Observations and asteroseismological analysis of the rapid subdwarf B pulsator EC 09582-1137

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

doi:10.1051/0004-6361/200912576

Cited by 30 publications

(34 citation statements)

References 29 publications

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“…It is however not established if in sdBs with small original metallicity there is enough Fe to sufficiently fill the region where the driving occurs. As noted in the conclusion to the tenth sdB for which a detailed asterosismic analysis had yielded the mass (Randall et al 2009), a more accurate fit to the asterosismic data requires evolutionary models of sdB stars. The approach to equilibrium in the driving region was studied by Fontaine et al (2006) starting from a solar Fe abundance.…”

Section: Asterosismologymentioning

confidence: 97%

Horizontal branch evolution, metallicity, and sdB stars

Michaud

Richer

Richard

2011

A&A

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Context. Abundance anomalies have been observed in field sdB stars and in nearly all horizontal branch (HB) stars of globular clusters with T eff > 11 000 K, whatever be the cluster metallicity. Aims. We aim to determine the abundance variations that are expected in sdB stars and in HB stars of metallicities Z ≥ 10 −4 and investigate what the observed abundances teach us about hydrodynamical processes competing with atomic diffusion. Methods. Complete stellar evolution models, including the effects of atomic diffusion and radiative acceleration, have been computed from the zero age main-sequence for metallicities of Z 0 = 0.0001, 0.001, 0.004 and 0.02. On the HB the masses were selected to cover the T eff interval from 7000 to 37 000 K. Some 60 evolutionary HB models were calculated. The calculations of surface abundance anomalies during the horizontal branch depend on one parameter, the surface mixed mass. Results. For sdB stars with T eff < 37 000 K and for HB stars with T eff > 11 000 K in all observed clusters, independent of metallicity, we found that most observed abundance anomalies (even up to ∼× 200) were compatible, within error bars, with expected abundances. A mixed mass of ∼10 −7 M was determined by comparison with observations. Conclusions. Observations of globular cluster HB stars with T eff > 11 000 K and of sdB stars with T eff < 37 000 K suggest that most observed abundance anomalies can be explained by element separation driven by radiative acceleration occuring at a mass fraction of ∼10 −7 M . Mass loss or turbulence appear to limit the separation between 10 −7 M and the surface.Key words. stars: evolution -stars: horizontal-branch -stars: abundances -stars: Population II -subdwarfs Astrophysical contextLarge abundance anomalies have been observed on the horizontal branch (HB) of NGC 6752, NGC 1904, NGC 2808, M 15, and M 13 (Behr et al. 1999Behr 2003;Moehler et al. 2000;Fabbian et al. 2005;Pace et al. 2006): whereas those stars cooler than about 11 000 K have the same composition as giants, those hotter than 11 000 K usually have larger abundances of some metals by large factors. This occurs in all clusters with sufficiently blue HB stars irrespective of their metallicity as defined by their giant branch stars.Field sdOB stars are observed to have large abundance anomalies compared with Pop I stars (for a review see Heber 2009). They were already recognized by Sargent & Searle (1968) to have a surface composition different from the one with which they formed. While cool (T eff < 10 4 K) field Pop II stars have low Z, the sdBs 1 which must come from the red giants often have iron peak abundances that are solar or even larger. While sdBs correspond to the blue end of the HB, the hotter sdO stars are apparently a mixed bag of post HB stars and other highly evolved evolutionary stages. Spectroscopically, sdOs have much Appendices are only available in electronic form at http://www.aanda.org 1 We use the expression HB stars for horizontal branch stars in clusters, and sdB stars for those ...

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Section: Asterosismologymentioning

confidence: 97%

Horizontal branch evolution, metallicity, and sdB stars

Michaud

Richer

Richard

2011

A&A

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“…Thus far, asteroseismic inferences could be successfully derived only from short period p-mode B subdwarf pulsators (see, e.g., Van Grootel et al 2008a,b;Charpinet et al 2008;Randall et al 2009;Charpinet et al 2009a, and reference therein). The rapid oscillations associated with relatively large amplitudes (up to 6% in some cases) provided more favorable conditions to perform seismic studies based on data obtained from the ground.…”

Section: Introductionmentioning

confidence: 99%

Deep asteroseismic sounding of the compact hot B subdwarf pulsator KIC02697388 fromKeplertime series photometry

