A method of computing periods of cyclic phenomena

Jurkevich, Igor

doi:10.1007/bf00656321

Cited by 155 publications

(118 citation statements)

References 9 publications

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“…Finally, when there were at least 15 RV measurements, including all available literature values (even if their error is unknown), we also analysed the RV datasets using the following period search algorithms: (1) the Fourier algorithm adapted to sparse/uneven datasets (Heck et al 1985;Gosset et al 2001;Zechmeister & Kürster 2009); (2) two different string length methods (Lafler & Kinman 1965;Renson 1978); (3) three binned analyses of variances (Whittaker & Robinson 1944;Jurkevich 1971, which is identical, with no bin overlap, to the "pdm" method of Stellingwerf 1978;and Cuypers 1987, which is identical to the "AOV" method of Schwarzenberg-Czerny 1989); and (4) conditional entropy Cincotta 1999, see also Graham et al 2013). Although the most trustworthy technique is the Fourier method, a reliable detection is guaranteed by the repeated recovery of the same signal with different methods.…”

Section: Radial Velocities and Binary Analysismentioning

confidence: 99%

Chemical abundances of fast-rotating massive stars

Cazorla

Morel

Nazé

et al. 2017

A&A

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Aims. Recent observations have challenged our understanding of rotational mixing in massive stars by revealing a population of fastrotating objects with apparently normal surface nitrogen abundances. However, several questions have arisen because of a number of issues, which have rendered a reinvestigation necessary; these issues include the presence of numerous upper limits for the nitrogen abundance, unknown multiplicity status, and a mix of stars with different physical properties, such as their mass and evolutionary state, which are known to control the amount of rotational mixing. Methods. We have carefully selected a large sample of bright, fast-rotating early-type stars of our Galaxy (40 objects with spectral types between B0.5 and O4). Their high-quality, high-resolution optical spectra were then analysed with the stellar atmosphere modelling codes DETAIL/SURFACE or CMFGEN, depending on the temperature of the target. Several internal and external checks were performed to validate our methods; notably, we compared our results with literature data for some well-known objects, studied the effect of gravity darkening, or confronted the results provided by the two codes for stars amenable to both analyses. Furthermore, we studied the radial velocities of the stars to assess their binarity.Results. This first part of our study presents our methods and provides the derived stellar parameters, He, CNO abundances, and the multiplicity status of every star of the sample. It is the first time that He and CNO abundances of such a large number of Galactic massive fast rotators are determined in a homogeneous way.

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Section: Radial Velocities and Binary Analysismentioning

confidence: 99%

Chemical abundances of fast-rotating massive stars

Cazorla

Morel

Nazé

et al. 2017

A&A

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“…To test for possible periodic changes in the component parameter variations, we applied a discrete autocorrelation function (Edelson & Krolik 1988), a data-compensated discrete Fourier transform (Ferraz-Mello 1981), and the Jurkevich method (Jurkevich 1971). All three methods were applied over the timerange 1981−2005 for all components out to C12.…”

Section: Periodicitiesmentioning

confidence: 99%

The kinematics in the pc-scale jets of AGN

Britzen¹,

Kudryavtseva

Witzel³

et al. 2010

A&A

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Context. BL Lac objects show core-jet structures with features moving outwards along the jet. We present a kinematic analysis of jet component motion in the pc-scale jet of the BL Lac object S5 1803+784, which does not reveal long-term outward motion for most of the components. Aims. S5 1803+784 shows complex kinematic phenomena; understanding these provides new insights into the emission processes in BL Lac objects and possibly into the differences between quasars and BL Lac objects. Methods. The blazar S5 1803+784 has been studied with VLBI at ν = 1.6, 2. 3, 5, 8.4, and 15 GHz between 1993.88 and 2005.68 in 26 observing runs. We (re)analyzed the data and present Gaussian model-fits. We collected the already published kinematic information for this source from the literature and re-identified the components according to the new scenario presented in this paper. Altogether, 94 epochs of observations have been investigated. Results. A careful study of the long-term kinematics reveals a new picture for jet component motion in S5 1803+784. In contrast to previously discussed motion scenarios, we find that the jet structure within 12 mas of the core can most easily be described by the coexistence of several bright jet features that remain on the long-term at roughly constant core separations (in addition to the already known "stationary" jet component ∼1.4 mas) and one faint component moving with an apparent superluminal speed (∼19c, based on 3 epochs). While most of the components maintain long-term roughly constant distances from the core, we observe significant, smooth changes in their position angles. We report on an evolution of the whole jet ridge line with time over the almost 12 years of observations. The width of the jet changes periodically with a period of ∼8−9 years. We find a correlation between changes in the position angle and maxima in the total flux-density light-curves. We present evidence for a geometric origin of the observed phenomena and discuss possible models. Conclusions. We find evidence for a significantly different scenario of jet component motion in S5 1803+784 compared to the generally accepted one of outwardly moving jet components, and conclude that the observed phenomena (evolution of the jet ridge line, roughly constant component core separations but with significant position angle changes) can most easily be explained within a geometric model.

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“…5. A detailed frequency analysis was performed on this data set, using two different algorithms: the Jurkevich-Stellingwerf pdm method (Jurkevich 1971;Stellingwerf 1978), and the Lomb-Scargle (Lomb 1976;Scargle 1982) periodogram. The latter one is essentially a Fourier technique, hence it is more sensitive for harmonic periodicities.…”

Section: Variability Analysismentioning

confidence: 99%

The rotation and coma profiles of comet C/2004 Q2 (Machholz)

Reyniers¹,

Degroote²,

Bodewits

et al. 2008

A&A

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Aims. Rotation periods of cometary nuclei are scarce, though important when studying the nature and origin of these objects. Our aim is to derive a rotation period for the nucleus of comet C/2004 Q2 (Machholz). Methods. C/2004 Q2 (Machholz) was monitored using the Merope CCD camera on the Mercator telescope at La Palma, Spain, in January 2005, during its closest approach to Earth, implying a high spatial resolution (50 km per pixel). One hundred seventy images were recorded in three different photometric broadband filters, two blue ones (Geneva U and B) and one red (Cousins I). Magnitudes for the comet's optocentre were derived with very small apertures to isolate the contribution of the nucleus to the bright coma, including correction for the seeing. Our CCD photometry also permitted us to study the coma profile of the inner coma in the different bands. Results. A rotation period for the nucleus of P = 9.1±0.2 h was derived. The period is on the short side compared to published periods of other comets, but still shorter periods are known. Nevertheless, comparing our results with images obtained in the narrowband CN filter, the possibility that our method sampled P/2 instead of P cannot be excluded. Coma profiles are also presented, and a terminal ejection velocity of the grains v gr = 1609 ± 48 m s −1 is found from the continuum profile in the I band.

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A method of computing periods of cyclic phenomena

Cited by 155 publications

References 9 publications

Chemical abundances of fast-rotating massive stars

Chemical abundances of fast-rotating massive stars

The kinematics in the pc-scale jets of AGN

The rotation and coma profiles of comet C/2004 Q2 (Machholz)

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