Using a ground-based photometric telescope for observing global modes of solar oscillation

摘要

A new technique for ground based photometric helioseismology has been implemented. The technique is able to detect low amplitude oscillations in the solar irradiance by making simultaneous measurements at continuum wavelengths of 0.507 μm, 0.747 μm, and 1.600 μm. Data is collected from a rectangular region covering approximately 57% of the solar disk, extending ±0.30 R(⊙) about the solar rotational axis, and ±0.38 R(⊙) about the solar equator, using square pixels varying in linear size from 0.032 R(⊙) to 0.053 R(⊙). A differential spatial filter is applied, taking advantage of cancellations of undesired variations and forming a signal which is sensitive to most modes with spherical harmonic index l ≤ 7. Linear combinations are made of the three solar signals and the telescope internal Temperature signal, mitigating the deleterious effects of the terrestrial atmosphere and of local temperature variations. Frequencies of local maxima in the Power Spectrum of the residual signal, in the 400 μHz to 850 μHz range, are found to be consistent with those determined by solar limb profile measurements made in 1979. The measured coincidence levels indicate that the probability that the 1979 and 1999 data sets are random with respect to one another is approximately 5 x 10⁻⁹. Frequency shifts between the 1979 data and the 1999 data, possibly related to the solar activity cycle, are found: δν(n=1;l=4,...,7) = -0.16 ± 0.01 μHz, δν(n=2;l=3,...,7) = -0.04 ± 0.01 μHz, and δν(n=3;l=2,...,4) = -0.11 ± 0.01 μHz.