Planetary Nebulae and Supernova Remnants

The elusive protostars may best be found by virtue of their cold dust emission at millimeter wavelengths. High angular resolution is required to distinguish objects at different evolutionary phases within the same star-forming region: the collapsing cloud cores, cool dust envelopes, hot dust cocoons, hot molecular cores, bipolar flows, ultracompact HII regions, etc. The ALMA will reveal the dynamics of the dust-obscured protostellar accretion disks, the rate of accretion and infall from the molecular clouds, and the mass distribution over the disk.

Indirect evidence for planet formation may be provided by the presence of gaps cleared by large bodies condensing around the stars. The molecular outflows will be observed in unprecedented detail; masers (both molecular and atomic) might make it possible to study the innermost regions, and could reveal the velocity structure of the accretion disk.

Stella Evolution

The ALMA will detect tens of thousands of stars over the entire H-R diagram, and allow major advances in virtually all fields of stellar astronomy. Millimeter emission has already been detected from O and B stars, W-R stars, hot stars with shells, pre-main sequence stars, late-type giants and supergiants, and optically variable stars. Circumstellar shells around evolved stars, observed at millimeter wavelengths, provide a unique probe of time-dependent chemistry. The ALMA will resolve thousands of such shells, and reach across the Galaxy, so that dependence on stellar type, local environment, and galactocentric distance can be studied.

Protostars and Young Stellar Objects

The ALMA will provide detailed line and continuum images of planetary nebulae and supernova remnants. Radio supernovae are first seen at high frequencies, and the ALMA will detect them out to large distances; VLBI can be used for absolute distance determination. SN 1987A in the Large Magellanic Cloud will be a prime target for the ALMA.

Evidence of a central source may require millimeter-wave observations because of possible free-free and dust absorption. The shock wave will hit the [OIII] ring in 2005+-3 , providing an incentive for early operation of at least part of the array!