date: 2011 April 20 (Wed) 15:00-16:00
room: Kobe University, Science and Technology Research Building #4-809
speaker: Takaya Tamura (Kyoto University)
organizer: Hiroshi Kimura
title: Gas Dispersal of Protoplanetary Disks due to FUV and EUV irradiation from a Nearby Massive Star
abstract: The gas in protoplanetary disks has great influence on the formation of planetesimals and gas giant planets.
Photoevaporation, a process by which the gas thermally escapes from the disks due to the heating by UV irradiation, is an important mechanism for the gas dispersal in the outer disk which contains most of the disk mass.
In particular, protoplanetary disks in star clusters are dominantly influenced by UV irradiation from a nearby massive star.

Actually, it is observationally known that the proplyds in the Trapezium cluster are illuminated by the nearby massive star, theta^1 Ori C, and surrounded by tear-drop-shaped ionization fronts which are thought to be formed in the photoevaporating flow from the disks.
Since stars are generally born in star clusters, it is important to study how the disk gas disperses.

In this work, we calculated the surface density evolution of the disks with considering photoevaporation due to the nearby massive star and gas accretion toward the central star.
As a result, photoevaporation efficiently disperses the gas in the outer region of the disk, and the radius of the edge of the disk shrinks to become several times 10 AU in ~10^6 yrs.
This is consistent with the disk radii of the proplyds observed in the Trapezium cluster.
The photoevaporation rate is ~10^{-7} M_sun/yr in this calculation.

Next, we performed hydrodynamical simulations of the photoevaporating flow from the disks.
And we studied how the size of the ionization front depends on the distance from the massive star and the photoevaporation rate from the disk.
As a result of our calculations, the observed correlation between the ionization front radii and the distances from the massive star is well reproduced by our model when we adopt the photoevaporation rate of 10^{-7} M_sun/yr which we obtained in the above-mentioned calculations of the evolution of the disk surface density.
These two results suggest that the photoevaporation and accretion model explains the gas dispersal of the proplyds.

I would like to discuss the various influences of the rapid dispersal of the gas in the proplyds in this talk.