The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Ehsan Moravveji - One of the best experts on this subject based on the ideXlab platform.
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SUB-INERTIAL GRAVITY MODES IN THE B8V STAR KIC 7760680 REVEAL MODERATE CORE OVERSHOOTING AND LOW VERTICAL Diffusive Mixing
The Astrophysical Journal, 2016Co-Authors: Ehsan Moravveji, Conny Aerts, Richard H. D. Townsend, Stéphane MathisAbstract:KIC 7760680 is so far the richest slowly pulsating B star, by exhibiting 36 consecutive dipole ($\ell=1$) gravity (g-) modes. The monotonically decreasing period spacing of the series, in addition to the local dips in the pattern confirm that KIC 7760680 is a moderate rotator, with clear mode trapping in chemically inhomogeneous layers. We employ the traditional approximation of rotation to incorporate rotational effects on g-mode frequencies. Our detailed forward asteroseismic modelling of this g-mode series reveals that KIC 7760680 is a moderately rotating B star with mass $\sim3.25$ M$_\odot$. By simultaneously matching the slope of the period spacing, and the number of modes in the observed frequency range, we deduce that the equatorial rotation frequency of KIC 7760680 is 0.4805 day$^{-1}$, which is 26\% of its Roche break up frequency. The relative deviation of the model frequencies and those observed is less than one percent. We succeed to tightly constrain the exponentially-decaying convective core overshooting parameter to $f_{\rm ov}\approx0.024\pm0.001$. This means that convective core overshooting can coexist with moderate rotation. Moreover, models with exponentially-decaying overshoot from the core outperform those with the classical step-function overshoot. The best value for extra Diffusive Mixing in the radiatively stable envelope is confined to $\log D_{\rm ext}\approx0.75\pm0.25$ (with $D_{\rm ext}$ in cm$^2$ sec$^{-1}$), which is notably smaller than theoretical predictions.
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Tight asteroseismic constraints on core overshooting and Diffusive Mixing in the slowly rotating pulsating B8.3V star KIC 10526294
Astronomy & Astrophysics, 2015Co-Authors: Ehsan Moravveji, Conny Aerts, Péter Pápics, Santiago Andrés Triana, Bram VandorenAbstract:Context. KIC 10526294 was recently discovered as a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the Mixing properties of the star. Aims. We revisit the asteroseismic modelling of this star with specific emphasis on the properties of the core overshooting, while considering additional Diffusive Mixing throughout the radiative envelope of the star. Methods. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra Diffusive Mixing throughout the radiative interior. Results. We find a tight mass, metallicity relation within the ranges M2 [3:13;3:25] M and Z2 [0:014;0:028]. We deduce that an exponentially decaying Diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of fov between 0.017 and 0.018. Moreover, the inclusion of extra Diffusive Mixing with a value of logDmix between 1.75 and 2.00 dex (with Dmix in cm 2 s 1 ) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra Mixing is considered, irrespective of the (M;Z) combination within the allowed seismic range. Conclusions. We find that the inclusion of Diffusive Mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, for the input physics and chemical mixtures we investigated, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function, regardless of the adopted mixture or choice of opacity tables. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.
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tight asteroseismic constraints on core overshooting and Diffusive Mixing in the slowly rotating pulsating b8 3v star kic 10526294
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Ehsan Moravveji, Conny Aerts, Péter Pápics, Santiago Andrés Triana, Bram VandorenAbstract:KIC 10526294 is a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the Mixing properties of the star. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra Diffusive Mixing. We find a tight mass, metallicity relation within the ranges $M$ ~ 3.13 to 3.25 Msun and $Z$ ~ 0.014 to 0.028. We deduce that an exponentially decaying Diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of $f_{ov}$ between 0.017 and 0.018. Moreover, the inclusion of extra Diffusive Mixing with a value of $\log D_{\rm mix}$ between 1.75 and 2.00 dex (with $D_{\rm mix}$ in cm^2/sec) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra Mixing is considered, irrespective of the $(M,Z)$ combination within the allowed seismic range. The inclusion of Diffusive Mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.
Bram Vandoren - One of the best experts on this subject based on the ideXlab platform.
