g-mode trapping and period spacings in hot B subdwarf stars

Charpinet, S.; Grootel, Valérie Van; Brassard, P.; Fontaine, G.

doi:10.1017/s1743921313014737

Cited by 15 publications

(18 citation statements)

References 2 publications

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“…The model with the sharpest composition profile shows a pattern similar to the ∆m = 0.001 M⊙ case, except with more extreme variation in ∆P . In both cases the amplitude of this variation oscillates, with a period of around 1.8 × 10 4 s. We also note the similarity between the period spacing pattern of these two models and the model by Charpinet et al (2014).…”

Section: Subdwarf B Modelssupporting

confidence: 62%

The treatment of mixing in core helium burning models – I. Implications for asteroseismology

Constantino

Campbell

Christensen‐Dalsgaard

et al. 2015

Mon. Not. R. Astron. Soc.

112

164

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The detection of mixed oscillation modes offers a unique insight into the internal structure of core helium burning (CHeB) stars. The stellar structure during CHeB is very uncertain because the growth of the convective core, and/or the development of a semiconvection zone, is critically dependent on the treatment of convective boundaries. In this study we calculate a suite of stellar structure models and their non-radial pulsations to investigate why the predicted asymptotic g-mode ℓ = 1 period spacing ∆Π 1 is systematically lower than is inferred from Kepler field stars. We find that only models with large convective cores, such as those calculated with our newly proposed "maximal-overshoot" scheme, can match the average ∆Π 1 reported. However, we also find another possible solution that is related to the method used to determine ∆Π 1 : mode trapping can raise the observationally inferred ∆Π 1 well above its true value. Even after accounting for these two proposed resolutions to the discrepancy in average ∆Π 1 , models still predict more CHeB stars with low ∆Π 1 ( < ∼ 270 s) than are observed. We establish two possible remedies for this: i) there may be a difficulty in determining ∆Π 1 for early CHeB stars (when ∆Π 1 is lowest) because of the effect that the sharp composition profile at the hydrogen burning shell has on the pulsations, or ii) the mass of the helium core at the flash is higher than predicted. Our conclusions highlight the need for the reporting of selection effects in asteroseismic population studies in order to safely use this information to constrain stellar evolution theory.

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Section: Subdwarf B Modelssupporting

confidence: 62%

The treatment of mixing in core helium burning models – I. Implications for asteroseismology

Constantino

Campbell

Christensen‐Dalsgaard

et al. 2015

Mon. Not. R. Astron. Soc.

112

164

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“…Finally, Charpinet et al (2011) have recently proposed two very similar seismic models for the g-mode pulsator KIC02697388, a newly-discovered variable sdB star in the Kepler field. Model I is characterized by values of log g = 5.489 ± 0.033, T eff = 25395 ± 225 K, M = 0.463 ± 0.009 M , and log M env /M = −2.30 ± 0.05, while Model II is defined by the values of log g = 5.499 ± 0.049, T eff = 25 395 ± 225 K, M = 0.452 ± 0.012 M , and log M env /M = −2.35 ± 0.05.…”

Section: The Asteroseismological Samplementioning

confidence: 99%

“…Thanks to the advent of space-borne photometers such as CoRoT and Kepler, however, suitable data have become available. We thus recently derived asteroseismological inferences (including measurements of the mass) for three sdB g-mode pulsators: KPD 0629−0016 (Van Grootel et al 2010c) from CoRoT photometry, KPD 1943+4058 (Van Grootel et al 2010b) and KIC02697388 (Charpinet et al 2011) from Kepler data.…”

