Author name code: isaak ADS astronomy entries on 2022-09-14 author:"Isaak, George R." ------------------------------------------------------------------------ Title: Anomalous variations in low-degree helioseismic mode frequencies Authors: Howe, R.; Chaplin, W. J.; Elsworth, Y.; Hill, F.; Komm, R. W.; Isaak, G. R.; New, R. Bibcode: 2006MNRAS.369..933H Altcode: 2006MNRAS.tmp..504H We compare changes in the frequencies of solar acoustic modes with degree between 0 and 2, as derived from Global Oscillation Network Group (GONG), Birmingham Solar Oscillations Network (BiSON) and Michelson Doppler Imager (MDI) spectra obtained between 1995 and 2003. We find that, after the solar-activity dependence has been removed from the frequencies, there remain variations that appear to be significant, and are often well correlated between the different data sets. We consider possible explanations for these fluctuations, and conclude that they are likely to be related to the stochastic excitation of the modes. The existence of such fluctuations has possible relevance to the analysis of other low-degree acoustic mode spectra such as those from solar-type stars. Title: Solar FLAG hare and hounds: on the extraction of rotational p-mode splittings from seismic, Sun-as-a-star data Authors: Chaplin, W. J.; Appourchaux, T.; Baudin, F.; Boumier, P.; Elsworth, Y.; Fletcher, S. T.; Fossat, E.; García, R. A.; Isaak, G. R.; Jiménez, A.; Jiménez-Reyes, S. J.; Lazrek, M.; Leibacher, J. W.; Lochard, J.; New, R.; Pallé, P.; Régulo, C.; Salabert, D.; Seghouani, N.; Toutain, T.; Wachter, R. Bibcode: 2006MNRAS.369..985C Altcode: 2006MNRAS.tmp..515C; 2006astro.ph..6748C We report on results from the first solar Fitting at Low-Angular degree Group (solar FLAG) hare-and-hounds exercise. The group is concerned with the development of methods for extracting the parameters of low-l solar p-mode data (`peak bagging'), collected by Sun-as-a-star observations. Accurate and precise estimation of the fundamental parameters of the p modes is a vital pre-requisite of all subsequent studies. Nine members of the FLAG (the `hounds') fitted an artificial 3456-d data set. The data set was made by the `hare' (WJC) to simulate full-disc Doppler velocity observations of the Sun. The rotational frequency splittings of the l = 1, 2 and 3 modes were the first parameter estimates chosen for scrutiny. Significant differences were uncovered at l = 2 and 3 between the fitted splittings of the hounds. Evidence is presented that suggests this unwanted bias had its origins in several effects. The most important came from the different way in which the hounds modelled the visibility ratio of the different rotationally split components. Our results suggest that accurate modelling of the ratios is vital to avoid the introduction of significant bias in the estimated splittings. This is of importance not only for studies of the Sun, but also of the solar analogues that will be targets for asteroseismic campaigns.

Solar FLAG URL: http://bison.ph.bham.ac.uk/~wjc/Research/FLAG.html

E-mail: wjc@bison.ph.bham.ac.uk ‡

George Isaak passed away in 2005 June 5, prior to the completion of this work. He is greatly missed by us all. Title: On model predictions of the power spectral density of radial solar p modes Authors: Chaplin, W. J.; Houdek, G.; Elsworth, Y.; Gough, D. O.; Isaak, G. R.; New, R. Bibcode: 2005MNRAS.360..859C Altcode: 2005MNRAS.tmp..510C We investigate the frequency dependence of the power spectral density of low-degree solar p modes by comparing measurements with the results of a stochastic-excitation model. In the past it was common practice to use the total power in such investigations. Using the maximum of the power spectral density instead provides a direct comparison with the measured mode heights in the observed power spectrum. This method permits a more careful calibration of the adjustable parameters in the excitation model, a model which we present here, for the first time, in a format that precisely and unambiguously relates the amplitudes of the modes of oscillation to the Reynolds stress in the equilibrium model. We find that errors in the theory of the linear mode damping rates, particularly at low frequency, have a dramatic impact on the predictions of the mode heights in the spectral density, whereas parameter changes in the stochastic excitation model, within a plausible domain of parameter space, have a comparatively small effect. Title: Noise characteristics of full-disc helioseismic observations made by resonant scattering spectrometers Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R.; Pintér, B. Bibcode: 2005MNRAS.359..607C Altcode: 2005MNRAS.tmp..294C Resonant scattering spectrometers (RSSs) have been used to make high-precision full-disc helioseismic observations since the 1970s. They are capable of very high-precision determinations of line-shift, meaning that they are used to obtain precise velocity measurements, and, for suitably configured RSSs, the disc-averaged longitudinal magnetic field (SMMF). In order to exploit fully the very extensive high-precision data sets, it is essential to understand the noise characteristics of the instruments. This paper re-examines the consequences for velocity and SMMF determinations of there being noise on the scattered light signals measured by an RSS. It presents a theoretical description, and analysis of simulations, which match well the noise variations found recently in both BiSON velocity and SMMF observations. It also outlines a method for using the differences between the power spectra of redundant channels to analyse instrumental noise characteristics. Title: The Search for Correlation between BiSON SMMF Data and CME Events Authors: Chaplin, William J.; Dumbill, Andrew M.; Elsworth, Yvonne P.; Isaak, George R.; McLeod, Clive P.; Miller, Brek A.; New, Roger; Pintér, Balázs Bibcode: 2005HiA....13..141C Altcode: The Birmingham Solar Oscillation Network (BiSON) has acquired high precision solar mean magnetic field (SMMF) data on a 40-second cadence for a decade. We present first attempts to compare such data from recent years with the occurence of CME's as recorded by LASCO using correlation techniques applied to measurements from different BiSON instruments to maximise the sensitivity to CME related SMMF responses. SMMF measurements were recorded at the time of occurence of several hundreds CME's. Title: Phase Variation as a New Tool in the Investigation of the Excitation and Damping of Solar p-modes Authors: Simoniello, R.; Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; New, R. Bibcode: 2004ApJ...616..594S Altcode: We report on a novel way of using the phase evolution in solar oscillation data as a tool in the study of p-mode excitation and damping. A mathematical formalism is presented, backed by extensive simulations, that enables the determination of the line width of modes close to the peak of the solar oscillation spectrum. The method potentially avoids the usual problem of strong correlation between the width and the height of the modes. We also identify further possible uses of the technique. Title: Flag Hare-And Exercise: on the Extraction of Sectoral Mode Splittings from Full-Disc Sun-As Data Authors: Chaplin, W. J.; Appourchaux, T.; Baudin, F.; Boumier, P.; Elsworth, Y.; Fletcher, S. T.; Fossat, E.; García, R. A.; Isaak, G. R.; Jiménez, A.; Jiménez-Reyes, S. J.; Lazrek, M.; Lochard, J.; New, R.; Pallé, P.; Régulo, C.; Salabert, D.; Toutain, T. Bibcode: 2004ESASP.559..356C Altcode: 2004soho...14..356C No abstract at ADS Title: Impact of Observational Duty Cycle on P-Mode Eigenfrequencies Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R.; Salabert, D. Bibcode: 2004ESASP.559..364C Altcode: 2004soho...14..364C No abstract at ADS Title: Twenty-Eight Years of BISON Data Authors: Miller, B. A.; Hale, S. J.; Elsworth, Y.; Chaplin, W. J.; Isaak, G. R.; New, R. Bibcode: 2004ESASP.559..571M Altcode: 2004soho...14..571M No abstract at ADS Title: The Phase of Global Solar Oscillations Authors: Simoniello, R.; Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R. Bibcode: 2004ESASP.559..251S Altcode: 2004soho...14..251S No abstract at ADS Title: Novel Techniques for the Identification of Noise Contributions to Full-Disc Helioseismic Power Spectra Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R.; Pintér, B. Bibcode: 2004ESASP.559..360C Altcode: 2004soho...14..360C No abstract at ADS Title: On comparing estimates of low-l solar p-mode frequencies from Sun-as-a-star and resolved observations Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R. Bibcode: 2004A&A...424..713C Altcode: Low-angular-degree (low-l) solar p modes provide a sensitive probe of the radiative interior and core of the Sun. Estimates of their centroid frequencies can be used to constrain the spherically symmetric structure of these deep-lying layers. The required data can be extracted from two types of observation: one where the modes are detected in integrated sunlight, i.e., a Sun-as-a-star view; and a second where the visible disc is imaged onto many pixels, and the collected images then decomposed into their constituent spherical harmonics. While the imaging strategy provides access to all of the individual components of a multiplet, the Sun-as-a-star technique is sensitive to only about two thirds of these (average over l=0 to 3) with those modes that are detected having different levels of visibility. Because the various components can have contrasting spatial structure over the solar surface, they can respond very differently to changes in activity along the solar cycle. Since the Sun-as-a-star and resolved analyses take as input a different ``subset'' of modes, the extracted frequency estimates are expected to differ depending upon the phase of the cycle. Differences also arise from the types of models used to fit the modes. Here, we present expressions that allow the sizes of these differences to be predicted. Title: Impact of observational duty cycle on the measurement of low-ℓ solar p-mode frequencies Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R.; Salabert, D. Bibcode: 2004A&A...424..301C Altcode: We investigate the impact of a multi-site, ground-based observational window function on the extraction of estimates of the frequencies of low-angular-degree (low-ℓ) solar p modes from decade-long datasets. To effect this study we have made use of some ≈10 yr of full-disc, ``Sun-as-a-star'' Doppler velocity data collected by the Birmingham-Solar Oscillations Network (BiSON). A coherent combination of observations made by all six BiSON sites provided the principal time series of data. This set was then modulated by a whole series of different window functions and the resulting sets analyzed. The windows were made from different combinations and numbers of BiSON stations. We find that for the majority of low-ℓ modes the bias in the frequencies given by the effects of the window function is not significant. However, for modes above ≈3300 μ Hz, and some ℓ=2 modes near ≈2500 μ Hz, the bias is important when the frequencies are extracted from long datasets.

Appendix A is only available in electronic form at http://www.edpsciences.org Title: The solar cycle as seen by low-l p-mode frequencies: comparison with global and decomposed activity proxies Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R. Bibcode: 2004MNRAS.352.1102C Altcode: 2004MNRAS.tmp..158C We present a detailed study of variations observed in low-angular degree solar p-mode frequencies during solar cycles 22 and 23, and their relation to global and spatially decomposed proxies of the surface activity. To do so, we have analysed 11yr of unresolved (Sun-as-a-star) Doppler velocity observations of the solar disc made by the Birmingham Solar-Oscillations Network (BiSON). The sensitivity of these observations to different azimuthal orders, m, is such that for the degree range studied (0 <=l<= 2) extracted frequencies can be regarded as providing a measure of the response of the sectoral modes (with |m| =l).

After allowing for the dependence of the frequency shifts on mode frequency and inertia, we find the average l= 0 shift is significantly weaker than that at l= 2; the magnitude of the average l= 1 shift lies in between the two. The comparative sizes of the shifts are observed to match those of the corresponding spherical harmonic (Legendre) components of both the Kitt Peak magnetogram (KPMI) and HeI equivalent width activity indices, and reflect, therefore, the sensitivity of the observed mode components to the distribution of activity over the solar surface (i.e. a `spatial' contribution to the shifts). When the falling and rising parts of the cycles are analysed independently, we uncover a significant difference in behaviour at l= 1. Possible reasons for this are discussed. Title: Extended search for correlation between solar mean magnetic field BiSON data and coronal mass ejections Authors: Chaplin, William J.; Dumbill, Andrew M.; Elsworth, Yvonne P.; Isaak, George R.; McLeod, Clive P.; Miller, Brek A.; New, Roger; Pintér, Balázs Bibcode: 2004SoPh..220..307C Altcode: The Birmingham Solar-Oscillations Network (BiSON) has acquired high-precision solar mean magnetic field (SMMF) data on a 40-s cadence for a decade. We present attempts to compare such data from recent years with the occurrence of coronal mass ejections (CMEs) as recorded by LASCO, using correlation techniques applied to measurements from different BiSON instruments to maximise the sensitivity to CME-related SMMF responses. SMMF measurements were recorded at the time of occurrence of several hundred CMEs. No CME event shows a convincing response in our SMMF data at short periods setting a threshold amplitude of 12 mG. By averaging data sets we are able to set lower thresholds, which depend somewhat on the distribution of response strengths. A brief summary of the very first results of this study is also given in Chaplin et al. Title: Solar p-mode frequencies at ℓ=2: What do analyses of unresolved observations actually measure? Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R.; Toutain, T. Bibcode: 2004A&A...416..341C Altcode: We have studied in detail the extraction of estimates of ℓ=2 p-mode frequencies from unresolved observations of the visible disc of the Sun. Examples of data of this type include ground-based observations made by the Birmingham Solar-Oscillations Network (BiSON), and space-borne observations made by the GOLF and VIRGO/SPM instruments on board the ESA/NASA SOHO satellite. The fitting of the modes is complicated in practice by the asymmetric arrangement in frequency of the three components (m=-2, 0 and 2) that are prominent in such data. In order to investigate the effect of this we used a series of 10-yr artificial datasets into which varying degrees of asymmetry were introduced. The sets were designed to mimic the characteristics of the BiSON and GOLF data, and were analyzed both with and without the BiSON window function from the period 1992 through 2001. Since reliable estimates of the asymmetry have only recently been extracted from unresolved observations (Chaplin et al. \cite{Chaplin03}a) it has for a long time been standard practice to fit the ℓ=2 modes to a model that assumes a symmetrically arranged multiplet. We have tested the impact of this on the accuracy of the extracted frequencies. Furthermore, we demonstrate that asymmetric models can be successfully applied, provided the data are of sufficient length and quality. We also discuss the implications of our simulations for analyses of real solar data. Title: Studies of the solar mean magnetic field with the Birmingham Solar-Oscillations Network (BiSON) Authors: Chaplin, W. J.; Dumbill, A. M.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R.; Pintér, B. Bibcode: 2003MNRAS.343..813C Altcode: The first analysis of 10 yr of solar mean magnetic field data from the Birmingham Solar-Oscillations Network (BiSON) instrument at Sutherland, SA is presented. Long-period (>1 d) variations correlate well with those observed by the Stanford group, but our daily mean values have a statistical precision over 10 times better than previous work. Differences between the absolute values determined from Sutherland and Stanford are discussed, as are systematic annual variations of the order of 15 per cent. At high frequencies (>0.5 mHz), the mean noise spectral density for our decade of observations is 0.53 G2 Hz-1, setting a lower limit to the noise level than that obtained from brief observations by GOLF on board the ESA/NASA satellite SOHO in 1996. The high-frequency mean noise spectral density is different in different years. The lowest annual value, obtained for 1997, is 0.22 G2 Hz-1, whilst the highest, for 1995, is 1.46 G2 Hz-1. It is not yet clear whether these variations are related to solar activity. Title: Observation of, and temporal variations in, solar p-mode multiplet frequency asymmetries at l= 2 Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R.; Thiery, S.; Boumier, P.; Gabriel, A. H. Bibcode: 2003MNRAS.343..343C Altcode: The predominant contribution to the frequency splitting of low-l solar p modes arises from the rotation of the solar interior and this lifts the frequency degeneracy in l to give a symmetric pattern where the observed (synodic) separation between adjacent m (i.e. for |Δm|= 1) is ~400 nHz. Magnetic fields can also contribute to the splitting, but they do so in such a way as to introduce asymmetries in the arrangement of the components within each multiplet. In disc-integrated data this effect may become apparent when l>= 2. Here, we attempt to extract estimates of the frequency asymmetries at l= 2 from the analysis of disc-integrated data collected by the ground-based Birmingham Solar Oscillations Network (BiSON) and the GOLF instrument on board the ESA/NASA SOHO satellite. Our analyses demonstrate that we have evidence for there being non-zero asymmetries present (significance ~3-4σ) during an epoch coincident with high levels of surface activity close to the maximum of solar cycle 23. The asymmetries are indistinguishable from zero at minimum levels of activity near the cycle 22/23 boundary.

