Monday 17^th, Tuesday 18^th, Wednesday 19^th January 2011, 9h00-12h30
John Hillier (University of Pittsburgh, USA)

CMFGEN: A non-LTE Radiative Transfer Code

• CMFGEN (pdf, 683 357 bytes)
• Basics of Radiative Transfer / Atmosphere Modeling part. 1 (pdf, 2 729 914 bytes)
• Basics of Radiative Transfer / Atmosphere Modeling part. 2 (pdf, 2 364 366 bytes)

CMFGEN is a non-LTE radiative transfer code which has been used to model the spectra of O stars, B stars, A stars, Wolf-Rayet stars, Luminous Blue Variables, Central Stars of Planetary Nebulae, Supernovae, and the spectra of CV accretion disks. Using CMFGEN we can derive fundamental parameters such as effective temperatures, surface gravities, and abundances, and place constraints on stellar wind properties. The latter is important since all massive stars are losing mass by a stellar wind that is driven from the star via radiation pressure, and this mass loss can substantially influence the spectral appearance and evolution of the star.
Originally CMFGEN was confined to stationary and relatively low velocity flows (v/c < 0.01) but over the last few years we have updated the code to handle relativistic and non-stationary flows with primary application to supernovae. In particular, CMFGEN can now treat the time-dependent rate equations, and time-dependent radiative transfer.
An auxiliary code, CMF_FLUX, is used to compute theoretical spectra. Other auxiliary codes are used to compare models with observation, and for understanding and analyzing results from model atmosphere calculations.
In our lecture series we will discuss the assumptions underlying CMFGEN, as well as its applications and limitations. Example models will be discussed and demonstrated.
We will also discuss the physics in the code, and some of the processes important for interpreting line spectra. These processes include collisional excitation, radiative recombination, dielectronic recombination, continuum fluorescence, and Bowen fluorescence. While it is possible to run CMFGEN as a blackbox, such an approach is not recommended.
Users need to be aware of the limitations in modeling -- limitations in both CMFGEN and limitations in our understanding of the sources we are modeling.
Further, atomic data is subject to uncertainties, and this must be taken into account in analyzing and interpreting results. The diagnostic routines available with CMFGEN should be used to understand results.

Monday 17^th January 2011, 14h00-16h00
Ronny Blomme (ROB, Belgium)

Radiative transfer in single and binary massive stars in the radio domain (pdf, 1 409 694 bytes)

Radio emission from massive, early-type stars has two possible causes. In single stars, it is due to free-free processes in the stellar wind. I will show how these processes are modelled in spherically symmetric radiative transfer models, and what information can be derived from the observed radio fluxes.
In massive binaries, the colliding-wind region between the two stars is responsible for non-thermal radio emission. Considerably more complicated modelling is required in this case. It includes the acceleration of a fraction of the electrons up to relativistic speeds, their subsequent synchrotron emission, and the transfer of that synchrotron radiation through the stellar wind material. All this requires a 3-dimensional radiative transfer code that follows the changing behaviour of the colliding-wind region as the binary components move in their (usually eccentric) orbit.

Tuesday 18^th January 2011, 14h00-16h00
Christophe Pinte (LAOG, France)

Radiative transfer in protoplanetary disks (pdf, 25 260 005 bytes)

Details of the evolution of circumstellar disks towards planetary systems remain poorly understood. Simultaneous studies of various observations: SEDs, scattered light images, polarization maps, infrared spectra, near-infrared interferometry, ... via detailed radiative transfer modeling give new insights on the processes by which discs and dust evolve.
I will present a few examples of multi-wavelength and multi-technique modeling of observations of circumstellar disks and illustrate how this allows us to draw quantitative constraints on the first steps of planet formation: the growth of dust grains and their settling towards the disk midplane.
I will also show why a full treatment of the radiative transfer, in particular including the contribution of scattered light, is necessary to interpret near-IR visibility measurements of T Tauri stars.

Wednesday 19^th January 2011, 14h00-16h00
Peter van Hoof (ROB, Belgium)

Photoionization Physics in the ISM and CSM (pdf, 21 325 001 bytes)

The photoionization code CLOUDY is used to model a wide range of physical states, such as photoionized and collisionally ionized plasmas, photo-dissociation regions and molecular material. In order to model all these states accurately, the code needs to include detailed treatment of many different microphysical processes. Dr van Hoof has been a core developer of CLOUDY for more than 10 years. In his presentation he will give an overview of the most important processes that determine the physical state of the material. He will also show several examples of how the code can be used to study interstellar and circumstellar material.