It was first shown by von Zeipel (1924) that strict radiative equilibrium is impossible in the radiative zones of a uniformly rotating star. This result lead Eddington (1925) and Vogt (1925) to independently suggest the existence of large-scale meridional currents in the radiative zones of rotating stars. Eddington argued that since these currents will transport angular momentum, the condition of strict radiative equilibrium would result in meridional currents combined with differential rotation.

The advent of new techniques to measure the global oscillation spectrum of the Sun has provided a new and powerful tool to investigate solar structure. One of the most challenging and potentially rewarding problems in contemporary astronomy is to devise techniques which will allow similar studies of other stars. This paper outlines the theory of global oscillations of late-type main-sequence stars, and summarises some of the achievements of global oscillation studies of the Sun. It then reviews the very few successful attempts that have been made to study stellar oscillations, and briefly discusses several apparently promising lines for further instrumental development.

This document is the final Phase A Science Report of the Australian LYMAN Science Working Group, and describes in detail the scientific objectives, technical feasibility, and engineering implementation of the LYMAN mission as developed in the Australian studies.

A great deal has been learnt about supernovae over the last 500 days, or so. The major deficiencies in theory highlighted by the case of SN 1987A are briefly reviewed, as are the sucesses.

The LYMAN project continues the distinguished US and European tradition of the exploration of the Universe at Ultraviolet Wavelengths accessible only from space. These earlier missions, which include OAO, TD-1, ANS, Copernicus and the International Ultraviolet Explorer (IUE), each demonstrated the existence of new and hitherto unsuspected physical phenomena and processes, and have collectively enhanced our understanding of the evolution of stars, galaxies and the Universe.

The importance of both the UV-spectral region as a cornerstone of astronomical research, and of an observatory mode of operation is apparent when it is noted that observations from the IUE satellite are now cited more often than observations from any earth- or sky- based observatory. However, IUE is not eternal, and LYMAN is the next step forward, pushing the sensitivity limit down by a factor of more than 100, and opening up new fields and wavelengths of study. LYMAN is planned as a grazing incidence Wolter-Schwartzschild Type II telescope with an aperture of 80cm, feeding an array of sensitive far-UV and EUV spectrographs equipped with Photon Counting Array (PCA) detectors.

A review is given of recent developments in the interpretation of the structure and heating of the solar corona, and of solar flares. An electric circuit model for a flaring magnetic loop is introduced, and used to discuss the closure of the current pattern. It is argued that cross-field current flow cannot be set up after a flux tube has emerged above the photosphere. The energy dissipated in a flare is attributed to a change in the inductance of the flaring loop, with the current remaining approximately constant. Emphasis is placed on the value of the resistance of the flaring loop, and on the associated inductive timescale.

The non-linear modal equations governing magnetoconvection in a fluid layer have been integrated forward in time incorporating a discrete spectrum of horizontal wave numbers, distributed within the range supporting convection. By progressively deleting some of the decaying modes and introducting additional modes within the range of growth it is possible to establish the evolution, or otherwise, of a preferred horizontal scale, which determines the horizontal cell size of the convective motions. Further, the influence of the magnetic field strength on cell extent can also be determined.

The story of the discovery of SN 1987A by Ian Shelton and Oscar Duhalde is well known, but many other events around the time of discovery are largely unknown. I shall describe these events and some of the confusion generated on 24 February 1987.

The height-integrated Pedersen and Hall conductivities are calculated for the weakly ionized region of the solar atmosphere in the vicinity of a sunspot. The values obtained are much larger than previous authors have estimated. Dynamo theories for solar flares which rely on the photospheric region having a large resistance are untenable.

The primary objective of the LYMAN Mission is to provide an Observatory for the study of the waveband between 900 and 1250Å. Only one previous mission, Copernicus, has given us a glimpse into the very rich astrophysical return offered in this far-ultraviolet part of the electromagnetic spectrum. However, LYMAN will provide a sensitivity some ten thousand times greater than Copernicus.

It is the enormous richness of this part of the electromagnetic spectrum which is the prime justification of the mission. No other region offers such a density and variety of atomic, ionic and molecular absorption lines. Collectively, these represent a tool of great diagnostic power in determining physical conditions and chemical compositions of astrophysical plasmas. These plasmas may be cool, and seen in absorption against a hot continuum source, or else they may be hot and emitting in their own right. In either case, LYMAN is the ideal vehicle for their study, be they in solar system objects, near newly-forming stars, in photospheres, transition layers, or coronae of stars, in interstellar or intergalactic space, or close to the active cores of galaxies. For this reason, LYMAN will be a uniquely powerful tool for use in all branches of modern day astrophysics.

