TURBULENCE AMPLIFICATION IN THE ATMOSPHERE OF PULSATING STARS - A FIRST APPROACH

This paper is devoted to the understanding of the ''missing temperatur e'', called microturbulence by the astrophysicists, which appears when we want to modelize the width of stellar line profiles, In the framew ork of the two limiting turbulent regimes called ''incompressible'' an d ''pressure released'' and expecting that the dissipation is negligib le (''rapid distortion'' or RDT case), it is shown that the turbulence amplification in the atmosphere of a radially pulsating star is not o nly due to the global compression of the atmosphere during the pulsati on. Strong shock waves propagating from the deep atmosphere to the ver y low density layers also play a role in the turbulence variation, esp ecially when they become very strong i.e., hypersonic. The predicted t urbulence amplification induced by the global atmospheric compression is consistent with the solenodial RDT. For shocks, the predicted turbu lence amplification in the ''pressure released'' regime is overestimat ed with respect to stellar observations when the compression rate beco mes larger than 2 which corresponds to a limit Mach number near 2. Thu s, when radiative effects take place, the present turbulence amplifica tion theory breaks down. A new approach is required.