EDP Sciences
Free access
Volume 463, Number 3, March I 2007
Page(s) 1181 - 1187
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20066419

A&A 463, 1181-1187 (2007)
DOI: 10.1051/0004-6361:20066419

Sun-as-a-star observations: evidence for degree dependence of changes in damping of low- $\mathsf{\ell}$ p modes along the solar cycle

D. Salabert1, 2, W. J. Chaplin3, Y. Elsworth3, R. New4, and G. A. Verner3

1  National Solar Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
    e-mail: dsalabert@nso.edu
2  High Altitude Observatory, National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307-3000, USA
3  School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
4  Faculty of Arts, Computing, Engineering and Sciences, Sheffield Hallam University, Sheffield S1 1WB, UK

(Received 19 September 2006 / Accepted 4 December 2006)

Aims.We use 9.5-yr of BiSON Sun-as-a-star data to search for dependence of solar-cycle parameter changes on the angular degree, $\ell$, of the data. The nature of the Sun-as-a-star observations is such that for changes measured at fixed frequency, or for changes averaged across the same range in frequency, any $\ell$ dependence present carries information on the latitudinal distribution of the agent (i.e., the activity) responsible for those changes.
Methods.We split the 9.5-yr timeseries into contiguous 108-d pieces, and determine mean changes in the damping of, power in, and energy supplied to the modes through the solar cycle. We also apply a careful correction to account for the deleterious effects of the ground-based BiSON window function on the results.
Results.From our full analysis we obtain a marginally significant result for the damping parameter, where the mean change is found to be weakest at $\ell=0$. The other parameters show hints of some dependence in $\ell$.
Conclusions.Our main conclusion is that the mean fractional solar-cycle change in the $\ell=0$ damping rates is approximately 50% smaller than was previously assumed. It had been common practice to use an average over all low-$\ell$ modes; our downward revision of the radial-mode value has implications for comparisons with models of the global solar cycle changes, which are usually based on a spherically symmetric geometry.

Key words: methods: data analysis -- Sun: helioseismology -- Sun: activity

© ESO 2007

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