The opacity mechanism in B-type stars - II. Excitation of high-order g-modes in main-sequence stars

Dziembowski, W. A.; Moskalik, P.; Pamyatnykh, A. A.

doi:10.1093/mnras/265.3.588

Cited by 221 publications

(180 citation statements)

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“…Secondly, only high-order g-modes (with long periods) can be excited, for low-order g-modes are affected by significant radiative damping. The same phenomenon occurs in SPB stars (Dziembowski et al 1993;Dupret et al 2008). Interestingly, the blue edge of the l ≤ 3 instability strip of our sdB models with OP opacities corresponds to the observed blue edge of the V1093 Her variables at log T eff = 4.47.…”

Section: Stability Analysis Of a Grid Of Sdb Modelssupporting

confidence: 81%

Impact of helium diffusion and helium-flash-induced carbon production on gravity-mode pulsations in subdwarf B stars

Nelemans²,

Aerts

et al. 2009

A&A

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Context. Realistic stellar models are essential to the forward modelling approach in asteroseismology. For practicality however, certain model assumptions are also required. For example, in the case of subdwarf B stars, one usually starts with zero-age horizontal branch structures without following the progenitor evolution. Aims. We analyse the effects of common assumptions in subdwarf B models on the g-mode pulsational properties. We investigate if and how the pulsation periods are affected by the H-profile in the core-envelope transition zone. Furthermore, the effects of Cproduction and convective mixing during the core helium flash are evaluated. Finally, we reanalyse the effects of stellar opacities on the mode excitation in subdwarf B stars. Methods. We computed detailed stellar evolutionary models of subdwarf B stars, and their non-adiabatic pulsational properties. Atomic diffusion of H and He is included consistently during the evolution calculations. The number fractions of Fe and Ni are gradually increased by up to a factor of 10 around log T = 5.3. This is necessary for mode excitation and to approximate the resulting effects of radiative levitation. We performed a pulsational stability analysis on a grid of subdwarf B models constructed with OPAL and OP opacities. Results. We find that helium settling causes a shift in the theoretical blue edge of the g-mode instability domain to higher effective temperatures. This results in a closer match to the observed instability strip of long-period sdB pulsators, particularly for l ≤ 3 modes. We show further that the g-mode spectrum is extremely sensitive to the H-profile in the core-envelope transition zone. If atomic diffusion is efficient, details of the initial shape of the profile become less important in the course of evolution. Diffusion broadens the chemical gradients, and results in less effective mode trapping and different pulsation periods. Furthermore, we report on the possible consequences of the He-flash for the g-modes. The outer edge of a flash-induced convective region introduces an additional chemical transition in the stellar models, and the corresponding spike in the Brünt-Väisälä frequency produces a complicated mode trapping signature in the period spacings.

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Section: Stability Analysis Of a Grid Of Sdb Modelssupporting

confidence: 81%

Impact of helium diffusion and helium-flash-induced carbon production on gravity-mode pulsations in subdwarf B stars

Nelemans²,

Aerts

et al. 2009

A&A

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“…This is well justified because the pulsational instability mechanism and theoretical oscillation spectra of B stars were already reviewed by Dziembowski & Pamyatnykh (1992), Gautsschy & Saio (1993), Dziembowski et al (1993), Moskalik (1995), Dupret (2001), and others. More recent investigations (e.g.…”

Section: Oscillation Spectra Of Early-type Starsmentioning

confidence: 84%

“…The properties of the basic eigenfunctions, kinetic energy distributions and work integrals for models of B stars were already discussed by Dziembowski & Pamyatnykh (1992), Dziembowski et al (1993), Pamyatnykh (1999), Dziembowski (2009), Dupret (2001, and others. The proper behavior of the Rosseland-mean opacity and eigenfunctions are necessary, but not sufficient conditions for the κ-mechanism to work.…”

Section: Seismic Modelsmentioning

confidence: 90%

Seismic models of O and B stars with Kurucz’s opacity data

Cugier

2014

A&A

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Aims. We investigated seismic models of O and B stars calculated with the new Kurucz opacities implemented in the Opacity Project (OP) and Rogers & Iglesias OPAL opacity tables (OPAL). Methods. We studied the problem using Dziembowski's computer codes for linear, nonadiabatic, and nonradial oscillations. We considered seismic models of main sequence (MS) stars for different chemical compositions of elements in the mass-range 9 ≤ M ≤ 70 M . Results. The new opacity bump at lg T ≈ 5.06 that occurs in Kurucz's data influences evolutionary tracks mainly for M ≥ 30 M and markedly changes the driving zone for pulsations of stars in the whole mass range studied. We obtained no unstable oscillation modes for models corresponding to the abundance parameter Z ≤ 0.013 and only unstable low-frequency g-modes for 0.013 < Z ≤ 0.021. Conclusions. The opacity bump at lg T ≈ 5.3 should be significantly larger than the opacity bump at lg T ≈ 5.06 to drive pulsations of B stars in low-degree p-modes. Models with an increased OPAL (or OP) opacity bump at lg T ≈ 5.3 by a factor of about 1.7 have sufficiently large driving zones to excite modes in the β Cephei frequency-domain for 0.003 ≤ Z ≤ 0.021. These values of Z are in a good agreement with those derived spectroscopically for stars in the Galaxy and Magellanic Clouds.

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“…The observational properties of the SPB stars were broadly discussed, e.g., by Balona (2000) and , 2007. These modes are driven by the classical κ-mechanism operating in the metal opacity bump (Dziembowski, Moskalik & Pamyatnykh 1993;Gautschy & Saio 1993). There are three basic problems which complicate the interpretation of the SPB pulsations and make seismic modelling of these pulsators particularly difficult.…”

Section: Introductionmentioning

confidence: 99%

Identification of pulsational modes in rotating slowly pulsating B-type stars

Szewczuk

Daszyńska‐Daszkiewicz

2015

Monthly Notices of the Royal Astronomical Society

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Knowledge of the geometry of pulsational modes is a prerequisite for seismic modelling of stars. In the case of slowly pulsating B-type (SPB) pulsators, the simple zero-rotation approach so far used for mode identification is usually not valid because pulsational frequencies are often of the order of the rotational frequency. Moreover, this approach allows us to determine only the spherical harmonic degree, , while the azimuthal order, m, is beyond its reach. On the other hand, because of the density of oscillation spectra of SPB stars, knowledge of m is indispensable if one wants to assign the radial order, n, to the observed frequency peaks. Including the effects of rotation via the traditional approximation, we perform identification of the mode angular numbers ( , m) for 31 SPB stars with available multicolour time series photometry. Simultaneously, constraints on the rotational velocity, V rot , and the inclination angle, i, are determined assuming uniform rotation and a constant value of V rot sin i. Dependence of the results on the adopted model is tested using HD 21071 as an example. Despite some model uncertainties and limitations of the method, our studies show the correct approach to identifying the low-frequency oscillation modes.

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The opacity mechanism in B-type stars - II. Excitation of high-order g-modes in main-sequence stars

Cited by 221 publications

References 0 publications

Impact of helium diffusion and helium-flash-induced carbon production on gravity-mode pulsations in subdwarf B stars

Impact of helium diffusion and helium-flash-induced carbon production on gravity-mode pulsations in subdwarf B stars

Seismic models of O and B stars with Kurucz’s opacity data

Identification of pulsational modes in rotating slowly pulsating B-type stars

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