Outflow Activity Is Associated with Early Stellar Evolution. When This Outflow Is Associated

Abstract

Outflow activity is associated with early stellar evolution. When this outflow is associated with optical

emission, it is classified as a Herbig Haro object. Analysis of Herbig Haro objects thus leads to better

understanding of both their launch mechanism and the young stellar objects they originate from.

In this thesis, for the first time, the complete jet kinematics of a Herbig Haro object (HH 1042) is simulatedby gasdynamical models combined with variable outflow functions.

The simulations are performedwith two models: one written from scratch in Python, and one using a gasdynamical code from withinAMUSE, a software framework for astrophysical simulations in which existing codes can be easily coupled.

The three main differences between the models concern the (in)compressibility of the jet, the shock

physics included in the models, and the solution method of the equations used. The AMUSE model is

the most accurate and complete in the physical sense. Each model is run for 2500 years with a time stepof 1 year. The resulting jet kinematics are compared to both each other and the observed jet. Withthe help of videos of the full simulations, each feature in the simulated jet kinematics can be explainedanalytically.

The variability in the outflow functions is needed to explain the 'knotted' structure in the observed jet.

Three sets of functions are used. Two parameters of these functions are varied in a parameter study,

to check the validility of the physics included in both models as well as the method used to obtain the

variable outflow functions. Calculating the root mean square value of the velocity fields of the simulatedjets when varying the velocity ratio of the first oscillation over the mean velocity is a promising measure;and can be used to improve the calculation of the velocity ratio of an observed velocity field.

The main conclusions of this thesis are that the observed jet can be well-simulated with the gasdynamicalmodels. The accuracy of both models is comparable; however, the AMUSE model describes the physicsbetter and, when combined with the constant mass flux option for the outflow functions, shows a bettermatch with the observations. Therefore this option is used in the parameter study, which led tosuggestions concerning the method of determining the parameters of the outflow functions (mainly thelaunching times of the knots and the amplitude of the first oscillation in the velocity outflow function). Itis however still not possible to exclusively define an outflow function for the jet. This might change whenthe calculation of launching times is improved. Suggestions are formulated to improve this calculation.