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Formation des raies dans les vents des étoiles Ae/Be de Herbig

Abstract : Herbig AejBe stars are pre-main sequence stars of intermediate masses (2-5 Mc) that exhibit strong signs of activity and stellar winds. The origin of these phenomenons remain unclear since mechanisms proposed for stars in other parts of the HR diagram do not apply here. We have studied the line formation in the winds of these stars thanks to a semiempirical, spherically symmetric model of wind. Modelling the resonance lin es of CIV and MgII, as weIl as the Balmer lines and continua of hydrogen for a representative sample of stars, we showed that the winds of these stars share the same structures, with, for instance, extended chromospheres of moderate temperatures (T ~ 20,000 K). Theoretical mass loss rates are consistent with those obtained from observations. When calculating the radiative losses in the winds, we found that they are larger than the amount of energy available in mechanisms proposed to explain the activity and involving accretion disks or internaI rotation of the stars. So as to explain the presence of the NV line at 1240 A in AB Aur's wind, as observed with the Hubble Space Telescope, we had to develop a method to simulate the presence of hot clumps, created by shocks. As a by product we were also able to explain the X-ray flux measured by ROSAT. Radiatives losses larger than the total kinetic energy flux suggest that other dissipative pro cesses are involved in this wind. This work represent the first step towards taking departure from spherical symmetry in AB Aur's wind, into account. Afterwads, the study of the He I D3 line provided us with informations on the base of the wind of AB Aur. So as to obtain a blue-shifted emission component as observed, we had to consider strong velocity gradient and high mass loss rates, which shows that AB Aur's wind is very unhomogeneous, even at its very base. On the other hand, the red-shifted emission component of this line cannot be formed in the wind itself but rather in accretion flows down to the stellar poles. The results obtained so far constitute a set of strong constraints which will be very useful to study Herbig AejBe stars from a theoretical point of vue.
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Contributor : Pascale Talour <>
Submitted on : Tuesday, August 14, 2012 - 8:40:57 AM
Last modification on : Monday, April 5, 2021 - 2:26:12 PM
Long-term archiving on: : Friday, December 16, 2016 - 5:44:10 AM

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  • HAL Id : tel-00723782, version 1

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Jean Claude Bouret. Formation des raies dans les vents des étoiles Ae/Be de Herbig. Astrophysique stellaire et solaire [astro-ph.SR]. Université Joseph-Fourier - Grenoble I, 1998. Français. ⟨tel-00723782⟩

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