The Nature of Anomalous Period Increase in the Pulsating Variable V725 Sgr

The evolutionary tracks of stars with masses on the main sequence $$0.84\;M_{\odot}\leq M_{\textrm{ZAMS}}\leq 0.95\;M_{\odot}$$ and initial metal abundances $$Z=0.006$$ $$0.01$$ were computed under various assumptions about mass loss rate at red giant stage as well AGB post-AGB stages. Among 160 sequences we selected nearly 30 where final thermal flash helium shell source occurs in early when ratio hydrogen envelope to stellar ranges from 0.01 0.08. Selected used for calculation inner boundary conditions solution equations radiation hydrodynamics turbulent convection describing evolution pulsations after flash. three dozen hydrodynamic models found ones demonstrating almost eightfold increase pulsation period observed V725 Sgr during last century gradual transformation fairly regular $$\Pi\approx 12$$ day semi–regular non-linear oscillations $$80\lesssim\Pi\lesssim 90\text{ day}$$ . We conclude that anomalous growth is due occurred star $$M\approx 0.53\;M_{\odot}$$ ranging $$0.013$$ $$0.019\;M_{\odot}$$