The combination of adaptive optics with a coronographic capability combines a high spatial resolution (~0.1") with high dynamic range and has the potential to be a powerful tool in the study of the close environment of bright objects. In particular the linking of such an AO Coronograph with a integral field spectrograph such as TEIFU or OASIS will enable important new areas of research to be undertaken.

The benefits of conventional coronographic imaging are well known, such as the imaging of the Beta Pictoris optical dust disk (Smith & Terrile 1984). The combination of AO with coronography will enable higher sensitivity and spatial resolution imaging of regions close to the central star. There is also a need for a coronographic spectroscopic capability because many bright point-like objects are known to possess active extended circum-nuclear or circumstellar emission regions. The study of these emission regions requires that the central point-like object first be suppressed. We know that these regions exist through imaging studies with the VLA, MERLIN and the HST, but the VLA and MERLIN only pick up their continuum emission, whereas the optical emission from these compact circum-nuclear or circumstellar regions comes out largely in narrow emission lines, whose intrinsic widths and velocities could be determined with a coronographic mode.

The science targets of interest for coronographic observations include:- 

1. Brown dwarfs and substellar companions. A coronograph will allow both the detection of such low luminosity companions and narrow band observations to measure colour-temperatures and critical atomic and molecular bands and lines.
2. Protoplanetary disks around young stellar objects including T-Tauri stars and pre T-Tauri stars. These are pre-Main Sequence stars still surrounded by the natal material out of which they formed. The stars are highly active and can ionize the surrounding material. The VLA and MERLIN have revealed the continuum emission from the compact regions around Herbig Ae/Be and T Tauri stars, but high spectral resolution coronographic studies of the optical emission lines from these compact regions are needed if we are to understand the earliest stages of star formation and planetary system clearing. The study of jet phenomena around these object is also an area of interest and the study of regions close to the central object is crucial for the understanding the origin and formation of these jets.
3. Circum-nuclear regions of AGNs and Seyfert galaxies. These possess very bright point-like cores, exhibiting very broad lines, but narrower emission lines are emitted by gas in the surrounding galaxy. A coronographic capability would allow this material to be mapped to much smaller radii than can currently be done using both broad and narrow bands.
4. QSO host galaxies. The environment of QSOs is a topic of much scientific debate. AO coronography will allow the imaging of the underlying galaxy and the study of its morphology.
5. Dust disks around main sequence stars (i.e. Vega phenomena). The IRAS satellite detected far-infrared excesses for a number of main sequence stars and in a few cases a dust disk has been observed directly at optical or near-IR wavelengths using coronographic techniques (eg. Smith & Terrile 1984, Weinburger et al. 1999). 
6. Symbiotic stars. These are cool red giants with hot subdwarf binary companions that ionize part of the red giant wind. Due to mass transfer and accretion runaways, novalike mass ejection events can occur. Extended emission up to 1 arcsec in size has been detected by MERLIN for a number of symbiotic stars, but coronographic spectroscopy is needed to study the dynamics, excitation and composition of this material.
7. Luminous Blue Variables (LBVs), such as P Cygni or Eta Carina, undergo periodic major mass ejection events (P Cyg erupted in 1600 AD, Eta Car in 1848). The material ejected by these events, and by similar phenomena around AG Car and other Galactic and Magellanic Cloud LBVs, has been detected through coronographic imaging (Nota et al. 1995). Spectroscopic studies of these compact regions reveal complex emission-line spectra, with unusual excitation conditions, but are hampered by the great brightness of the central stars (Barlow et al. 1994).

References

Weinburger A.J, E. E. Becklin E.E, Schneider G, Smith B.A., Lowrance P.J., Silverstone M.D., Zuckerman B., and R. J. Terrile , ApJ, 525, L53, 1999

Nota A, Livio M., Clampin M. and R. Schulte-Ladbeck, ApJ, 448:788-796, 1995