EDP Sciences
Free access
Volume 424, Number 1, September II 2004
Page(s) 301 - 309
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20040372

A&A 424, 301-309 (2004)
DOI: 10.1051/0004-6361:20040372

Impact of observational duty cycle on the measurement of low- $\mathsf{\ell}$ solar p-mode frequencies

W. J. Chaplin1, Y. Elsworth1, G. R. Isaak1, B. A. Miller1, R. New2 and D. Salabert1

1  School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
    e-mail: salabert@bison.ph.bham.ac.uk
2  School of Science and Mathematics, Sheffield Hallam University, Sheffield S1 1WB, UK

(Received 2 March 2004 / Accepted 21 May 2004 )

We investigate the impact of a multi-site, ground-based observational window function on the extraction of estimates of the frequencies of low-angular-degree (low- $\ell$) solar p modes from decade-long datasets. To effect this study we have made use of some $\approx$ $10~\rm yr$ of full-disc, "Sun-as-a-star" Doppler velocity data collected by the Birmingham-Solar Oscillations Network (BiSON). A coherent combination of observations made by all six BiSON sites provided the principal time series of data. This set was then modulated by a whole series of different window functions and the resulting sets analyzed. The windows were made from different combinations and numbers of BiSON stations. We find that for the majority of low- $\ell$ modes the bias in the frequencies given by the effects of the window function is not significant. However, for modes above $\approx$ $3300~\rm\mu Hz$, and some $\ell=2$ modes near $\approx$ $2500~\rm\mu Hz$, the bias is important when the frequencies are extracted from long datasets.

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

© ESO 2004