Herbig stars are young stars surrounded by dust and gas, probably in
the form of a protoplanetary disk.They are on going phases of activity
through winds and accretion. Their study is expected to bring clues
to early stages of planetary systems formation. Young objects are also
widely thought to be formed in binary or multiple environments, and
many studies have been devoted to star and disk formation around
binary and/or multiple systems during the past years.
We started the study of a relatively evolved, Herbig
binary star TY CrA. From high resolution (HR) spectroscopy, we found
this star to be a double-lined eclipsing spectroscopic binary with a
period of 2.9 days and determined the orbital parameters and masses of
both components of the system. This is the first double-lined eclipsing
binary known among HAEBE stars. It thus offers a unique opportunity for
a detailed study of its circumstellar matter (both gas and dust) in the
framework of star/disk formation and evolution around binary systems.
HR spectroscopy suggests the presence of a third component, much cooler
and probably of T Tauri type. Part of the strong IR excess of TY CrA
 might come from this third companion; if its presence is confirmed
through proposed HST and ground based observations, circumstellar
environment models developed so far for this system should be revised.
Furthermore recent 10 micron imaging revealed on top of the complex 10
micron emission region associated to TY CrA, an intense close-by
emitting region, which may as well have been erroneously included in
the photometry of TY CrA. We propose here to perform IR imaging with
ISOCAM, as well photometry with ISOPHOT, to get an accurate IR
photometric budget of the star and its close environment, so as to
perform new and more adequate models. In addition, photometric
observations during primary and secondary eclipses will allow us to
investigate the immediate circumstellar environment. Spectroscopic
observations are planned to study the structure of the surrounding gas.