EVAPORATION OF STAR-GRAZING BODIES IN THE VICINITY OF UX ORI-TYPE STARS

This paper studies the behaviour of star-grazing planetesimal bodies i n the neighbourhood of UX Ori-type stars. When approaching a star, lar ge size bodies (diameteres of ten meters or more) disintegrate into a number of small fragments under the effect of thermal stresses. In tur n, the fragments sublimate within a sphere of about ten stellar radii and form a circumstellar gas envelope. An important feature of this en velope is a strong excess of heavy elements. Our calculations show tha t the radiative force on the metal-enriched gas is much larger than in the case of standard chemical composition and exceeds by few times th e gravity of the star. As a result, the evaporated matter is accelerat ed outward and is expelled from the system by radiative pressure. Thus , the evaporation of planetesimals in the vicinity of young stars lead s to complex gas motions which include infall, quasi-keplerian rotatio n and the radial outflow typical of radiatively driven stellar winds.