scholarly journals Similar but different: the varied landscape of Onfp/Oef stars variability

2020 ◽  
Vol 500 (2) ◽  
pp. 2096-2111
Author(s):  
Gregor Rauw ◽  
Yaël Nazé
Keyword(s):  
Time Series ◽  
Alternative Explanation ◽  
Rotational Frequency ◽  
Spectral Lines ◽  
Low Frequencies ◽  
Rotational Modulation ◽  
The Subject ◽  
Radial Pulsations ◽  
Gaia Dr2 ◽  
High Cadence

ABSTRACT The Oef category gathers rapidly rotating and evolved O-stars displaying a centrally reversed He ii λ 4686 emission line. The origin of the variability of their photospheric and wind spectral lines is debated, with rotational modulation or pulsations as the main contenders. To shed new light on this question, we analysed high-quality and high-cadence Transiting Exoplanet Survey Satellite photometric time series for five Oef stars. We also collected a new time series of spectra for one target (λ Cep) which had been the subject of specific debates in the last years. These observations reveal the variety of Oef behaviours. While space-based photometric data reveal substantial red noise components in all targets, only ζ Pup seems to display a long-lived periodicity. In our sample, stars exhibit a dominant signal at low frequencies but it appears relatively short-lived. This is reminiscent of rotational modulations by transient photospheric spots, though this scenario is challenged by the case of HD 14 442, whose 1.230 d−1 signal significantly exceeds the critical rotational frequency. In parallel, no evidence of persistent p mode non-radial pulsations is found in either photometry or spectroscopy of the stars, only temporary excitation of g mode pulsations could offer an alternative explanation for the dominant signals. Finally, the revised luminosities of the stars using GAIA-DR2 show that they are not all supergiants as ζ Pup. The question then arises whether the Oef peculiarity denotes a homogeneous class of objects after all.

scholarly journals Time-Series Spectroscopy of ζ Ophiuchi

1993 ◽  
Vol 139 ◽  
pp. 190-190
Author(s):  
A.H.N. Reid ◽  
C.T. Bolton ◽  
R.A. Crowe ◽  
M.S. Fieldus ◽  
A.W. Fullerton ◽  
...  
Keyword(s):  
Time Series ◽  
Rotation Period ◽  
Phase Changes ◽  
High Signal ◽  
Line Profiles ◽  
Rotational Modulation ◽  
Multi Wavelength ◽  
Rapid Rotator ◽  
Multi Mode ◽  
Radial Pulsations

AbstractWe have undertaken a multi-site, multi-wavelength observing campaign on the archetypal O stars ζ Puppis (O4 I(n)f) and ζ Ophiuchi (O9.5 V). Both stars are well known for the strength of their line profile variations (lpv's), and represent extremes of O spectral type and luminosity class. UV time-series spectroscopy of ζ Pup and ζ Oph is described by Prinja et al. (Ap.J. 1992, 390, 266), and Howarth et al. (Ap.J. 1992, submitted) respectively. The optical spectroscopic results of ζ Oph are reported by Reid et al. (1992, ApJ submitted), of which some of the principal results are given here.During late April, and early May, 1989, we obtained high-resolution, high signal-to-noise optical spectra of the late O-type, rapid rotator ζ Oph. Time-series analysis, using the CLEAN algorithm, has shown that the characteristic lpv seen in HeI λ447lÅ, Si III λλ4552, 4567, 4575Å, and MgII λ448lÅ can be satisfactorily represented as a set of 4 sinusoids. No substantial variation is observed in HeII λ4541, or NIII λ4517Å. We attribute this behaviour to a combination of equatorial gravity-darkening and a latitudinally-confined origin for the lpv.The phase changes over the line profiles indicate repetitive patterns of axial symmetry, rotating prograde in the co-rotating frame of the star. The periods are 3.339 hours (-m = 4), 2.435 hours (-m = 5 or -m = 6), 1.859 hours (-m = 9 ± 1), and either 1.366 hours or 1.292 hours (-m = 11 ± 1); -m represents the spatial frequency around the stellar equator. The first three periods confirm those found at earlier epochs, and we conclude that some lpv characteristics are reproduced over at least a 2-year interval.Since no commensurate superperiod (|m|P) exists, and since the super-periods are less than our estimated minimum rotation period for ζ Oph (> 18 hours), we reject a rotational modulation origin for the lpv and conclude that the star is undergoing multi-mode, sectorial, non-radial pulsations.

