This dissertation deals with normal-mode vibrations of the Sun, as measured by their effect on the solar total irradiance. I have studied "5-minute" p-mode oscillations of radial order n (TURNEQ) 16 - 26 and degree l = 0 - 2 in the 1980 data from the Active Cavity Radiometer Irradiance Monitor (ACRIM) on the Solar Maximum Mission satellite (SMM). The frequencies of separate (n,l) peaks in the spectrum of ACRIM data agree with those of previous observers to within ('(TURN))3 parts in 10('4). For the oscillatory peaks of highest signal quality the frequency error is estimated to be less than one part in 10('4). Discrepancies between observed and theoretical frequencies are already much greater than discrepancies among observed frequencies. Quasi -degenerate m states, of which the (n,l) peaks are in principle comprised, cannot be distinguished in the ACRIM power spectrum, contrary to previous claims. The mean amplitudes of individual (n,l) peaks have been established with 10 - 20% accuracy; r.m.s. fractional irradiance variations of up to 3 parts per million occur. The observed amplitude ratio of 5-min modes in velocity and intensity agrees roughly with preliminary theoretical estimates, but more theory and observation are required. The 5-min oscillation data from the ACRIM have been interpreted in terms of a theoretically motivated picture in which the modes behave like independently and randomly excited harmonic oscillators. The relative frequency width of the most prominent l = 0 modes is about one part in 2000, implying an oscillator time constant (e-folding time for energy decay) of 1 to 2 days. This lifetime is approximately confirmed by direct observations of amplitude variations in these modes. The lifetime of these modes was previously a matter of controversy. Solar rotation will split the m states belonging to a given (n,l) multiplet, making the l > 1 peaks broader than they would otherwise be. From the widths of the l = 1 peaks I deduce an upper limit on the separation of adjacent m states of 1.0 (mu)Hz with ('(TURN))99% confidence. This is 2.2 times the splitting that solid-body rotation at the observed ('(TURN))1/25-day sidereal equatorial surface rate would imply. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI.
- Pub Date:
- Physics: Astronomy and Astrophysics