A Driving Mechanism for the Newly Discovered Long‐Period Pulsating Subdwarf B Stars

Fontaine, G.; Brassard, P.; Charpinet, S.; Green, E. M.; Chayer, P.; Billères, M.; Randall, S. K.

doi:10.1086/378270

Cited by 175 publications

(180 citation statements)

References 37 publications

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“…6 shows which modes are driven along the evolutionary track of an sdB with a total mass of 0.47 M and an envelope mass of 9.0×10 −5 M . Fontaine et al (2003) showed that the blue-edge of the instability strip is highly sensitive to the spherical degree. This can also be seen in this example, in which g-modes of degree l = 2-4 are excited at all ages (except for the very first model), while the l = 1 g-modes are not excited during the first 50 Myr, and then only 1 mode is excited until almost the end of the evolutionary track.…”

Section: Pressure and Gravity Mode Instability Stripsmentioning

confidence: 99%

The blue-edge problem of the V1093 Herculis instability strip revisited using evolutionary models with atomic diffusion

Bloemen

Aerts

et al. 2014

A&A

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We have computed a new grid of evolutionary subdwarf B star (sdB) models from the start of central He burning, taking into account atomic diffusion due to radiative levitation, gravitational settling, concentration diffusion, and thermal diffusion. We have computed the non-adiabatic pulsation properties of the models and present the predicted p-mode and g-mode instability strips. In previous studies of the sdB instability strips, artificial abundance enhancements of Fe and Ni were introduced in the pulsation driving layers. In our models, the abundance enhancements of Fe and Ni occur naturally, eradicating the need to use artificial enhancements. We find that the abundance increases of Fe and Ni were previously underestimated and show that the instability strip predicted by our simulations solves the so-called blue edge problem of the subdwarf B star g-mode instability strip. The hottest known g-mode pulsator, KIC 10139564, now resides well within the instability strip even when only modes with low spherical degrees (l ≤ 2) are considered.

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Section: Pressure and Gravity Mode Instability Stripsmentioning

confidence: 99%

The blue-edge problem of the V1093 Herculis instability strip revisited using evolutionary models with atomic diffusion

Bloemen

Aerts

et al. 2014

A&A

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“…The presence of excited pulsation modes in sdB stars is understood by the action of a κ-effect associated with an opacity bump caused by partial ionization of heavy metals -especially iron -that are locally enhanced by radiative levitation at work in the envelope (Charpinet et al 2001;Fontaine et al 2003). Although our current models fairly well match the instability strip observed for the short-period p-mode pulsators, there is a well known discrepancy for the g-mode pulsators that remains to be solved (Charpinet et al 2007).…”

Section: Period Fit and Mode Identificationmentioning

confidence: 99%

Structural and core parameters of the hot B subdwarf KPD 0629-0016 from CoRoT g-mode asteroseismology

Grootel

Charpinet

Fontaine

et al. 2010

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Context. The asteroseismic exploitation of long period, g-mode hot B subdwarf pulsators (sdBV s ), undermined so far by limitations associated with ground-based observations, has now become possible, thanks to high quality data obtained from space such as those recently gathered with the CoRoT (COnvection, ROtation, and planetary Transits) satellite. Aims. We propose a detailed seismic analysis of the sdBV s star KPD 0629-0016, the first compact pulsator monitored with CoRoT, using the g-mode pulsations recently uncovered by that space-borne observatory during short run SRa03. Methods. We use a forward modeling approach on the basis of our latest sdB models, which are now suitable for the accurate computation of the g-mode pulsation properties. The simultaneous match of the independent periods observed in KPD 0629-0016 with those of the models leads objectively to the identification of the pulsation modes and, more importantly, to the determination of the structural and core parameters of the star.Results. The optimal model we found closely reproduces the 18 observed periods retained in our analysis at a 0.23% level on average. These are identified as low-degree ( = 1 and 2), intermediate-order (k = −9 through −74) g-modes. The structural and core parameters for KPD 0629-0016 are the following (formal fitting errors only): T eff = 26 290 ± 530 K, log g = 5.450 ± 0.034, M * = 0.471 ± 0.002 M , log (M env /M * ) = −2.42 ± 0.07, log (1 − M core /M * ) = −0.27 ± 0.01, and X core (C+O) = 0.41 ± 0.01. We additionally derive an age of 42.6 ± 1.0 Myr after the zero-age extreme horizontal branch, the radius R = 0.214 ± 0.009 R , the luminosity L = 19.7 ± 3.2 L , the absolute magnitude M V = 4.23 ± 0.13, the reddening index E(B − V) = 0.128 ± 0.023, and the distance d = 1190 ± 115 pc. Conclusions. The advent of high-precision time-series photometry from space with instruments like CoRoT now allows as demonstrated with KPD 0629-0016 the full exploitation of g-modes as deep probes of the internal structure of these stars, in particular for determining the mass of the convective core and its chemical composition.

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“…The opacity mechanism operating in the Fe opacity bump around log T = 5.3 has been successfully used to explain the excitation of p-as well as the g-modes (Charpinet et al 1996;Fontaine et al 2003). This opacity bump is caused by Fe accumulation owing to the competing diffusion processes of gravitational settling and radiative levitation.…”

Section: Introductionmentioning

confidence: 99%

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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A Driving Mechanism for the Newly Discovered Long‐Period Pulsating Subdwarf B Stars

Cited by 175 publications

References 37 publications

The blue-edge problem of the V1093 Herculis instability strip revisited using evolutionary models with atomic diffusion

The blue-edge problem of the V1093 Herculis instability strip revisited using evolutionary models with atomic diffusion

Structural and core parameters of the hot B subdwarf KPD 0629-0016 from CoRoT g-mode asteroseismology

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

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