Post on 24-Feb-2016
description
Dispersal of protoplanetary disks by central wind stripping
Isamu MatsuyamaUniversity of California Berkeley
David HollenbachSETI Institute
Doug Johnstone Herzberg Institute of Astrophysics
The outcome for a particular planetary system might be very different if the parent disk is dispersed faster or slower than in our solar system
Disk dispersal mechanisms:
•Stellar encounters•Planet formation•Viscous accretion•Photoevaporation•Stellar wind stripping ?
(Hollenbach et al. 2000, PPIV)
Image credit: Dan Bruton
Wind stripping
Previous studies: • Hadbury & Williams (1976): stellar wind pushes the solar nebula as a
whole. See also Cameron (1973), Horedt (1978, 1982).• Elmegreen (1978): addition of low angular momentum wind material to
the disk, the net radial flow is inward in this case.
•Wind-disk mixing layer moves outward•Mass and momentum input from the wind•Mass and angular momentum input from the disk•Normal pressure balance
Mass, momentum, and angular momentum conservation; and normal pressure balance:
Normal pressure balance and mixing layer curvature
Disk pressure Wind pressure Curvature of the wind-disk mixing layer
Wind mass loss rate= 10-
8
M
yr-
1
Disk mass = 0.01 M, Wind velocity = 200 km s-
1
, Entrainment efficiency(ε) = 0.1
Different entrainment efficiencies
Canto and Raga (1991): ε = 0.01 – 0.1
Analytic approximation
“Early time”
“Intermediate time”
“Late time”
Summary• Dispersal time proportional to mass of disk/ (wind mass loss
rate×wind velocity×entrainment efficiency)• When compared to photoevaporation and viscous evolution,
wind stripping can be a dominant mechanism in a small range of outer disk only for the combination of– low accretion rates – High efficiency ε (> 0.1)– AND wind outflow rates approaching these accretion
rates • This case is unusual since generally outflow rates are < 0.1 of
accretion rates