Institute of Astronomy

External photoevaporation imprints in protoplanetary discs

SpeakerTalk DateTalk Series
Stefano Facchini28 July 2014Across HR 2014 Posters


Stars are likely to form in groups and clusters. Such environments can significantly affect the evolution of the protoplanetary discs associated with the new-born stars. In relatively small groups ($N > 50$) FUV radiation from the most massive stars permeates the young association, with typical intensity values $G_0 = 30 – 3000$ Draines. The radiation interacts with the gaseous discs heating them up to few hundred Kelvin. Such high temperatures generate a pressure-driven gaseous wind flowing from the discs outer edge. If the mass loss rates are significant, they can affect the secular evolution of the disc, and consequently inhibit planet formation. We have built a new 1D model computing the steady-state radial structure of the flow by solving the hydrodynamical equations in a quasi – spherical geometry. The temperature is computed via the 3D-PDR code, and coupled with the hydro equations. We found new solutions for the wind’s steady-state radial profiles, as a function of stellar mass, disc radius and FUV intensity. We obtain mass loss rated for a large sample of discs outer radii and G0 values. Large discs ($R=200$ AU) show high mass loss rates ($> 10^{-8}M_\odot /$yr) even for a very low FUV flux ($G_0=30$). Moreover, we couple the dusty component to the gaseous one via dragging terms, and we obtain the radial surface density profile of the dust as a function of grain size. The wind is found to be strongly dust-depleted in the large ($>0.2\ \mu$m) grains tail of the distribution. This mechanism could therefore explain discs with an observed smaller dust extent with respect to the gaseous component.