Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...314..465l&link_type=abstract
Astronomy and Astrophysics, v.314, p.465-476
Astronomy and Astrophysics
Astrophysics
26
Turbulence, Stars: Pre-Main Sequence, Chromosphere, Interior, Mass Loss, Rotation
Scientific paper
Pre-main-sequence stars between 2 and 5Msun_ (Herbig Ae/Be stars) possess strong stellar winds and extended chromospheres. The non-radiative heating necessary to fuel such chromospheres is considerable. Unlike solar type stars, this heating can not be related to the existence of a subphotosopheric convection zone, as their envelope are in radiative equilibrium. Another possibility advanced for T Tauri stars is to use the gravitational energy contained in an accretion disk; however, the presence of optically thick disks around Herbig Ae/Be stars has been seriously questioned recently. The kinetic energy of stellar rotation is potentially sufficient to support this chromospheric heating during the evolution towards the main-sequence. The problem is to find an efficient mechanism to extract rotational energy, to transfer and dissipate it in the outer layers of the star. We investigate the effect of the angular momentum losses driven by a strong stellar wind on the distribution of the angular momentum inside the star. We propose that the braking torque exerted by the wind forces turbulent motions below the stellar surface. Guided by an analogy with geophysical and experimental fluids, a simplified model shows that the wind-induced angular momentum losses are efficiently transferred through the stellar interior by these turbulent motions. This transfer occurs in a turbulent layer which deepens towards the stellar interior in a time-scale of 10^6^years, comparable with the Kelvin time-scale of Herbig Ae/Be stars. It results that, during their pre-main-sequence evolution, Herbig Ae/Be stars convert part of their rotational energy into turbulent motions. This provides appropriate physical conditions to produce a magnetic field which could transfer and dissipate this turbulent kinetic energy in the outer layers of the star.
Catala Claude
Lignières François
Mangeney Andre
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