A Model of the Mira–Type Star T UMi

Fadeyev, Yu. A.

doi:10.1134/s1063773718070010

Cited by 4 publications

(11 citation statements)

References 20 publications

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“…As Templeton et al (2005) pointed out, models in the 1990s usually used time steps in the order of centuries-far too sparse for a quantitative comparison with the changes seen in T UMi. The only attempt so far to model T UMi both in terms of evolution and pulsation was done very recently by Fadeyev (2018). He found that a 1.2 M initial-mass model fit the observations best, transitioning from a fundamental-mode pulsation around 315 d to first-overtone pulsation near 114 d. He also derived physical parameters, obtaining a luminosity of 4080 L , a radius of 220 R , and an age of 4.3 × 10 9 yr.…”

Section: T Ursae Minorismentioning

confidence: 99%

“…While this range is very broad, the lower limit rules out stars above 3 M . The upper limit corresponds to masses around 1.2-1.3 M , meaning that the 1.2 M model preferred by Fadeyev (2018) is already bordering this constraint. Feast & Whitelock (2000) collected average [Fe/H] indices of globular clusters with Miras and semiregular variables in them.…”

Section: Age and [Fe/h]mentioning

confidence: 99%

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Stellar Evolution in Real Time. I. Models Consistent with the Direct Observation of a Thermal Pulse in T Ursae Minoris

Molnár

Joyce

Kiss

2019

ApJ

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Most aspects of stellar evolution proceed far too slowly to be directly observable in a single star on human timescales. The thermally pulsing asymptotic giant branch is one exception. The combination of state-of-the-art modelling techniques with data assimilated from observations collected by amateur astronomers over many decades provide, for the first time, the opportunity to identify a star occupying precisely this evolutionary stage. In this study, we show that the rapid pulsation period change and associated reduction in radius in the bright, northern variable star T Ursae Minoris are caused by the recent onset of a thermal pulse. We demonstrate that T UMi transitioned into a double-mode pulsation state, and we exploit its asteroseismic features to constrain its fundamental stellar parameters. We use evolutionary models from MESA and linear pulsation models from GYRE to track simultaneously the structural and oscillatory evolution of models with varying mass. We apply a sophisticated iterative sampling scheme to achieve time resolution ≤ 10 years at the onset of the relevant thermal pulses.We report initial mass of 2.0 ± 0.15 M and an age of 1.17 ± 0.21 Gyr for T UMi. This is the most precise mass and age determination for a single asymptotic giant branch star ever obtained. The ultimate test of our models will be the continued observation of its evolution in real time: we predict that the pulsation periods in T UMi will continue shortening for a few decades before they rebound and begin to lengthen again, as the star expands in radius.

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Section: T Ursae Minorismentioning

confidence: 99%

Section: Age and [Fe/h]mentioning

confidence: 99%

Stellar Evolution in Real Time. I. Models Consistent with the Direct Observation of a Thermal Pulse in T Ursae Minoris

Molnár

Joyce

Kiss

2019

ApJ

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“…The photometric variability due to stellar pulsations is a typical property of post-AGB stars. The period of light variations ranges from several dozen days (Arkhipova et al, 2010;Hrivnak et al2015;2018) to Π ≈ 200 day (Arkhipova et al, 2009;Ikonnikova et al, 2018). Moreover, the pulsating variable AI CMi with period Π ≈ 310 day seems to be the early post-AGB star (Arkhipova et al, 2017).…”

Section: Introductionmentioning

confidence: 94%

“…As in our earlier studies devoted to nonlinear pulsations of AGB stars (Fadeyev, 2017;2018) the pulsation period Π was determined using the discrete Fourier transform of the kinetic energy of the pulsating stellar envelope. Thus, the period estimate of each hydrodynamic model was obtained by averaging over the time interval of the solution of the equations of hydrodynamics.…”

Section: Hydrodynamic Models Of Post-agb Starsmentioning

confidence: 99%

“…The goal of the present work is to investigate nonlinear oscillations of post-AGB stars with effective temperatures 3.6×10 3 K ≤ T eff ≤ 2×10 4 K. The equations of radiation hydrodynamics and time-dependent convection are solved with initial conditions obtained from selected models of previously calculated evolutionary sequences. Computations of stellar evolution were done with the MESA code version 10398 (Paxton et al, 2018) from the main sequence to the stage of the proto-planetary nebula with effective temperature T eff ≈ 2 × 10 4 K. Details of evolutionary computations (the nuclear network, convective mixing, mass loss rates) are described in our previous study (Fadeyev, 2018). The initial composition of stellar material was assumed to correspond to population I stars with fractional mass abundances of hydrogen and helium X = 0.70 and Y = 0.28, respectively.…”

Section: Introductionmentioning

confidence: 99%

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Evolution and Pulsations of Population I Post-AGB Stars

Fadeyev

2019

Astron. Lett.