We also compare the observed asymmetries with those calculated from a model that is based upon the recent predictions of Moreno-Insertis & Solanki. While the level of agreement between the two is found to be reasonable, the observations suggest (though with poor constraints placed upon this) that the influence on the mode frequencies of high-latitude activity may not be as strong as in the model. Title: A Comparison of Low-Degree Solar p-Mode Parameters from BiSON and GONG: Underlying Values and Temporal Variations Authors: Howe, R.; Chaplin, W. J.; Elsworth, Y. P.; Hill, F.; Komm, R.; Isaak, G. R.; New, R. Bibcode: 2003ApJ...588.1204H Altcode: Approximately 5 years of the l=0 time series from the GONG project have been analyzed using the algorithm developed for the BiSON zero-dimensional data. The data cover the period 1995-2000. The results are compared with those from a parallel analysis of contemporaneous BiSON data and also with the results of the traditional GONG analysis of the low-degree time series. The spectra analyzed were prepared using the multitaper spectral analysis technique used in the recent reanalysis of the GONG data. We consider both solar cycle trends and temporally averaged values for mode frequencies, line widths, amplitudes, and asymmetry parameters. Title: Degree dependence of mode parameters with solar activity in BiSON data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; New, R. Bibcode: 2003ESASP.517..119C Altcode: 2003soho...12..119C The line-width, velocity power and rate of supply of energy to the low-degree p modes of the Sun are investigated over falling phase of cycle 22 and the rising phase of cycle 23 by fitting in the Fourier transform domain. We see that for the first time for low-degree modes we are able to parameterise the solar activity dependence as a function of the angular degree of the mode. Title: Probing the solar core with BiSON: the challenge at low l and low frequency Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R.; Pintér, B. Bibcode: 2003ESASP.517..183C Altcode: 2003soho...12..183C In this contribution we touch upon a few issues of relevance to the current status of low-angular-degree (low-l) p-mode Helioseismology. In particular: the precision in frequency, both historic and current, achievable at low l; the quest to extend the low-frequency detection threshold nearer to the p-mode fundamental; and the level of agreement between frequencies extracted from different data using various analysis techniques. Title: Comparing results from the GONG l = 0 and BiSON time series Authors: Howe, R.; Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Komm, R. W.; New, R. Bibcode: 2003ESASP.517..303H Altcode: 2003soho...12..303H Approximately 5 years of the l = 0 time series from the GONG project have been analysed using the algorithm developed for the BiSON 0-dimensional data. The data cover the period 1995-2000. The results are compared with those from a parallel analysis of contemporaneous BiSON data, and also with the results of the traditional GONG analysis of the low-degree time series. The spectra analysed were prepared using the multitaper spectral analysis technique used in the recent re-analysis of the GONG data. We consider both solar-cycle trends and temporally averaged values for mode frequencies, linewidths, amplitudes and asymmetry parameters. Title: High-frequency interference peaks in BiSON data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Marchenkov, K. I.; Miller, B. A.; New, R. Bibcode: 2003ESASP.517..247C Altcode: 2003soho...12..247C We have analyzed 9 yr of non-imaged Doppler velocity observations of the visible disc of the Sun in an effort to search for pseudo-mode-like structure in the data above the acoustic cut-off frequency of the solar atmosphere (≍5400 μHz). These data were collected by the ground-based Birmingham Solar-Oscillations Network (BiSON) over the period 1992 January through 2000 December. Our analysis uncovers the presence of a pseudo-mode-like structure above the acoustic cut-off frequency that persists up to ≍8500 μHz, with a spacing between adjacent peaks (or troughs) of ~68 μHz. The signature - which disappears at higher frequencies - has a slightly different repeat period (i.e., frequency separation between successive peaks or troughs) to that found by Garcia et al. (1998) in full-disc GOLF data. Title: The Search for Correlation Between BISON Smmf Data and Cme's Authors: Chaplin, William J.; Dumbill, Andy M.; Elsworth, Yvonne; Isaak, George R.; McLeod, Clive P.; Miller, Brek A.; New, Roger; Pinter, Balazs Bibcode: 2003IAUJD...3E..30C Altcode: The Birmingham Solar Oscillation Network (BiSON) has acquired high precision solar mean magnetic field (SMMF) data on a 40-second cadence for a decade. We present first attempts to compare such data from recent years with the occurence of CME's as recorded by LASCO using correlation techniques applied to measurements from different BiSON instruments to maximise the sensitivity to CME related SMMF responses. SMMF measurements were recorded at the time of occurence of several hundreds CME's. Title: On the measurement bias of low-l solar p-mode excitation parameters: The impact of a ground-based window function Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R.; Pintér, B.; Thiery, S. Bibcode: 2003A&A...398..305C Altcode: We present a study of the impact of a ground-based, multi-station window function on estimates of the power and damping of low-l solar p modes extracted from fits to resonant structure in the frequency domain. The window functions come from six-site observations made by the Birmingham Solar-Oscillations Network (BiSON) over the 10-yr period beginning 1991 January. Two strategies were adopted. In the first, we used an 800-d time series of continuous observations made by the GOLF instrument on board the ESA/NASA SOHO satellite. These data were modulated by a variety of BiSON window functions, with fractional duty cycles ranging from ~ 0.4 to ~ 0.8, and the resulting series analyzed. In the second we generated artificial 10-yr time series and studied the effect on these of the complete BiSON window. Title: Does the Energy Supplied to Low-l Solar p-Modes Vary over the Activity Cycle? Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R.; Toutain, T. Bibcode: 2003ApJ...582L.115C Altcode: We report on the average behavior of the excitation and damping of low angular degree (low l) solar p-mode oscillations over the decade from 1991 to 2000 using both long and short time duration Fourier transforms. The data in question were collected by the ground-based Birmingham Solar Oscillations Network. Throughout most of the period under study, the energy supply rate to the modes remains roughly constant-implying a near-constant level of forcing-while the damping and velocity power show a fairly smooth increase and decrease, respectively, in response to increasing levels of solar activity (in line with previous findings). However, here we uncover evidence of there being a sharp increase in the mode velocity power over a brief period of approximately 100 days centered on 1998 late March. The magnitude and sign of this are contrary to the expectation based on the long-timescale, solar-cycle trend; such unusual behavior is absent in the damping. This implies that the forcing of, or rate of energy supplied to, the modes increased in magnitude over this period. Title: Peak finding at low signal-to-noise ratio: low-ℓ solar acoustic eigenmodes at n≤9 from the analysis of BiSON data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Marchenkov, K. I.; Miller, B. A.; New, R.; Pinter, B.; Appourchaux, T. Bibcode: 2002MNRAS.336..979C Altcode: We make use of 9 yr of full-disc helioseismic data - as collected by the ground-based Birmingham Solar-Oscillations Network (BiSON) - to search for low-frequency, low-angular-degree (low-l) acoustic modes. A range of tests are applied to the power spectrum of the observations that search for prominent mode-like structure: strong spikes, structure spanning several bins signifying the presence of width (from damping), and the occurrence of prominent multiplet structure at l>= 1 arising principally from the solar rotation and made from several spikes separated suitably in frequency. For each test we present analytical expressions that allow the probability that the uncovered structure is part of the broad-band noise background to be assessed. These make use of the cumulative binomial (Bernoulli) distribution and serve to provide an objective measure of the significance of the detections. This work has to date uncovered nine significant detections of non-broad-band origin that we have identified as low-l modes with radial overtone numbers n<= 9. Title: An oblique magnetic rotator in the Sun? Authors: Isaak, G. R.; Isaak, K. G. Bibcode: 2002AN....323..436I Altcode: The current paradigm for the origin of sunspots and a global solar magnetic field is a dynamo, located near the bottom of the convection zone (CZ). We propose an alternative model. By interpolating in evolution between early-type stars and evolved white dwarfs and neutron stars, we suggest that the Sun (and indeed probably most stars) has a fossil magnetic field in the form of an oblique magnetic rotator (OMR) in the radiative zone (RZ). This rotator is electromagnetically screened by the skin-effect, produced by the differentially rotating CZ. The OMR provides a natural explanation for many solar phenomena, including the rigid rotation of the interior of the Sun, the long-term phase stability of the solar cycle, as well as diametrically opposing active longitudes. Nutation of the OMR can be invoked to explain the solar cycle and some of its features, including the sunspot butterfly diagram, Hale's law for the polarity of sunspots and their reversal every 11 years. An extension of the OMR model provides a natural explanation of the spatial and temporal variations of sunspots based on such a primordial magnetic field. Here, sunspots are bundles of magnetic flux that have broken off the extremities of the OMR. These rise by magnetic buoyancy and, on reaching the RZ-CZ boundary, suffer a deflection in a direction dependent upon the algebraic difference between the tangential zone velocities. This reverses during the nutation cycle and thus the leading and trailing sunspots reverse in magnetic polarity every 11 years. The flux fibrils, tubes, or possibly ropes, convey magnetic flux, energy, angular momentum, and, perhaps most importantly, frozen-in matter to the solar surface, each with a fingerprint characteristic of the radiative zone. More tentatively, the flux tubes may originate from even deeper within the Sun - the nuclear active zone (NZ). The resulting isotopic enhancements would have implications on abundance in the interstellar medium, and so on nucleosynthesis and its cosmological inferences. Title: Observation of, and variations in, multiplet frequency asymmetries at low l Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Marchenkov, K. I.; Miller, B. A.; New, R.; Pinter, B.; Thiery, S. Bibcode: 2002ESASP.508...71C Altcode: 2002soho...11...71C The predominant contribution to the frequency splitting of low-l solar p modes arises from the rotation of the solar interior and this lifts the frequency degeneracy in l to give a symmetric pattern where the observed (synodic) separation between adjacent m (i.e., for |Δm| = 1) is ~400nHz. Magnetic fields can also contribute to the splitting, but they do so in such a way as to introduce asymmetries in the arrangement of the components within each multiplet. In full-disc data this effect may become apparent when l >= 2. Here, we extract estimates of the frequency asymmetry for l = 2, investigate variations over the activity cycle and compare the results with the near-surface predictions of Dziembowski et al. (2000) which are based upon observations from higher l. Title: Does the energy supply rate to the p modes vary over the solar cycle? Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; New, R. Bibcode: 2002ESASP.508...33C Altcode: 2002soho...11...33C The rate of supply of energy to the low-degree p modes of the Sun is investigated using both long and short time-duration Fourier transforms. We see that, although on average the energy supply rate to the modes is independent of solar activity, there is a period of high solar activity where the energy-supply rate is increased. Furthermore we see that the correlations between the mode line width and the power in the modes are different on the falling phase of cycle 22 and the rising phase of cycle 23 with a strong correlation between the energy supply rate and the mode power on the rising phase of cycle 23. Title: On the measurement precision of solar p-mode eigenfrequencies Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R. Bibcode: 2002MNRAS.330..731C Altcode: We make use of 3456d of observations of the low-l p-mode oscillations of the Sun in order to study the evolution over time of the measurement precision of the radial eigenfrequencies. These data were collected by the ground-based Birmingham Solar-Oscillations Network (BiSON) between 1991 January and 2000 June. When the power spectrum of the complete time series is fitted, the analysis yields frequency uncertainties that are close to those expected from the returned coherence times of the modes. The slightly elevated levels compared with the prediction appear to be consistent with a degradation of the signal-to-noise ratio in the spectrum that is the result of the influence of the window function of the observations (duty cycle 71 per cent). The fractional frequency precision reaches levels of a several parts in 106 for many of the modes. The corresponding errors reported from observations made by the GOLF instrument on board the ESA/NASA SOHO satellite, when extrapolated to the length of the BiSON data set, are shown to be (on average) about ~25 per cent smaller than their BiSON counterparts owing to the uninterrupted nature of the data from which they were derived.