It is shown that for the eclipsing variable stars MP Mus and SV Cen a least squares fitting procedure is more accurate when a linear (intensity) rather than a logarithmic (magnitude) scale is used.

The optical spectra of the AM Herculis binaries are characterized by extremely complex emission lines whose profiles can be resolved into at least three components which are formed in different regions of the accretion stream leading from the companion star towards the magnetic white dwarf. We present a theoretical model which localizes the formation region of the broad emission line component and provides information regarding the structure of this emitting region. In our model the particle trajectories are integrated in a Roche potential and the volume between the white dwarf and the companion has been divided into two different regimes of motion. In one region the gas escapes from the secondary near the inner Lagrange point and is accelerated along a straight line towards the white dwarf. In the other region the magnetic field is strong enought to divert the gas out of the orbital plane and to channel it towards the white dwarfs surface. The model has been used to interpret radial velocity and velocity dispersion data from the AM Herculis system E1405-451.

Several critical issues recently raised by observations of SN 1987A are addressed. These include: 1) the evolution of the pre-supernova star, why it was blue, what its composition and core structure were; 2) the detailed isotopic composition of the ejecta; 3) why and to what extent the supernova composition was mixed in velocity space; 4) the interpretation of recently observed infrared lines, especially their profiles and the existence of red-shifted ‘wings’; and 5) what has become of the neutron star.

In an earlier paper with the same title, I showed how knowledge of the non-corotational electric potential required to support particles in corotation with the star can be used to deduce the global qualitative forms that the potential can take in axisymmetric pulsar magnetospheres, in the absence of outflowing particles. Those arguments will now be combined with work on the outflow zone to deduce qualitative features of the potential structure in the MRW2 model.

The LYMAN Observatory payload is mounted on a service module which which offers pointing, power and telemetry and which has substantial commonality with the SOHO concept. The payload consists of a Wolter-Schwartzschild Type II Grazing Incidence telescope with monolithic primary and secondary elements feeding far-UV and extreme-UV spectrographs. It is designed to offer an effective collecting area of greater than 10 cm2 over a limited field of view with a spectral resolution on astronomical targets of 30000 in the prime ( λ900 - 1250 Å ) spectral range. This will allow high-resolution observations on sources as faint as 15 mag. LYMAN will also be capable of high resolution observations up to 1800Å, and will offer low-resolution spectroscopy in the extreme-UV down to about 100Å.

We discuss the properties of cyclotron radiation from accretion shocks located above the atmospheres of magnetic white dwarfs taking into account the effects of field spread and density and temparture structure. The models which are an improvement on previous point source models are shown to have characteristics that are in better overall agreement with the properties of AM Herculis type systems. Our calculations of the polarization properties of large polar cap emission regions are used to discuss the recent null measurements of circular polarization in DQ Herculis type systems.

The theory of neutron star formation is addressed in the light of the detected neutrino burst from SN 1987A. A brief review of how supernova neutrino theory has evolved over the last 30 years and a general analysis of the SN 1987A detections is presented.

It is believed that the splitting of the SMC into two fragments and the production of the Inter-Cloud gas and the Magellanic Stream occurred in the one event 4 × 108 years ago. This event was a collision between the LMC and SMC. This time is too short for the Stream to be tidal, or be the result of stripping of the Inter-Cloud gas by a diffuse gaseous halo. It is proposed that the clouds in the Stream are the results of collisions between the Inter-Cloud gas and HVCs in the Galactic halo. A model of this process accounts for all of the observational features of the Stream. Observations of HVCs in the path of the Magellanic Clouds are used to predict the development of the Stream. The HVCs in our halo are thought to be a result of a collision of a galaxy with our Galaxy 6 × 109 years ago.

The LYMAN project has been the subject of industrial Phase A studies in both Australia, and within ESA. These studies have demonstrated an extremely useful international collaboration, as well as a very successful collaboration between University and Industry. Working together, we have identified all critical problems of feasibility, and have developed at least one, usually more than one, method of overcoming these while remaining within the cost and complexity envelope of the overall mission.

The LYMAN mission will be the subject of a competitive selection process within ESA at the end of November 1988. One of five projects will be selected to go forward into later phases. However, the Australian LSWG are confident that, with the enormous support that the LYMAN project commands on both sides of the Atlantic, with the tremendous scientific merit of the proposed mission, and with the demonstration of feasibility of the mission in two separate Phase A studies, that LYMAN will be the successful candidate.