Abstract

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 \(1.7\;M_{\odot}\leq M_{\textrm{ZAMS}}\leq 5.2\;M_{\odot}\). 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 \(\Pi\approx\) 495 d in the second half of the eighteenth century to \(\Pi\approx 380\) d in the 1950s is due to 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 \(M=4.8\;M_{\odot}\) and the mass loss rate parameter of the Blöcker formula \(0.03\leq\eta_{\textrm{B}}\leq 0.07\). Theoretical mass estimates of R Hya are in the range \(4.44\;M_{\odot}\leq M\leq 4.63\;M_{\odot}\), whereas the mean stellar radius (\(421\;R_{\odot}\leq\bar{R}\leq 445\;R_{\odot}\)) corresponding to the pulsation period \(\Pi\approx 380\) d agrees well with measurements of the angular diameter by methods of the optical interferometric imaging.

中文翻译：

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Mira 型可变 R 九头蛇的理论质量估计

摘要

对于质量位于主序带上的恒星\ ( 1.7 \ ;M_{\odot}\leq M_{ \textrm{ZAMS}}\leq 5.2\;M_{\odot}\)。对应于 AGB 阶段的进化序列被用来模拟近两个世纪以来在 Mira 型变量 R Hya 中观察到的脉动周期减少。从十八世纪下半叶的\(\Pi\approx\) 495 d 缩短到\(\Pi\approx\)20世纪50年代的d是由于氦闪产生的辐射扩散波的消散导致恒星半径减小。在所有的观测历史中，R Hya 都是基本模式脉动器。对于初始质量为\(M=4.8\;M_{\odot}\)且 Blöcker 公式的质量损失率参数为\(0.03\leq\eta_{\textrm{B }}\leq 0.07\)。R Hya 的理论质量估计范围为\(4.44\;M_{\odot}\leq M\leq 4.63\;M_{\odot}\) ，而平均恒星半径 ( \(421\;R_{\ odot}\leq\bar{R}\leq 445\;R_{\odot}\) ) 对应于脉动周期\(\Pi\approx 380\)d 与通过光学干涉成像方法测量的角直径非常吻合。