The nonradial mode identification of 53 Persei during late 1977 and 1978

1979 ◽  
Vol 232 ◽  
pp. L193 ◽  
Author(s):  
M. A. Smith ◽  
R. J. Buta
Keyword(s):  
Mode Identification ◽  
Nonradial Mode

scholarly journals Radial and Nonradial Mode Instability in B-Type Stars

1993 ◽  
Vol 137 ◽  
pp. 721-723 ◽  
Author(s):  
W.A. Dziembowski ◽  
A.A. Pamyatnykh
Keyword(s):  
Electronic Mail ◽  
Variable Stars ◽  
Mode Identification ◽  
Star Models ◽  
Extensive Search ◽  
Oscillation Modes ◽  
High Metal ◽  
Metal Abundance ◽  
Spin Orbit Interactions ◽  
Nonradial Mode

Recently three independent groups(Cox et al. 1992; Kiriakidis et al. 1992; Moskalik and Dziembowski, 1992), using opacity tables published by Iglesias and Rogers (1991), demonstrated that β Cep star models are pulsationally unstable. The instability is driven by the classical к- mechanism acting in the layer with temperatures near 2 × 105K where there is a bump in metal opacity. The groups reported results of calculations made for rather narrow ranges of stellar parameters and oscillation modes. We conducted an extensive search for unstable modes in complete evolutionary models of B-type stars of luminosity classes III - V. Our aim was to determine the domain of instability and examine its role not only in β Cep stars but also in variable stars located in the nearby areas of the H-R diagram.An unexpected new aspect of our calculations is the use of the improved opacity data. In a very recent work Iglesias, Rogers and Wilson (1992) showed that effects of spin-orbit interactions significantly enhance opacity in the critical region for driving the pulsations in β Cep stars. These effects and improved information about the solar metal mixture have been included in the updated opacity tables kindly provided to us via electronic mail by Dr. Rogers. The consequences of this change in opacity for stability of B-type star models are indeed quite important. Contrary to previously announced results, that only the fundamental mode is unstable, we now find the first two radial overtones to be unstable, as well. Thus, the discrepancy between the theoretical prediction and the mode identification suggested by observers has been removed. Furthermore, no longer is a high metal abundance (Z > 0.03) required to explain the occurrence of pulsation in most of the objects. In fact, the theoretical instability domain in the H-R diagram, based on the models calculated with Z = 0.02, agrees better with the observational β Cep domain than that based on the models Z = 0.03.

Anomaly Detection and Mode Identification in Multimode Processes Using the Field Kalman Filter

2020 ◽  
pp. 1-14
Author(s):  
Tian Cong ◽  
Ruomu Tan ◽  
James R. Ottewill ◽  
Nina F. Thornhill ◽  
Jerzy Baranowski
Keyword(s):  
Kalman Filter ◽  
Anomaly Detection ◽  
Mode Identification

Methods to isolate retrograde and prograde Rayleigh-wave signals

2019 ◽  
Vol 219 (2) ◽  
pp. 975-994 ◽  
Author(s):  
Gabriel Gribler ◽  
T Dylan Mikesell
Keyword(s):  
Rayleigh Wave ◽  
Time Domain ◽  
Fundamental Mode ◽  
Poisson Ratio ◽  
Low Frequency ◽  
Wave Dispersion ◽  
Low Frequencies ◽  
Retrograde Motion ◽  
Mode Identification ◽  
Time Frequency

SUMMARY Estimating shear wave velocity with depth from Rayleigh-wave dispersion data is limited by the accuracy of fundamental and higher mode identification and characterization. In many cases, the fundamental mode signal propagates exclusively in retrograde motion, while higher modes propagate in prograde motion. It has previously been shown that differences in particle motion can be identified with multicomponent recordings and used to separate prograde from retrograde signals. Here we explore the domain of existence of prograde motion of the fundamental mode, arising from a combination of two conditions: (1) a shallow, high-impedance contrast and (2) a high Poisson ratio material. We present solutions to isolate fundamental and higher mode signals using multicomponent recordings. Previously, a time-domain polarity mute was used with limited success due to the overlap in the time domain of fundamental and higher mode signals at low frequencies. We present several new approaches to overcome this low-frequency obstacle, all of which utilize the different particle motions of retrograde and prograde signals. First, the Hilbert transform is used to phase shift one component by 90° prior to summation or subtraction of the other component. This enhances either retrograde or prograde motion and can increase the mode amplitude. Secondly, we present a new time–frequency domain polarity mute to separate retrograde and prograde signals. We demonstrate these methods with synthetic and field data to highlight the improvements to dispersion images and the resulting dispersion curve extraction.

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