[en] Subdwarf B (sdB) stars show chemical peculiarities that cannot be explained by diffusion theory alone. Both mass loss and turbulence have been invoked to slow down atomic diffusion in order to match observed abundances. The fact that some sdB stars show pulsations give upper limits on the amount of mass loss and turbulent mixing allowed. Consequently, non-adiabatic asteroseismology has the potential to decide which process is responsible for the abundance anomalies. We compute for the first time seismic properties of sdB models with atomic diffusion included consistently during the stellar evolution. The diffusion equations with radiative forces are solved for H, He, C, N, O, Ne, Mg, Fe and Ni. We examine the effects of various mass-loss rates and mixed surface masses on the abundances and mode stability. It is shown that the mass-loss rates needed to simulate the observed He abundances (?) are not consistent with observed pulsations. We find that for pulsations to be driven the rates should be ?. On the other hand, weak turbulent mixing of the outer 10[SUP]-6[/SUP] M[SUB]&sun;[/SUB] can explain the He abundance anomalies while still allowing pulsations to be driven. The origin of the turbulence remains unknown but the presence of pulsations gives tight constraints on the underlying turbulence model.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Hu, Haili; Institute of Astronomy, The Observatories, Madingley Road, Cambridge CB3 0HA
Tout, C. A.; Institute of Astronomy, The Observatories, Madingley Road, Cambridge CB3 0HA
Glebbeek, E.; Department of Physics & Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1, Canada
Dupret, Marc-Antoine ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astrophysique stellaire théorique et astérosismologie
Language :
English
Title :
Slowing down atomic diffusion in subdwarf B stars: mass loss or turbulence?
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