2023/05/31 by Yuri A. Fadeyev, Fadeyev, Yuri A.
Physics and Astronomy · #Stellar, planetary, and galactic studies #Astrophysics and Star Formation Studies #Astro and Planetary Science
paper · pdf · doi:10.48550/arxiv.2305.19657
Calculations of stellar evolution at initial abundances of helium Y=0.28 and heavier elements Z=0.014 were done for stars with masses on the main sequence 1.7M_\odot≤ M_\textrmZAMS≤ 5.2M_\odot. Evolutionary sequences corresponding to the AGB stage were used for modelling the pulsation period decrease observed for almost two centuries in the Mira--type variable R Hya. Diminution of the period from Π≈ 495 d in the second half of the eighteenth century to Π≈ 380 d in the 1950s is due stellar radius decrease accompanying dissipation of the radiation--diffusion wave generated by the helium flash. For all the history of its observations R Hya was the fundamental mode pulsator. The best agreement with observations is obtained for eight evolutionary models with initial mass M_\textrmZAMS=4.8M_\odot and the mass loss rate parameter of the Blöcker formula 0.03≤ηB≤ 0.07. Theoretical mass estimates of R Hya are in the range 4.44M_\odot≤ M≤ 4.63M_\odot, whereas the mean stellar radius (421R_\odot≤ R ≤ 445R_\odot) corresponding to the pulsation period Π≈ 380 agrees well with measurements of the angular diameter by methods of the optical interferometric imaging.