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Tight asteroseismic constraints on core overshooting and Diffusive Mixing in the slowly rotating pulsating B8.3V star KIC 10526294
Astronomy & Astrophysics, 2015Co-Authors: Ehsan Moravveji, Conny Aerts, Péter Pápics, Santiago Andrés Triana, Bram VandorenAbstract:Context. KIC 10526294 was recently discovered as a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the Mixing properties of the star. Aims. We revisit the asteroseismic modelling of this star with specific emphasis on the properties of the core overshooting, while considering additional Diffusive Mixing throughout the radiative envelope of the star. Methods. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra Diffusive Mixing throughout the radiative interior. Results. We find a tight mass, metallicity relation within the ranges M2 [3:13;3:25] M and Z2 [0:014;0:028]. We deduce that an exponentially decaying Diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of fov between 0.017 and 0.018. Moreover, the inclusion of extra Diffusive Mixing with a value of logDmix between 1.75 and 2.00 dex (with Dmix in cm 2 s 1 ) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra Mixing is considered, irrespective of the (M;Z) combination within the allowed seismic range. Conclusions. We find that the inclusion of Diffusive Mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, for the input physics and chemical mixtures we investigated, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function, regardless of the adopted mixture or choice of opacity tables. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.
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tight asteroseismic constraints on core overshooting and Diffusive Mixing in the slowly rotating pulsating b8 3v star kic 10526294
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Ehsan Moravveji, Conny Aerts, Péter Pápics, Santiago Andrés Triana, Bram VandorenAbstract:KIC 10526294 is a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the Mixing properties of the star. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra Diffusive Mixing. We find a tight mass, metallicity relation within the ranges $M$ ~ 3.13 to 3.25 Msun and $Z$ ~ 0.014 to 0.028. We deduce that an exponentially decaying Diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of $f_{ov}$ between 0.017 and 0.018. Moreover, the inclusion of extra Diffusive Mixing with a value of $\log D_{\rm mix}$ between 1.75 and 2.00 dex (with $D_{\rm mix}$ in cm^2/sec) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra Mixing is considered, irrespective of the $(M,Z)$ combination within the allowed seismic range. The inclusion of Diffusive Mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.
Conny Aerts - One of the best experts on this subject based on the ideXlab platform.
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SUB-INERTIAL GRAVITY MODES IN THE B8V STAR KIC 7760680 REVEAL MODERATE CORE OVERSHOOTING AND LOW VERTICAL Diffusive Mixing
The Astrophysical Journal, 2016Co-Authors: Ehsan Moravveji, Conny Aerts, Richard H. D. Townsend, Stéphane MathisAbstract:KIC 7760680 is so far the richest slowly pulsating B star, by exhibiting 36 consecutive dipole ($\ell=1$) gravity (g-) modes. The monotonically decreasing period spacing of the series, in addition to the local dips in the pattern confirm that KIC 7760680 is a moderate rotator, with clear mode trapping in chemically inhomogeneous layers. We employ the traditional approximation of rotation to incorporate rotational effects on g-mode frequencies. Our detailed forward asteroseismic modelling of this g-mode series reveals that KIC 7760680 is a moderately rotating B star with mass $\sim3.25$ M$_\odot$. By simultaneously matching the slope of the period spacing, and the number of modes in the observed frequency range, we deduce that the equatorial rotation frequency of KIC 7760680 is 0.4805 day$^{-1}$, which is 26\% of its Roche break up frequency. The relative deviation of the model frequencies and those observed is less than one percent. We succeed to tightly constrain the exponentially-decaying convective core overshooting parameter to $f_{\rm ov}\approx0.024\pm0.001$. This means that convective core overshooting can coexist with moderate rotation. Moreover, models with exponentially-decaying overshoot from the core outperform those with the classical step-function overshoot. The best value for extra Diffusive Mixing in the radiatively stable envelope is confined to $\log D_{\rm ext}\approx0.75\pm0.25$ (with $D_{\rm ext}$ in cm$^2$ sec$^{-1}$), which is notably smaller than theoretical predictions.
