1997/10/05 by D. R. Xiong, Q. L. Cheng, L. Deng · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Cepheid variable #Convection #Convection zone #Coupling (piping) #Instability #Instability strip #RR Lyrae variable #Stellar, planetary, and galactic studies #Turbulence #Variable star #astro-ph
paper · pdf · doi:10.1086/305695
30 pages, Latex uses aaspp4.sty, 7 figures and 3 tables included. Submitted to Apj
arxiv created 1997/10/05 · openalex publication_date 1998/06/10 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
Using a nonlocal time-dependent theory of convection, we have calculated the linear nonadiabatic oscillations of horizontal branch (HB) stars, carefully treating both the dynamic and thermodynamic coupling between convection and oscillations. Turbulent pressure and turbulent viscosity have been included consistently in our equations of nonadiabatic pulsation. When the coupling between convection and oscillations is ignored, for all models with T e ≤ 7350 K, the fundamental through the second overtone are pulsationally unstable, while for T e ≤ 6200 K all the models are unstable up to (at least) the 9th overtone. When the coupling between convection and oscillations is included, the RR Lyrae instability strip is very well predicted. Within the strip, most models are pulsationally unstable only for the fundamental and the first few low-order overtones. The turbulent viscosity is an important damping mechanism. Being exclusively distinct from the luminous red variables (long-period variables), the HB stars to the right of the RR strip are pulsationally stable for the fundamental and low-order overtones, but become unstable for some of the high-order overtones. This may provide a valuable clue to the short-period, low-amplitude red variables found outside the red edge of the RR strip on the H-R diagram of globular clusters. We also present a new radiation-modulated excitation mechanism functioning in a zone of radiation flux gradient. The effects of nonlocal convection and the dynamic coupling between convection and oscillations are discussed. The spatial oscillations of the thermal variables in the pulsational calculations have been effectively suppressed.