An analysis of the BiSON data in contiguous segments of different lengths, T, demonstrates that the frequency uncertainties scale as T-1/2. This is to be expected in the regime where the coherence (life) times of the modes, τnl, are smaller than the observing time T (the `oversampled' regime). We show that mode detections are only now beginning to encroach on the `undersampled' regime (where T<τnl). Title: Variation of acoustic mode centroid frequencies over the solar cycle Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; Isaak, G. R.; New, R. Bibcode: 2002AdSpR..29.1881C Altcode: Together with a brief historical overview, we use high-quality helioseismic data collected by three different observational programmes during the declining phase of activity cycle 22, and a substantial portion of the rising phase of the current cycle (23), to study the phenomenological nature of the cycle-induced (centroid) eigenfrequencies. Our analyses (for 1600 ≤ ν ≤ 4000 μHz) make use of observations made by the ground-based GONG over the angular degree range 4 ≤ l ≤ 150; the ground-based BiSON over 0 ≤ l ≤ 2; and the VIRGO/LOI instrument on board the ESA/NASA SOHO satellite over 0 ≤ l ≤ 8. We show that GONG shifts averaged over different ranges in l, together with the BiSON and LOI data averaged over their full quoted ranges, all scale at a given frequency with the normalized mode inertia ratio Qnl (Christensen-Dalsgaard & Berthomieu 1991). This is to be expected if the time-dependent perturbation affecting the modes is confined in the surface layers; the excellent agreement also reflects favourably on the external consistency of the different observations. We have also analyzed the frequency dependence of the shifts by fitting a power-law of the form δν nl ∝ (ν nl/ Enl to the data (where the Enl are the mode inertias, and α is the power-law index to be extracted). Previous studies have suggested that a relation with α = 0 provides an adequate description of the shifts up to ν ≈ 3500 μHz. However, here we show that while nevertheless describing the shifts well up to ∼ 2500 μHz, the linear scaling breaks down conspicuously at higher frequencies. Above this threshold, the shifts follow a power-law dependence with α ∼ 2. Title: Rigid rotation of the solar core? On the reliable extraction of low-l rotational p-mode splittings from full-disc observations of the Sun Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Marchenkov, K. I.; Miller, B. A.; New, R. Bibcode: 2001MNRAS.327.1127C Altcode: We present low-l rotational p-mode splittings from the analysis of 8yr of observations made by the Birmingham Solar-Oscillations Network (BiSON) of the full solar disc. These data are presented in the light of a thorough investigation of the fitting techniques used to extract them. Particular attention is paid to both the origin and magnitude of bias present in these estimates. An extensive Monte Carlo strategy has been adopted to facilitate this study - in all, several thousand complete, artificial proxies of the 96-month data set have been generated to test the analysis of real `full-disc' data. These simulations allow for an assessment of any complications in the analysis which might arise from variations in the properties of the p modes over the 11-yr solar activity cycle. The use of such an extended data set affords greater precision in the splittings, and by implication the rotation rate inferred from these data, and reduces bias inherent in the analysis, thereby giving a more accurate determination of the rotation. The grand, weighted sidereal average of the BiSON set is 434+/-2nHz, a value consistent with that expected were the deep radiative interior (r/R<0.5) to rotate at the same frequency, and in the same `rigid' manner, as the more precisely and accurately studied outer part of the radiative zone. Title: Changes in convective properties over the solar cycle: effect on p-mode damping rates Authors: Houdek, G.; Chaplin, W. J.; Appourchaux, T.; Christensen-Dalsgaard, J.; Däppen, W.; Elsworth, Y.; Gough, D. O.; Isaak, G. R.; New, R.; Rabello-Soares, M. C. Bibcode: 2001MNRAS.327..483H Altcode: Measurements of both solar irradiance and p-mode oscillation frequencies indicate that the structure of the Sun changes with the solar cycle. Balmforth, Gough & Merryfield investigated the effect of symmetrical thermal disturbances on the solar structure and the resulting pulsation frequency changes. They concluded that thermal perturbations alone cannot account for the variations in both irradiance and p-mode frequencies, and that the presence of a magnetic field affecting acoustical propagation is the most likely explanation of the frequency change, in the manner suggested earlier by Gough & Thompson and by Goldreich et al. Numerical simulations of Boussinesq convection in a magnetic field have shown that at high Rayleigh number the magnetic field can modify the preferred horizontal length scale of the convective flow. Here, we investigate the effect of changing the horizontal length scale of convective eddies on the linewidths of the acoustic resonant mode peaks observed in helioseismic power spectra. The turbulent fluxes in these model computations are obtained from a time-dependent, non-local generalization of the mixing-length formalism. The modelled variations are compared with p-mode linewidth changes revealed by the analysis of helioseismic data collected by the Birmingham Solar-Oscillations Network (BiSON); these low-degree (low-l) observations cover the complete falling phase of solar activity cycle 22. The results are also discussed in the light of observations of solar-cycle variations of the horizontal size of granules and with results from 2D simulations by Steffen of convective granules. Title: The phenomenology of solar-cycle-induced acoustic eigenfrequency variations: a comparative and complementary analysis of GONG, BiSON and VIRGO/LOI data Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; Isaak, G. R.; New, R. Bibcode: 2001MNRAS.324..910C Altcode: We use high-quality helioseismic data collected by three different observational programmes during the declining phase of activity cycle 22,Q7 and a substantial portion of the rising phase of the current cycle (23), to study the phenomenological nature of the cycle-induced (centroid) eigenfrequency variations. We have analysed the frequency dependence of the shifts by fitting a power law of the form δνnl~(νnl)α/Enl to the data (where the Enl are the mode inertias, and α is the power-law index to be extracted). Previous studies have suggested that a relation with α=0 provides an adequate description of the shifts up to ν~3500μHz. However, here we show that while nevertheless describing the shifts well up to ~2500μHz, the linear scaling breaks down conspicuously at higher frequencies. Above this threshold, the shifts follow a power-law dependence with α~2. Our analyses (for 1600<=ν<=4000μHz) make use of observations made by the ground-based GONG over the angular degree range 4<=l<=150 the ground-based BiSON over 0<=l<=2 and the VIRGO/LOI instrument on board the ESA/NASA SOHO satellite over 0<=l<=8. We show that GONG shifts averaged over different ranges in l, together with the BiSON and LOI data averaged over their full quoted ranges, all scale at fixed frequency with the normalized mode inertia ratio QnlQ1. This is to be expected if the solar-cycle perturbation affecting the modes is confined in the surface layers; the excellent agreement also reflects favourably on the external consistency of the different observations. Title: Changes to low-ll solar p-mode frequencies over the solar cycle: correlations on different time-scales Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Marchenkov, K. I.; Miller, B. A.; New, R. Bibcode: 2001MNRAS.322...22C Altcode: We have studied variations in the frequencies of low-l solar p modes through the analysis of nine years of helioseismic data collected by the Birmingham Solar Oscillations Network (BiSON)†. This is the first time that such a long data set has been explored with the extra accuracy afforded by fitting the modes to asymmetric profiles. The epoch covered (1991-99) spans the declining activity phase of solar cycle 22, and a substantial portion of the initial activity increase during cycle 23. The complete time series has been split into contiguous segments of length 27, 54, 108 and 216d in order to facilitate the study of changes occurring on different time-scales. Further, we have characterized the observed shifts as a function of six well-known indicators of solar activity. These indices reflect changes taking place in the photosphere, chromosphere and corona, but only over the visible hemisphere of the Sun. Since the low-l eigenfrequencies respond to global variations in activity, we discuss the implications of this mismatch for the analyses performed. We demonstrate that, as expected, the low-l modes adjust to changes in the activity measures on time-scales as short as a few months. Our analysis indicates that all six proxies correlate equally well (at the level of precision of the data) with the measured shifts. Further, the sensitivity of the shifts to changes in five of the activity indices is the same, to within ~15per cent (1σ) or so, on the falling and rising phases considered. There is, however, a slight suggestion that the sensitivity to changes in the disc-averaged line-of-sight magnetic field component (as determined from daily Kitt Peak magnetograms) may be higher on the rising phase of the cycle. Title: Non linear inversion for the sound speed in the solar interior using BiSON and SOI/MDI p-mode frequencies Authors: Marchenkov, K. I.; Roxburgh, I. W.; Vorontsov, S. V.; Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; New, R. Bibcode: 2001ESASP.464..531M Altcode: 2001soho...10..531M The results of the global sound-speed inversion obtained with solar p-mode frequencies provided by the recent high-quality observational data (BiSON, SOI/MDI) are presented and discussed. The iterative nonlinear inversion technique used here is a generalization (for the case of exact solution of the adiabatic oscillation equations) of the Born quasiasymptotic approximate inversion developed by Marchenkov et al. (2000). Title: BiSON Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Marchenkov, K.; Miller, B. A.; New, R.; Pinter, B. Bibcode: 2001ESASP.464..313C Altcode: 2001soho...10..313C The current status of the Birmingham Solar Oscillation Network (BiSON) is discussed. Title: Helioseismic signatures of localized structural discontinuities in BiSON and GONG data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; New, R. Bibcode: 2001ESASP.464...79C Altcode: 2001soho...10...79C We use high-quality helioseismic data collected by BiSON and GONG in an attempt to search for variations over time of the influence on the acoustic mode frequencies of localized structural perturbations located beneath the solar surface. Our analysis of the BiSON data is aimed at a study of the effects of the He II ionization zone. We use GONG data (4 <= l <= 140) to extract estimates of the solar-cycle-induced eigenfrequency shifts over the range 1600 <= ν <= 4000 μHz. A careful analysis of these data may have uncovered tentative evidence for an oscillatory behaviour that would be the signature of a time-dependent solar cycle perturbation located approximately ~20 Mm beneath the photosphere. Title: A long-term look at acoustic modes with a nine-year BiSON spectrum Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Marchenkov, K.; Miller, B. A.; New, R.; Pinter, B. Bibcode: 2001ESASP.464...51C Altcode: 2001soho...10...51C We present data taken from BiSON to illuminate solar-activity related changes in the oscillation parameters. We also use the full dataset to hunt for low order p-modes. Title: Stellar Seismology, Stellar Ages, and the Cosmological Constant Authors: Isaak, G. R.; Isaak, K. G. Bibcode: 2001ASPC..245..199I Altcode: 2001aats.conf..199I; 2001astro.ph..9444I Solar seismology has allowed precision measurements of both the static and dynamic structure of our local star, the Sun. In the near future, seismology of solar-like stars of different ages and masses, necessarily restricted by angular resolution to low l-modes, will allow studies of the internal structure of stars at various stages of evolution. Such studies will test not only the theory of stellar evolution, but also allow the determination of ages of stars from the helium content in their cores. Such observations can be made photometrically from space, but also spectroscopically from the ground. We outline ground-based schemes. By correlating the external properties of nearby stars with their internal properties, it will be possible to extend local studies to distant open and globular clusters, and thereby to obtain an age of the Universe, based on many stars. The combination of the age, the density parameter Omega and Hubble's constant will allow strong limits to be placed on the cosmological constant. Title: Characteristics of full-disc BiSON power spectra above the acoustic cut-off frequency of the solar atmosphere Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Marchenkov, K. I.; Miller, B. A.; New, R. Bibcode: 2001ESASP.464..191C Altcode: 2001soho...10..191C We have analyzed 60 months of non-imaged Doppler velocity observations of the visible disc of the Sun in an effort to search for pseudo-mode-like structure in the data above the acoustic cut-off frequency of the solar atmosphere (≍5400 μHz). These data were collected by the ground-based Birmingham Solar-Oscillations Network (BiSON). Our analysis uncovers marginally significant evidence for the presence of a pseudo-mode-like structure in the range 5900 <= ν <= 6600 μHz, with a spacing between adjacent peaks (or troughs) of ~70 μHz. The signature - which, owing to the low signal to noise, disappears at higher frequencies - has a similar repeat period and phase to that found by Garcia et al. (1998) in full-disc GOLF data. However, the zero-to-peak power is a factor of ~10 weaker in strength. Title: Probing the solar cycle: a comparative and complementary analysis of GONG BiSON and VIRGO/LOI eigenfrequency shifts Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; New, R.; Appourchaux, T. Bibcode: 2001ESASP.464...83C Altcode: 2001soho...10...83C We use high-quality helioseismic data collected by GONG (over 4 <= l <= 140), BiSON (0 <= l <= 2) and VIRGO/LOI (0 <= l <= 8) to study the phenomenological nature of the cycle-induced (centroid) eigenfrequency variations. We have analyzed the frequency dependence of the shifts by fitting a power-law of the form δνnl ~ (νnl)α/Enl to the data (where the Enl are the mode inertias, and α is the power-law index to be extracted). Previous studies have suggested that a relation with α = 0 provides an adequate description of the shifts up to ν ≍ 3500 μHz. However, here we show that while nevertheless describing the shifts well up to ~2500 μHz, the linear scaling breaks down conspicuously at higher frequencies. Above this threshold, the shifts follow a power-law dependence with α ~ 2. We also ahow that GONG shifts, averaged over different ranges in l together with the BiSON and LOI data averaged over their full quoted ranges, all scale at fixed frequency with the normalized mode inertia ratio Qnl (Christensen-Dalsgaard & Berthomieu 1991). This is to be expected if the solar-cycle perturbation affecting the modes is confined in the surface layers; the excellent agreement also reflects favourably on the external consistency of the different observations. Title: g-mode detection: Where do we stand? Authors: Appourchaux, T.; Andersen, B.; Berthomieu, G.; Chaplin, W.; Elsworth, Y.; Finsterle, W.; Frölich, C.; Gough, D. O.; Hoeksema, T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T. Bibcode: 2001ESASP.464..467A Altcode: 2001soho...10..467A We review the recent developments in determining the upper limits to g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We address how this limit can be improved by way of new helioseismic instruments and/or new collaborations, hopefully providing in the not too distant future unambiguous g-mode detection. Title: Observational Upper Limits to Low-Degree Solar g-Modes Authors: Appourchaux, T.; Fröhlich, C.; Andersen, B.; Berthomieu, G.; Chaplin, W. J.; Elsworth, Y.; Finsterle, W.; Gough, D. O.; Hoeksema, J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.; Toutain, T. Bibcode: 2000ApJ...538..401A Altcode: Observations made by the Michelson Doppler Imager (MDI) and Variability of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and Heliospheric Observatory (SOHO) and by the ground-based Birmingham Solar Oscillations Network (BiSON) and Global Oscillations Network Group (GONG) have been used in a concerted effort to search for solar gravity oscillations. All spectra are dominated by solar noise in the frequency region from 100 to 1000 μHz, where g-modes are expected to be found. Several methods have been used in an effort to extract any g-mode signal present. These include (1) the correlation of data-both full-disk and imaged (with different spatial-mask properties)-collected over different time intervals from the same instrument, (2) the correlation of near-contemporaneous data from different instruments, and (3) the extraction-through the application of complex filtering techniques-of the coherent part of data collected at different heights in the solar atmosphere. The detection limit is set by the loss of coherence caused by the temporal evolution and the motion (e.g., rotation) of superficial structures. Although we cannot identify any g-mode signature, we have nevertheless set a firm upper limit to the amplitudes of the modes: at 200 μHz, they are below 10 mm s-1 in velocity, and below 0.5 parts per million in intensity. The velocity limit corresponds very approximately to a peak-to-peak vertical displacement of δR/Rsolar=2.3×10-8 at the solar surface. These levels which are much lower than prior claims, are consistent with theoretical predictions. Title: Source of excitation of low-l solar p modes: characteristics and solar-cycle variations Authors: Chaplin, W. J.; Appourchaux, T.