Diploma Thesis
Hydrodynamik des Einfalls klumpiger Materie in protostellare Akkretionsscheiben im Hinblick auf
H2O-Maseremission
(Accretion Disk-Impinging-Clumps and H2O Maser Activity)
Christof Keller
Abstract:
Recent observations have increasingly revealed characteristic structures in the distributions
of H2O masers in low-mass star-forming regions, that indicate protostellar accretion disks as
being the maser's likely origin. This may open up hitherto unique ways to determine velocity fields,
densities and temperatures of deeply imbedded star/disk systems. Accretion shocks produced by
diskimpinging-clumps had been proposed as hydrodynamic trigger mechanism for 22 GHz H2O maser excitation
(Fiebig 1997). To investigate the consequences of clumpy mass infall in detail, two-dimensional
SPH simulations were carried out. An isothermal stratification was assumed for a model disk surrounding a
2 MSun protostar and the infall of clumps of sizes 0.1 to 1 AU with densities of
nclumpH2 ~ 108 ... 109 cm-3
has been simulated. Also a variety of infall angles and velocities of order
10 km/s have been tested. Those velocities agree with estimates from zero-energy infall trajectories.
The shock-structure produced by clumpy infall has been analysed in detail and different boundary
conditions have been investigated in regard to their ability to foster observable H2O maser activity.
Thesis: ps.gz file (1426990 Bytes)
only available in German