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Evolutionary calculations of population I stars with initial masses M 0 = 1M ⊙ , 1.5M ⊙ and 2M ⊙ were carried out up to the stage of the proto-planetary nebula. Selected models of post-AGB evolutionary sequences with effective temperatures 3.6 × 10 3 K T eff 2 × 10 4 K were used as initial conditions in calculations of self-escited stellar oscillations. For the first time the sequences of hydrodynamic models of radially pulsating post-AGB stars were computed using the self-consistent solution of the equations of radiation hydrodynamics and time-dependent convection. Within this range of effective temperatures the post-AGB stars are the fundamental mode pulsators with period decreasing as the star evolves from Π ≈ 300 day to several days. Period fluctuations are due to nonlinear effects and are most prominent at effective temperatures T eff < 5000 K. The amplitude of bolometric light variations is ∆M bol ≈ 1 at T eff 6000 K and rapidly decreases with increasing T eff . The theoretical dependence of the pulsation period as a function of effective temperature obtained in the study can be used as a criterion for the evolutionary status of pulsating variables suspected to be post-AGB stars. 1 introduction The red giant evolutionary stage of stars with solar composition and the zero-age main sequence mass M 0 9M ⊙ is completed due to the strong stellar wind and the loss of the major fraction of the hydrogen envelope. The star leaves the asymptotic giant branch (AGB) and crosses the Hertzsprung-Russel diagram (HRD) at nearly constant luminosity towards the region of planetary nebula cores with effective temperatures T eff ∼ 10 5 K. An idea that the planetary nebulae originate from red giants was suggested by Shklovsky (1956) and was later confirmed by evolutionary computations (PaczyńskiFormation of the opaque gas-dust envelope surrounding the star on the tip of the AGB substantially restricts abilities of optical observations, so that the evolutionary transition to the post-AGB stage still remains unclear. The strong stellar wind on the tip of the AGB seems to be due to nonlinear stellar pulsations that lead to dynamical instability of the outer stellar layers (Tuchman et al., 1978). Therefore, large infrared (IR) excesses detected in post-AGB stars (Volk, Kwok, 1989; Hrivnak et al., 1989; 1994; Ikonnikova et al., 2018) indicate existence of circumstellar dust grains condensed during the preceding evolutionary stage with high mass loss rates. The photometric variability due to stellar pulsations is a typical property of post-AGB stars. The period of light variations ranges from several dozen days (Arkhipova et al., 2010; Hrivnak et al.2015; 2018) to Π ≈ 200 day (Arkhipova et al. Ikonnikova et al., 2018). Moreover, the pulsating variable AI CMi with period Π ≈ 310 day seems to be the early post-AGB star (Arkhipova et al., 2017). A common feature of post-AGB stars is a lack of strict repetition in light variations, so that observational estimates of the period are often highly uncertain.The post-AGB stars are on the late...

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Hydrodynamic modelling of pulsation period decrease in the Mira-type variable T UMi

Fadeyev

2022

Monthly Notices of the Royal Astronomical Society

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Pulsation period decrease during the initial stage of the thermal pulse in the helium–burning shell of the Mira–type variable T UMi is investigated with numerical methods of stellar evolution and radiation hydrodynamics. To this end, a grid of evolutionary tracks was calculated for stars with masses on the main sequence 1 M⊙ ≤ MZAMS ≤ 2.2 M⊙ and metallicity Z = 0.01. Selected models of AGB evolutionary sequences were used for determination of the initial conditions and the time–dependent inner boundary conditions for the equations of hydrodynamics describing evolutionary changes in the radially pulsating star. The onset of period decrease during the initial stage of the thermal pulse is shown to nearly coincide with the peak helium–burning luminosity. The most rapid decrease of the period occurs during the first three decades. The pulsation period decreases due to both contraction of the star and mode switching from the fundamental mode to the first overtone. The time–scale of mode switching is of the order of a few dozen pulsation cycles. The present–day model of the Mira–type variable T UMi is the first–overtone pulsator with small-amplitude semi–regular oscillations. Theoretical estimates of the pulsation period at the onset of period decrease and the rate of period change three decades later are shown to agree with available observational data on T UMi for AGB stars with masses 1.04 M⊙ ≤ M ≤ 1.48 M⊙.

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A Model of the Mira–Type Star T UMi

Cited by 4 publications

References 20 publications

Stellar Evolution in Real Time. I. Models Consistent with the Direct Observation of a Thermal Pulse in T Ursae Minoris

Stellar Evolution in Real Time. I. Models Consistent with the Direct Observation of a Thermal Pulse in T Ursae Minoris

Evolution and Pulsations of Population I Post-AGB Stars

Hydrodynamic modelling of pulsation period decrease in the Mira-type variable T UMi

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