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Tight asteroseismic constraints on core overshooting and Diffusive Mixing in the slowly rotating pulsating B8.3V star KIC 10526294
Astronomy & Astrophysics, 2015Co-Authors: Ehsan Moravveji, Conny Aerts, Péter Pápics, Santiago Andrés Triana, Bram VandorenAbstract:Context. KIC 10526294 was recently discovered as a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the Mixing properties of the star. Aims. We revisit the asteroseismic modelling of this star with specific emphasis on the properties of the core overshooting, while considering additional Diffusive Mixing throughout the radiative envelope of the star. Methods. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra Diffusive Mixing throughout the radiative interior. Results. We find a tight mass, metallicity relation within the ranges M2 [3:13;3:25] M and Z2 [0:014;0:028]. We deduce that an exponentially decaying Diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of fov between 0.017 and 0.018. Moreover, the inclusion of extra Diffusive Mixing with a value of logDmix between 1.75 and 2.00 dex (with Dmix in cm 2 s 1 ) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra Mixing is considered, irrespective of the (M;Z) combination within the allowed seismic range. Conclusions. We find that the inclusion of Diffusive Mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, for the input physics and chemical mixtures we investigated, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function, regardless of the adopted mixture or choice of opacity tables. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.
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tight asteroseismic constraints on core overshooting and Diffusive Mixing in the slowly rotating pulsating b8 3v star kic 10526294
arXiv: Solar and Stellar Astrophysics, 2015Co-Authors: Ehsan Moravveji, Conny Aerts, Péter Pápics, Santiago Andrés Triana, Bram VandorenAbstract:KIC 10526294 is a very slowly rotating and slowly pulsating late B-type star. Its 19 consecutive dipole gravity modes constitute a series with almost constant period spacing. This unique collection of identified modes probes the near-core environment of this star and holds the potential to reveal the size and structure of the overshooting zone on top of the convective core, as well as the Mixing properties of the star. We pursue forward seismic modelling based on adiabatic eigenfrequencies of equilibrium models for eight extensive evolutionary grids tuned to KIC 10526294, by varying the initial mass, metallicity, chemical mixture, and the extent of the overshooting layer on top of the convective core. We examine models for both OP and OPAL opacities and test the occurrence of extra Diffusive Mixing. We find a tight mass, metallicity relation within the ranges $M$ ~ 3.13 to 3.25 Msun and $Z$ ~ 0.014 to 0.028. We deduce that an exponentially decaying Diffusive core overshooting prescription describes the seismic data better than a step function formulation and derive a value of $f_{ov}$ between 0.017 and 0.018. Moreover, the inclusion of extra Diffusive Mixing with a value of $\log D_{\rm mix}$ between 1.75 and 2.00 dex (with $D_{\rm mix}$ in cm^2/sec) improves the goodness-of-fit based on the observed and modelled frequencies with a factor 11 compared to the case where no extra Mixing is considered, irrespective of the $(M,Z)$ combination within the allowed seismic range. The inclusion of Diffusive Mixing in addition to core overshooting is essential to explain the structure in the observed period spacing pattern of this star. Moreover, we deduce that an exponentially decaying prescription for the core overshooting is to be preferred over a step function. Our best models for KIC 10526294 approach the seismic data to a level that they can serve future inversion of its stellar structure.
David Risk - One of the best experts on this subject based on the ideXlab platform.
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Technical Note: Isotopic corrections for the radiocarbon composition of CO 2 in the soil gas environment must account for diffusion and Diffusive Mixing
Biogeosciences, 2019Co-Authors: Jocelyn Egan, David R. Bowling, David RiskAbstract:Abstract. Earth system scientists working with radiocarbon in organic samples use a stable carbon isotope ( δ13C ) correction to account for mass-dependent fractionation, but it has not been evaluated for the soil gas environment, wherein both Diffusive gas transport and Diffusive Mixing are important. Using theory and an analytical soil gas transport model, we demonstrate that the conventional correction is inappropriate for interpreting the radioisotopic composition of CO2 from biological production because it does not account for important gas transport mechanisms. Based on theory used to interpret δ13C of soil production from soil CO2 , we propose a new solution for radiocarbon applications in the soil gas environment that fully accounts for both mass-dependent diffusion and mass-independent Diffusive Mixing.