Prediction of Atmospheric Turbulence Characteristics for Surface Boundary Layer using Empirical Spectral Methods

2020 ◽  
Author(s):  
Yagya Dutta Dwivedi ◽  
Vasishta Bhargava Nukala ◽  
Satya Prasad Maddula ◽  
Kiran Nair
Keyword(s):  
Boundary Layer ◽  
Time Series ◽  
Surface Roughness ◽  
Wind Speed ◽  
Atmospheric Turbulence ◽  
Surface Boundary ◽  
Low Frequencies ◽  
Surface Boundary Layer ◽  
Power Spectral ◽  
Mean Wind Speed

Abstract Atmospheric turbulence is an unsteady phenomenon found in nature and plays significance role in predicting natural events and life prediction of structures. In this work, turbulence in surface boundary layer has been studied through empirical methods. Computer simulation of Von Karman, Kaimal methods were evaluated for different surface roughness and for low (1%), medium (10%) and high (50%) turbulence intensities. Instantaneous values of one minute time series for longitudinal turbulent wind at mean wind speed of 12 m/s using both spectra showed strong correlation in validation trends. Influence of integral length scales on turbulence kinetic energy production at different heights is illustrated. Time series for mean wind speed of 12 m/s with surface roughness value of 0.05 m have shown that variance for longitudinal, lateral and vertical velocity components were different and found to be anisotropic. Wind speed power spectral density from Davenport and Simiu profiles have also been calculated at surface roughness of 0.05 m and compared with k−1 and k−3 slopes for Kolmogorov k−5/3 law in inertial sub-range and k−7 in viscous dissipation range. At high frequencies, logarithmic slope of Kolmogorov −5/3rd law agreed well with Davenport, Harris, Simiu and Solari spectra than at low frequencies.

scholarly journals The band spectrum of hydrogen

1924 ◽  
Vol 106 (735) ◽  
pp. 69-82 ◽  
Keyword(s):  
Molecular Hydrogen ◽  
Hydrogen Molecule ◽  
Spectral Lines ◽  
Wave Number ◽  
Band Spectrum ◽  
Wave Numbers ◽  
Experimental Side ◽  
The Subject ◽  
The Moment ◽  
Theoretical Side

Many attempts have been made to detect regularities amongst the numerous lines which constitute the secondary or many-lined spectrum of hydrogen. The extreme complexity of the spectrum may be realised from the fact that in the Bakerian Lecture of 1922 Merton and Barratt record some 750 lines in the interval between Hα (wave-number v = 5233.216) and Hβ ( v = 20564.793). Three methods of investigation may be employed in the search for regularities. (1) The lines may be classified according to their physical characteristics, such as intensity or mode of excitation, as in the tables of Merton and Barrat ( loc. cit .). (2) Lines may be grouped together by the discovery of relations between their wave-lengths or wave-numbers, as in the important groups of lines which have been arranged in bands by Fulcher. (3) Lastly, the question may be attacked from the theoretical side, and a model of the hydrogen molecule may be imagined, which will give rise to the emission of certain characteristic spectral lines. Thus Sutherland, working on the foundation of the classical mechanical laws, more than twenty years ago, came to the conclusion that spectral series must arise from kinematical considera­tions, and explained them by considering the nodal sub-divisions of a circle. At the present time we may expect more successful results to follow from the application of the quantum theory, and in this paper an endeavour will be made to examine the secondary spectrum of hydrogen, and more particularly the Fulcher bands, from this standpoint. I may add that my interest in the subject was aroused when attempting to construct a model of the hydrogen molecule, for it seemed that the most likely method of obtaining reliable information from the experimental side as to the moment of inertia of the molecule would be from a study of the spectrum of molecular hydrogen.

scholarly journals On external influences on the radioactive decay rate fluctuations

2020 ◽  
Author(s):  
Victor Panchelyuga ◽  
Maria Panchelyuga ◽  
Olga Seraya
Keyword(s):  
Time Series ◽  
Decay Rate ◽  
Radioactive Decay ◽  
Theoretical Curve ◽  
External Influence ◽  
Intensive Study ◽  
External Influences ◽  
Universal Spectrum ◽  
The Subject

The evolution of views on the possibility of external influence on the process of radioactive decay is briefly presented. Such an effect can lead to the appearance of periods in the time series of the radioactive decay rate fluctuations, which have been the subject of intensive study in the last decade. Two mechanisms for identifying periods are considered: the study of deviations from the theoretical curve of the radioactive decay law and the study of the properties of fluctuations. It is shown that the latter method leads to a universal spectrum of periods observed not only in the time series of the radioactive decay rate fluctuations, but also in the time series of fluctuations of processes of various nature. The main object of our study are periods in the radioactive decay rate fluctuations. The presence of such periods suggests the possibility of external influence on the process of radioactive decay. Therefore, we briefly consider the evolution of views on the possibility of such an effect. To do this, we distinguish several stages. The division into stages is only partially historical, but, mainly, each stage characterizes a certain ideas that is implemented in it.

