Oscillation Mode Variability in Evolved Compact Pulsators from Kepler Photometry. I. The Hot B Subdwarf Star KIC 3527751

Zong, Weikai; Charpinet, S.; Fu, Jian-Ning; Vauclair, G.; Niu, Jia-Shu; Su, Jie

doi:10.3847/1538-4357/aaa548

Cited by 47 publications

(57 citation statements)

References 55 publications

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“…The mechanisms controlling mode amplitude saturation are not well known. Moreover, amplitudes can change over long timescales in g-mode sdB pulsators, probably because of nonlinear mode interactions, as documented by Zong et al (2016aZong et al ( , 2018. In this context, bottom panel of Fig.…”

Section: Systemmentioning

confidence: 81%

“…From a pulsation perspective, these frequencies could very well be real independent modes of different degree that happen to have very close frequencies, barely resolved with the current data set. However, they may also be the signature of intrinsic amplitude and/or frequency modulations of the dominant peak, as discussed by Zong et al (2016bZong et al ( ,a, 2018. Therefore, as a precaution, we retain only the main (highest amplitude) peak of each complex, namely f 7 and f 14 , for the detailed asteroseismic study of TIC 278659026.…”

Section: Pulsation Spectrum In G-modementioning

confidence: 99%

“…This difficulty was overcome when CoRoT and Kepler observations Østensen et al 2010 first provided much clearer views of the g-mode spectrum in these stars. Since then, many studies based mostly on Kepler and K2 data have enriched our general understanding of g-mode pulsations in sdBs, and in some cases have provided new insights into various properties of these stars (e.g., Reed et al 2011Reed et al , 2019Østensen et al 2014;Telting et al 2014;Zong et al 2016aZong et al , 2018Baran et al 2017;Kern et al 2017;Ketzer et al 2017), such as their rotation rates (see, e.g., Pablo et al 2012;Reed et al 2014;Charpinet et al 2018, and references therein).…”

Section: Introductionmentioning

confidence: 99%

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TESS first look at evolved compact pulsators

Charpinet

Brassard

Fontaine

et al. 2019

A&A

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Context. The TESS satellite was launched in 2018 to perform high-precision photometry from space over almost the whole sky in a search for exoplanets orbiting bright stars. This instrument has opened new opportunities to study variable hot subdwarfs, white dwarfs, and related compact objects. Targets of interest include white dwarf and hot subdwarf pulsators, both carrying high potential for asteroseismology. Aims. We present the discovery and detailed asteroseismic analysis of a new g-mode hot B subdwarf (sdB) pulsator, EC 21494−7018 (TIC 278659026), monitored in TESS first sector using 120-s cadence. Methods. The TESS light curve was analyzed with standard prewhitening techniques, followed by forward modeling using our latest generation of sdB models developed for asteroseismic investigations. By simultaneously best-matching all the observed frequencies with those computed from models, we identified the pulsation modes detected and, more importantly, we determined the global parameters and structural configuration of the star. Results. The light curve analysis reveals that EC 21494−7018 is a sdB pulsator counting up to 20 frequencies associated with independent g-modes. The seismic analysis singles out an optimal model solution in full agreement with independent measurements provided by spectroscopy (atmospheric parameters derived from model atmospheres) and astrometry (distance evaluated from Gaia DR2 trigonometric parallax). Several key parameters of the star are derived. Its mass (0.391 ± 0.009 M⊙) is significantly lower than the typical mass of sdB stars and suggests that its progenitor has not undergone the He-core flash; therefore this progenitor could originate from a massive (≳2 M⊙) red giant, which is an alternative channel for the formation of sdBs. Other derived parameters include the H-rich envelope mass (0.0037 ± 0.0010 M⊙), radius (0.1694 ± 0.0081 R⊙), and luminosity (8.2 ± 1.1 L⊙). The optimal model fit has a double-layered He+H composition profile, which we interpret as an incomplete but ongoing process of gravitational settling of helium at the bottom of a thick H-rich envelope. Moreover, the derived properties of the core indicate that EC 21494−7018 has burnt ∼43% (in mass) of its central helium and possesses a relatively large mixed core (Mcore = 0.198 ± 0.010 M⊙), in line with trends already uncovered from other g-mode sdB pulsators analyzed with asteroseismology. Finally, we obtain for the first time an estimate of the amount of oxygen (in mass; X(O)core = 0.16+0.13−0.05) produced at this stage of evolution by an helium-burning core. This result, along with the core-size estimate, is an interesting constraint that may help to narrow down the still uncertain 12C(α, γ)16O nuclear reaction rate.

