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The internal intensity calibration of the Coronal Diagnostic Spectrometer (CDS) - Grazing Incidence Spectrometer (GIS) is studied using the Arcetri diagnostic method. A large number of spectral lines observed by the four GIS detectors in solar active and quiet regions is analysed in order to determine the relative intensity calibration curve of the instrument. The plasma diagnostic method developed in Arcetri allows the measurement of the correction factors to the pre-flight CDS - GIS internal intensity calibration curves and of the relative calibration between different detectors. No gross deviations from the pre-flight calibration are found. Also the GIS 3 and GIS 4 second order sensitivites are measured. The problems of fixed patterning, ghosting, anomalous line profiles and widths are also discussed, and a list of lines suitable for further diagnostic studies with GIS is presented.

The abundance of helium relative to hydrogen has been measured with the “Coronal Helium Abundance Spacelab Experiment” (CHASE) from the space shuttle Challenger in 1985. Previous solar measurements have proved difficult due to the temperature-sensitivity of the electron excitation rates for the observed lines. In this approach scattered Lyman Alpha (Lyα) radiation of belium and hydrogen formed in the corona were measured with a grazing-incidence spectrometer and compared with the intensity of the illuminating flux from the solar chromosphere. The abundance ratio by number of atoms was found to be 0.070 with an uncertainty of 0.011. Scattered light in the telescope is the main source of error.

Following a successful launch on 1990 June 1, the ROSAT spacecraft and its payload, consisting of an X-ray and an EUV telescope, underwent two months of in-orbit calibration and detailed performance checks. A preliminary observation of a small section of the sky, carried out over July 11-16 (the mini-survey) showed all ROSAT systems to be functioning well and has allowed predictions to be made on the ultimate productivity of both ROSAT all-sky surveys. An analysis of the mini-survey data from the UK Wide Field Camera, has revealed 35 EUV sources, including several white dwarf stars, a variety of active cool stars and several other objects. In all, 23 sources have probable optical counterparts

DETAILED understanding of the evolution of main-sequence stars into white dwarfs depends on knowledge of the chemical composition of white-dwarf atmospheres, but the hottest white dwarfs emit much of their radiation in the extreme ultraviolet (EUV), a part of the spectrum that has been generally inaccessible to astronomers. We report here the discovery of a new white dwarf as a bright EUV source found during the first observations using the Wide Field Camera1 on the Rosat satellite. Within the 1-arcmin error box of the EUV source is an unusually blue star, which we show to be a binary system consisting of a DA white dwarf and a cool companion in the classification range dM2–dM5. There are some similarities between this new object and the binary system Feige 24 (ref. 2), but spectral differences in the EUV emission can be attributed to significantly different atmospheric compositions for the two white dwarfs.

The laboratory end-to-end testing of the Coronal Diagnostic Spectrometer (CDS) experiment on the ESA/NASA SOHO mission is reported. A brief overview of CDS, which operates in the extreme-ultraviolet wavelength range, is given. Pertinent details of the calibration source are presented, followed by an account of the source beam characterization. A section is devoted to the determination of the instrument apertures and this includes an outline of the measurements, the results from both the grazing incidence and normal incidence aperture scans and their interpretation to yield estimated aperture areas. Next the measurement of spectrometer bandwidths and their comparison with expected values are described. Then the pre-launch wavelength calibrations are obtained. The section on sensitivity starts with an evaluation of the effects of polarization on the measurements. The expected sensitivities are then derived. The measurements, their analysis and a comparison of measured and expected sensitivities are presented for both the normal incidence and grazing incidence spectrometers. The application of the laboratory calibration to in-flight solar data is discussed.

TMs paper presents first results of the Coronal Diagnostic Spectrometer (CDS) recently launched aboard the Sol, and Heliospheric observatory (SOHO). CDS is a twin spectrometer, operating in the extreme ultraviolet range 151-785 A. Thus, it can detect emission lines from trace elements in the corona and transition region which will be used to provide diagnostic information on the solar atmosphere. In this paper, we present early spectra and images, to illustrate the performance of the instrument and to pave the way for future studies.

The Coronal Diagnostic Spectrometer is designed to probe the solar atmosphere through the detection of spectral emission lines in the extreme ultraviolet wavelength range 150–800 A. By observing the intensities of selected lines and line profiles we may derive temperature, density, flow and abundance information for the plasmas in the solar atmosphere. Spatial and temporal resolutions of down to a few arcseconds and seconds, respectively, allow such studies to be made within the fine-scale structure of the solar corona. Furthermore, coverage of large wavelength bands provides the capability for simultaneously observing the properties of plasmas across the wide temperature ranges of the solar atmosphere.

We present early results from observations made by the UK’s imaging EUV telescope, the Wide Field Camera (WFC). This telescope is being flown aboard the West German satellite ROSAT. In conjunction with a large X-ray telescope, built by the West Germans, the WFC is conducting a survey of the whole sky. This is the first in the EUV waveband. Afterwards ROSAT will be devoted to pointed observations of specific objects. We use results from the earliest phases of the ROSAT mission to highlight the importance of WFC observations for the study of white dwarfs and related objects such as the central stars of planetary nebulae.

The main design features and the early findings of the Rosat XUV wide field camera (WFC) are discussed. The most important data on the WFC telescope and detectors are presented. The WFC operational features, observing efficiency, filter performance, thermal performance star tracker performance, and single-event upsets are discussed. The first WFC images are compared with preflight calibration data.