But ULIRGs and AGNs are not the only fields that will benefit from this increase in angular resolution. By accurately measuring the change in diameter of cepheids (as shown by Mourard et al, 1997 [11]) and measuring their effective temperature, one can get an independent measure of their distance, thereby reducing the uncertainty of this particular rung of the cosmic distance ladder. Such observations will be possible with VLTI on the largest and closest cepheids, but `Ohana will open up the galactic sample tremendously.
Young stellar objects and protostellar accretion disks may also be highly interesting targets because, even though the high extinction in the surrounding molecular clouds or of the accretion disk itself may make them generally inaccessible to direct optical observations, there may be special circumstances where it will be possible to catch accretion disks, after the extinction has been reduced by evolution or transient processes. For example, the YSO FU Ori is visible through negligible extinction, and may have such an accretion disk (Bell, 1994 [1]). The `Ohana angular resolution will be approximately equal to the stellar diameter. Models (Bouvier, 1994 [2]) clearly show that high angular resolution will be the key to distinguishing centrally localized viscous heating and reprocessing emissions (inside 1-10 AU) from the broadly diffused scattering fluxes (100 AU). `Ohana resolution of 0.04 AU is well suited for studying the innermost accretion zone.
The study of bipolar outflow and/or jets would also benefit from `OHANA: processes that have such a wide generality are often the most important in astronomy; these are observed in red giants, protoplanetary nebulae and planetary nebulae, symbiotic stars, cataclysmic variables and novae (Cohen, 1986 [5]).
Cataclysmic variables have broad, single peaked emission lines similar to those of AGNs (Chiang, 1997 [4]) and the study of wind driving mechanisms in CVs may advance the understanding of winds in AGNs. For example, the prototypical CV U Gem has Roche lobe, disk and orbit diameters on the order of the solar radius (Cherepashchuk, 1996 [3]). At its distance of about 100 pc, `Ohana could resolve the binary orbit, and partially resolve the diameters of the components mentioned, thus allowing model dependent measurement of the systems physical dimensions. (Baselines much longer than 1000 meters would be required to resolve accretion flow details.)
The binary SS433 is well known for extreme kinematic and energetic behavior associated with precessing jets which are believed to originate in a relativistic accretion disk. This perhaps unique galactic object offers a rare view of physical processes in a relatively nearby, highly observable, relativistic source. VLBI observations (Vermeulen, 1993 [14]) reach to the 10 milliarcsec (50 AU) level, which is insufficient to resolve the Roche lobe, the accretion disk, or the binary separation. According to both neutron star and black hole models (Fukue, 1992 [7]) all of these should be detected and partially resolved with `Ohana.
This brief overview of the scientific potentials of `Ohana is by no means exhaustive, but the science case is still being evaluated (see section 4.2) and there are still many other applications that need to be studied; for example, it has been suggested by Antoine Labeyrie to directly make images by densifying the full pupil of `Ohana. This mode is particularly adapted to punctual objects and could be applied to the direct imaging of extra-solar planetary systems.