Diffusion, meridional circulation, and mass loss in Fm-Am stars

Michaud, G.; Tarasick, D. W.; Charland, Y.; Pelletier, C.

doi:10.1086/161034

Cited by 125 publications

(101 citation statements)

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“…However, according to his results, only heavier elements are evacuated by the radiative field. Similarly, Michaud et al (1983, see also Michaud & Charland 1986 suggested that mass loss rates between 10 −14 M yr −1 and 10 −15 M yr −1 could satisfy observational constraints from CP star surface anomalies. Given the large disparity in values, the mass loss rates used in this study will be constrained strictly by surface abundance variations (see also Sect.…”

Section: Astrophysical Contextmentioning

confidence: 71%

“…With the addition of turbulent mixing, the Montreal group's stellar evolution code Richard et al 2001;Michaud et al 2004Michaud et al , 2005Talon et al 2006) was able to explain and reproduce the particular abundances of many cluster and field stars with a single tunable parameter: the mixed mass. Nonetheless, other studies have suggested that mass loss could also reduce the predicted anomalies to observed levels (Michaud et al 1983;Michaud & Charland 1986;Alecian 1996). Since these studies considered static stellar models incorporating a limited number of species, a rigorous investigation of the effects of mass loss on stellar chemical evolution is warranted.…”

Section: Astrophysical Contextmentioning

confidence: 94%

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AmFm and lithium gap stars

Vick

Michaud

Richer

et al. 2010

A&A

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102

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Aims. A thorough study of the effects of mass loss on internal and surface abundances of A and F stars is carried out in order to constrain mass loss rates for these stars, as well as further elucidate some of the processes which compete with atomic diffusion. Methods. Self-consistent stellar evolution models of 1.3 to 2.5 M stars including atomic diffusion and radiative accelerations for all species within the OPAL opacity database were computed with mass loss and compared to observations as well as previous calculations with turbulent mixing. Results. Models with unseparated mass loss rates between 5 × 10 −14 and 10 −13 M yr −1 reproduce observations for many cluster AmFm stars as well as Sirius A and o Leonis. These models also explain cool Fm stars, but not the Hyades lithium gap. Like turbulent mixing, these mass loss rates reduce surface abundance anomalies; however, their effects are very different with respect to internal abundances. For most of the main-sequence lifetime of an A or F star, surface abundances in the presence of such mass loss depend on separation which takes place between log ΔM/M * = −6 and −5. Conclusions. The current observational constraints do not allow us to conclude that mass loss is to be preferred over turbulent mixing (induced by rotation or otherwise) in order to explain the AmFm phenomenon. Internal concentration variations which could be detectable through asteroseismic tests should provide further information. If atomic diffusion coupled with mass loss are to explain the Hyades Li gap, the wind would need to be separated.

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Section: Astrophysical Contextmentioning

confidence: 71%

Section: Astrophysical Contextmentioning

confidence: 94%

AmFm and lithium gap stars

Vick

Michaud

Richer

et al. 2010

A&A

Self Cite

102

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“…In guiding elements, the effect depends on the state of ionization and would so lead to concentrations in different parts of the surface for different elements (Michaud, Mégessier, Charland 1981;BM91b) but on time scales of 10 8 yr or so. If the wind is differentiated (Babel 1995), it leads to surface abundance anomalies where it occurs while an undifferentiated wind would normally reduce anomalies (Michaud et al 1983). The horizontal radiative acceleration acts on a factor of 10 shorter of use, available at https://www.cambridge.org/core/terms.…”

Section: Resultsmentioning

confidence: 99%

Particle transport and surface abundance inhomogeneities

Michaud¹

1996

Symp. - Int. Astron. Union

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Abstract. The various mechanisms leading to the appearance of horizontal inhomogeneities at the surface of ApBp stars are critically reviewed. The effect of magnetic fields is essential but is it more to control locally, on the surface, the appearance of anomalies that are caused by the vertical transport of particles, or is it to create directly the horizontal inhomogeneities by horizontal transport? The time scales for horizontal and vertical transport will be discussed in this context. The processes discussed include: a) ambipolar diffusion of protons and hydrogen in the presence of magnetic fields; b) the guiding of diffusion by magnetic fields; c) the horizontal component of radiative accelerations; d) mass loss; e) light induced drift. 1· IntroductionIn this paper, will be briefly reviewed some of the processes that are believed to play a role in leading to the observed surface variations of magnetic Ap stars. The large abundance and magnetic field variations over their surface (Wolff 1983, Landstreet 1991 are well modeled by an oolique rotator. Both these variations and the presence of the magnetic field are bound to affect the analysis. First the effect of the magnetic field on the structure of the atmosphere will be discussed. Then how the magnetic field may affect the concentration of abundances on the surface and how this can lead to the appearance of patches. Finally we will also mention how mass loss may play a role by varying over the surface presumably because of the topology of the magnetic field.

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“…Our simplified model takes into account only the mixing generated by the anisotropic component of the radiative diffusion; it ignores the radiative acceleration and so cannot describe the AmFm phenomenon (Michaud et al 1983;Alecian 1996;Hui-Bon-Hua & Alecian 1998;Richer et al 2000). We are aware that our estimation of the radiative diffusivity is only a first approximation; owing to its efficiency we are confident of the fact that the diffusivity generated by the radiative collisions is a part of the missing physical process responsible for the too large efficiency of the microscopic diffusion coefficient.…”

Section: Discussionmentioning

confidence: 99%

Atomic diffusion in star models of type earlier than G

Morel

Thévenin

2002

A&A

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Abstract. We introduce the mixing resulting from the radiative diffusivity associated with the radiative viscosity in the calculation of stellar evolution models. We find that the radiative diffusivity significantly diminishes the efficiency of the gravitational settling in the external layers of stellar models corresponding to types earlier than ≈G. The surface abundances of chemical species predicted by the models are successfully compared with the abundances determined in members of the Hyades open cluster. Our modeling depends on an efficiency parameter, which is evaluated to a value close to unity, that we calibrate in this study.

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Diffusion, meridional circulation, and mass loss in Fm-Am stars

Cited by 125 publications

References 0 publications

AmFm and lithium gap stars

AmFm and lithium gap stars

Particle transport and surface abundance inhomogeneities

Atomic diffusion in star models of type earlier than G

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