The Best Tools for Reaching High Dynamical Range Imaging

Pierre Baudoz
IfA

While access to the diffraction limit of ground-based telescopes 
is now routinely obtained thanks to adaptive optic systems, the 
dynamical range accessible for the images is still very poor. 
Increasing the detection capabilities of faint structures around 
bright objects is crucial for targets such as circumstellar disks 
and low mass stars as companions. Lately, coupling of coronagraphs 
with adaptive optic systems or space-based observations has helped 
in improving the dynamical range of the images. I will show that 
the coronagraphs used in these recent experiments were Lyot 
coronagraphs that can be replaced by coronagraphs more suited to 
the high dynamical range problem. This is even more true as new AO 
systems with a large number of actuators come online. Among the 
ideas that can be used to increase the dynamical range, I shall 
describe recent developments in stellar coronagraphy such as 
phase masks techniques, nulling techniques, and apodisation. 
I will also show how observational techniques such as dual 
imaging or field rotation combined with such instruments can 
increase dramatically the dynamical range of images. Different 
types of objects that could benefit from such new instruments 
will be outlined.