scholarly journals TIME SERIES PROCESSING USING WAVELET-TRANSFORMATIONS FOR ACCURACY INCREASE IN INFORMATION PRESENTATION

2018 ◽  
Vol 2018 (8) ◽  
pp. 67-75
Author(s):  
Юрий Кропотов ◽  
Yuriy Kropotov ◽  
Алексей Белов ◽  
Aleksey Belov ◽  
Александр Проскуряков ◽  
...  
Keyword(s):  
Time Series ◽  
Wavelet Decomposition ◽  
Statistical Processing ◽  
Threshold Level ◽  
Information Presentation ◽  
Statistical Parameters ◽  
Noise Component ◽  
Low Frequencies ◽  
Accuracy Increase ◽  
Approximation Coefficients

The purpose of this work is development of the method for error decrease in information presentation in telecommunication systems of monitoring by means of filtering noise and fluctuations of levels in time series counts. To solve this problem there is used a method of wavelet processing. In particular, the decrease of time series fluctuation impact is carried out by means of the computation of approximating coefficients of the n-th level which corresponds to the fulfillment of multi-level statistical processing the values of time series counts and equivalent to a signal passage through a filter of low frequencies. There was developed and investigated a simulator and its statistical parameters of processing with a wavelet transformation of time series counts. It is shown that time series wavelet processing and the application of approximation coefficients of waveletdecomposition increase the accuracy of data presentation. It is also ensured at the expense of noise component suppression through a method of thresholding upon detailing coefficients of decomposition. In the paper there are shown investigations of the dependence of approximation coefficient correlation time upon a wavelet decomposition level. There was also investigated a depression dependence of noise components of time series count fluctuations of emission at the processing with the wavelet decomposition with obtaining approximation coefficients of different levels. The fulfilled analysis of the results of different criteria application and approaches to smoothing on the basis of threshold processing the detail coefficients of wavelet decomposition has shown that at smoothing time series there will be an optimum choice of an adaptive penalty threshold level. The presented results of smoothing with an adaptive penalty threshold have shown that the signal-noise ratio increased for more than 2.53dB in comparison with the initial one.

Exploring Working-Class Consciousness: A Critique of the Theory of the ‘Labour-Aristocracy’*

2010 ◽  
Vol 18 (4) ◽  
pp. 3-38 ◽  
Author(s):  
Charles Post
Keyword(s):  
Twentieth Century ◽  
Working Class ◽  
Alternative Explanation ◽  
World Market ◽  
Capitalist Class ◽  
Capitalist Production ◽  
Leading Role ◽  
Victorian Period ◽  
The World ◽  
The Subject

AbstractThe notion of the labour-aristocracy is one of the oldest Marxian explanations of working-class conservatism and reformism. Despite its continued appeal to scholars and activists on the Left, there is no single, coherent theory of the labour-aristocracy. While all versions argue working-class conservatism and reformism reflects the politics of a privileged layer of workers who share in ‘monopoly’ super-profits, they differ on the sources of those super-profits: national dominance of the world-market in the nineteenth century (Marx and Engels), imperialist investments in the ‘colonial world’/global South (Lenin and Zinoviev), or corporate monopoly in the twentieth century (Elbaum and Seltzer). The existence of a privileged layer of workers who share monopoly super-profits with the capitalist class cannot be empirically verified. This essay presents evidence that British capital’s dominance of key-branches of global capitalist production in the Victorian period, imperialist investment and corporate market-power can not explain wage-differentials among workers globally or nationally, and that relatively well-paid workers have and continue to play a leading rôle in radical and revolutionary working-class organisations and struggles. An alternative explanation of working-class radicalism, reformism, and conservatism will be the subject of a subsequent essay.

scholarly journals Non-radial Pulsations of BA Supergiants and Be Stars

1999 ◽  
Vol 169 ◽  
pp. 312-319
Author(s):  
Dietrich Baade
Keyword(s):  
Mass Loss ◽  
Background Noise ◽  
The Other ◽  
Be Stars ◽  
Physical Processes ◽  
Other Hand ◽  
Be Star ◽  
The Subject ◽  
Radial Pulsations