Section: Introductionmentioning

confidence: 99%

A preliminary look at the empirical mass distribution of hot B subdwarf stars

Fontaine

Brassard

Charpinet

et al. 2012

A&A

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114

109

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We present the results of about a decade of efforts toward building an empirical mass distribution for hot B subdwarf stars on the basis of asteroseismology. So far, our group has published detailed analyses pertaining to 16 pulsating B subdwarfs, including estimates of the masses of these pulsators. Given that measurements of the masses of B subdwarfs through more classical methods (such as full orbital solutions in binary stars) have remained far and few, asteroseismology has proven a tool of choice in this endeavor. On the basis of a first sample of 15 pulsators, we find a relatively sharp mass distribution with a mean mass of 0.470 M , a median value of 0.470 M , and a narrow range 0.441−0.499 M containing some 68.3% of the stars. We augmented our sample with the addition of seven stars (components of eclipsing binaries) with masses reliably established through light curve modeling and spectroscopy. The new distribution is very similar to the former one with a mean mass of 0.470 M , a median value of 0.471 M , and a slightly wider range 0.439−0.501 M containing some 68.3% of the stars. Although still based on small-number statistics, our derived empirical mass distribution compares qualitatively very well with the expectations of stellar evolution theory.

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“…The most convincing explanation so far brought forward for this phenomenon is the perturbation of the levitating iron reservoir within the stellar envelope by weak winds (Fontaine et al 2006), but this remains to be modelled in detail. On the other hand, the quantitative interpretation of the observed period spectra based on adiabatic pulsation calculations is well-advanced for these stars and has led to the asteroseismic inference of fundamental parameters (including a very precise estimate of the mass, surface gravity, the thickness of the H envelope and in some cases the determination of the internal rotation) for some 15 targets (see Charpinet et al 2015, for a recent review on sdB star asteroseismology).…”

Section: Introductionmentioning

confidence: 99%

Pulsating hot O subdwarfs inωCentauri: mapping a unique instability strip on the extreme horizontal branch

Randall¹,

Calamida

Fontaine

et al. 2016

A&A

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We present the results of an extensive survey for rapid pulsators among Extreme Horizontal Branch (EHB) stars in ω Cen. The observations performed consist of nearly 100 hours of time-series photometry for several off-centre fields of the cluster, as well as low-resolution spectroscopy for a partially overlapping sample. We obtained photometry for some 300 EHB stars, for around half of which we are able to recover light curves of sufficient quality to either detect or place meaningful non-detection limits for rapid pulsations. Based on the spectroscopy, we derive reliable values of log g, T eff and log N(He)/N(H) for 38 targets, as well as good estimates of the effective temperature for another nine targets, whose spectra are slightly polluted by a close neighbour in the image. The survey uncovered a total of five rapid variables with multi-periodic oscillations between 85 and 125 s. Spectroscopically, they form a homogeneous group of hydrogen-rich subdwarf O stars clustered between 48,000 and 54,000 K. For each of the variables we are able to measure between two and three significant pulsations believed to constitute independent harmonic oscillations. However, the interpretation of the Fourier spectra is not straightforward due to significant fine structure attributed to strong amplitude variations. In addition to the rapid variables, we found an EHB star with an apparently periodic luminosity variation of ∼2700 s, which we tentatively suggest may be caused by ellipsoidal variations in a close binary. Using the overlapping photometry and spectroscopy sample we are able to map an empirical ω Cen instability strip in log g − T eff space. This can be directly compared to the pulsation driving predicted from the Montréal "second-generation" models regularly used to interpret the pulsations in hot B subdwarfs. Extending the parameter range of these models to higher temperatures, we find that the region where p-mode excitation occurs is in fact bifurcated, and the well-known instability strip between 29,000-36,000 K where the rapid subdwarf B pulsators are found is complemented by a second one above 50,000 K in the models. While significant challenges remain at the quantitative level, we believe that the same κ-mechanism that drives the pulsations in hot B subdwarfs is also responsible for the excitation of the rapid oscillations observed in the ω Cen variables. Intriguingly, the ω Cen variables appear to form a unique class. No direct counterparts have so far been found either in the Galactic field, nor in other globular clusters, despite dedicated searches. Conversely, our survey revealed no ω Cen representatives of the rapidly pulsating hot B subdwarfs found among the field population, though their presence cannot be excluded from the limited sample.

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g-mode trapping and period spacings in hot B subdwarf stars

Cited by 15 publications

References 2 publications

The treatment of mixing in core helium burning models – I. Implications for asteroseismology

The treatment of mixing in core helium burning models – I. Implications for asteroseismology

A preliminary look at the empirical mass distribution of hot B subdwarf stars

Pulsating hot O subdwarfs inωCentauri: mapping a unique instability strip on the extreme horizontal branch

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