Linear and nonlinear pulsation models with the variable 
 Eddington factor approximation of radiative hydrodynamics

Aikawa, Toshiki

doi:10.1051/0004-6361:20078496

Cited by 3 publications

(6 citation statements)

References 32 publications

(32 reference statements)

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“…Aikawa [34,35] demonstrated that, in the case of low-mass UU Her supergiants, low-amplitude pulsations could appear when the luminosity was sufficiently high, and the pulsations of higher-luminosity objects could become irregular and even chaotic. Pulsations with an amplitude of about 15 km/s were detected in the atmosphere of the closest relative of LN Hya-the high-latitude supergiant UU Her, whose pulsation periods, P = 73 d in the fundamental mode and P = 45 d in the first overtone, are known from photometric data [36].…”

Section: Pulsations and Atmospheric Kinematics Of Ln Hyamentioning

confidence: 99%

High-latitude supergiants: Anomalies in the spectrum of LN Hya in 2010

Клочкова

Панчук

2012

Astron. Rep.

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High-spectral-resolution observations with the Special Astrophysical Observatory 6-m telescope obtained in 2003-2011 are used to study features of the optical spectrum and the velocity field in the atmosphere of the semiregular variable LN Hya in detail. The weak, symmetric, photospheric absorption lines indicate radial-velocity variations from night to night (by as much as 3 km/s), resulting from small pulsations. Peculiarities and profile variations were found for strong lines of FeI, FeII, BaII, SiII, etc. The profiles of these lines were asymmetric: their short-wavelength wings were extended and their cores were either split or distorted by emission. During the 2010 observing season, the position and depth of the Hα absorption component, the intensities of the short-and long-wavelength emission components, and the intensity ratio of the latter components varied from spectrum to spectrum. Weak emission lines of neutral atoms (VI, MnI, CoI, NiI, FeI) appeared in the spectrum of June 1, 2010. These spectral peculiarities, recorded for the first time, suggest that we have detected rapid changes in the physical conditions in the upper atmospheric layers of LN Hya in 2010.

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Section: Pulsations and Atmospheric Kinematics Of Ln Hyamentioning

confidence: 99%

High-latitude supergiants: Anomalies in the spectrum of LN Hya in 2010

Клочкова

Панчук

2012

Astron. Rep.

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“…The hydrostatic equilibrium envelope models were constructed as described by Aikawa (2008). In this method the variable Eddington factor approximation is applied to radiative hydrodynamics instead of the diffusion approximation.…”

Section: Hydrostatic Modelsmentioning

confidence: 99%

“…We thus followed Aikawa (2008) to get the periods and the growth rates of radial pulsation at the fully nonadiabatic condition. Starting in the adiabatic condition, the periods and the growth rates were calculated step-by-step by increasing the effects of nonadiabaticity.…”

Section: Linear Analysismentioning

confidence: 99%

“…Nonlinear simulations for models with pulsationally unstable modes were performed with the variable Eddington factor, f dyn (Aikawa 2008), snapshot values of the Eddington factor at each time step. The simulation of each model was started from the hydrostatic equilibrium except for the velocity perturbation.…”

Section: Nonlinear Simulationmentioning

confidence: 99%

“…We first examine the linear stability of radial modes, and then the nonlinear simulations are performed for the models with pulsationally unstable modes. The nonlinear simulation, as well as linear analysis, are performed with a hydrodynamic code with the variable Eddington factor approximation of radiative transfer (Aikawa 2008).…”

Section: Introductionmentioning

confidence: 99%

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The instability strip and pulsation features of post-AGB star models

Aikawa

2010

A&A

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Aims. The instability strip and characteristics of the nonlinear behavior of the radial pulsation are examined for the observed photometric variability of post-AGB stars. Methods. A linear stability analysis for radial pulsation modes is performed in the domain 3.70 ≤ log T eff ≤ 3.90, 0.0 ≤ log g ≤ 1.8, assuming a total mass 0.6 M and 0.8 M for post-AGB stars. Radial modes up to the 5th overtone are considered, since we expect that there are some strange modes amongst high-order modes. Nonlinear simulations are tried for all the models, which have at least one pulsationally unstable mode. Results. Pulsationally unstable modes are found in a large region of the domain, and these modes may be responsible for the observed variability. Nonlinear simulations on models that have unstable modes with higher overtones reveal the variability through small peakto-peak variations. These variations are characteristics of the observed variations for some post-AGB stars located in the bluer region of the classical instability strip.

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Bridging theory and observations in stellar pulsations: the impact of convection and metallicity on the instability strips of classical and type-II cepheids

Deka,

Bellinger,

Kanbur

et al. 2024

Monthly Notices of the Royal Astronomical Society

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The effect of metallicity on the theoretical and empirical period-luminosity (PL) relations of Cepheid variables is not well understood and remains a highly debated issue. Here, we examine empirical colour-magnitude diagrams (CMDs) of Classical and Type-II Cepheids in the Magellanic Clouds and compare those with the theoretically predicted instability strip (IS) edges. We explore the effects of incorporating turbulent flux, turbulent pressure, and radiative cooling into the convection theory on the predicted IS at various metallicities using mesa-rsp. We find that the edges become redder with the increasing complexity of convection physics incorporated in the fiducial convection sets, and are similarly shifted to the red with increasing metallicity. The inclusion of turbulent flux and pressure improves the agreement of the red edge of the IS, while their exclusion leads to better agreement with observations of the blue edge. About $90\%$ of observed stars are found to fall within the predicted bluest and reddest edges across the considered variations of turbulent convection parameters. Furthermore, we identify and discuss discrepancies between theoretical and observed CMDs in the low effective temperature and high luminosity regions for stars with periods greater than ∼20 days. These findings highlight the potential for calibrating the turbulent convection parameters in stellar pulsation models or the prediction of a new class of rare, long-period, ‘red Cepheids’, thereby improving our understanding of Cepheids and their role in cosmological studies.

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Linear and nonlinear pulsation models with the variable Eddington factor approximation of radiative hydrodynamics

Cited by 3 publications

References 32 publications

High-latitude supergiants: Anomalies in the spectrum of LN Hya in 2010

High-latitude supergiants: Anomalies in the spectrum of LN Hya in 2010

The instability strip and pulsation features of post-AGB star models

Bridging theory and observations in stellar pulsations: the impact of convection and metallicity on the instability strips of classical and type-II cepheids

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