Measurements of Frequencies of Solar Oscillations from the Mdi Medium-l Program

Inversions of solar internal structure employ both the frequencies and the associated uncertainties of the solar oscillation modes as input parameters. In this paper we investigate how systematic errors in these input parameters may affect the resulting inferences of the sun's internal structure. Such systematic errors are likely to arise from inaccuracies in the theoretical models which are used to represent the spectral lines in the observational power spectra, from line blending, from asymmetries in the profiles of these lines, and from other factors. In order to study such systematic effects we have employed two different duration observing runs (one of 60 days and the second of 144 days) obtained with the Medium-l Program of the Michelson Doppler Imager experiment onboard the SOHO spacecraft. This observing program provides continuous observations of solar oscillation modes having angular degrees, l, ranging from 0 to ∼ 300. For this study intermediate- and high-degree p-mode oscillations having degrees less than 251 were employed.