LECTURER:

Ivan Hubeny, University of Arizona

TITLE : 

From stars to quasars: Modeling radiation-dominated objects in
astrophysics

ABSTRACT:

There is a whole class of astronomical objects in which radiation plays
a crucial role. Typical examples of such a situation are stellar 
atmospheres and accretion disks.  I will give a brief overview of recent 
progress in their modeling.
On the stellar atmospheres side, very sophisticated models including millions
of lines are now being constructed without the approximation of Local
Thermodynamic Equilibrium - the so-called non-LTE line-blanketed models. 
It is
shown that they provide an excellent match to high-quality ground- and 
space-based spectra. In accretion disk modeling, we have constructed 
several grids of non-LTE disk models for a wide range of parameters for 
disks around white dwarfs (cataclysmic variables), solar-mass black holes 
(X-ray binaries), and supermassive black holes (quasars) , and used them 
to analyze various observed data.


TITLE: 

Will we see a new stellar spectral class soon?
Atmospheres and spectra of the coolest brown dwarfs

ABSTRACT:

I will briefly  review basic physics and chemistry of the
brown dwarf atmospheres, with emphasis on two essential problems:
i) cloud formation (including cloud position and extent, cloud particle
size distribution, cloud absorption and scattering), and ii) departures
from chemical equilibrium.   A brief overview of predicted spectra and
their comparison to existing observations of warm brown dwarfs will be
presented. It is argued that in order to define meaningfully a new spectral
class (already agreed to be called Y) one will have to go to much cooler
objects than so far observed.