High Mass X-ray Binary systems are a class of accreting binary that
consist of an early type star (O or B) that is orbiting with a compact
object, typically a neutron star. This proposal is concerned with
the types of HMXB containing Be or Supergiant stars - an
early type emission star that is orbiting with a neutron star. These
systems exhibit transient bursts of X-ray emission. Sometimes on a
regular basis corresponding to the periastron passage of the neutron
star giving rise to accretion of circumstellar or stellar wind
material onto the surface of the neutron star.
   However, the mechanism for this accretion is still not certain.
In particular, it is not known whether an accretion disc is present
during the accretion phase, or if it is only present for some of
the time, or if matter accretes directly onto the neutron star without
a disc being present. One of the critical factors influencing the
creation of an accretion disc is the condition of the material
being accreted, in particular the velocity of the material relative
to the neutron star. This affects the ability of the neutron star
to capture material flowing past it, and hence its ability to form
an accretion disc.
   The aim of this proposal is to observe such systems while
they are undergoing an X-ray outburst and hence they should have an
unusually active and large circumstellar disk. We wish to obtain infrared
line data from the circumstellar disc/wind to use as a diagnostic of
conditions in the disc. This will then be combined with
simultaneous X-ray observations of the system obtained with CGRO,
in an attempt to determine what modes of accretion are taking
place on to the neutron star. We will be
able to detect within one day if any of our systems go into an
active phase and alert ISO accordingly.