Spurious results from Fourier analysis of data with closely spaced frequencies

Loumos, G. L.; Deeming, Terence J.

doi:10.1007/bf01879560

Cited by 150 publications

(139 citation statements)

References 3 publications

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“…However, to test the reality of this peak we subdivided the data in two nearly equal parts, and found it to be present in both, showing that this peak is not an artifact of f 1 . Furthermore, the resolving power in each of the two subsets is, with time bases of 70 days, about 0.02 d −1 (Loumos & Deeming 1978), ten times higher than the separation between the two peaks in question. The 12.94 d −1 peak is also found in the SAAO data alone (and subsets thereof) and is thus not a spurious effect of merging data from several sites.…”

Section: The Campaign Datamentioning

confidence: 85%

V 1162 Ori: A multiperiodicδScuti star with variable period and amplitude

Arentoft¹,

Sterken²,

Handler

et al. 2001

A&A

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Abstract. We present the results of multisite observations of the δ Scuti star V 1162 Ori. The observations were done in the period October 1999 -May 2000, when 18 telescopes at 15 observatories were used to collect 253 light extrema during a total of 290 hours of time-series observations. The purpose of the observations was to investigate amplitude and period variability previously observed in this star, and to search for low-amplitude frequencies. We detect, apart from the main frequency and its two first harmonics, four additional frequencies in the light curves, all with low amplitudes (1-3 mmag). Combining the present data set with data obtained in 1998-99 at ESO confirms the new frequencies and reveals the probable presence of yet another pulsational frequency. All five low-amplitude frequencies are statistically significant in the data, but at least one of them (f5) suffers from uncertainty due to aliasing. Using colour photometry we find evidence for a radial main frequency (f1), while most or all low-amplitude frequencies are likely non-radial. We show that the main frequency of V 1162 Ori has variable amplitude and period/phase, the latter is also displayed in the O-C diagram from light extrema. The amplitude variability in our data is cyclic with a period of 282 d and a range of nearly 20 mmag, but earlier amplitude values quoted in the literature cannot be explained by this cyclic variation. O-C analysis including data from the literature show that the period of V 1162 Ori displays a linear period change as well as sudden or cyclic variations on a time scale similar to that of the amplitude variations.

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Section: The Campaign Datamentioning

confidence: 85%

V 1162 Ori: A multiperiodicδScuti star with variable period and amplitude

Arentoft¹,

Sterken²,

Handler

et al. 2001

A&A

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“…The resolution criterion for this is that frequencies should be separated by at least 1.5/T to be considered unique (Loumos & Deeming 1978). Applying this to our list of 500 frequencies, we find that 276 of them are unique.…”

Section: Stopping Criteriamentioning

confidence: 96%

“…The limited lifetime also raises doubts about the applicability of the 1.5/T criterion (Loumos & Deeming 1978) to resolve frequencies (see Sect. 2.5).…”

Section: Time-frequency Analysismentioning

confidence: 99%

“…(6)) with the assumption of white noise results in all 500 terms being significant. The Loumos & Deeming (1978) test shows 296 of these to be unique. Multifrequency fitting (see Sect.…”

Section: Hd 46150mentioning

confidence: 99%

“…The list of frequencies and corresponding semi-amplitudes and phases is given in Table 4 (this table is only available in electronic form at CDS). The Loumos & Deeming (1978) criterion shows 196 of these to be unique. The amplitude spectrum (Fig.…”

Section: Hd 46966mentioning

confidence: 99%

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Variability in the CoRoT photometry of three hot O-type stars

Blomme

Mahy

Catala

et al. 2011

A&A

103

121

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Context. The detection of pulsational frequencies in stellar photometry is required as input for asteroseismological modelling. The second short run (SRa02) of the CoRoT mission has provided photometric data of unprecedented quality and time-coverage for a number of O-type stars. Aims. We analyse the CoRoT data corresponding to three hot O-type stars, describing the properties of their light curves and search for pulsational frequencies, which we then compare to theoretical model predictions. Methods. We determine the amplitude spectrum of the data, using the Lomb-Scargle and a multifrequency HMM-like technique. Frequencies are extracted by prewhitening, and their significance is evaluated under the assumption that the light curve is dominated by red noise. We search for harmonics, linear combinations, and regular spacings among these frequencies. We use simulations with the same time sampling as the data as a powerful tool to judge the significance of our results. From the theoretical point of view, we use the MAD non-adiabatic pulsation code to determine the expected frequencies of excited modes. Results. A substantial number of frequencies is listed, but none can be convincingly identified as being connected to pulsations. The amplitude spectrum is dominated by red noise. Theoretical modelling shows that all three O-type stars can have excited modes, but the relation between the theoretical frequencies and the observed spectrum is not obvious. Conclusions. The dominant red noise component in the hot O-type stars studied here clearly points to a different origin than the pulsations seen in cooler O stars. The physical cause of this red noise is unclear, but we speculate on the possibility of sub-surface convection, granulation, or stellar wind inhomogeneities being responsible.

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