Emmy Noether Application

self-consistently magnetically launched outflows (Banerjee & Pudritz, 2006) but has to be
extended to capture effects from non-ideal MHD (i.e. ambipolar diffusion and Ohmic resistivity)
and to handle stellar magnetic fields.
PhD Thesis: Radiation feedback from massive stars
One of the key issues to understand the formation of massive stars is the proper treatment
of feedback from the progenitor stars. As mentioned earlier, massive stars accrete a substantial
fraction of their final mass by the time they already start their nuclear burning phase,
i.e. approached the main-sequence track. The resulting radiation feedback cloud in principal
set a mass limit for such stars via radiation pressure (Kahn, 1974; Wolfire & Cassinelli, 1987;
Yorke & Sonnhalter, 2002). Despite such theoretical upper limits on the mass of massive
stars, observations reveal more and more massive stars whose mass exceed the predicted
limitations. Typically, the theoretically predicted limits are two to four times below the masses
from the observed most massive stars (e.g. Pistol star, Eta Carinae, dozens of stars in 30
Doradus). Therefore, we have to considerably improve our models of radiation feedback to
close the gap between theory and observations. So far very few attempts have been made
to tackle this problem in a self-consistent way, i.e. including the collapse phase as well as
the radiation feedback in the same calculation. One of the most sophisticated calculations
was done by Yorke & Sonnhalter (2002) who implemented a wavelength dependent radiation
transfer treatment in their collapse simulations. Although they could show that the wavelength
dependent radiation transfer relaxes the upper mass limits, the final masses are still substantially
below the observed ones. These simulations were restricted to two-dimensional,
axi-symmetric cases. Fully three-dimensional calculations will lead to more realistic results.
In particular outflows and instabilities of radiation bubbles might help to elevate or rid mass
limitations as proposed by Krumholz et al. (2005b,a). This has yet to be shown in a selfconsistent
calculation and will be a main aspect of the proposed research project.
Furthermore the emitted radiation from young stars heat, ionise, and can even photoevaporate
the surrounding gas. These processes, if once operative, will alter the cluster evolution.
Whether the feedback from the first formed massive star will initiate or inhibit nearby star
formation should also be investigated in this thesis project. The implementation of the photoheating
and ionisation should be based on the ray-tracing module developed by Rijkhorst
et al. (2006) for the FLASH code. This module calculates the column density for different
sources with a parallel ray-tracing algorithm which in turn is used to compute the ionisation
and heating rates. We already performed several successful test calculations with this
module which convinced us of the usability of it. This treatment has to be adapted for the
purpose studied in this project. In particular it should be able to handle different chemical
compositions which will alter the ionisation cross sections and the cooling and heating rates.
Furthermore, the calculations should also take into account the possibility of moving sources
which will be important in studying star forming cluster. It should be mentioned here again
that the two PhD candidates should exchange their design and technical concepts before
implementation so that both parts can be smoothly merged for future calculations.
Despite the vast developments of computer technology in the last couple of years we are still
far from being able to calculate the complete radiative transfer equations in three-dimensions.
The complete treatment of these equations would involve the knowledge of the intensity as
a function of eight independent variables (i.e. three spacial variables of the intensity location,
three directional angles, frequency, and time). The storage and computation of such an
eight dimensional variable with sufficient resolution can not be handled with the presently
accessible computing clusters. Therefore the radiative transfer part of this projects has to
be based on reasonable approximations which will reduce the degrees of freedom for the
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