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R. Bibcode: 2000MNRAS.314...75C Altcode: We investigate various properties of the excitation source that is responsible for driving the acoustic p-mode oscillations of the Sun. Current prejudice places this in the superadiabatic layer of the convection zone. We consider in detail how the precise nature of the resonant mode spectrum is modified: (i) as a result of the impact of different source-multipole mixtures; and (ii) as a function of the radial extent of the source. To do this, we model the observed resonant spectra with the solutions to a simple, one-dimensional wave equation which is intended to describe the essential elements of the solar resonant acoustic cavity. Further, we also fit these models to the low-l peaks in a high-resolution power spectrum generated from data collected by the Birmingham Solar-Oscillations Network (BiSON). We also use the extensive BiSON data set to search for variations in the source characteristics over the solar cycle. Title: Variations in the excitation and damping of low-l solar p modes over the solar activity cycle* Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R. Bibcode: 2000MNRAS.313...32C Altcode: We have searched helioseismic data collected by the Birmingham Solar Oscillations Network (BiSON) for solar-cycle changes to those low-l p-mode parameters that relate to the excitation and damping of the resonances. These data - collected between 1991 and 1997 - cover the complete declining phase of solar activity cycle 22 (up to and including the cycle 22/23 boundary). Over the range 2600<=ν<=3600μHz, we uncover a mean 24+/-3per cent increase in the frequency-domain linewidths; a mean decrease of 46+/-5per cent decrease in the mode heights, and a mean decrease of 22+/-3per cent in the modal velocity powers. The rate at which energy is supplied to the modes remains constant, at the level of precision of the observations (measured change 0+/-4per cent). We use expressions derived from the equation of a damped harmonic oscillator to illustrate the diagnostic properties of the observables: these indicate that both the signs and relative sizes of the extracted variations can arise from changes solely to the net damping; the net forcing of the modes need not change. The results possibly hint at the changes being maximal at frequencies near ~3100μHz. They might therefore suggest an origin for the observed variations that is peaked in the superadiabatic layer of the convection zone, which couples most strongly to the eigenfunctions of modes at the centre of the p-mode spectrum. Title: Skew-symmetric solar P modes in low-l BiSON ^* data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R. Bibcode: 1999MNRAS.308..424C Altcode: The p-mode oscillations of the Sun are manifestations of resonantly trapped acoustic waves propagating within its interior. The effective size of the resulting resonant cavity changes with the properties of the modes - the interaction of this phenomenon with a highly localized excitation source in the upper layers of the convection zone gives rise to skew-symmetric resonant profiles whose degree of asymmetry changes with frequency. Here, we have fitted low-angular-degree (low-l) resonant p-mode peaks - in a power spectrum generated from 32 months of BiSON Doppler velocity observations of the visible solar disc - to a skew-symmetric formalism to account for this effect. We present the fitted frequencies, fine-structure spacings [d_0(n) and d_1(n)] and mode-skewness estimates; and discuss the quantitative impact of fitting a skew, rather than symmetric, limit model. We also consider the reliability of the extracted parameters through the application of a useful statistical test, and extensive Monte Carlo fits to artificial data. Title: Rotation of the solar core from BiSON and LOWL frequency observations Authors: Chaplin, W. J.; Christensen-Dalsgaard, J.; Elsworth, Y.; Howe, R.; Isaak, G. R.; Larsen, R. M.; New, R.; Schou, J.; Thompson, M. J.; Tomczyk, S. Bibcode: 1999MNRAS.308..405C Altcode: Determination of the rotation of the solar core requires very accurate data on splittings for the low-degree modes which penetrate to the core, as well as for modes of higher degree to suppress the contributions from the rest of the Sun to the splittings of the low-degree modes. Here we combine low-degree data based on 32 months of observations with the BiSON network and data from the LOWL instrument. The data are analysed with a technique that specifically aims at obtaining an inference of rotation that is localized to the core. Our analysis provides what we believe is the most stringent constraint to date on the rotation of the deep solar interior. Title: An analysis of solar p-mode frequencies extracted from BiSON data: 1991-1996 Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Lines, R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1998MNRAS.300.1077C Altcode: We present a comprehensive frequency analysis of Doppler velocity observations of the visible solar disc made by the Birmingham Solar Oscillations Network (BiSON) from 1990-1996, i.e. covering the falling phase of activity cycle 22, up to and including the cycle 22/23 boundary. We have fitted low-degree (low-l) solar p modes in a variety of power spectra of differing lengths generated from these data. The analysis of the extracted frequencies reveals the expected clear solar-cycle dependence; in addition, there is now sufficient accuracy in the data to show that the low-l modal eigenfrequencies are less affected by the solar cycle than their higher l counterparts. The observed low-degree frequency shifts up to ~3900muHz are consistent - at the level of precision of the data - with an inverse mode-mass scaling. At frequencies above this, the blending of modes adjacent in frequency space makes it increasingly difficult to extract reliable frequency estimates. However, our data show indications of a turnover and possibly also an eventual sign change in the solar cycle shifts at frequencies above ~4000muHz, as seen in higher l data. We have parametrized the observed shifts as a function of the 10.7-cm radio flux, and produced an activity-corrected, average frequency table which incorporates eigenfrequencies from 18 4-month and 9 8-month spectra. We also present the fitted frequencies from a 32-month power spectrum, generated from data collected at or close to solar minimum. In addition, we also searched for frequency asymmetries in the l=2 mode multiplets. These could result from strong near-surface magnetic activity, or a buried magnetic field. Our fits merely place an upper limit to any mean asymmetry - over the range 10<=n<=21 - of between ~-80 and ~170nHz (3sigma). Title: Solar p-mode excitation: further insight from recent low-l BiSON helioseismological data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Lines, R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1998MNRAS.298L...7C Altcode: We present measurements of low-degree solar p-mode velocity powers, energies and energy supply rates between ~1600muHz and ~4700muHz, as derived from the analysis of several years of high-quality helioseismological data collected by the Birmingham Solar-Oscillations Network (BiSON). For the radial (l=0) modes, we find that the total energy E per mode (kinetic plus potential) peaks at ~3200muHz, reaching ~10^28erg. The rate at which energy is supplied to the modes E=2piDeltanu.E, where Deltanu is the FWHM modal line width, is observed to plateau between ~3000 and ~4000muHz, reaching a maximum of ~10^23ergs^-1. At frequencies below the plateau, the supply rate follows a simple power law with a dependence of E~nu^7.0+/-0.4 and at very-high frequencies the data follow E~nu^-4.5+/-1.1. These assume modal inertias normalized at T=T_eff with the mode-mass calculation normalized at the optical depth of the BiSON observations, the fitted power laws in E are approximately ~nu^6.5+/-1.1 and ~nu^-6.2+/-1.1 respectively. Title: Solar p-mode Excitation: Further Insights from Recent Low-l BiSON Helioseismological Data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Lines, R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1998ESASP.418..879C Altcode: 1998soho....6..879C We present measurements of low-degree solar p-mode velocity powers, energies and energy supply rates between ~1600 μ Hz and ~4700 μ Hz, as derived from the analysis of several years of high-quality helioseismological data collected by the Birmingham Solar-Oscillations Network (BiSON). For the radial (ell = 0) modes, we find that the total energy E per mode (kinetic plus potential) peaks at ~3200 μ Hz, reaching ~1028 ergs. The rate at which energy is supplied to the modes dot{E} = 2pi Δ ν cdot E, where Δ ν is the fwhm modal line width, is observed to plateau between ~3000 μ Hz and ~4000 μ Hz, reaching a maximum of ~1023 ergs s-1. At frequencies below the plateau, the supply rate follows a simple power law with a dependence of dot{E} propto nu7.0 plus or minus 0.4; and at very-high frequencies the data follow dot{E} propto nu-4.5 plus or minus 1.1. Title: Low Degree p-mode solar cycle trends from BISON data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1998IAUS..185..171C Altcode: The resonant p-mode oscillations of the Sun are manifestations of trapped, standing sound waves in the solar interior. The frequencies of the discrete spectrum of sustained modes are consequently modified by the mechanical properties of the layers through which the waves traverse. Quasi-periodic changes to the solar structure -- on an 11 (22)-year timescale -- result in certain measurable mode properties being affected. Here, we have used high-quality Doppler velocity data, collected in integrated sunlight by the Birmingham Solar-Oscillations Network (BiSON), in order to assess the resulting impact on the low-degree modes of oscillation over the falling phase of solar cycle 22, and the beginning of cycle 23. Title: Further inside into p-mode excitation and damping from recent BiSON data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1998IAUS..185..221C Altcode: The resonant p-mode oscillations of the Sun are believed to be excited stochastically in its outer layers. Here, we seek to gain additional insight into the p-mode excitation and damping problem by following the power evolution, with time, of individual low-degree (low-ell) multiplets. Sine-wave fits have been performed -- at the appropriate frequencies -- on short stretches of high-quality Doppler velocity data, collected in integrated sunlight by the Birmingham Solar-Oscillations Network (BiSON). The results of these analyses will be presented and discussed. Title: Observational Upper Limits for Low-Degree Solar g-modes Authors: Fröhlich, C.; Finsterle, W.; Andersen, B.; Appourchaux, T.; Chaplin, W. J.; Elsworth, Y.; D. O. Gough; Hoeksema, J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.; Toutain, T. Bibcode: 1998ESASP.418...67F Altcode: 1998soho....6...67F No abstract at ADS Title: Touching on the effects of an imperfect Window Function Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1998IAUS..185...47C Altcode: No abstract at ADS Title: A comparison of low-degree solar p-mode frquencies from BISON and LOI Authors: Appourchaux, T.; Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1998IAUS..185...45A Altcode: Here, we compare the low-degree solar p-mode frequencies returned from the analysis of two, contemporaneous, independent helioseismological data sets collected during 1996. The first comprises Doppler velocity observations of the 770-nm line of potassium, made in integrated sunlight by the six-station, terrestrial Birmingham Solar-Oscillations Network (BiSON). The second consists of irradiance distribution measurements of the solar disc, made at 500rm nm, by the Luminosity Oscillations Imager (LOI), which is part of the VIRGO experiment on the ESA/NASA SOHO satellite. Title: Comparative Studies of Low-Order and Low-Degree Solar p Modes Authors: Appourchaux, T.; Andersen, B.; Chaplin, W.; Elsworth, Y.; Finsterle, W.; Frohlich, C.; Gough, D.; Hoeksema, J. T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T. Bibcode: 1998ESASP.418...95A Altcode: 1998soho....6...95A The amplitudes of solar p-modes decrease steeply with decreasing radial order below about 17. The background solar signal (solar noise) in general increases steadily with decreasing frequency. For the irradiance and radiance measurements with VIRGO or SOI/MDI on SOHO this combination makes it difficult to detect low degree modes below about 1.8 mHz. The solar noise as observed in velocity with SOI/MDI or the ground based BISON network is significantly lower in this region than in intensity measurements. This allows low degree modes to be observed close to 1 mHz. We present results of detection and charaterization of the lowest order observable p-modes both in velocity and intensity measurements. Where applicable the properties of the modes observed with the two methods are compared. Title: The Extraction of Rotational Splittings from Monte Carlo Simulations of Unresolved Low-l Data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Miller, B. A.; New, R. Bibcode: 1998ESASP.418..135C Altcode: 1998soho....6..135C The rotation of the Sun lifts the frequency degeneracy in ell of the acoustic eigenmode spectrum. The extraction of reliable estimates of these splittings is a particularly challenging task. Here, we address the problem in the context of the analysis of full-disc helioseismological data. In essence, a set of ``zero-dimensional'' data are collected. Consequently: (i) a power spectrum of the data will consist of many closely spaced resonant peaks, with the most prominent aspect being an alternating quadrupole-monopole and octupole-dipole mode-pair structure; (ii) the data cannot be spatially filtered to extract ``single-mode'' power spectra -- however, this does mean that they are unaffected by spatial sideband leakage (which presents its own set of problems for resolved data); and (iii) the composition of the power spectrum may be further complicated by the introduction of temporal sidebands and other window-function-aliased power as a result of an imperfect observational duty cycle. At low frequencies, the modes are very weak -- however, their long coherence times give sharp, well defined resonant peaks in the frequency domain, enabling the m-dependent structure of the mode to be well resolved (given a sufficiently long integration time). At higher frequencies, despite increased signal-to-noise, the increasing mode line widths lead to a substantial blending of adjacent features in the frequency domain -- as the frequency-domain line widths increase still further, so the problems associated with extracting reliable estimates of the mode splittings become ever more severe. Here, we have used artificial p-mode data -- generated by a model which is based upon a randomly forced, damped harmonic oscillator -- to assess the veracity of maximum-likelihood fitting approaches for different parts of the low-ell spectrum. Among other points of interest, the results of these simulations reveal a clear tendency for the formal uncertainty of the fitted splitting to be anti-correlated with the magnitude of the splitting for modes at higher n. Title: A search l=2 asymmetries in BISON data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1998IAUS..185..169C Altcode: The rotation of the Sun lifts the frequency degeneracy in the angular degree ell of the resonant p-mode oscillations of the solar cavity, giving rise to a multiplet structure, each resulting component being identified by an azimuthal order m. A buried magnetic field will perturb these frequencies still further via the Lorentz force. Here, we have used low-degree solar p-mode data, collected by the Birmingham Solar-Oscillations Network (BiSON) in integrated sunlight, in an effort to search for such an effect in modes of degree ell=2. The Lorentz perturbation will shift the outer, sectoral (m=pm 2) components in the same sense, while the m=0 component remains unaffected, giving the integrated-sunlight-observed ell=2 multiplet an asymmetric frequency structure. The degree of asymmetry is expected to change with the solar cycle. Results obtained by attempting to fit explicitly the asymmetric structure, and by overlaying many independent mode realizations, will be presented and discussed. Title: Solar internal sound speed as inferred from combined BiSON and LOWL oscillation frequencies Authors: Basu, Sarbani; Christensen-Dalsgaard, J.; Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; New, R.; Schou, J.; Thompson, M. J.; Tomczyk, S. Bibcode: 1997MNRAS.292..243B Altcode: 1997astro.ph..2105B Observations of the Sun with the LOWL instrument provide a homogeneous set of solar p-mode frequencies from low to intermediate degree that allow one to determine the structure of much of the solar interior avoiding systematic errors that are introduced when different data sets are combined, i.e., principally the effects of solar cycle changes on the frequencies. Unfortunately, the LOWL data set contains very few of the lowest-degree modes, which are essential for determining reliably the structure of the solar core - in addition, these lowest-degree data have fairly large associated uncertainties. However, observations made by the Birmingham Solar-Oscillations Network (BiSON) in integrated sunlight provide high-accuracy measurements of a large number of low-degree modes. In this paper we demonstrate that the low-degree mode set of the LOWL data can be successfully combined with the more accurate BiSON data, provided the observations are contemporaneous for those frequencies where the solar cycle induced effects are important. We show that this leads to a factor of 2 decrease in the error on the inferred sound speed in the solar core. We find that the solar sound speed is higher than in solar models for r<0.2Rsolar. The density of the solar core is, however, lower than that in solar models. Title: Techniques used in the analysis of data collected by the Birmingham Solar-Oscillations Network (BiSON). II. Frequency domain analysis & data merging Authors: Chaplin, W. J.; Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1997A&AS..125..195C Altcode: The Birmingham Solar-Oscillations Network (BiSON) consists of 6 solar observatories dedicated to the collection of full-disc solar Doppler velocity data -- these data are sensitive to the lowest spatial degrees of oscillation (0 <= l <= 4). In Paper I of this series, we described the calibration of raw data from the BiSON instruments to produce solar velocity residuals representing the oscillations of the Sun's surface. In this paper, we discuss the combination of velocity residuals into time series -- including a thorough discussion of the treatment of data overlaps between sites -- and the analysis of the power spectra computed from such time series to derive the characteristics of the acoustic modes. Title: Solar p-mode linewidths from recent BiSON helioseismological data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1997MNRAS.288..623C Altcode: We present low-degree solar p-mode linewidths from the analysis of several high-resolution frequency spectra generated from high-quality Doppler velocity data collected - in integrated sunlight - by the Birmingham Solar-Oscillations Network (BiSON) between 1991 July and 1995 July. We have used linewidths, Deltanu, measured in a 32-month frequency spectrum, to test the power-law dependence of the widths at low frequencies. Over the range 1473<=nu<=1822Hz, we find Deltanu~nu^7.0+/-1.5. If an effort is made to correct for finite observing time systematics, the fitted index increases to 7.3 (and even higher, to 7.8, if a naive, single-bin-width correction is applied). This is somewhat steeper than reported in previous observations of intermediate-degree modes, and is more in line with theoretical calculations which predict Deltanu~nu^8 over this frequency range. If one assumes that the steep dependence reported here persists down to lower frequencies, low-degree-mode coherence (e-folding) times at 800Hz of >14yr, and at 300 muHz (i.e. near the frequency expected for the fundamental) of >13000yr are implied. Title: The observation and simulation of stochastically excited solar p modes Authors: Chaplin, W. J.; Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1997MNRAS.287...51C Altcode: We use low-degree p-mode data, collected in integrated sunlight by the Birmingham Solar-Oscillations Network (BiSON), to derive the distribution of the observed strengths of the solar oscillations. We demonstrate that certain features of the observations cannot be explained by a model of the oscillations that is based upon a stochastically forced, damped harmonic oscillator. The solution of the equation of motion of the oscillator, as derived by the use of the Laplace transform, is presented, and its application to the simulation of real p-mode data, in the form of a coded algorithm, is discussed. A variety of tests are applied - both in the time and in the frequency domains - to artificially generated time series. These confirm that the model serves both as a useful diagnostic tool and for providing additional insight into the p-mode excitation and damping problem. Title: The Solar Core: New Low-l p-Mode Fine-Spacing Results from BiSON Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1997ApJ...480L..75C Altcode: 1997astro.ph..2141C The fine-structure spacing dl(n) = νl,n - νl+2,n-1 for low-degree solar p modes of angular degree l and radial order n is sensitive to conditions in the deep radiative interior of the Sun. Here we present fine-structure spacings derived from the analysis of nearly 5 years of helioseismological data collected between 1991 July and 1996 February by the Birmingham Solar Oscillations Network (BiSON). These data cover 9 <= n <= 28 for d0(n), and 11 <= n <= 27 for d1(n). The measured spacings are much more precise and cover a greater range than earlier measurements from BiSON data (Elsworth et al. 1990a). The predicted fine-structure spacings for a ``standard'' solar model are clearly excluded by the BiSON data (at ~10 σ) models that include helium and heavy-element settling provide a much better match to the observed spacings (see also Elsworth et al. 1995). Since the inclusion of core settling in solar models will tend to increase slightly the predicted neutrino flux, the BiSON fine-structure data appear to reinforce previous conclusions, i.e., an astrophysical solution to the solar neutrino problem seems unlikely.

