The Extreme Ultraviolet Explorer spectrometer

The main components of EUVE have been described in detail in chapter 4 with the exception of the spectrometer. This instrument made use of part of the converging beam of the Wolter type II deep survey telescope, intercepting this with three variable line space reflection gratings (Hettrick et al. 1985). Such gratings are mechanically ruled plane gratings with a line density that varies continuously from one end of the grating to another to correct first order aberration arising from the varying...

Hidden white dwarfs in binary systems

The overwhelming majority of known white dwarfs are isolated stars. This is perhaps not surprising, as they have mostly been identified through optical blue star colour and proper motion surveys (e.g. Green et al. 1986b). Thus there exists an inherent bias against the detection of white dwarfs in unresolved binary systems, particularly if there is no active mass transfer which might otherwise draw the observer's attention, as in the cataclysmic variables. For example, the spectrum of any...

Ehb

Main Sequence Starting Point (core H burning) - S Giant Branch (H-shell burning) Main Sequence Starting Point (core H burning) Fig. 2.20. White dwarf evolutionary path in the HR diagram (courtesy M. Marsh). Convective mixing, accretion or mass-loss via a weak wind may also play a signficant role. These ideas are summarised in a schematic diagram of possible hot white dwarf evolution (figure 2.21). An aim of many studies of white dwarf photospheric composition has been to understand the...

Info

Prior to this the only EUV observations of the Moon had been made by the UV spectrometer on board Mariner 10, which obtained albedos in the 550-1250 A wavelength range (Wu and Broadfoot 1977). Gladstone et al. (1994) have reported on a detailed analysis of the EUVE observations. In its all-sky survey mode, EUVE rotated three times during each 96 min orbit. Since the scan path was perpendicular to the Earth-Sun axis, the Moon was scanned each month at first and last quarter and was...

Sources of EUV sky background 171 Geocoronal background

So far, our discussion has concentrated on the development of EUV astronomy in the context of the detection of EUV sources. However, the EUV sky background plays a significant role in the process of source detection since the source flux must be sufficient to render the source visible above the background. There are two separate sources of background the yet to be detected cosmic sky background, arising from hot gas in the ISM, and emission arising from the Earth's local environment. The cosmic...

EUV emission from latetype stars

Late-type stars constitute the largest single class of objects in the WFC EUV source catalogue. With EUV luminosities in the range 1027-1028 ergs s-1 (the EUV luminosity of the Sun is 1027 ergs s-1), one to two orders of magnitude below those of typical white dwarfs, this source population is expected to occupy a smaller volume within 10 to 25 pc of the Sun. Hence, most of these objects should be found in the third catalogue of nearby stars (CNS3 Gleise and Jahreiss 1991), the most complete...

The Rosat Wide Field Camera

The WFC was designed to cover the EUV range during the ROSAT mission, principally from 60 to 200 A during the survey itself, but with a capability of observing at longer wavelengths, to 600 A, during the pointed phase of the mission. The instrument consisted of a grazing incidence telescope comprising a set of three Wolter-Schwarzchild Type I gold-coated aluminium mirrors (Willingale 1988), with a MCP detector in the focal plane (Barstow et al. 1985 Fraser et al. 1988 Barstow and Sansom 1990)....

Physical models

Most of the work dealing with the EUV spectroscopy of stellar coronae has been phenomeno-logical, associated with determining plasma temperatures, emisson measures, densities and abundances. Important discussions concerning departures from photospheric abundance in the coronae, dealing with the FIP effect or the MAD syndrome, have begun to establish patterns for stars with different levels of activity. However, little work has been done to link the observational parameters to physical...