Nonlinear pulsations of stars with initial mass 3 $${M_ \odot }$$ M ⊙ on the asymptotic giant branch

Abstract

-Pulsation period changes in Mira type variables are investigated using the stellar evolution and nonlinear stellar pulsation calculations. We considered the evolutionary sequence of stellar models with initial mass M ZAMS = 3M ⊙ and population I composition.Pulsations of stars in the early stage of the asymptotic giant branch are shown to be due to instability of the fundamental mode. In the later stage of evolution when the helium shell source becomes thermally unstable the stellar oscillations occur in either the fundamental mode (for the stellar luminosuty L < 5.4 × 10 3 L ⊙ ) or the first overtone (L > 7 × 10 3 L ⊙ ). Excitation of pulsations is due to the κ-mechanism in the hydrogen ionization zone. Stars with intermediate3 L ⊙ were found to be stable against radial oscillations.The pulsation period was determined as a function of evolutionary time and period change ratesΠ were evaluated for the first ten helium flashes. The period change rate becomes the largest in absolute value (Π/Π ≈ −10 −2 yr −1 ) between the helium flash and the maximum of the stellar luminosity. Period changes with rate |Π/Π| 10 −3 yr −1 take place during ≈ 500 yr, that is nearly one hundredth of the interval between helium flashes.

Pulsations of intermediate–mass stars on the asymptotic giant branch

“…Below we extend our earlier results obtained for the first ten thermal pulses of the population I AGB star with initial mass M ZAMS = 3M ⊙ (Fadeyev, 2016).…”

“…Second, models with initial masses M ZAMS ≥ 4M ⊙ and pulsation periods Π > 300 d show the presence of the hump on the bolometric light and the surface velocity curves.Evolution of the eAGB red giant is accompanied by increase of the pulsation period and the rate of period change but even in most luminous red giants the rate of period change is insignificant:Π/Π < 10 −5 yr −1 .3.2 TP-AGB starsDependence of pulsation properties of TP-AGB stars on the stellar mass M, the surface luminosity L and chemical composition is quite complicated. In particular, hydrodynamic models of the evolutionary sequence M ZAMS = 3M ⊙ exhibit fundamental mode pulsations near the minimum of the surface luminosity and first overtone pulsations at the maximum luminosity(Fadeyev, 2016). Hydrodynamic computations done in the present study show that fundamental mode and first overtone pulsations appear in stars with initial mass M ZAMS ≤ 3M ⊙ , whereas more massive red giants pulsate only in the fundamental mode.Red giants with initial mass M ZAMS = 2M ⊙ and 3M ⊙ .Fig.…”

Radial pulsations of red giant branch stars

“…Results of evolutionary and hydrodynamic computations for models of RGB stars presented in this study supplement ones from our previous works devoted to investigation of pulsations in stars of the asymptotic giant branch (Fadeyev 2016;2017). The main conclusion of these works is that the RGB stars as well as the more luminous AGB stars are the fundamental mode pulsators.…”

“…The results presented below are based on consistent stellar evolution and stellar pulsation computations. The methods of computations are described in our previous papers(Fadeyev 2016;…”

AGB winds in interacting binary stars

“…We assume an initial position of pulsation of R 0 = 0.9 R 1 . This value is chosen because pulsations in AGB stars are believed to be driven in the hydrogen-ionization zone, located approximately at 0.1 − 0.2 R 1 below the photosphere (Berlioz-Arthaud 2003;Fadeyev 2016). ∆u = 5 km s −1 and P = 300 d are the constant velocity amplitude and period of the pulsations, respectively.…”