If observing time and number of photons are not the limit, it will probably be very difficult to find any Be star or BA supergiant that is not variable. Moreover, there is hardly any major set of observations that is not tempting to explain at least partly in terms of nonradial (g-mode) pulsations. Since a few years ago, such conjectures are also theoretically permissible because improved opacity calculations have established the classical к-mechanism as a viable source of pulsation driving (cf. Pamyatnykh, these proceedings).Contrary to Be stars, it can for any given BA supergiant nevertheless be arbitrarily difficult to diagnose nonradial pulsations (NRP’s) with certainty because they need to be detected against considerable background ‘noise’ of other physical processes, most of which are related to mass loss and/or rotation. To make things worse, there is some evidence that NRP’s can have some effect on the dynamics of the mass loss. On the other hand, variable and non-spherical winds is the subject of this Colloquium, and this paper is accordingly biased towards the interplay between pulsation and mass loss.

A Rediscussion of the Radio Spectrum of the Orion Nebula

1969 ◽  
Vol 1 (5) ◽  
pp. 217-218
Author(s):  
P. A. Shaver ◽  
B. Y. Mills
Keyword(s):  
Electron Temperature ◽  
Radio Spectrum ◽  
Radio Continuum ◽  
Orion Nebula ◽  
Low Frequencies ◽  
Continuum Spectrum ◽  
The Subject ◽  
Bright Emission

The Orion Nebula is the best known and most often observed of the bright emission nebulae. However, the radio continuum spectrum of the nebula has been the subject of some misconception, particularly at low frequencies. A rediscussion is worthwhile as the spectrum has been used to derive an electron temperature for the nebula which is at variance with other determinations and carries important implications. Also some of the difficulties of measurement and problems of interpretation are relevant to similar investigations of other emission nebulae.

scholarly journals Variability of the Solar He I 10830 Å Triplet

1994 ◽  
Vol 154 ◽  
pp. 59-64 ◽  
Author(s):  
J. W. Harvey ◽  
W. C. Livingston
Keyword(s):  
Time Series ◽  
Water Vapor ◽  
Coronal Holes ◽  
Solar Chromosphere ◽  
Solar Cycles ◽  
Rotational Modulation ◽  
General Variation ◽  
Line Equivalent Width ◽  
Activity Indices ◽  
Full Disk

The He I 10830 Å triplet gives a unique view of the solar chromosphere. Digital spectroheliograms have been made regularly since early 1974 using this line and the NSO Vacuum Telescope on Kitt Peak. For many purposes (detection of coronal holes, giant two-ribbon flares, and dark point events) these images are sufficient. A Sun-as-a-star signal is also produced by averaging all the pixels in each daily image. To calibrate this ‘irradiance’ signal in terms of line equivalent width, a comparison is made with integrated sunlight spectrophotometric measurements obtained less frequently. After correction for the effects of water vapor blends, we find a linear relation between the two measurements. The daily averages have been assembled into a time series covering nearly two solar cycles. This time series shows cycle modulation of about ±30% and rotational modulation of about ±10%. The general variation is similar to that of other activity indices but with some interesting small differences. Since images are available, it has been possible to decompose the full disk index into components due to plages, filaments, coronal holes and background. At all times during the cycle, most of the signal comes from the background but most of the variability from plages.

Acceleration time series resulting from repetitive extension-flexion of the hand

1975 ◽  
Vol 38 (1) ◽  
pp. 101-107 ◽  
Author(s):  
R. N. Stiles
Keyword(s):  
Frequency Band ◽  
Normal Subjects ◽  
Peak Frequency ◽  
Hand Tremor ◽  
Low Frequencies ◽  
Frequency Bands ◽  
Normal Hand ◽  
The Subject ◽  
The Time Domain ◽  
Oscillation Frequencies

Power, or variance, spectra of acceleration records obtained from normal subjects during extension-flexion oscillations of a hand at frequencies between 0.5–5.0 Hz generally contained two or three frequency bands. Partial separation of these oscillations in the time domain was obtained using the method of digital filtering (smoothing). In general, the peak frequency of the lowest frequency band occurred at, or nearly at, the frequency that the subject attempted to maintain during a 16-s digitization period. Consideration of absolute frequencies and the effect of mass on frequency indicated that one of the higher frequency bands was the result of normal hand tremor. For low frequencies of voluntary oscillation (0.5–1.25 Hz), a second, higher frequency band occurred with a peak frequency (3.0–4.25 Hz) within the range (3–6 Hz) usually reported for abnormal hand tremor. For voluntary oscillation frequencies above about 1.5 Hz, this second, higher frequency oscillation generally occurred at twice the frequency of the voluntary oscillation.

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