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Section: Systemmentioning

confidence: 81%

Section: Pulsation Spectrum In G-modementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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TESS first look at evolved compact pulsators

Charpinet

Brassard

Fontaine

et al. 2019

A&A

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“…The model was then optimized to find the maximum a posteriori (MAP), using the L-BFGS-S routine (Zhu et al 1994) as implemented in SciPy (Jones et al 2001).…”

Section: Examplesmentioning

confidence: 99%

Forward Modeling the Orbits of Companions to Pulsating Stars from Their Light Travel Time Variations

Hey

Murphy

Foreman-Mackey

et al. 2020

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Mutual gravitation between a pulsating star and an orbital companion leads to a time-dependent variation in path length for starlight traveling to Earth. These variations can be used for coherently pulsating stars, such as the δ Scuti variables, to constrain the masses and orbits of their companions. Observing these variations for δ Scuti stars has previously relied on subdividing the light curve and measuring the average pulsation phase in equally sized subdivisions, which leads to under-sampling near periapsis. We introduce a new approach that simultaneously forward-models each sample in the light curve and show that this method improves upon current sensitivity limits -especially in the case of highly eccentric and short-period binaries. We find that this approach is sensitive enough to observe Jupiter mass planets around δ Scuti stars under ideal conditions, and use gravity-mode pulsations in the subdwarf B star KIC 7668647 to detect its companion without radial velocity data. We further provide robust detection limits as a function of the SNR of the pulsation mode and determine that the minimum detectable light travel time amplitude for a typical Kepler δ Scuti is around 2 s. This new method significantly enhances the application of light travel time variations to detecting short period binaries with pulsating components, and pulsating A-type exoplanet host stars, especially as a tool for eliminating false positives.

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“…Winget et al 1983Winget et al , 1994Vauclair et al 2011) and subdwarf B stars (e.g. Kilkenny 2010;Zong et al 2018), as well as in a diverse range of main-sequence pulsators, including β Cepheid (Pigulski & Pojmański 2008;Degroote et al 2010), δ-Scuti (e.g. Breger & Pamyatnykh 1998;Bowman et al 2016;Breger et al 2017), and rapidly oscillating Ap stars (e.g.…”

Section: Introductionmentioning

confidence: 99%

Modelling stochastic signatures in classical pulsators

Avelino

Cunha

Chaplin

2020

Monthly Notices of the Royal Astronomical Society

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We consider the impact of stochastic perturbations on otherwise coherent oscillations of classical pulsators. The resulting dynamics are modelled by a driven damped harmonic oscillator subject to either an external or an internal forcing and white noise velocity fluctuations. We characterize the phase and relative amplitude variations using analytical and numerical tools. When the forcing is internal the phase variation displays a random walk behaviour and a red noise power spectrum with a ragged erratic appearance. We determine the dependence of the root mean square phase and relative amplitude variations (σ ∆ϕ and σ ∆A/A , respectively) on the amplitude of the stochastic perturbations, the damping constant η, and the total observation time t obs for this case, under the assumption that the relative amplitude variations remain small, showing that σ ∆ϕ increases with t 1/2 obs becoming much larger than σ ∆A/A for t obs η −1 . In the case of an external forcing the phase and relative amplitude variations remain of the same order, independent of the observing time. In the case of an internal forcing, we find that σ ∆ϕ does not depend on η. Hence, the damping time cannot be inferred from fitting the power of the signal, as done for solar-like pulsators, but the amplitude of the stochastic perturbations may be constrained from the observations. Our results imply that, given sufficient time, the variation of the phase associated to the stochastic perturbations in internally driven classical pulsators will become sufficiently large to be probed observationally.

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Oscillation Mode Variability in Evolved Compact Pulsators from Kepler Photometry. I. The Hot B Subdwarf Star KIC 3527751

Cited by 47 publications

References 55 publications

TESS first look at evolved compact pulsators

TESS first look at evolved compact pulsators

Forward Modeling the Orbits of Companions to Pulsating Stars from Their Light Travel Time Variations

Modelling stochastic signatures in classical pulsators

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