Birmingham Solar Oscillations Network; http://bison.ph.bham.ac.uk. Title: On the spectroscopic detection from the ground of Earth-like planets circling solar-like stars Authors: Isaak, G. R. Bibcode: 1997IAUJD..13E...6I Altcode: Planets with masses and orbits similar to those of the Earth, revolving around a solar-like star, give rise to recoil effects with amplitudes of the order of ~0.1 m s^{-1}, and periodicities of the order of a year. Spectroscopic methods, developed by the author in the late 1950's -- extended by him, together with collaborators, since the early 1970's -- led to the discovery of global solar oscillations in 1979, and can be extended to tackle the above problem. The methods, and their potential, will be presented and discussed. Title: Solar core rotation from low-degree BiSON p-mode splittings: 1981-95 Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1996MNRAS.283L..31C Altcode: In this paper, we present an analysis of the rotational splittings of low-degree solar p modes, as measured in full-disc helioseismological data collected by the Birmingham Solar-Oscillations Network (BiSON) between 1981 and 1995. These data provide coverage over solar activity cycles 21 and 22. Rotationally split multiplets were fitted in two 4-month and seven 8-month frequency spectra with a technique that minimizes a maximum-likelihood function consistent with chi^2 2-d.o.f. statistics. The fitted modes used in the analysis map the range 1<=l<=3 and 2.0<=nu<=3.1mHz. The lower limit to the analysed frequency range was determined by the poorer quality of the pre-1990 data; the upper, very conservative, cut-off was imposed in order to avoid using data where the linewidths of the modes begin to increase substantially above 1muHz. Global splitting averages (for 1<=l<=3) were computed over the quoted mode-frequency range by: (i) weighting each datum according to the scatter observed in the sectoral splittings as a function of l and (ii) weighting each datum according to its formal uncertainty, as computed by the mode-fitting procedure. The l-weighted averages show a slight decline over the period 1981-95: however, the gradient is only significant at the ~2sigma level (-3.8+/-1.8nHz yr^-1). If one were to interpret any trends in the low-degree splittings as being indicative of a modification of the rotational behaviour of the solar core (for r/R_solar<=0.25), we would estimate that a ~60 per cent change in the core rotation rate is excluded at the 3sigma level by the l-weighted data. The `formally' weighted averages imply a very significant change with epoch. However, an analysis of the data appears to show that the formal uncertainties may somewhat underestimate the actual errors on the measured splittings, leading to an overestimation of the significance of any inferred change with epoch. Title: Low-frequency, low-degree solar p-mode measurements from recent BiSON* data Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; Lines, R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1996MNRAS.282L..15C Altcode: We present high-quality measurements of the frequencies of some acoustic modes of oscillation of the Sun, as determined from recent full-disc BiSON data. These cover the range 0<=<~<=3 and 7<=<e1>n<=</e1>14. Several of the mode frequencies have been measured to accuracies as high as 5 parts in 10^6, as determined by the formal mode-fitting uncertainties. When compared with the model frequencies of the AARHUS group (model OPAL1 from Basu et al.) in which the Livermore equation of state, the Livermore opacities and both helium and heavy element diffusion and settling have been incorporated, the frequency differences (in the sense BiSON minus OPAL1) are typically of the order of only ~-0.1 muHz over this frequency region. Title: BiSON Performance Authors: Chaplin, William J.; Elsworth, Yvonne; Howe, Rachel; Isaak, George R.; McLeod, Clive P.; Miller, Brek A.; van der Raay, H. B.; Wheeler, Sarah J.; New, Roger Bibcode: 1996SoPh..168....1C Altcode: Since 1981 we have been operating the Birmingham Solar-Oscillations Network (BiSON), a global network of resonant-scattering spectrometers, observing the low-l solar p modes. Here we discuss historical developments, culminating in the establishment of a 6-station network in 1992 September, and the subsequent performance of that network. The data record of each station from 1992 to 1994 has been analysed in terms of weather and equipment breakdowns. Our early experience suggests that the best long-term coverage possible with a 6-station network is limited in practice to about 80%, which falls short of previous predictions. Title: Low-degree, L=4 modes in full-disc BiSON* helioseismological data Authors: Chaplin, W. J.; Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1996MNRAS.280.1162C Altcode: We demonstrate that some L=4 acoustic eigenmodes of the Sun are clearly distinguishable in long power spectra generated from Doppler velocity residuals collected in unimaged sunlight by the six-station Birmingham Solar Oscillations Network (BiSON). Modes covering the range n=17 to 21 have been measured in 16-month-long power spectra. They have typical amplitudes -when measured in full-disc Doppler velocity data - of less than ~1 cm s^-1 per root bin, and their frequencies have been determined to fractional accuracies of the order of 3 parts in 10^5. The sensitivity of the whole-disc observations to these modes - as implied by the data - appears to be approximately a factor of 2 greater than the theoretical predictions of Christensen-Dalsgaard. Title: Solar core rotation: low-degree solar p-mode rotational splitting results from BiSON* Authors: Chaplin, W. J.; Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1996MNRAS.280..849C Altcode: In a recent paper (Elsworth et al.), we presented rotational splitting measurements of low-degree, low-frequency solar p modes, which, for the first time, show visually well-separated components at frequencies as low as ~1.5 mHz. At the present time, these data appear to rule out a rapidly rotating solar core. Here, we expand our analysis of these data to a full discussion of the statistical properties of the measured splittings. We have considered two fully independent Fourier spectra, generated from Doppler velocity residuals collected by the six-station Birmingham Solar-Oscillations Network (BiSON) between 1992 January 1 and 1994 August 23 (Fourier spectra 16A and 16C from Elsworth et al.). We present formal uncertainties from maximum-likelihood fits to the mode multiplets, analyse and compare the statistical properties of the sets, and search for possible trends in the splitting measures with n. Title: Recent results from the Birmingham Solar-Oscillations Network (BiSON). Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1996BAAS...28..936C Altcode: No abstract at ADS Title: Recent Results from the Birmingham Solar-Oscillations Network (BiSON) Authors: Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1996AAS...188.6904C Altcode: 1996BAAS...28R.936C The Birmingham Solar-Oscillations Network (BiSON) consists of 6 semi and fully automatic observatories, dedicated to the collection of low-degree solar oscillations data in integrated sunlight. The network was established in 1981 with two permanent stations; the addition of several more sites culminated with the addition of a sixth in 1992. Here, we give an update on the current status of the network. In addition, we discuss recent important scientific results from analysed data, including: low-degree rotational splitting results covering the period 1981 to 1995; and the measurement of low-frequency modes, down to ~ 1.2mHz, in a power spectrum generated from 32 months of recent BiSON data. Title: Observing the sun with the Birmingham Solar-Oscillations Network (BISON) Authors: Chaplin, W. C.; Elsworth, Y.; Isaak, G. R.; Lines, R.; McLeod, C. P.; Miller, B. A.; New, R.; van der Raay, H. B. Bibcode: 1996Obs...116...32C Altcode: No abstract at ADS Title: Techniques used in the analysis of solar oscillations data from the BiSON (University of Birmingham) network. I. Daily calibration. Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R.; Wheeler, S. J. Bibcode: 1995A&AS..113..379E Altcode: In this, the first of a pair of linked papers, we discuss the methods used to convert raw data from the BiSON network of resonant-scattering spectrometers to velocity residuals, from which the low-degree, five-minute solar oscillations are studied. We describe our standard calibration and some alternative methods. The rejection of bad data, and the corrections applied for unwanted low-frequency effects, are also discussed. Title: Slow rotation of the Sun's interior Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R.; Wheeler, S. J.; Gough, D. O. Bibcode: 1995Natur.376..669E Altcode: THE rotation of the Sun is not that of a rigid body; at its surface, the gas near the poles has a lower angular velocity than that near the equator1. This latitudinal variation persists to the base of the convection zone, below which the angular velocity becomes approximately uniform2,3. Any variations of angular velocity at much greater depths are, however, poorly constrained4-10. Observations of solar oscillation modes have been used to probe density variations in the Sun; rotational splitting of degenerate modes, although difficult to resolve, provides important constraints on the dynamical structure11. Here we report observations of rotationally split modes made over a three-year period with the Birmingham Solar Oscillations Network. Our results indicate that there is a substantial region inside the Sun that is rotating more slowly than the surface. This situation seems likely to be transient—the minimum-energy state would have all the deeper regions rotating with the same angular velocity—and is at variance with our current ideas about the rotational evolution of main-sequence stars12. We have no solution to the dynamical problem this poses. Title: The Recent Performance of the 6-STATION BISON Network Authors: Chaplin, W. J.; Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; van der Raay, H. B. Bibcode: 1995ESASP.376b.391C Altcode: 1995help.confP.391C; 1995soho....2..391C No abstract at ADS Title: Automated Photometry of Bright Stars Using the BISON Network Authors: Monks, P. D.; Isaak, G. R.; Lines, R.; Litherland, J. W.; McLeod, C. P. Bibcode: 1995ESASP.376b.539M Altcode: 1995soho....2..539M; 1995help.confP.539M No abstract at ADS Title: Some Notes on the Calibration of Doppler Velocity Residuals Collected by a Resonant Scattering Spectrometer Authors: Chaplin, W. J.; Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1995ESASP.376b.163C Altcode: 1995soho....2..163C; 1995help.confP.163C Discusses three alternative calibration techniques for Doppler velocity data collected by a resonant-scattering spectrometer viewing the unimaged solar disc, that allow long-term, low-frequency information to be preserved. In the first, the effects of curvature in the solar reference line are removed by normalizing the observed ratio, R(v) - the difference between the resonantly-scattered intensities in the blue and red wings of the source line, normalized by the scattered sum - by a function that reflects the variation of the total intensity over the instrument bandwidth. In the second method, a linearized function is formed from a power series of R(v). A straight forward example of this technique appears to be subject to systematic, low-frequency errors of the order of ≡1 to 2 m s-1. And in the third method, Doppler velocity data collected over a full observing season could, in principle, form an internal reference - a look-up curve. Title: The Measurement of L = 4 Modes in Full-Disc BISON Data Authors: Chaplin, W. J.; Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A. Bibcode: 1995ESASP.376b.387C Altcode: 1995help.confP.387C; 1995soho....2..387C No abstract at ADS Title: An Investigation of the Correlation Between Unusually Large Amplitude P-Modes and Solar Activity Authors: Chaplin, W. J.; Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R. Bibcode: 1995ESASP.376b.335C Altcode: 1995help.confP.335C; 1995soho....2..335C No abstract at ADS Title: A search for small-amplitude, acoustic, p-mode oscillations on alpha CMi Authors: Bedford, D. K.; Chaplin, W. J.; Coates, D. W.; Davies, A. R.; Innis, J. L.; Isaak, G. R.; Speake, C. C. Bibcode: 1995MNRAS.273..367B Altcode: We have searched for small-amplitude, acoustic, p-mode oscillations on the F5 IV-V subgiant alpha CMi (HR 2943) in high-quality Doppler velocity measurements made in 1991, 1992 and 1993 with a magneto-optical-filter spectrometer. An internal precision of 0.13 m^-2 s^-2 muHz^-1 (1 sigma) has been achieved in one of the 1993 data sets. Conclusive evidence for the presence of a p-mode spectrum may be established by extracting the mean first-order-half spacing 1/2Deltav. Fourier analysis of the 1991 and 1992 data appears to indicate the presence of a strong concentration of periodic power. However, the analysis of substantially higher quality 1993 data fails to reveal a strong peak; we are therefore forced to conclude tentatively that we have, at present, failed to find conclusive evidence for an acoustic oscillation spectrum on alpha CMi. Title: Fine Spacing of L = 0, L = 2 Acoustic Eigenmodes and the Solar Neutrino Problem: Particle Physics and Cosmological Implications Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; Wheeler, S. J.; New, R. Bibcode: 1995ASPC...76...51E Altcode: 1995gong.conf...51E No abstract at ADS Title: Observations of Global Solar Oscillations in Moonlight Authors: Fussell, J. A.; Brazier, R. I.; Davies, A. R.; Isaak, G. R.; McCleod, C. P.; Morgan-Vandome, S. C.; Speake, C. C. Bibcode: 1995ASPC...76..452F Altcode: 1995gong.conf..452F No abstract at ADS Title: Rotational Splitting of Low-Degree Solar P Modes Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; Wheeler, S. J.; New, R.; Gough, D. O. Bibcode: 1995ASPC...76...43E Altcode: 1995gong.conf...43E No abstract at ADS Title: Performance of the BISON Network 1981-Present Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; van der Raay, H. B.; Wheeler, S. J.; New, R. Bibcode: 1995ASPC...76..392E Altcode: 1995gong.conf..392E No abstract at ADS Title: Statistical Distribution of Solar p-Mode Amplitudes Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; Wheeler, S. J.; New, R. Bibcode: 1995ASPC...76..318E Altcode: 1995gong.conf..318E No abstract at ADS Title: High-precision, longitudinal, disc-averaged magnetic field measurements of α Canis Minoris and β Leporis. Authors: Bedford, D. K.; Chaplin, W. J.; Davies, A. R.; Innis, J. L.; Isaak, G. R.; Speake, C. C. Bibcode: 1995A&A...293..377B Altcode: High-precision longitudinal, disc-averaged magnetic field measurements have been made on two late-type stars, α CMi (HR 2943) and β Lep (HR 1829). A magneto-optical filter has been used to measure the degree of circular polarization in the wings of a line of neutral potassium (7699 A) formed in the atmosphere of the target star. From 10 nights of data taken on α CMi on the 1.9-m reflector at the South African Astronomical Observatory (SAAO) in 1993 January, an upper limit to any net longitudinal field component present - assuming the field to be constant over the period of observation - of -0.40+/-0.26G was established. Similarly, upper limits for β Lep of -4.3+/-6.4G and -0.7+/-1.6G were established, from 4 and 10 nights of data taken in 1992 and 1993 January respectively. No significant, periodic, day-to-day variations were seen in the three time series of data. Title: High-precision velocity observations of Procyon A - II. Measurement