external galaxies. It is intended to produce a more sensitive and higher resolution far-UV sky survey than previous, similar investigations. The observations provide information on the temperatures and total luminosities of hot stars, and on the far-UV extinction and reflection by interstellar dust, which cannot be obtaihed with ground-based instrumentation or as efficiehtly with other space-based instruments. The measurements complement and support those to be made with the Hubble Space Telescope and the Astro Ultraviolet Imaging Telescope, which have higher angular resolutions and point-source sensitivities but smaller fields of view and lower diffuse-source sensitivities than the Mark II Far UV Camera. The instrument is an electrographic Schmidt camera, similar to but larger (and having higher resolution and point-source sensitivity) than similar cameras we have used in numerous other space flight experiments. The principles, design, and sounding rocket flight history of the Mark II camera are discussed, as well as modifications required to adapt the instrument for the Spartan flight. Target selection criteria, tentative observing plans, and growth potential in the Space Station era are also discussed. Data reduction and analysis plans are described.

The Spartan-281 Far Ultraviolet Imaging Spectrograph

The Naval Research Laboratorys Far Ultraviolet Imaging Spectrograph (FUVIS) is currently under development for flight as a Spartan shuttle payload. The science objectives are concerned with spectroscopy of diffuse sources in the far-UV (1000-2000 A) with very high sensitivity and with moderate spatial and spectral resolution. Sources of interest include diffuse nebulae, the gener-al galactic background radiation, and artificially induced radiations associated with the space shuttle vehicle (e.g., surface glow and RCS thruster firings). The measurements complement and support other investigations, such as with the Hubble Space Telescope and the Astro shuttle instruments, which have higher spectral and spatial resolutions but lower diffuse-source sensitivities and smaller fields of view. The principles, design, and sounding-rocket flight experience of FUVIS are discussed, as well as the adaptations required for flight in the Spartan mission. The instrument can be adapted for future, missions by use Of an electron-bombarded CCD array in place of electrographic film recording. The data reduction and analysis plans for the Spartan-281 FUVIS results are presented.