SOLAR g-MODE OSCILLATIONS: EXPERIMENTAL DETECTION EFFORTS AND THEORETICAL ESTIMATES

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Abstract
In the early days of helioseismology, around 1975, independent detections of an oscillation with a period of 160 min in solar spectral line-shift data caused very substantial interest: it was suggested that this resulted from a solar g mode, whose frequency would then provide a tight constraint on the structure of the solar core. Also, it was noted that such modes, which involve a substantial fraction of the solar mass, might lead to a detectable gravitational-wave signal. Later observations have, however, failed to confirm the solar nature of the originally detected oscillation. Extensive data on the low-frequency part of the solar oscillation spectrum have been obtained from several experiments over the last decade, including instruments on the SOHO spacecraft. These have provided stringent limits on amplitudes of solar g modes and a few tentative detections, although so far not independently confirmed. Theoretical estimates of g-mode amplitudes, while highly uncertain, suggest that direct detection of the modes on the solar surface may be difficult. However, detection with the ASTROD mission may be possible, although identification of the solar signal will require careful analysis.

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