of the orbital motion of Procyon A during 1986-90. Authors: Innis, J. L.; Isaak, G. R.; Speake, C. C.; Chaplin, W. J.; Brazier, R. I.; Jones, A. R. Bibcode: 1994MNRAS.271..573I Altcode: Radial velocity observations of high internal precision have been obtained, with the Birmingham stellar spectrometer, of the F5 IV-V star Procyon A. The velocities have been derived using a `null technique' by determining the time when the topocentric velocity of Procyon A passes through zero (which occurs in January each year). At this time, the barycentric velocity of the star is equal to the barycentric velocity of the instrument, which can be calculated to a high accuracy. Seven such velocities have been determined from five observing runs during the years 1986 to 1990 inclusive. The internal precision and external errors (e.g. our zero-point) cannot be uniquely determined from so few points but the former appears to be in the range 10 to 40 m s- . We have compared our data with the orbit of Procyon recently derived by Irwin et al. The mean annual acceleration of Procyon A over the two years 1988 to 1990, according to the orbit of Irwin et al., is 133 m s- yr . Our measured value is 122 m s1 yr , with an error of the order oft 10 m s- , in reasonable agreement with the value obtained by Irwin et al. A detailed comparison will be possible when several more years of data have been obtained. Key words: techniques: radial velocities - binaries: spectroscopic - stars: individual: Procyon. Title: Corrigendum - Low-L P-Mode Solar Eigenfrequency Measurements from the Birmingham Network Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; New, R. Bibcode: 1994MNRAS.270..720E Altcode: Key words: Sun: oscillations. Title: Solar p-Mode Frequencies and Their Dependence on Solar Activity: Recent Results from the BISON Network Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R.; Speake, C. C.; Wheeler, S. J. Bibcode: 1994ApJ...434..801E Altcode: We present here high-accuracy determinations of the frequencies of low-l solar p-modes and their solar-cycle dependence. The data were obtained using the Birmingham network of solar spectrometers (BISON). The precision of the measurements is discussed. Our previously published results of a significant frequency shift between solar minimum and solar maximum, apparently independent of l and similar to that found by other workers for intermediate-l modes, is confirmed and extended. This suggests that at most only a small fraction of the variation is due to the solar core. Sets of frequencies at high and low solar activity, and an average corrected for solar-activity effects, are presented. There is now evidence that the solar-activity dependence of the frequencies varies across the 5 minute spectrum. Title: Solar Seismology - the Velocity Continuum Spectrum Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R.; Speake, C. C.; Wheeler, S. J. Bibcode: 1994MNRAS.269..529E Altcode: The discrete spectrum of global solar modes was discovered in 1979 by Claverie et al. Here we report the first determination of the continuum spectrum in velocity, where atmospheric and instrumental effects have been significantly reduced. Crosscorrelations of velocity measurements at four observing stations of a global network have made this possible. The solar noise power is a factor of 5 lower than expectations. Key words: methods: data analysis - Sun: oscillations. Title: The longitudinal magnetic field of Procyon. Authors: Bedford, D. K.; Chaplin, W. J.; Innis, J. L.; Isaak, G. R.; McLeod, C. P.; Speake, C. C. Bibcode: 1994MNRAS.269..639B Altcode: An upper limit of 4.3 G (3 u) on the longitudinal magnetic field, and its variation, of the bright star Procyon is placed by the extended measurement of the circular polarization in the blue and red wings of the 770-nm absorption line of neutral potassium. Key words: line: profiles - polarization - stars: individual: Procyon - stars: magnetic fields. Title: An Epoxy Coated Flux Collector for Stellar Seismology Authors: Bedford, D. K.; Chaping, W. J.; Isaak, G. R.; Litherland, J. W. Bibcode: 1994MNRAS.269..679B Altcode: A programme directed towards the discovery in solar-like stars of small-amplitude, pressure-driven oscillations analogous to those observed of the Sun, and to search for planetary companions, has been pursued for several years, principally at the SAAO 1.9-m telescope. Here we describe a 0.9-m, spun epoxy flux collector of - 1-arcmin quality, a prototype towards larger, inexpensive flux collectors dedicated to a stellar seismology programme. This prototype has been used to gather preliminary stellar data. Key words: techniques: miscellaneous - telescopes - stars: oscillations. Title: A high-precision determination of the radial velocity of the G5 II giant beta Lep. Authors: Bedford, D. K.; Chaplin, W. J.; Davies, A. R.; Innis, J. L.; Isaak, G. R.; Speake, C. C. Bibcode: 1994MNRAS.269..435B Altcode: We apply a null technique to measure to a high accuracy the barycentric radial velocity of the G5 II giant P Lep (HR 1829). We use a magneto-optical filter as a spectroscopic bridge to determine the time at which the geocentric velocity of the star passes through zero. From data taken on the 1.9-m reflector at the South African Astronomical Observatory (SAAO) in 1992 and 1993 January, the barycentric radial velocity of P Lep is calculated to be -13.6+0.2 and -13.576+0.040 km s ' respectively. Key words: techniques: radial velocities - stars: individual: P Lep - stars: oscillations. Title: Solar Structure from Global Studies of the Five-Minute Oscillation Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Roca Cortes, T. Bibcode: 1994snft.book..407C Altcode: No abstract at ADS Title: The variation in the strength of low-l solar p-modes - 1981-92 Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; Speake, C. C.; Wheeler, S. J.; New, R. Bibcode: 1993MNRAS.265..888E Altcode: The acoustic eigenmodes of the sun are a well-recognized probe of the structure of the solar interior. We report here on a measurement of the strength of the low-l p-mode oscillations throughout a solar cycle. There is an increase of 35 +/-5 percent in the strength of the modes from solar maximum to solar minimum, consistent for all the l-values measured. The observations were made with the Birmingham Solar Oscillations Network. Title: Metal epoxy-coated mirrors for stellar seismology Authors: Bedford, David K.; Chaplin, W. J.; Isaak, G. R. Bibcode: 1993SPIE.1931...96B Altcode: A 0.9 m diameter f/1.8 paraboloidal mirror of moderate quality (approximately 2 arcmin) has been produced by spinning an epoxy- coated spherical substrate. This mirror has been used to build a prototype flux collector for stellar seismology. The objective is to produce 2 m mirrors for this application. Title: Avalanche Photodiodes in Stellar Spectroscopy Authors: Davies, A. R.; Isaak, G. R.; Speake, C. C. Bibcode: 1993ASPC...42..493D Altcode: 1993gong.conf..493D No abstract at ADS Title: High Precision Velocity Measurements of the Star Procyon - a Possible Stellar Signal Authors: Bedford, D. K.; Chaplin, W. J.; Davies, A. R.; Innis, J. L.; Isaak, G. R.; Speake, C. C. Bibcode: 1993ASPC...42..383B Altcode: 1993gong.conf..383B No abstract at ADS Title: High-Frequency Solar Velocity Noise Authors: Elsworth, Y.; Howe, R.; Isaak, G.; McLeod, C.; Miller, B.; Speake, C.; Wheeler, S.; New, R. Bibcode: 1993ASPC...42..107E Altcode: 1993gong.conf..107E No abstract at ADS Title: Low-l p-mode solar eigenfrequency measurements from the Birmingham Network Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; New, R. Bibcode: 1991MNRAS.251P...7E Altcode: Observations of the acoustic oscillations of the sun taken over a period of eight years are presented and discussed in terms of their implications regarding the nature of the deep solar interior. Stable atomic standards are used to integrate light from the whole solar disc, and the data taken over the course of the measurements are averaged to examine the mean frequencies for all the modes. The quality of the data allows comparisons with solar theories as well as the analysis of long-term solar cycle trends. Title: High-precision velocity observations of Procyon A - I. Search for p-mode oscillations from 1988 and 1990 observations. Authors: Innis, J. L.; Isaak, G. R.; Speake, C. C.; Brazier, R. I.; Williams, H. K. Bibcode: 1991MNRAS.249..643I Altcode: An analysis for the presence of small, low-degree p-mode oscillations of high-precision velocity observations of Procyon is presented. Examination of solar data taken during the Procyon observing runs at higher counting rates yields correspondingly lower noise levels, indicating that the spectrometer performance is, as yet, essentially limited by photon statistics. The power spectra are also studied for possible periodicities due to the presence of equifrequency spaced modes of comparable power to the background noise. It is observed that while some periodicities were seen they were not reproducible in all three data sets, and therefore are probably not of stellar origin. Title: Oscillation observations. Authors: Hill, Frank; Deubner, Franz-Ludwig; Isaak, George Bibcode: 1991sia..book..329H Altcode: This chapter reviews recent observations of solar oscillations. The oscillations discussed are global and local 5-min p-modes, the 160-min oscillation and oscillations in the solar atmosphere. Experimental and data reduction methods are described. Summaries of recent results are provided, including measurements of frequencies, amplitudes, line widths and splittings. Other topics include active-region tomography, solar cycle changes, the chromospheric cavity and diameter measurements. Title: A preliminary investigation of the suitability of the Mount Stromlo coude spectrograph for very precise radial-velocity measurements Authors: Innis, J. L.; Isaak, G. R.; Isaak, K. Bibcode: 1990Obs...110..188I Altcode: No abstract at ADS Title: Evidence from solar seismology against non-standard solar-core models Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; New, R. Bibcode: 1990Natur.347..536E Altcode: GLOBAL oscillations of the Sun1 have been used to test solar models2, but modelling the oscillation frequencies to their measured accuracies of a few microhertz has proved difficult, mostly owing to ignorance of the structure of the Sun's outer layers3. The frequency separation between closely spaced modes in the acoustic spectrum is expected to depend more on core properties4, however, and thus to provide constraints on models of the solar core. Our observations combine data from a global network of observing stations, which reduces the masking effect of daily sidebands in the spectral analysis. Here we present precision measurements of fine structure and its variation with frequency. Our results agree with standard solar models5-7, and seem to remove the need for significant mixing8,9 or weakly interacting massive particles (WIMPS)10,11 in the core, both of which have been advanced to explain the low measured flux of solar neutrinos12,13. This suggests that the solar neutrino problem must be resolved within neutrino physics, not solar physics; neutrino oscillations and a finite neutrino mass form a possible explanation. Title: Solar and Stellar Seismology Authors: Isaak, G. R. Bibcode: 1990Obs...110...80I Altcode: No abstract at ADS Title: Variation of low-order acoustic solar oscillations over the solar cycle Authors: Elsworth, Y.; Howe, R.; Isaak, G. R.; McLeod, C. P.; New, R. Bibcode: 1990Natur.345..322E Altcode: GLOBAL acoustic oscillation modes of the Sun were discovered eleven years ago1. The possibility of temporal variations in the oscillation frequencies was suggested by fluctuations in the flux of solar neutrinos2, and would also be implied by changes in the size of the solar cavity or in the speed of sound within the Sun. Our group has studied solar oscillations for many years1,3; over the past decade, a network of three stations deployed at sites that can permit 24-h data collection has provided p-mode (acoustic) spectra of very high quality. Here we present evidence that the frequencies of the lowest-order (l<=2) modes have varied over the period of observation (1977-88) in a manner that is correlated with solar activity (as measured by sunspot number). The frequency variation has a peak-to-peak amplitude of 0.46+/-0.06μHz, and could reflect variations in the solar dimensions or in the sound speed in the Sun, which might in turn be due to changes in solar temperature and/or magnetic field. Title: Linewidths of low-degree acoustic modes of the sun Authors: Elsworth, Y.; Isaak, G. R.; Jefferies, S. M.; McLeod, C. P.; New, R. Bibcode: 1990MNRAS.242..135E Altcode: Estimates of the spectral linewidths of low degree (l = 0 and l = 1), 5-min p-modes obtained from Doppler shift observations in 1984 (63 d) and 1986 (63 d) are reported. The observed linewidths increase from 0.5 micro-Hz at 2000 micro-Hz to 3 micro-Hz at 3800 micro-Hz for l = 0. Comparison with other data suggests that for a given frequency the linewidth increases with increasing values of l. On the assumption that the linewidth is substantially due to damping processes, the linewidths are consistent with e-folding times between 3.7 and 0.6 d. Title: Camera obscura and sunspots Authors: Isaak, G. R. Bibcode: 1989Obs...109..152I Altcode: No abstract at ADS Title: Observations of solar p-modes with L of not greater than 5 Authors: Palle, P. L.; Perez Hernandez, F.; Roca Cortes, T.; Isaak, G. R. Bibcode: 1989A&A...216..253P Altcode: Results are presented for the sun's radial velocity in integrated sunlight. A resonant scattering spectrometer has been used to determine the frequencies and amplitudes of p-modes with spherical harmonics of degree (l) of less than 3, and a second spectrophotometer, which observes part of the sun by means of a spatial filter, has been used to measure the frequencies and amplitudes of p-modes with l of not greater than 5. The frequencies at both ends of the p-mode 5-minute oscillations with l of between 3 and 5, inclusively, are obtained with greater precision than previous determinations. Title: Solar Seismology Authors: Isaak, G. R. Bibcode: 1989QJRAS..30...93I Altcode: No abstract at ADS Title: Solar oscillations as seen in the Na I and K I absorption lines. Authors: Isaak, G. R.; McLeod, C. P.; Palle, P. L.; van der Raay, H. B.; Roca Cortes, T. Bibcode: 1989A&A...208..297I Altcode: Data on the solar p modes observed simultaneously in the solar NaI and KI absorption lines were obtained in 1985 by operating two independent resonant scattering spectrometers at the same site (Observatorio del Teide, Tenerife). Since the abundances of the ground state atoms of these two elements are not the same, different depths of the solar photosphere are sampled. A comparison of the data obtained is given. Title: The current status of the Birmingham solar seismology network. Authors: Aindow, A.; Elsworth, Y. P.; Isaak, G. R.; McLeod, C. P.; New, R.; Vanderraay, H. B. Bibcode: 1988ESASP.286..157A Altcode: 1988ssls.rept..157A Some aspects of the performance of a network of solar seismology stations are presented. Duty cycles for 1986 and 1987 are given and examples of window functions and p-mode spectra are shown. Sideband powers down to 2% of peak power have been achieved for spans of 16 days and 3% for 64 days. Noise levels of 7 (ms-1)2Hz-1 and 13 (ms-1)2Hz-1 have been achieved in regions just above and below the p-mode spectrum. A new station in Birmingham is discussed. Its importance as a testing and training station is outlined and plans to deploy replicas around the globe are described. Title: A detector of small