Helio- and asteroseismology study the interior of the Sun and other stars, by means of observations of oscillations on their surfaces. The last 10 years in the study of the solar interior, to a has witnessed a very rapid evolution point where we can now contemplate investigating the physical state of matter, or the details of rotation and other large-scale motion, in the Sun. The stellar studies are in some respects at the point of the solar studies 10 years ago, but appear poised to take off. Thus the time was deemed ripe for lAO Symposium No 123, to assess the present status of this work, and plan for its future development. Apart from the seismic data, few observations are available to provide information about stellar interiors. Detailed studies, by spectral analysis, can be made of stellar surface properties, including atmospheric temperature and chemical composition. However, the stellar radiative spectrum is almost entirely fixed by the mass, luminosity, radius and surface rotation of the star, and contains essentially no other information about the interior. An important test of stellar evolution theory is provided by observations of stel­ lar clusters, whose members can reasonably be assumed to have the same age and chemical composition. The location of such stars in a HR diagram, where luminosity is plotted against the effective temperature, can roughly be understood in terms of stellar evolution calculations.

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An overview of helio- and asteroseismology.- 1. Observations of Solar Oscillations.- Helioseismology from the South Pole. The 1984/85 campaign.- Splitting of the low l solar p modes.- Helioseismic Observations at Stanford, 1977-1986.- Observations of solar global oscillations (1983 - 1985) and potential influence of terrestrial sources of errors.- Intermediate degree solar oscillations.- Measurements of solar internal rotation obtained with the Mt. Wilson 60-foot solar tower.- Solar equatorial rotation rate inferred from inversion of frequency splitting of high-degree modes.- Rotation in the solar convection zone inferred from Fabry-Perot observations of the 5-min oscillations.- Comparison of solar oscillation data obtained from a study of the Na and K Fraunhoffer absorption lines.- Response of the solar five-minute oscillations to a major flare.- Solar 5-min oscillation amplitude anisotropy and Doppler velocity systematics.- Ground based observations of solar luminosity oscillations.- Earth based observations of solar luminosity oscillations.- On the 160 minute oscillation.- Search for solar g-modes from 1981 to 1985.- Solar gravity modes from ACRIM/SMM irradiance data.- Limb darkening oscillations: the discrepancy with Doppler data and the 160-min period.- 2. Theory of Solar Oscillations.- Sensitivity of solar p-modes to solar envelope structure.- A solar model with turbulent diffusion mixing: surface abundances and oscillations.- The influence of a modified mixing-length theory and of an adopted description of the atmosphere on the solar five-minute oscillations.- Constraints on central solar conditions from helioseismology and neutrino counts.- Do solar models with weakly interacting massive particles reproduce the Stanford seismic data?.- The study of oscillations localized near a layer of density discontinuity in an example of solar model.- Inertial modes trapped in the solar convective envelope.- Non-newtonian forces and the observed solar oscillation spectrum.- Asymptotic properties of low degree gravity modes.- Stellar acoustic ray patterns.- An optimal approach to the inverse problem.- Inverse problem: acoustic potential vs acoustic length.- On the technique of the inversion of helioseismological data.- An attempt to determine the structure of the solar core from observed g-mode frequencies.- Inversion of asymptotic gravity-mode frequencies and its application to the Sun.- A search of the effects of magnetic field in the solar five-minute oscillations.- Magnetic perturbations to stellar oscillation eigenfrequencies.- Magnetic effects on solar p-modes.- The effect of toroidal magnetic fields in the overshoot layer on the eigenfrequencies of stellar oscillations.- The magnetic field inside the Sun.- On the implications of the symmetric component of the frequency splitting reported by Duvall, Harvey and Pomerantz.- Sunspot seismology.- Oscillations in sunspot umbra, -penumbra and the surrounding photosphere.- The energy conversions and enhancement caused by the unsteady plasma motion in the active region.- Radial and non-radial oscillations of spherically symmetric stellar systems.- 3. Longterm Variations in the Sun.- Time variations of the frequencies of low-degree solar p modes.- Solar cycle dependence of solar p modes.- The solar oscillations spectrum and the solar cycle.- The 13 day period oscillation and the solar cycle.- Variations in the mean line of sight velocity of the Sun: 1976-1985.- Study of long period global oscillations of Sun through spherical harmonic Fourier analysis of sunspot activity.- Long periods in diameter, irradiance and activity of the Sun.- Solar diameter and solar rotation during the Maunder minimum.- 4. Asteroseismology: Results and Prospects.- Asteroseismology: results and prospects.- Evidence for global pressure oscillations in Procyon and ? Centauri.- A photometric search for '5-min' oscillations in the components of Alpha Centauri and two other double stars.- A spectroscopic search for oscillations in the 769.9 nm potassium line of Procyon.- The rich p-mode pulsation spectrum of HD 60435.- Search for oscillations in some Ap stars.- A search for rapidly oscillating Ap stars in the northern hemisphere.- The radius and the pulsation constant of the primary of Spica.- A survey for Doppler-shift oscillations in K giants.- Modeling the global oscillations of Epsilon Eridani.- Stellar models of Epsilon Eridani constrained by stellar seismology.- Internal constitution and oscillation spectrum of Procyon.- Helium diffusion in rapidly oscillating Ap stars.- A Hertzsprung-Russell diagram for stellar oscillations.- Can stellar mass be measured by asteroseismology?.- 5. Seismological Investigations of Compact Stars.- Seismological investigations of compact stars.- An improved limit for the rate of period change in the ZZ Ceti star G117-B15A.- The stellar seismology of the hot white dwarf star PG1159-035.- Pulsations of White Dwarf Stars with Thick Hydrogen or Helium Surface Layers.- The non linear dynamic of the ZZ Ceti variable GD 66.- 6. Excitation and Damping of Solar and Stellar Oscillations.- Excitation and damping of solar and stellar oscillations.- What do the observations tell us about the excitation of solar oscillation modes?.- The role of nuclear reactions in the excitation of stellar oscillations.- On the excitation of solar five-minute oscillations.- Influence of the perturbation of the Reynolds tensor on the stability of the solar 5 min oscillations.- Interaction of convection and oscillations in the solar atmosphere: numerical results.- Gravity wave generation by large scale bubbles.- The evolution to steady nonlinear pulsation in stellar models.- Finally a double-mode RR Lyrae model?.- Overstable convection in a non-uniform magnetic field.- The critical mass for the overstability of massive zero-age main sequence stars.- 7. Oscillations in the Solar Atmosphere.- Diagnosis of the solar atmosphere using solar oscillations.- Chromospheric seismology.- Infrared Helioseismology: Detection of the chromospheric mode.- Variations of the solar limb brightness with the oscillations.- Oscillatory properties of meso-scale intensity structures at chromospheric level.- On the energy of short period acoustic waves in the solar atmosphere.- Convective overshoot and upper boundary conditions.- Variation of the generalized Compton red shift in the Sun.- 8. Techniques for Observing Solar Oscillations.- Techniques for observing solar oscillations.- Continuous magnetic calibration of (v…