Pulsations of intermediate–mass stars on the asymptotic giant branch

Fadeyev, Yu. A.

doi:10.1134/s1063773717080059

Cited by 5 publications

(8 citation statements)

References 37 publications

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“…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%

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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Section: Hydrodynamic Models Of Post-agb Starsmentioning

confidence: 99%

Evolution and Pulsations of Population I Post-AGB Stars

Fadeyev

2019

Astron. Lett.

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“…In our previous work (Fadeyev 2017), we investigated hydrodynamic models of stars with initial masses 2M ⊙ ≤ M ZAMS ≤ 5M ⊙ on the stage of thermal instability of the helium burning shell (TP-AGB). In particular, it was shown that reduction of the pulsation period in T UMi 2 cannot be explained by models with initial mass M ZAMS > 2M ⊙ .…”

Section: Introductionmentioning

confidence: 99%

“…The mean time interval between helium flashes depends on the stellar mass and ranges from 10 4 to 10 5 yr (Herwig 2000;Weiss, Ferguson 2009), whereas the time scale of the changes in the helium burning shell luminosity is ≤ 10 3 yr (Wood, Zarro, 1981; Boothroyd, Sackmann 1988). One of the consequences of thermal instability is secular period change observed in some Miras because during the short-term variation of the helium burning shell luminosity the stellar radius varies by as much as a factor of three (Wood, Zarro, 1981;Fadeyev 2016Fadeyev , 2017.…”

Section: Introductionmentioning

confidence: 99%

“…The mira-type star T UMi is a rare exception which allows us to obtain an another relationship between observational properties of the star and its evolutionary status. This red giant of spectral type M5.5e (Keenan 1966) was pulsating with period Π ≈ 315 day before 1970s but later the period commenced its rapid shortening (Gál, Szatmáry 1995) In our previous work (Fadeyev 2017), we investigated hydrodynamic models of stars with initial masses 2M ⊙ ≤ M ZAMS ≤ 5M ⊙ on the stage of thermal instability of the helium burning shell (TP-AGB). In particular, it was shown that reduction of the pulsation period in T UMi 2 cannot be explained by models with initial mass M ZAMS > 2M ⊙ .…”

Section: Introductionmentioning

confidence: 99%

“…Similar to our previous works the selected models of evolutionary sequences are used as initial conditions in solution of the Cauchy problem for equations of radiation hydrodynamics and time-dependent convection describing radial stellar oscillations. Methods of the solution are discussed in our earlier papers (Fadeyev 2016;2017).…”

Section: Introductionmentioning

confidence: 99%

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A Model of the Mira–Type Star T UMi

Fadeyev

2018

Astron. Lett.

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Stellar evolution calculations were carried out from the main sequence to the final stage of the asymptotic giant branch for stars with initial masses 1M ⊙ ≤ M ZAMS ≤ 2M ⊙ and metallicity Z = 0.01. Selected models of evolutionary sequences were used as initial conditions for solution of the equations of radiation hydrodynamics and time-dependent convection describing radial stellar pulsations. The study was aimed to construct the hydrodynamic models of Mira-type stars that show the secular decrease in the pulsation period Π commenced in 1970-th at Π = 315 day. We show that such a condition for the period change is satisfied with evolutionary sequences 1M ⊙ ≤ M ZAMS ≤ 1.2M ⊙ and the best agreement with observations is obtained for M ZAMS = 1.2M ⊙ . The pulsation period reduction is due to both the stellar radius decrease during the thermal pulse of the helium burning shell and mode switch from the fundamental mode to the first overtone. Theoretical estimates of the fundament parameters of the star at the onset of pulsation period reduction are as follows: the mass is M = 0.93M ⊙ , the luminosity is L = 4080L ⊙ , and the radius is R = 220R ⊙ . The mode switch occurs 35 years after the onset of period reduction.

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The ASAS-SN catalogue of variable stars IX: The spectroscopic properties of Galactic variable stars

Jayasinghe

Kochanek

Stanek

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The All-Sky Automated Survey for Supernovae (ASAS-SN) provides long baseline (∼4 yrs) V −band light curves for sources brighter than V≲ 17 mag across the whole sky. We produced V-band light curves for a total of ∼61.5 million sources and systematically searched these sources for variability. We identified ∼426, 000 variables, including ∼219, 000 new discoveries. Most (${\sim }74\%$) of our discoveries are in the Southern hemisphere. Here we use spectroscopic information from LAMOST, GALAH, RAVE, and APOGEE to study the physical and chemical properties of these variables. We find that metal-poor eclipsing binaries have orbital periods that are shorter than metal-rich systems at fixed temperature. We identified rotational variables on the main-sequence, red giant branch and the red clump. A substantial fraction (${\gtrsim }80\%$) of the rotating giants have large vrot or large NUV excesses also indicative of fast rotation. The rotational variables have unusual abundances suggestive of analysis problems. Semi-regular variables tend to be lower metallicity ($\rm [Fe/H]{\sim }-0.5$) than most giant stars. We find that the APOGEE DR16 temperatures of oxygen-rich semi-regular variables are strongly correlated with the WRP − WJK color index for $\rm T_{eff}\lesssim 3800$ K. Using abundance measurements from APOGEE DR16, we find evidence for Mg and N enrichment in the semi-regular variables. We find that the Aluminum abundances of the semi-regular variables are strongly correlated with the pulsation period, where the variables with $\rm P\gtrsim 60$ days are significantly depleted in Al.

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Pulsations of intermediate–mass stars on the asymptotic giant branch

Cited by 5 publications

References 37 publications

Evolution and Pulsations of Population I Post-AGB Stars

Evolution and Pulsations of Population I Post-AGB Stars

A Model of the Mira–Type Star T UMi

The ASAS-SN catalogue of variable stars IX: The spectroscopic properties of Galactic variable stars

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