Collective pulsational velocity broadening due to gravity modes as a physical explanation for macroturbulence in hot massive stars

Aerts, C.; Puls, J.; Godart, M.; Dupret, Marc‐Antoine

doi:10.1051/0004-6361/200810471

Cited by 140 publications

(218 citation statements)

References 46 publications

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“…The five stars color coded in blue are bona fide γ Dor pulsators. Right: as in left panel, with overplotted the location of ≈300 γ Dor stars analyzed by Bruntt et al (2008), Catanzaro et al (2011), Fossati et al (2011), Tkachenko et al (2012, Bradley et al (2015), and Van Reeth et al (2015) and some hybrid γ Dor-δ Sct stars from Catanzaro et al (2011) and Tkachenko et al (2012). broadening of spectral lines (Aerts et al 2009). If indeed turbulent pressure fluctuations excite high-order modes, a connection with γ Dor may be present as well, which could involve finite amplitude pressure fluctuations in the HCZ.…”

Section: Discussionmentioning

confidence: 99%

Relating turbulent pressure and macroturbulence across the HR diagram with a possible link toγDoradus stars

Grassitelli

Fossati

Langer

et al. 2015

A&A

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A significant fraction of the envelope of low-and intermediate-mass stars is unstable to convection, leading to sub-surface turbulent motion. Here, we consider and include the effects of turbulence pressure in our stellar evolution calculations. In search of an observational signature, we compare the fractional contribution of turbulent pressure to the observed macroturbulent velocities in stars at different evolutionary stages. We find a strong correlation between the two quantities, similar to what was previously found for massive OB stars. We therefore argue that turbulent pressure fluctuations of finite amplitude may excite high-order, high-angular degree stellar oscillations, which manifest themselves at the surface an additional broadening of the spectral lines, i.e., macroturbulence, across most of the HR diagram. When considering the locations in the HR diagram where we expect high-order oscillations to be excited by stochastic turbulent pressure fluctuations, we find a close match with the observational γ Doradus instability strip, which indeed contains high-order, non-radial pulsators. We suggest that turbulent pressure fluctuations on a percentual level may contribute to the γ Dor phenomenon, calling for more detailed theoretical modeling in this direction.

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Section: Discussionmentioning

confidence: 99%

Relating turbulent pressure and macroturbulence across the HR diagram with a possible link toγDoradus stars

Grassitelli

Fossati

Langer

et al. 2015

A&A

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“…Indeed, oscillations change the shape of spectral lines in an asymmetric and time-dependent way, i.e., the level of deformation depends on the phase in the overall oscillation cycle. To compensate for this deformation and absence of pulsational broadening, one usually introduces a time-independent ad-hoc parameter called macroturbulence (e.g., Aerts et al 2009) and/or a rotational profile with a wrong v sin i, each of which are usually deduced from metal lines and have a different functional shape than the true time-dependent line-broadening function. This is then compensated for by an incorrect value of the gravity and/or microturbulence, which can either be too high or too low.…”

Section: Discussionmentioning

confidence: 99%

Seismic modelling of theβ Cephei star HD 180642 (V1449 Aquilae)

Aerts

Briquet

Degroote

et al. 2011

A&A

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Context. We present modelling of the β Cep star HD 180642 based on its observational properties deduced from CoRoT and groundbased photometry as well as from time-resolved spectroscopy. Aims. We investigate whether present-day state-of-the-art models are able to explain the full seismic behaviour of this star, which has extended observational constraints for this type of pulsator. Methods. We constructed a dedicated database of stellar models and their oscillation modes tuned to fit the dominant radial mode frequency of HD 180642, by means of varying the hydrogen content, metallicity, mass, age, and core overshooting parameter. We compared the seismic properties of these models with those observed. Results. We find models that are able to explain the numerous observed oscillation properties of the star, for a narrow range in mass of 11.4-11.8 M and no or very mild overshooting (with up to 0.05 local pressure scale heights), except for an excitation problem of the = 3, p 1 mode. We deduce a rotation period of about 13 d, which is fully compatible with recent magnetic field measurements. The seismic models do not support the earlier claim of solar-like oscillations in the star. We instead ascribe the power excess at high frequency to non-linear resonant mode coupling between the high-amplitude radial fundamental mode and several of the low-order pressure modes. We report a discrepancy between the seismic and spectroscopic gravity at the 2.5σ level.

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“…Cantiello et al (2009) evoke the subphotospheric convection to account for the microturbulent motions, while Aerts et al (2009Aerts et al ( , 2014 suggest that macro-turbulence could be ascribed to low-amplitude gravity modes of nonradial pulsations. Similar conclusions are also put forward by Simón-Díaz (2015).…”

Section: Preliminary Commentsmentioning

confidence: 99%

Critical study of the distribution of rotational velocities of Be stars

Zorec

Frémat

Souza

et al. 2016

A&A

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Context. Among intermediate-mass and massive stars, Be stars are the fastest rotators in the main sequence (MS) and, as such, these stars are a cornerstone to validate models of structure and evolution of rotating stars. Several phenomena, however, induce under-or overestimations either of their apparent Vsin i, or true velocity V. Aims. In the present contribution we aim at obtaining distributions of true rotational velocities corrected for systematic effects induced by the rapid rotation itself, macroturbulent velocities, and binarity. Methods. We study a set of 233 Be stars by assuming they have inclination angles distributed at random. We critically discuss the methods of Cranmer and Lucy-Richardson, which enable us to transform a distribution of projected velocities into another distribution of true rotational velocities, where the gravitational darkening effect on the Vsin i parameter is considered in different ways. We conclude that iterative algorithm by Lucy-Richardson responds at best to the purposes of the present work, but it requires a thorough determination of the stellar fundamental parameters. Results. We conclude that once the mode of ratios of the true velocities of Be stars attains the value V/V c 0.77 in the main-sequence (MS) evolutionary phase, it remains unchanged up to the end of the MS lifespan. The statistical corrections found on the distribution of ratios V/V c for overestimations of Vsin i, due to macroturbulent motions and binarity, produce a shift of this distribution toward lower values of V/V c when Be stars in all MS evolutionary stages are considered together. The mode of the final distribution obtained is at V/V c 0.65. This distribution has a nearly symmetric distribution and shows that the Be phenomenon is characterized by a wide range of true velocity ratios 0.3 V/V c 0.95. It thus suggests that the probability that Be stars are critical rotators is extremely low. Conclusions. The corrections attempted in the present work represent an initial step to infer indications about the nature of the Be-star surface rotation that will be studied in the second paper of this series.

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Collective pulsational velocity broadening due to gravity modes as a physical explanation for macroturbulence in hot massive stars

Cited by 140 publications

References 46 publications

Relating turbulent pressure and macroturbulence across the HR diagram with a possible link toγDoradus stars

Relating turbulent pressure and macroturbulence across the HR diagram with a possible link toγDoradus stars

Seismic modelling of theβ Cephei star HD 180642 (V1449 Aquilae)

Critical study of the distribution of rotational velocities of Be stars

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