Infrared Speckle Interferometry

A particularly interesting area for speckle interferometry
and image restoration has been the application of these
methods at infrared (IR) wavelengths, where the atmo-
sphere is more benign than at optical wavelengths and
where there exist classes of objects of moderate complex-
ity that are ideal candidates for high-resolution imaging.
As wavelengths increase, both t0 and r0 increase, and
the observational requirements are relaxed. The first IR
speckle observations were made with single-pixel detec-
tors across which were scanned at high speeds the im-
ages of objects to be analyzed. This approach has been
used to measure the heated dust shells surrounding such
supergiants as Betelgeuse and Antares and other hot and
highly evolved stars. The sizes of protostellar objects from
which normal stars will eventually evolve have been mea-
sured. These objects are typically enshrouded in dense
dust clouds that obscure the visible radiation while radiat-
ing at IR wavelengths because of heating from the central
hot-star-forming gas. IR sources discovered by standard
methods have been found to be highly complex, and very
faint and cool companions have been found in orbit around
a number of stars. The star T Tauri, the prototype of a class
of stars thought to represent the transition between proto-
stars and normal hydrogen-burning stars, has been found
to have a companion. This provides a rare opportunity to
study the circumstances surrounding the formation of a
binary star system.
IR speckle methods were particulary advanced by the
advent of extremely sensitive solid-state detectors with
full two-dimensional pixel coverage. These powerful new
devices combined with the wealth of objects to which
they can be applied make IR speckle interferometry and
direct imaging an extremely productive tool for exploring
a variety of phenomena, especially those associated with
young stars and star-forming regions.
Surveys for companions to young and pre-main se-
quence stars in several star-forming regions have shown
that the occurrence of duplicity for these young objects
is at least as high as for older stars like the Sun. This
indicates that the formation of binary and multiple star
systems is a natural consequence of the earliest stages of
star formation.