The purpose of the present paper is to give an introduction to the nomenclature, and a few of the results, of helio- and asteroseismology. It is hoped that this may provide a useful background for the more specialized reviews, and the contributed papers, in these proceedings. Other recent, general reviews are, e.g., Deubner & Gough (1984), Leibacher et al (1985), and Christensen-Dalsgaard et al (1985a).

More than 700 hours of full disk line of sight solar velocity have been recorded at the Geographic South Pole between late november 1984 and early february 1985. This paper presents very briefly some preliminary result of the analysis of this data.

An analysis of full disc line of sight velocity data yield line splitting values of the low ℓ-value non-radial modes. Possible variations of the line splitting with the solar cycle are investigated.

Observations of low degree modes of solar oscillation have been made at The Wilcox Solar Observatory at Stanford University for more than a decade. We are presently re-examining the set of observations from 1977 through 1986. We have first tested the stability of the p-mode frequencies for modes of degree l=2–5 in each year. We find a marginally significant trend of a decrease in p-mode frequencies of 0.06 μHz per year. We have also examined the continuity of the observed signal at 160.01 minutes. We find that the previously reported phase stability is no longer present. However, due to uncertainties in calibration we can not exclude the reality of the reported signal.

The Earth atmospheric pressure fluctuations in the 5-min range of periods are analysed and their influence on observations of solar 5-min oscillations are briefly discussed. New series of observations confirmed the oscillations of the Sun with period of 160.010 min.

Spectra of solar intensity oscillations in the degree range ℓ = 20–98 were obtained with a 92% duty cycle over a 50 hour period from the geographic South Pole. After correction for solar rotation, the spectra have been averaged over azimuthal order m and fit with Lorentzian functions to provide values of background noise, amplitude, frequency and line width for 636 oscillation modes. The background noise is nearly independent of frequency in the range containing strong p-modes. The amplitude envelope shows little dependence on ℓ value and a frequency dependence similar to that of Doppler oscillations but shifted to higher frequency. Line widths increase at higher frequency and at higher ℓ values.

We have obtained estimates of the solar internal rotational velocity from measurements of the frequency splittings of p-mode oscillations. Specifically, we have analyzed a 10-day time series of full-disk Dopplergrams obtained during July and August 1984 at the 60-Foot Tower Telescope of the Mt. Wilson Observatory. The Dopplergrams were obtained with a Na magneto-optical filter and a 244 × 248-pixel CID camera. From the time series we computed power spectra for all of the prograde and retrograde sectoral p-modes from ℓ = 0 to 200 and for all of the tessaral harmonics up to ℓ = 89. We then applied a cross-correlation analysis to the resulting sectoral power spectra to obtain estimates of the frequency splittings. From ℓ = 4 to ℓ = 30 we obtained a mean value of the frequency spitting of roughly 450 nHz (sidereal) in close agreement with most previously published results, while from ℓ = 40 to ℓ = 140 we obtained a mean value of about 470 nHz. We believe that the latter value is slightly higher than the surface rotational splitting of 461 nHz because of possible confusion due to the temporal sidelobes introduced by the day/night observing cycle. Confirmation of this possibility will have to await our computation of tesseral power spectra for degrees greater than our current limit of 89. Finally, for degrees between 140 and 200, the frequency splittings are indistinguishable from the surface rotation rate.

The equatorial rotation rate has been inferred as a function of depth through the outer 16 Mm of the Sun from observations of high-degree five-minute oscillations. An optimal averaging inversion procedure due to Backus & Gilbert (1970) has been applied to frequency splittings measured from power spectra obtained using Doppler data spanning three and five consecutive days. The resulting rotation curves have proven to be much more stable than the curves obtained from data sets of single days. The results imply that the solar rotation rate increases with depth by 0.023 μHz reaching a maximum at about 2 Mm below the surface, then decreases by 0.037 μHz down to 16 Mm.

