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(1) For 29 (and possibly 30) multimode radial variables in the Cepheid instability strip I suggest that necessary and sufficient conditions for the existence of their multimode excitation may be that the excited periods be close to a direct resonance with each other and that their excitation growth rates be relatively small. (2) Discussion of the observational evidence on nonradial modes observed...
An attempt is made to interpret the differences in pulsational behavior between horizontal branch and main sequence (or early post-main sequence) variables. Results of linear stability studies for d Scuti stars are reviewed and supplemented with new calculations. The function of the opacity mechanism in generating instability to a variety of radial and nonradial modes is discussed. The highest excitation...
Using the von Sengbusch-Stellingwerf relaxation method, hydrodynamic calculations have been made to find strictly periodic solutions for the fundamental mode pulsations of 7 M⊙ models. These models have a helium enrichment in the surface convection zones up to Y = 0.78. From the linear theory period ratio π2/π0 and the Simon and Schmidt resonance hypothesis, the observed Hertzsprung progression of...
Using results from earlier studies of double-mode dwarf Cepheids by Cox, King and Hodson (1979), hydrodynamic calculations have been undertaken for AI Vel. The evolution theory mass of 1.8 M⊙ previously derived, together with a luminosity of 23 L⊙ and a Te of 7500 K, give the observed period of 0.11 day and the observed period ratio π1/π0 = 0.773. Although the observed Te was 7620 K, a cooler Te is...
For nonlinear models of 0.4 M⊙ and 2.0 M⊙ δ Scuti stars, pulsation amplitudes obtained in this region depend critically upon artificial viscosity parameters. Models with limited viscosity attain huge amplitudes. Furthermore, it is found that nonlinear stability properties depend primarily upon the amplitude. Determination of the actual dissipation mechanism is thus crucial to our understanding of...
The University of Arizona Radial Velocity Spectrometer is probably capable of attaining a resolution of 100 m/s or less on slowly rotating stars of blue magnitude 5.5 or brighter and pulsation periods of 0.02 days or greater in the δ Scuti instability region of the H-R diagram. Such performance is approximately equivalent to a photometric resolution of 10−3 magnitudes, and thus represents a possible...
In this paper several observational characteristics of the line profile variable B stars (“53 Persei variables”) are discussed. These stars reside between 08 and B5 on the main sequence and extend perhaps to class I. We believe the 53 Per variables are a separate group related to the classical β Cephei variables. Line profiles of 53 Per variables exhibit periodic changes in line width and asymmetry...
We have presented a short summary of the observed properties of the B Cephei stars and discussed recent analytical work dealing with them. In spite of the intensive efforts by a number of independent groups, the origin and cause of the β Cephei phenomenon remain unknown.
Equations for linear nonadiabatic pulsation and the method of their solution are discussed in some detail. The numerical results presented concern mainly 7 Mδ stellar models in early evolutionary phase. A driving zone at a temperature of 1.5 x 105 K was found to be present for both radial and nonradial modes, but no net pulsational instability was observed. Effects of rotation on pulsation frequencies...
Beta Cephei stars which are located in clusters and associations can be used to gather information on their evolutionary phase when they are placed on the color magnitude diagram. A tentative study is presented which attempts to use this idea to answer several important questions concerning B Cephei stars.
A discussion of the long period R Coronae Borealis stars is presented. The constraints on theoretical models imposed by their age, kinematics and distribution led to difficulties in formulating an evolutionary sequence to the formation of this type of star. Several types of models are investigated and the results given.
The results of many observations have been interpreted as evidence for global oscillations of the sun. The periods found in these analyses range from minutes to hundreds of years. The shorter period oscillations are usually interpreted as the normal modes proper whereas the longer period features may be manifestations of superpositions and/or nonlinear coupling of these normal modes. The work done...
Isaak's announcement (Claverie et al. 1980) of the discovery by his group of distinct, approximately evenly spaced peaks in the power spectra of whole-disk Doppler measurements immediately raised the issue of what they imply about the structure of the solar interior. Here we report our immediate reactions, and infer that the observations seem to imply a lower sound speed, appropriately averaged throughout...
The evidence presented here demonstrates the reality of long period brightness oscillations in the solar limb darkening function. This extension of the FFTD, the simultaneous application of multiple edge definitions, provides another test for establishing the reality of long period solar oscillations. Additional information, namely the signature, characterizes the signal measured, and can be used...
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