The exponential nature of the energy distribution of each mode has been used to compute their mean correlation coefficient with a consistent error bar.
Two tests based on Montecarlo simulations, and one analytical formulae, applied to 310 days of GOLF data, support the null hypothesis of no mean correlation among the modes , , with an accuracy of .
Our analysis of the modes correlation in IPHIR data, using these statistical tools, gives an accurate statistical support to the tentative conclusions of Baudin et al. (1996). The variance test rejects the null hypothesis with a confidence level.
The presence of a clear correlation among p-mode energies in IPHIR data strongly constrains the standard picture of stochastic excitation. If really of solar origin, it suggests the existence of an additional source of excitation, other than the granules. We have built a one parameter model of random excitations separated by a time comparable to the damping time of the modes, added to the usual granule excitations. IPHIR data are fully compatible with this " -hypothesis", if a fraction of each mode energy is due to this additionnal source of excitation, resulting in a mean correlation among the modes.
On the other hand, the absence of correlation in GOLF data support the standard picture of stochastic excitation by the granules only.
This difference between IPHIR and GOLF data can be interpreted as a change from in IPHIR data to less than in GOLF data.
This evolution could be related to the change in magnetic activity, since the GOLF data correspond to a period close to the solar minimum while the IPHIR data correspond to a period closer to the solar maximum. If this is true, a confirmation will be obtained by performing this same analysis on GOLF data when we approach the solar maximum, in a couple of years. VIRGO data will also be useful in order to identify the possible role of the measurement techniques (velocity/intensity) in the determination of the correlation.
However, the mechanism by which the magnetic field influences the excitation of the modes, i.e. the nature of these hypothetical exciting events remains to be explored in more detail.
© European Southern Observatory (ESO) 1998
Online publication: January 8, 1998