Full disk observations of the 5-min solar oscillations have been obtained with a lithium niobate Fabry-Perot filter. The equatorial solar rotation rate as a function of depth has been inferred from the sectoral modes of oscillation using the Backus-Gilbert optimal averaging inversion method. The results show a rotation rate that slowly decreases over the depths of 15 to 56 Mm below the photosphere. The results are in agreement with the previous Duvall-Harvey observations.

Two independent resonant scattering spectrometers one using a sodium and the other a potassium vapour cell, were operated simultaneously at the same site. Due to the differing abundances of ground state atoms of these two elements different depths of the photosphere are sampled. An inter-comparison of solar p modes obtained with these spectrometers is given.

Solar five-minute oscillations of intermediate-degree ℓ were observed both before and after a very strong white-light flare. Intensity images of the full Sun taken on two sides of the Fe I λ 5576 spectral line were recorded on film, digitized with 8″ spatial resolution, and then converted into Doppler velocities. The data were projected onto both equatorial and polar sectoral modes and Fourier transformed in time. Comparing the resulting power spectra, we find a substantial increase in power in the p5 ridge of the equatorial modes on the day after the flare; such an increase may be a consequence of the solar flare. When data from all the ridges are considered, there is an average increase in power of only a few percent the day after the flare. This overall increase is probably not significant due to uncertainties from effects of the beating of unresolved modes.

Several measurements of 5-min velocity amplitudes have yielded confusing and conflicting information on the l and m dependence of the modal excitation (Kuhn and O'hanlon, 1983 – henceforth KO; Deubner, 1985; and Hill et al. 1985). We have obtained considerably more data than was described in KO using similar observing techniques. Additional analysis has illuminated a systematic effect related to the finite spatial resolution, and line asymmetry of the data that can lead to errors in inferred velocity amplitudes. Even though Doppler shifts are calculated from the Fraunhofer line center positions the effect can lead to 5-min oscillation amplitude errors at the 10 percent or greater level. Line wing observations should be more susceptible, and comparable resolution 2-dimensional data may be less sensitive to this systematic.

Results from ground based observations of low degree solar luminosity variations are presented. By using data from up to 15 consecutive excellent days the majority of the 1=0, 1 and 2 peaks in the region 2.5–3.5 mHz may marginally be identified.

Earth based multichannel photometry of integral sunlight has been obtained at Izaña (Tenerife) during 1984–1986. Power spectra of the solar luminosity variations of individual days show power in the 5 minute interval above noise at a level comparable to SMM datad). When combining contigous days of data the signature of p mode solar oscillations spectrum appears* although individual peak identification is difficult.

Solar velocity data collected at Izaña (Tenerife) over the years 1980–1985 have been used to search for the 160 minute oscillation. The peculiar behaviour of the ninth harmonic of a day, in amplitude and phase, suggests the existence of a solar signal with a 160.02 ± .01 minute period, which can be interpreted as a g-mode.

Analysis of solar velocity data obtained at Izaña (Tenerife) over the years 1981–1985, has shown the existence of significant signals in the frequency range 25–125 μHz. Several ways of analyzing the data have been used in order to interpret these as solar internal gravity modes of degree ℓ≤ 3.

Solar irradiance data from the ACRIM solar constant experiment on board the Solar Maximum Mission satellite (SMM) have been used to search for solar gravity modes. The power spectra of the time series of 270 days in 1980 and of 240 days in 1984 are analysed using a statistical method for the determination of the basic g-mode period separation To and the rotational frequency vR. In the view of the proposal of weakly interacting massive particles (WIMP) in the solar core and their impact on To the search has been extended down to 25 minutes. The results of the analysis of both time series in the frequency range from 10 to 40 μHz are best fitted by a To of 29.85 minutes. This is close to the expected value for the WIMP model. The angular velocity in the center of the Sun inferred from the rotational splitting of the g-modes amounts to 6.6·10−6 per sec, which is 2.3 times the photospheric rate.