Charpinet

Grootel

Fontaine

et al. 2011

A&A

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Context. Contemporary high precision photometry from space provided by the Kepler and CoRoT satellites generates significant breakthroughs in terms of exploiting the long-period, g-mode pulsating hot B subdwarf (sdBV s ) stars with asteroseismology. Aims. We present a detailed asteroseismic study of the sdBV s star KIC02697388 monitored with Kepler, using the rich pulsation spectrum uncovered during the ∼27-day-long exploratory run Q2.3. Methods. We analyse new high-S/N spectroscopy of KIC02697388 using appropriate NLTE model atmospheres to provide accurate atmospheric parameters for this star. We also reanalyse the Kepler light curve using standard prewhitening techniques. On this basis, we apply a forward modelling technique using our latest generation of sdB models. The simultaneous match of the independent periods observed in KIC02697388 with those of models leads objectively to the identification of the pulsation modes and, more importantly, to the determination of some of the parameters of the star. Results. The light curve analysis reveals 43 independent frequencies that can be associated with oscillation modes. All the modulations observed in this star correspond to g-mode pulsations except one high-frequency signal, which is typical of a p-mode oscillation. Although the presence of this p-mode is surprising considering the atmospheric parameters that we derive for this cool sdB star (T eff = 25 395 ± 227 K, log g = 5.500 ± 0.031 (cgs), and log N(He)/N(H) = −2.767 ± 0.122), we show that this mode can be accounted for particularly well by our optimal seismic models, both in terms of frequency match and nonadiabatic properties. The seismic analysis leads us to identify two model solutions that can both account for the observed pulsation properties of KIC02697388. Despite this remaining ambiguity, several key parameters of the star can be derived with stringent constraints, such as its mass, its H-rich envelope mass, its radius, and its luminosity. We derive the properties of the core proposing that it is a relatively young sdB star that has burnt less than ∼34% (in mass) of its central helium and has a relatively large mixed He/C/O core. This latter measurement is in line with the trend already uncovered for two other g-mode sdB pulsators analysed with asteroseismology and suggests that extra mixing is occurring quite early in the evolution of He cores on the horizontal branch. Conclusions. Additional monitoring with Kepler of this particularly interesting sdB star should reveal the inner properties of KIC02697388 and provide important information about the mode driving mechanism and the helium core properties.

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“…Thus far, a dozen asteroseismic inferences have been successfully obtained from pulsating hot subdwarf stars (e.g., van Grootel et al 2008a,b;Charpinet et al 2008;Randall et al 2009;Charpinet et al 2009), but all were short period p-mode pulsators. The rapid oscillations associated with relatively large amplitudes (∼1% of the mean brightness, but up to 6% in some cases) have indeed favoured these pulsators as preferred targets for seismic analysis based on data obtained from the ground.…”

Section: Introductionmentioning

confidence: 99%

CoRoT opens a new era in hot B subdwarf asteroseismology

Charpinet¹,

Green

Baglin

et al. 2010

A&A

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Context. The asteroseismic exploitation of long period, g-mode hot B subdwarf (sdB) pulsators has been a long sought objective undermined, thus far, by the difficulty of obtaining sufficiently precise and continuous time series data from the ground. Aims. Fast photometry from space appears to be the only means of gathering the appropriate asteroseismic data for this type of star. We explore this possibility with the CoRoT (COnvection, ROtation, and planetary Transits) satellite. Methods. We obtained ∼24 days of high quality, nearly continuous photometric data with CoRoT during a short run (SRa03) dedicated to the long period sdB pulsator KPD 0629−0016. We analysed the frequency (period) content of the CoRoT time series by combining Fourier analysis, nonlinear least squares fitting, and prewhitening techniques. Results. Our study has led to the detection of a large number of g-mode pulsations in KPD 0629−0016, with 17 frequencies clearly identified in addition to 7 possible (although more uncertain) peaks emerging above the mean noise level (estimated at ∼57 ppm). This is more than is typically detected for sdB stars from the ground and, more importantly, the frequencies of all uncovered g-modes are, for the first time, reliably measured. This paves the way for a detailed asteroseismic analysis of this star. The oscillations are found in the 90−400 μHz frequency range with a dominant mode at 205.29 μHz (P = 1.353 h) of amplitude 0.246% of the mean brightness, i.e., typical of mid-radial order g-mode pulsations. Conclusions. These photometric observations of KPD 0629−0016 demonstrate that g-mode sdB pulsators have rich oscillation spectra that are accessible to current space-based facilities. CoRoT opens up a new era in asteroseismology of hot B subdwarf stars.

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Observations and asteroseismological analysis of the rapid subdwarf B pulsator EC 09582-1137

Cited by 30 publications

References 29 publications

Horizontal branch evolution, metallicity, and sdB stars

Horizontal branch evolution, metallicity, and sdB stars

Deep asteroseismic sounding of the compact hot B subdwarf pulsator KIC02697388 fromKeplertime series photometry

CoRoT opens a new era in hot B subdwarf asteroseismology

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