脉动稳定性对恒星对流包层氦丰度的依赖

Dependence of Pulsation Stability on Helium Abundance of Stellar Convection Envelope

利用一种非局部和非定常的恒星对流理论,计算了3种不同氦丰度（y=0.28,0.13,0.00）、太阳金属丰度（Z=0.02）、质量1.4～3.0 M⊙恒星演化模型的径向和低球谐阶F-p8模的线性非绝热脉动.数值计算结果表明,理论的δ Scuti变星脉动不稳定区红边界几乎不随氦丰度变化而改变.随着氦丰度降低,δScuti变星脉动不稳定区蓝边界向低温方向推移,脉动不稳定区中热方的高温星变得脉动更稳定;而冷方的低温星则变得脉动更不稳定.这似乎表明不大可能用氦弥散去解释δ Scuti脉动不稳定带中的不变星.然而脉动不稳定带热方和冷方中的不变星与变星的比例可能作为是否存在氦弥散的一种观测证据.

By using a non-local and time-dependent theory of convection,the linear nonadiabatic oscillations of radial and low-degree nonradial F-p8 modes for the evolutionary models in the mass range of 1.4-3.0 M⊙ and with three helium abundances of convective envelope （Y=0.28,0.13,0.00; Z=0.02） are calculated.The numerical results show that the red edge of theoretical δ Scuti instability strip almost does not change with the helium abundance.The blue edge of δ Scuti instability strip moves towards low temperature.With decrease of helium abundance,the high-temperature stars on the hot side of instability strip become more stable,and the low-temperature stars on the cold side of instability strip become more unstable.It seems impossible to explain the nonvariable stars in δ Scuti strip by using diffusion of helium.However,the ratios of nonvariable stars to variable stars in the hot and cold sides of the δ Scuti strip may be as an observational evidence of helium diffusion.