| Issue |
A&A
Volume 424, Number 2, September III 2004
|
|
|---|---|---|
| Page(s) | 713 - 717 | |
| Section | The Sun | |
| DOI | https://doi.org/10.1051/0004-6361:20040501 | |
| Published online | 23 August 2004 | |
Research Note
On comparing estimates of low-
solar p-mode frequencies
from Sun-as-a-star and resolved observations
1
School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK e-mail: wjc@bison.ph.bham.ac.uk
2
ESA Research and Science Support Department, ESTEC, 2200 AG Noordwijk, The Netherlands
3
School of Science & Mathematics, Sheffield Hallam University, Sheffield S1 1WB, UK
Received:
23
March
2004
Accepted:
5
July
2004
Low-angular-degree (low-l) solar p modes
provide a sensitive probe of the radiative interior and core of
the Sun. Estimates of their centroid frequencies can be used to
constrain the spherically symmetric structure of these deep-lying
layers. The required data can be extracted from two types of
observation: one where the modes are detected in integrated
sunlight, i.e., a Sun-as-a-star view; and a second where the
visible disc is imaged onto many pixels, and the collected images
then decomposed into their constituent spherical harmonics. While
the imaging strategy provides access to all of the individual
components of a multiplet, the Sun-as-a-star technique is
sensitive to only about two thirds of these (average over
to 3) with those modes that are detected having different
levels of visibility. Because the various components can have
contrasting spatial structure over the solar surface, they can
respond very differently to changes in activity along the solar
cycle. Since the Sun-as-a-star and resolved analyses take as input
a different “subset” of modes, the extracted frequency estimates
are expected to differ depending upon the phase of the
cycle. Differences also arise from the types of models used to fit
the modes. Here, we present expressions that allow the sizes of
these differences to be predicted.
Key words: methods: data analysis / Sun: helioseismology
© ESO, 2004
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