  After the recent beautiful results on gamma-ray lines obtained with CGRO, the
INTEGRAL mission with the imaging-spectrometer SPI will set the next milestone,
combining improved sensitivity and angular resolution with a considerable
increase in spectral resolution. SPI is expected to provide significant new
information on galactic nucleosynthesis processes and star formation activity,
as traced by the distributions of annihilation radiation and radioactive
isotopes such as 26Al and 60Fe. The unprecedented spectral resolution will
allow the study of dynamic processes in stellar mass ejections and will provide
access to kinematic distance estimates for gamma-ray line sources. The study of
supernovae and their remnants will be prime objectives for SPI observations.
Nearby type Ia SN, within 15 Mpc or so, are in reach of the instrument and a
few such events are expected during the lifetime of INTEGRAL. Young galactic
supernova remnants, possibly hidden by interstellar dust, may be unveiled by
their characteristic gamma-ray line signature from the radioactive decay of
44Ti, as has been demonstrated by COMPTEL for Cas A and possibly RX
J0852.0-4622. Classical novae are also among the SPI targets, which may observe
the gamma-ray lines from radioactive 7Be and 22Na. Such observations can
constrain the physics of the nova explosions and will allow to evaluate their
role as nucleosynthesis sites. The interaction of cosmic rays with the dense
matter in molecular clouds may be another source of gamma-ray lines that is
potentially accessible to SPI. Finally after the SIGMA results on Nova Muscae
and 1E1740.7-2942, and a possible 2.223 MeV line detection by COMPTEL, the
search for lines from X novae is another way to participate in the
understanding of the physical conditions in these close binary systems.