gradients of transparency of the terrestrial atmosphere. Authors: McLeod, D. B.; Isaak, G. R. Bibcode: 1988ESASP.286..223M Altcode: 1988ssls.rept..223M In the study of low l p-modes of the Sun in integrated sunlight with ground based spectrometers even small (10-3) gradients in transparency across the solar disk give rise to displacements of centroids of spectral lines at the m/s level. The authors describe a prototype instrument which measures this atmospheric gradient continuously and thereby makes it possible to subtract these artefacts from the measurements. Title: High precision velocity observations of Arcturus using the 7699 Å line of potassium. Authors: Innis, J. L.; Isaak, G. R.; Brazier, R. I.; Belmonte, Juan A.; Palle, Pere L.; Roca Cortés, Teodoro; Jones, A. R. Bibcode: 1988ESASP.286..569I Altcode: 1988ssls.rept..569I The K giant Arcturus (α Boo) was observed with the Birmingham double magneto-optical filter spectrometer using the GHRIL facility at the Nasmyth focus of the 4.2 m William Herschel Telescope of the Observatorio del Roque de los Muchachos in 1988 April - May. Approximately 80 hours of data were obtained over a 2 week interval. The authors' preliminary analysis of the data shows the presence of the large (≡200 m s-1) amplitude velocity variation reported earlier by other observers. However, this more extensive data set strongly suggests that this variation is not singly periodic, as was previously indicated. The authors present some speculative comments as to the nature of this variation, and the implications for stellar seismology. Title: Linewidth of low degree acoustic modes of the Sun. Authors: Elsworth, Y. P.; Isaak, G. R.; Jefferies, S. M.; McLeod, C. P.; New, R.; Palle, Pere L.; Regulo, C.; Roca Cortés, Teodoro Bibcode: 1988ESASP.286...27E Altcode: 1988ssls.rept...27E Estimates of the spectral linewidths of low degree (l = 0 and l = 1), "5 minute" p-modes obtained from Doppler shift observations in 1984, 1986 and 1987 are reported. The observed linewidths increase from 0.5 μHz at 2000 μHz to 3.8 μHz at 4300 μHz for l = 0. Comparison with other data suggest that for a given frequency the linewidth increases with increasing l value. On the assumption that the linewidth is substantially due to damping processes the linewidths are consistent with e-folding times between 3.7 and 0.5 days. Title: High precision velocity measurements of Procyon using the 7966 Å line of potassium. Authors: Innis, J. L.; Isaak, G. R. Bibcode: 1988ESASP.286..583I Altcode: 1988ssls.rept..583I The Star Procyon (α CMi) was observed for 2 weeks using the Brimingham double magneto-optical filter spectrometer on the 1.9 m reflector of the South African Astronomical Observatory in 1988 January. Analysis of these velocity data shows that the noise level (per frequency channel of ≡1 μHz) in the power spectrum of the combined nightly runs is approximately 12 m2s-2. These data were searched for the presence of small scale oscillations, but none were obviously present. On one night the surface integrated magnetic field of Procyon was measured using a rotating quarter wave plate to select alternatively opposite senses of circularly polarised light. Preliminary analysis indicates that |B| is 1.3±4.0 Gauss (standard error), consistent with a non detection at the few Gauss level. Title: Effect of atmospheric extinction on solar radial velocity measurements. Authors: Belmonte, Juan A.; Elsworth, Y. P.; Isaak, G. R.; New, R.; Palle, Pere L.; Roca Cortés, Teodoro Bibcode: 1988ESASP.286..177B Altcode: 1988ssls.rept..177B Differential extinction across the Earth's atmosphere affects astronomical photometry in a well known way. Under the same circumstances when a rotating extended object is observed spectrometrically, a residual radial velocity is obtained which varies during the day. In the case of integral sunlight observations, this effect has been calculated along the day in all possible observing situations during the year. Applications to real observations are shown and discussed leading to some conclusions specially relevant to ground-based networks. Title: Stellar seismology at Birmingham. Authors: Isaak, G. R.; Innis, J. L. Bibcode: 1988MNSSA..47...34I Altcode: No abstract at ADS Title: A Spectroscopic Search for Oscillations in the 769.9-NM Potassium Line of Procyon Authors: Isaak, G. R.; Jones, A. R. Bibcode: 1988IAUS..123..255I Altcode: A double magneto optical filter attached to the Cassegrain focus of the 1.9 m reflector of the South African Astronomical Observatory was used to observe Procyon in the 769.9 nm line of potassium during all clear hours of six nights. Velocity calibration was provided by the rotational and orbital velocity changes of the observer as well as by a continuous magnetic modulation. Title: Solar Cycle Dependence of Solar P-Modes Authors: Isaak, G. R.; Jefferies, S. M.; McLeod, C. P.; New, R.; van der Raay, H. B.; Palle, P. L.; Regulo, C.; Roca-Cortes, T. Bibcode: 1988IAUS..123..201I Altcode: Data obtained at Izaña (Tenerife) and Haleakala (Maui), using optical resonant scattering with a potassium vapour cell over the years 1980 - 84, are used to determine the frequencies of the low l p modes. Possible variation in these frequencies with the solar cycle are investigated. Title: Variations in the Mean Line-Of Velocity of the Sun - 1976-1985 Authors: Jimenez, A.; Palle, P. L.; Regulo, C.; Roca-Cortes, T.; Elsworth, Y. P.; Isaak, G. R.; Jefferies, S. M.; McLeod, C. P.; New, R.; van der Raay, H. B. Bibcode: 1988IAUS..123..215J Altcode: Measurements of the line of sight velocity of the sun with respect to earth have been obtained at Izaña (Tenerife) during the years 1976 to 1985. The mean values found for each year show a trend of ≡30 m/s from minimum to maximum. Their mean value is of 583.1±0.2 m/s which is 92% of the gravitational redshift predicted by theory and their variation seems to be related to the solar cycle with the clear exception of 1985. Title: Experience in Operating a Limited Global Network of Stations Measuring Full-Disc Oscillations of the Sun Authors: Elsworth, Y. P.; Isaak, G. R.; Jefferies, S. M.; McLeod, C. P.; New, R.; van der Raay, H. B.; Palle, P. L.; Regulo, C.; Roca-Cortes, T. Bibcode: 1988IAUS..123..535E Altcode: Details are given about the operation of a two station network and of a new semi-automatic station which has recently been added. Comparison is made with predicted duty cycles. A possible way of quantifying the sky quality is also given. Title: Comparison of Solar Oscillation Data Obtained from a Study of the NA and K Fraunhoffer Absorption Lines Authors: Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Palle, P. L.; Roca-Cortes, T. Bibcode: 1988IAUS..123...53I Altcode: 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. Title: The Solar Oscillations Spectrum and the Solar Cycle Authors: Jimenez, A.; Palle, P. L.; Perez, J. C.; Regulo, C.; Roca-Cortes, T.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B. Bibcode: 1988IAUS..123..205J Altcode: During the summer seasons of the years 1977 to 1985 daily velocity measurements of solar global oscillations have been obtained using a resonant scattering spectrometer. After calculating the power spectra of the daily residuals, the mean for each season is found. Several discrete frequency intervals are defined in the spectrum. The mean power in these intervals and the cut-off frequency of the p-mode spectrum, determined for each year, are correlated with the solar activity cycle. Furthermore, several series of 13 contiguous days for each year are analyzed. Title: The 13-DAY Period Oscillation and the Solar Cycle Authors: Jimenez, A.; Palle, P. L.; Regulo, C.; Roca-Cortes, T.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B. Bibcode: 1988IAUS..123..211J Altcode: From the analysis of radial velocity measurements of the Sun, obtained at Izaña from 1976 to 1985, stable periods longer than 1 day, have been found in the observed signal. The appearance of an oscillation with a 13 day period has been confirmed. The comparison, for 1981 - 84, of the observations with a calibrated numerical model of the passage of inhomogeneities (spots and plages) on the solar surface, shows that the signal is not only due to this effect. It is believed that a velocity field, probably related to the surface inhomogeneities, contributes to the observed signal. Title: Continuous Magnetic Calibration of Velocity Sensitivity of Oscillation Spectrometers Authors: Isaak, G. R.; Jones, A. R. Bibcode: 1988IAUS..123..467I Altcode: Modulation of the magnetic field in optical resonance spectrometers in order to calibrate the slope of the observable intensity ratios in terms of differential velocities is described. Title: Search for solar g modes. Authors: Palle, P. L.; Roca Cortes, T.; Isaak, G. R.; van der Raay, H. B. Bibcode: 1987PAICz..66..177P Altcode: 1987eram....1..177P Using a resonant scattering spectrophotometer the authors measured the radial velocity of the Sun at the K I 769.9 nm line with very high resolution and temporal stability. The observations carried out at Izaña (Tenerife) continuously for the last three years, have been used to search for solar g modes. Individual peaks, well above noise level, are identified and their frequencies are likely to correspond with g modes. Title: The Limb Shift Effect and its Variation with the Solar Cycle Authors: Anguera, M.; Pallé, P. L.; Régulo, C.; Roca Cortés, T.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B. Bibcode: 1987rfsm.conf...24A Altcode: The radial velocity limb shift effect has been measured for the K I 7699 Å line using a resonant scattering spectrophotometer in the summer of 1982. On the other hand, using integral sunlight, the line of sight velocity has been measured during the years 1976 to 1986 and the gravitational redshift determined. This value shows a variation over those years and, when compared with the phase of the solar activity cycle, the most probable interpretation is a change of the limb shift effect with the cycle. Title: The global oscillation spectrum of the sun. I - Analysis of daily power spectra of velocity measurements Authors: Palle, P. L.; Perez, J. C.; Regulo, C.; Roca Cortes, T.; Isaak, G. R. Bibcode: 1986A&A...169..313P Altcode: Daily observations of solar global oscillations using a resonant scattering spectrometer have been obtained by observing integral sunlight during the summer seasons of the years 1977 to 1984. The power spectra of the daily residuals are calculated and the mean for each observing season is found. Several discrete frequency intervals are defined in the spectrum which yield information on the characteristics of the p-mode and noise levels. The power in these intervals and the cut-off frequency of the p-mode spectrum determined for each year, show no correlation with the solar activity cycle. Title: Linewidth and rotational splitting of low degree modes in the 5 minute region. Authors: Isaak, G. R. Bibcode: 1986ASIC..169..223I Altcode: 1986ssds.proc..223I The linewidth of low degree modes in the 5 minute region of the Sun's acoustic spectrum increases dramatically with frequency over the range of 2 mHz to some 5 mHz, in approximate agreement with theory. Below some 2.5 mHz the linewidth is narrow enough to allow rotational splitting of l = 1 modes to be measured. These measurements seem to confirm earlier results. Title: The radial velocity of the sun as a star and the solar cycle Authors: Jiménez, A.; Pallé, P. L.; Régulo, C.; Roca Cortés, T.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B. Bibcode: 1986AdSpR...6h..89J Altcode: 1986AdSpR...6...89J Radial velocity measurements of the sun as a star using a resonant scattering spectrometer have been obtained at Izan~a (Tenerife) during long observing seasons from 1976 to 1985. Its analysis shows that except for the global oscillations with periods shorter than one day there are stable signals with longer periods: at ~13 days with mean amplitude of ~ 3 m/s (it changes with the solar cycle) and another one of ~ 15 m/s amplitude which shows a temporal variation of various years related to the solar cycle. The first signal has a partial explanation as an effect produced by the passage of active regions through the visible surface of the sun but it does not completely explain the observed signal. The second one, related to the limb shift, is probably due to changes in the convection zone in connection with the solar cycle. Title: Global Oscillations of the Sun Authors: Isaak, G. R. Bibcode: 1985PhyBl..41..176I Altcode: 1985PhB....41..176I No abstract at ADS Title: Solar G modes Authors: Isaak, G. R.; van der Raay, H. B.; Palle, P. L.; Roca Cortes, T.; Delache, P. Bibcode: 1984MmSAI..55...91I Altcode: A statistical analysis of the frequency spectrum of 85 days of data obtained from integral solar velocity signals, has shown that significant signals exist in the frequency range 25 - 150 μHz. The signal structure is shown to have characteristics of constant period spacings indicative of the existence of g modes in the solar oscillation spectrum. Utilising the asymptotic Tassoul relation a total of 58 lines are identified covering the l1, l2, l3 and l4 modes. Title: Further experimental evidence of the 13 day solar periodicity Authors: Isaak, G. R.; van der Raay, H. B.; Palle, P. L.; Roca Cortes, T. Bibcode: 1984MmSAI..55..353I Altcode: Extensive solar data obtained over the period May to August 1982 are analyzed to show the continued existence, over a six-year period, of a 13-day velocity signal of 6 m/s amplitude. Mean daily velocity signals are shown with a superimposed best-fit sine wave, and the power spectrum obtained from that fit is presented. Data comparing measured and calculated relative phases for the 13.035 day period are given. The constancy of the signal's amplitude and its long coherence time may be partly explained by velocity signals induced by active region rotation, but some fundamental cause, possibly related to the rapid rotation of the solar core, is strongly suggested. Title: Observations of global solar oscillations: past, present, future (invited paper) Authors: Isaak, G. R. Bibcode: 1984MmSAI..55...45I Altcode: No abstract at ADS Title: Continuous observation of solar oscillations from two suitably spaced ground stations Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P.; van der Rasy, H. B.; Palle, P. L.; Roca Cortes, T. Bibcode: 1984MmSAI..55...63C Altcode: By operating two observing stations, one at Izana on Tenerife and the other at Haleakala on Maui, up to 22 hours of continuous solar surface velocity data per day are obtained. Correlation of two station data provides confirmation of the solar origin of the signals and the improved window function and long time span of data collection yield clear power spectra of the 5 minute oscillations. Detailed analysis of a prominent l1 mode indicates that coherence exists over the 88 days of observation. Title: Solar oscillations and the effect of a comet impact Authors: Isaak, G. R.; van der Raay, H. B.; Palle, P. L.; Roca Cortes, T. Bibcode: 1984MmSAI..55..263I Altcode: If such external influences as the impact of a comet on the solar surface could destroy or mask the coherence of observed solar oscillations, the scope and effectiveness of extended study in this field would be considerably limited. It is therefore important to investigate any possible effects due to the recently reported comet impacts on the sun. Three such events were recorded by Sheely et al. (1982), and the last of these, on 8.0 UT July 20, 1981, occurred while full disk optical resonant scattering determinations of the solar velocity spectrum were being made. It is found that