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Isotopic fractionation corrections for the radiocarbon composition ofCO 2 in the soil gas environment must include diffusion and Mixing
2018Co-Authors: Jocelyn Egan, David R. Bowling, David RiskAbstract:Abstract. Earth system scientists working with radiocarbon in organic samples use a stable carbon isotope (δ13C) correction to account for mass-dependent fractionation caused primarily by photosynthesis. Although researchers apply this correction routinely, it has not been evaluated for the soil gas environment, where both Diffusive gas transport and Diffusive Mixing are important. Towards this end we applied an analytical soil gas transport model across a range of soil diffusivities and biological CO2 production rates, allowing us to control the radiocarbon (Δ14C) and stable isotope (δ13C) compositions of modeled soil CO2 production and atmospheric CO2. This approach allowed us to assess the bias that results from using the conventional correction method for estimating Δ14C of soil production. We found that the conventional correction is inappropriate for interpreting the radio-isotopic composition of CO2 from biological production, because it does not account for diffusion and Diffusive Mixing. The resultant Δ14C bias associated with the traditional correction is highest (up to 150 ‰) in soils with low biological production and/or high soil diffusion rates. We propose a new solution for radiocarbon applications in the soil gas environment that fully accounts for diffusion and Diffusive Mixing.
Andrew Yool - One of the best experts on this subject based on the ideXlab platform.
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Simulated impact of double‐Diffusive Mixing on physical and biogeochemical upper ocean properties
Journal of Geophysical Research, 2008Co-Authors: Mirjam S. Glessmer, Andreas Oschlies, Andrew YoolAbstract:A nested‐grid ocean circulation modeling system is used to study the response of Lunenburg Bay in Nova Scotia, Canada, to local wind‐forcing, tides, remotely generated waves, and buoyancy forcing in the summer and fall of 2003. Quantitative comparisons between observations and model results demonstrate that the modeling system reproduces reasonably well the observed sea level, temperature, salinity, and currents in the bay. Numerical results reveal that the spatial and temporal variability of temperature and salinity in the bay during the study period is mainly forced by the local wind stress and surface heat/freshwater fluxes, with some contribution from tidal circulation. In particular, the local heat balance on the monthly timescale is dominated by cooling due to vertical advection and warming due to horizontal advection and net surface heat flux, while high‐frequency variations (timescales of 1–30 days) are mainly associated with vertical advection, i.e., wind‐induced upwelling and downwelling. There is also a strong baroclinic throughflow over the deep water region outside Lunenburg Bay that is strongly influenced by wind‐forcing. The vertically integrated momentum balance analysis indicates a modified geostrophic balance on the monthly timescale and longer, and is dominated by the pressure term and wind minus bottom stress in the high‐frequency band.
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simulated impact of double Diffusive Mixing on physical and biogeochemical upper ocean properties
Journal of Geophysical Research, 2008Co-Authors: Mirjam S. Glessmer, Andreas Oschlies, Andrew YoolAbstract:A nested‐grid ocean circulation modeling system is used to study the response of Lunenburg Bay in Nova Scotia, Canada, to local wind‐forcing, tides, remotely generated waves, and buoyancy forcing in the summer and fall of 2003. Quantitative comparisons between observations and model results demonstrate that the modeling system reproduces reasonably well the observed sea level, temperature, salinity, and currents in the bay. Numerical results reveal that the spatial and temporal variability of temperature and salinity in the bay during the study period is mainly forced by the local wind stress and surface heat/freshwater fluxes, with some contribution from tidal circulation. In particular, the local heat balance on the monthly timescale is dominated by cooling due to vertical advection and warming due to horizontal advection and net surface heat flux, while high‐frequency variations (timescales of 1–30 days) are mainly associated with vertical advection, i.e., wind‐induced upwelling and downwelling. There is also a strong baroclinic throughflow over the deep water region outside Lunenburg Bay that is strongly influenced by wind‐forcing. The vertically integrated momentum balance analysis indicates a modified geostrophic balance on the monthly timescale and longer, and is dominated by the pressure term and wind minus bottom stress in the high‐frequency band.