Issue |
A&A
Volume 463, Number 3, March I 2007
|
|
---|---|---|
Page(s) | 1181 - 1187 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20066419 | |
Published online | 19 December 2006 |
Sun-as-a-star observations: evidence for degree dependence of changes in
damping of low-
p modes along the solar cycle
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,
, 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
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 . The other parameters
show hints of some dependence in
.
Conclusions.Our main conclusion is that the mean fractional solar-cycle change in the damping rates is approximately 50% smaller than was previously assumed. It had
been common practice to use an average over all low-
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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