its effect on the 5-min oscillations is not noticeable,and that it is therefore meaningful to study solar oscillation data in order to resolve the question as to the internal rotation of the sun. Title: Laboratory Work on Noise and Stability of Detectors and Calibration Lamps Authors: Isaak, G. R. Bibcode: 1984srps.conf..133I Altcode: No abstract at ADS Title: A New Method for Determining the Helium Abundance in the Solar Atmosphere Authors: Isaak, G. R. Bibcode: 1983SoPh...82..205I Altcode: 1983IAUCo..66..205I Recent observations of a cut-off frequency in the acoustic modes of the Sun (Claverie et al., 1981b) should help determine the mean molecular weight and, thereby, the helium abundance in the visible layers of the solar atmosphere. A first preliminary result of Y = 0.42 ± 0.04 is obtained for an assumed minimum photospheric temperature of 4400 K ± 200 K. Title: Rotational splitting of solar five-minute oscillations of low degree Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Roca Cortes, T. Bibcode: 1983SoPh...82..233C Altcode: 1983IAUCo..66..233C An analysis of 28 contiguous days of whole disk observations of the solar surface by means of optical resonant scattering in the K 769.9 nm line, taken at the Teide Observatory at Izana during July-August 1980, have thus far yielded two significant facts. Firstly when the results of an iterative sine-wave fitting procedure are considered in the period range 2-3 h, although the expected daily harmonics corresponding to 1/8, 1/10, 1/11, and 1/12 of a day are clearly seen the l/9th contribution is significantly absent. It is suggested that this results from an interference between a signal of 160 min (1/9th of a day) with the daily harmonic. It is further pointed out that the observatories at which the 160 min oscillation has been seen, Crimea, Pic du Midi, and Stanford are all separated by integral numbers of 160 min, and thus the phase of the 160 min oscillation relative to the daily observation window is constant. However, the Teide Observatory is situated at a half integral number of 160 min periods relative to the others. Thus when constructive interference exist at the first three sites destructive interference will exist at the latter. It is thus concluded that the non-existence of a peak corresponding to the 1/9th harmonic of a day in the sine-wave fit data is strong indirect evidence for the existence of the 160 min signal. Title: Is there an oblique magnetic rotator inside the Sun? Authors: Isaak, G. R. Bibcode: 1983SoPh...82..235I Altcode: 1983IAUCo..66..235I The size of the rotational splitting recently observed (Claverie et al., 1981) is correlated with the 12.2d variation in the measurements of solar oblateness observed by Dicke (1976) and implies a convection zone of depth of 0.1 R⊙. The near equality of amplitudes of global velocity oscillations (Claverie et al., 1981) of the various m components of the l = 1 and l = 2 modes as seen from the Earth viewing the Sun nearly along the equator is unexpected for pure rotational splitting. It is suggested that a magnetic perturbation is present and an oblique asymmetric magnetic rotator with magnetic fields of a few million gauss is responsible. A more detailed account was submitted to Nature. Title: Solar core rotation Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Palle, P. L.; Roca Cortes, T. Bibcode: 1982Natur.299..704C Altcode: Data from solar line of sight velocity measurements are presented to demonstrate the existence of a synodic signal with a 6.5 m/sec amplitude. Recordings of alternate measurements of the resonantly scattered light intensity were made at 1 sec intervals and a mean ratio for the laboratory and solar lines was calculated over a 42 sec interval, yielding 900 points each day of observation. An oscillation which was in phase at both observation points was found. A peak was found at 0.88 micro-Hz, with a 13.15 day period. The 6.6 m/sec velocity amplitude of the peak was calculated to indicate a mean surface displacement of 1,000,000 m. The magnitude of the Doppler shift is taken as evidence that a core moving at a greater speed than the surface of the sun is responsible for the observed signal. It is further suggested that the core is moving twice as fast as the surface. Title: Abundances of Elements of Cosmological Interest: Discussion Authors: Isaak, G. R. Bibcode: 1982RSPTA.307...35I Altcode: No abstract at ADS Title: Is the Sun an oblique magnetic rotator? Authors: Isaak, G. R. Bibcode: 1982Natur.296..130I Altcode: No abstract at ADS Title: A two-dimensional solar spectrometer. Authors: Brookes, J. R.; Isaak, G. R.; van der Raay, H. B. Bibcode: 1981SoPh...74..503B Altcode: A precise two-dimensional positioning device has been developed for use in conjunction with a resonant scattering spectrometer to study the spatial distribution of solar velocity fields. The principle of operation and constructional details are discussed and the experimental performance is evaluated. As an illustration of its use preliminary data obtained from a meridional scan are presented. Title: Short-Period Intensity Fluctuations of Integral Sunlight Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P. Bibcode: 1981SoPh...74...73C Altcode: An attempt has been made to detect short-period solar luminosity fluctuations in the vicinity of 5 min, analogous to the observed velocity oscillation. Using silicon photodiodes to monitor integral sunlight, an upper limit for the amplitude of the intensity fluctuations of 3 x 10-5 rms was found. Title: Solar oscillations: Past, present, and future Authors: Isaak, G. R. Bibcode: 1981SoPh...74...43I Altcode: Observation of global oscillations of the Sun constitutes a primitive seismology of the solar interior. The frequencies, if correctly identified with definite normal modes of vibration, provide a measure of the average velocity of sound in the interior and thereby of its composition and temperature. Fine structure in the frequencies of nonradial modes may provide information on their character (multiplicity) and on the rotation of the solar interior. Study of the amplitudes and phase fluctuations of the vibrations may clarify the excitation and damping of the vibrations. Title: Structure of the 5-minute solar oscillations 1976 1980 Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Roca Cortes, T. Bibcode: 1981SoPh...74...51C Altcode: The discrete structure in the 5 min velocity oscillations of the solar surface has been confirmed by a re-analysis of data obtained between 1976 and 1979, and in addition a preliminary analysis of 1980 data show excellent consistency of the determined frequencies over the five year period. It is further shown that atmospheric transparency, as measured by the power in the solar intensity fluctuations, shows no correlation with the measured amplitude of the velocity fluctuations, over 2 orders of magnitude. Title: A two dimensional solar spectrometer Authors: Brookes, J. R.; Isaak, G. R.; van der Raay, H. B. Bibcode: 1981JPhE...14.1288B Altcode: A precise two-dimensional positioning device has been developed for use in conjunction with a resonant scattering spectrometer to study the spatial distribution of solar oscillations. The principle of operation and constructional details are discussed and the experimental performance is evaluated by analyzing the results obtained from sequentially scanning four quadrants of the solar disc. Title: Rapid rotation of the solar interior Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Roca Cortes, T. Bibcode: 1981Natur.293..443C Altcode: Evidence for the rapid internal rotation of the sun obtained from Doppler shift measurements of the Fraunhofer absorption lines is reported. An improved version of the Doppler shift optical resonance spectrometer was used to record the resonantly scattered intensities corresponding to the two wings of the 769.9-nm Fraunhofer absorption lines of neutral potassium on 28 continuous days in July and August 1980. A total of 33 lines was identified which were found to be split into components corresponding to the l = 1, l = 2 and l = 0 modes of the spherical harmonic. Superposed frequency spectra for each mode exhibit a width indicative of high-Q oscillations, with a mean value of 0.75 microHz. Comparison of this value with that anticipated for the case of uniform rotation (0.4 microHz) reveals that the core of the sun rotates two to nine times as rapidly as the surface. Title: Global Oscillations of the Sun Authors: Isaak, G. R. Bibcode: 1981IrAJ...15..119I Altcode: No abstract at ADS Title: Structure in the 5 minute oscillations of integral sunlight Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Roca Cortes, T. Bibcode: 1980A&A....91L...9C Altcode: The discovery of structure in the 5 minute oscillations of the sun, integrated over the full disk, was reported by Claverie et al. (1979). This paper presents additional information on the discrete structure in the 5-minute velocity oscillation observed in integral sunlight. Measurements taken at Pic-du-Midi and Izana (on Tenerife) from 1976 to 1979 show good consistency, and some 25 discrete frequencies (established to an accuracy of about 1:1000) are tabulated. Title: Solar oscillations, stellar oscillations and cosmology Authors: Isaak, G. R. Bibcode: 1980Natur.283..644I Altcode: Two implications of the recent observations1 of low angular, high radial overtones of the whole Sun are reported here. The first implication is that other main sequence stars are likely to be oscillating in similar modes and that precision spectroscopy as well as photometry from space is capable of detecting these oscillations, thereby extending seismology to stars. The second implication is a solar helium abundance Y≲0.17 with implications for cosmological models. Title: The Latest Results of the Velocity Spectroscopy of the Sun Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Roca-Cortes, T. Bibcode: 1980LNP...125..181C Altcode: 1980nnsp.work..181C No abstract at ADS Title: Solar structure from global studies of the 5-minute oscillation Authors: Claverie, A.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Roca Cortes, T. Bibcode: 1979Natur.282..591C Altcode: An overall view of the solar surface is presented with emphasis on the study of low 1 value oscillations. Line of sight velocity measurements of the whole solar disk were made using optical resonance spectroscopy. Constancy of the peak of spectral emission is demonstrated in two ways; first, the observed peaks in the power spectra are numbered sequentially and plotted against the observed frequency of the order of the peaks. Secondly, the mean power spectra data are screened by a high pass filter by subtracting a moving mean over three points and then subjecting the resulting points to an autocorrelation. Title: A resonant-scattering solar spectrometer Authors: Brookes, J. R.; Isaak, G. R.; van der Raay, H. B. Bibcode: 1978MNRAS.185....1B Altcode: Summary. The resonant-scattering spectrometer, developed in Birmingham and used to study the radial velocity of the solar surface, is described as it was during 1976. Possible instrumental sources of error are analysed and evaluated. It is shown that angular changes in the light path through the electro-optic modulator can give rise to an oscillatory error of up to 1 rn/s, and that no other instrumental effects give rise to errors of this order. Title: The observation of a rotating body using high-resolution spectroscopy Authors: Brookes, J. R.; Isaak, G. R.; van der Raay, H. B. Bibcode: 1978MNRAS.185...19B Altcode: Summary - If a high-resolution specotroscopic instrument is used to observe a rotating body in the light from a narrow spectral line, significant factors affect the apparent field of view when both the line width and the instrumental resolution, expressed as their equivalent Doppler velocities, are less than, or comparable to, the surface velocity of the observed body. The particular case of the Sun observed with the Birmingham resonant scattering spectrometer is considered, and the effect on the apparent velocity oscillations produced by supergranulation is discussed. Title: The search for solar oscillations, 1974 to 1976. Authors: Brookes, J. R.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. B.; Roca Cortes, T. Bibcode: 1978MNRAS.184..759B Altcode: Using a resonant scattering spectrometer, observations of integral solar light have been recorded and analyzed to determine the existence of solar oscillations. Although the data from individual days do confirm the existence of long-period oscillations, these do not seem to be consistent in either period, amplitude or phase. Possible interpretation and further experimental verifications are considered. Title: Does the Sun ring? Authors: Isaak, G. R. Bibcode: 1978PhB....29..127I Altcode: An investigation of solar oscillations is proposed, whereby small velocity perturbations of the surface layers are studied in order to measure sound waves (or phonons) in the solar atmosphere. Such observations would also provide information on the solar interior. Excitation mechanisms include shocks from the core due to uneven or explosive nuclear burning, and flares from the surface with energies on the order of 10 to the 23rd J for a photospheric velocity amplitude of 1 m/sec. Fraunhofer absorption lines are used as indicators of Doppler shifts to evaluate velocity noise. Attention is given to detailed observations of solar cells, where oscillation is more pronounced than on the sun as a whole. It is pointed out that oscillations occurring on the sun probably occur on most, if not all, other stars. Title: Solar Oscillations Authors: Brookes, J. R.; Isaak, G. R.; McLeod, C. P.; van der Raay, H. R.; Roca Cortes, T. Bibcode: 1978pfsl.conf..115B Altcode: 1978ESPM....2..115B No abstract at ADS Title: Oscillations of the Sun Authors: Isaak, G. R. Bibcode: 1976Obs....96..221I Altcode: No abstract at ADS Title: Talk on Solar Oscillations Authors: Isaak, G. R. Bibcode: 1976Obs....96..132I Altcode: No abstract at ADS Title: Observation of free oscillations of the Sun Authors: Brookes, J. R.; Isaak, G. R.; van der Raay, H. B. Bibcode: 1976Natur.259...92B Altcode: The Fraunhofer absorption lines for potassium and sodium on the Sun are compared with the corresponding lines in the laboratory using a resonant optical scattering method. The observed shifts between the Sun and laboratory lines may be interpreted in terms of the gravitational redshift (GRS), motion of the laboratory relative to the Sun and oscillatory terms which may be related to oscillations of the Sun. Title: Improved Limit on the Absence of Dispersion of the Velocity of Light Authors: Isaak, G. R. Bibcode: 1969Natur.223..161I Altcode: LABORATORY measurements have duly verified that the velocity of light is independent of the velocity of the source to an accuracy of 1.3 in 104 for γ-rays from π0 meson decay at 6 GeV (ref. 1) and is also isotropic to better than 6 in 108 (ref. 2), 2 in 108 (ref. 3) and 2 in 1010 (ref. 4) in a frame of reference attached to the Earth. The best evidence that the velocity of light is independent of frequency probably depends on astronomical observations of Cepheids in the nearest galaxies, and makes it possible to set a limit of 1 in 108 on dispersion. Somewhat poorer limits over a much wider range of frequencies, from the visible to the radio-frequency region, have been provided by observations of flare stars5. Title: An Atomic Beam Spectrophotometer Authors: Isaak, G. R. Bibcode: 1961Natur.189..373I Altcode: No abstract at ADS Title: An Atomic Beam Spectrophotometer Authors: Isaak, G. R. Bibcode: 1961Natur.189.4373I Altcode: No abstract at ADS