Radial and Nonradial Oscillations of 44 Tauri

Abstract

Evolutionary stellar models of 44 Tauri, a multiperiodic δ Scuti star, have been developed theoretically and compared with earlier observational reports. The models depict 44 Tau at the hydrogen-shell–burning stage, when it is in radiative equilibrium with a very thin surface convective layer. Using the models, we performed calculations to obtain radial and nonradial adiabatic oscillation frequencies, and the equations were treated linearly. The results showed that the radial fundamental (6.899 cycles day-1) and first-overtone (8.961 cycles day-1) frequencies and the five nonradial modes of low harmonic degree that had been determined theoretically were in agreement with the observed values of previous authors to an accuracy of a few parts in 103. However, a difference emerged in the nonradial frequencies, which we classified as g-modes of low harmonic degree, whereas the observational reports had classified them as p-modes. In addition, even though 44 Tau has a rotation v sin i = 6.8 km s-1 (according to Solano and Fernley), which we considered negligible, we analyzed the effect of rotation. Our findings revealed that rotation modulated the oscillation frequencies of the nonrotating model on the order of 10-2.