Models of pulsating low-massive yellow supergiants

Abstract

The nonlinear self-excited oscillations of the envelopes of low-massive highly luminous stars are described. The parameters for these models wereM=0.8M _⊙,M _bol=−5.5, −5.84 mag,T _eff=4500, 5000, 5500 K. The oscillations have been found to consist of the standing wave pulsation near the envelope bottom and running waves in outer layers. The ratio of the standing wave frequency ω _s to the average frequency of the running waves ω _r increases with the stellar luminosity: ω _s /ω _r =1.7 whenM _bol=−5.5 mag and ω _s /ω _r =2.4 whenM _bol=−5.84 mag. The frequency of oscillations near the photosphere is found to be in close agreement with the critical frequency for running waves. Mass loss from these stars is caused by shocks. It has been shown that agreement between FG Sge's period change observed during the last decade and the period-luminosity relation for double shell stars takes place when FG Sge's luminosity isM _bol=−5.96 mag.