Touching on the Effects of an Imperfect Window Function

Chaplin, W. J.; Elsworth, Y.; Isaak, G. R.; McLeod, C. P.; Miller, B. A.; New, R.

doi:10.1007/978-94-011-4982-2_9

Cited by 13 publications

(16 citation statements)

References 2 publications

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“…1, was derived from GONG, BiSON and LOI/VIRGO observations by Chaplin et al (2001b). Chaplin et al (2003c) used BiSON observations to extract estimates of the g m for |m| = modes. Here, we use their value of g 2,2 = 3.05 nHz RF −1 to describe the shift given to the (2, 2) components.…”

Section: Introduction Of Asymmetrymentioning

confidence: 99%

Solar p-mode frequencies at $\mathsf{\ell=2}$: What do analyses of unresolved observations actually measure?

Chaplin

Appourchaux

Elsworth

et al. 2004

A&A

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Abstract.We have studied in detail the extraction of estimates of = 2 p-mode frequencies from unresolved observations of the visible disc of the Sun. Examples of data of this type include ground-based observations made by the Birmingham SolarOscillations Network (BiSON), and space-borne observations made by the GOLF and VIRGO/SPM instruments on board the ESA/NASA SOHO satellite. The fitting of the modes is complicated in practice by the asymmetric arrangement in frequency of the three components (m = −2, 0 and 2) that are prominent in such data. In order to investigate the effect of this we used a series of 10-yr artificial datasets into which varying degrees of asymmetry were introduced. The sets were designed to mimic the characteristics of the BiSON and GOLF data, and were analyzed both with and without the BiSON window function from the period 1992 through 2001. Since reliable estimates of the asymmetry have only recently been extracted from unresolved observations (Chaplin et al. 2003a) it has for a long time been standard practice to fit the = 2 modes to a model that assumes a symmetrically arranged multiplet. We have tested the impact of this on the accuracy of the extracted frequencies. Furthermore, we demonstrate that asymmetric models can be successfully applied, provided the data are of sufficient length and quality. We also discuss the implications of our simulations for analyses of real solar data.

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Section: Introduction Of Asymmetrymentioning

confidence: 99%

Solar p-mode frequencies at $\mathsf{\ell=2}$: What do analyses of unresolved observations actually measure?

Chaplin

Appourchaux

Elsworth

et al. 2004

A&A

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“…We suspect that not only is this bias the reason for the disparate inferences of rotational splitting that have been drawn from analyses of data from different instruments, as we mentioned in the introduction, but also that the greater linewidths at solar maximum (e.g. Chaplin et al 2000), and consequently greater bias, has possibly led to an erroneous conclusion from data from a single instrument concerning a purported solar‐cycle variation of the angular velocity of the solar core (Jiménez et al. 1994).…”

Section: Discussionmentioning

confidence: 99%

On measuring low-degree p-mode frequency splitting with full-disc integrated data

Appourchaux¹,

Chang²,

Gough³

et al. 2000

Monthly Notices RAS

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A B S T R A C TThe standard method of measuring rotational splitting from solar full-disc oscillation data, based on maximum-likelihood fitting of multi-Lorentzian profiles to oscillation power spectra, systematically overestimates the splitting. One of the reasons is that the maximum likelihood estimators (MLE) become unbiased only asymptotically as the number of data tends to infinity; for a finite data set they are often biased, inducing a systematic error. In this paper we assess by Monte Carlo simulations the amount of systematic error in the splitting measurement, using artificially generated power spectra. The simulations are carried out for multiplets of degree l 1Y 2 and 3 with various signal-to-noise ratios, linewidths and observing times. We address the possible use of non-MLE estimators that could provide a smaller or negligible systematic error. The implication for asteroseismology is also discussed.

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“…see fig. 2 of Chaplin et al 2000). The interaction of this with the modes – masked by the realization noise – can in principle have a subtle impact on the parameters extracted by the fitting procedure, e.g.…”

Section: Testing the Fitting Proceduresmentioning

confidence: 97%

Observation of, and temporal variations in, solar p-mode multiplet frequency asymmetries at = 2

Chaplin

Elsworth

Isaak

et al. 2003

Monthly Notices of the Royal Astronomical Society

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The predominant contribution to the frequency splitting of low-solar p modes arises from the rotation of the solar interior and this lifts the frequency degeneracy in to give a symmetric pattern where the observed (synodic) separation between adjacent m (i.e. for | m| = 1) is ∼400 nHz. Magnetic fields can also contribute to the splitting, but they do so in such a way as to introduce asymmetries in the arrangement of the components within each multiplet. In disc-integrated data this effect may become apparent when 2. Here, we attempt to extract estimates of the frequency asymmetries at = 2 from the analysis of disc-integrated data collected by the ground-based Birmingham Solar Oscillations Network (BiSON) and the GOLF instrument on board the ESA/NASA SOHO satellite. Our analyses demonstrate that we have evidence for there being non-zero asymmetries present (significance ≈3-4σ ) during an epoch coincident with high levels of surface activity close to the maximum of solar cycle 23. The asymmetries are indistinguishable from zero at minimum levels of activity near the cycle 22/23 boundary.We also compare the observed asymmetries with those calculated from a model that is based upon the recent predictions of Moreno-Insertis & Solanki. While the level of agreement between the two is found to be reasonable, the observations suggest (though with poor constraints placed upon this) that the influence on the mode frequencies of high-latitude activity may not be as strong as in the model.

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Touching on the Effects of an Imperfect Window Function

Cited by 13 publications

References 2 publications

Solar p-mode frequencies at $\mathsf{\ell=2}$: What do analyses of unresolved observations actually measure?

Solar p-mode frequencies at $\mathsf{\ell=2}$: What do analyses of unresolved observations actually measure?

On measuring low-degree p-mode frequency splitting with full-disc integrated data

Observation of, and temporal variations in, solar p-mode multiplet frequency asymmetries at = 2

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