HOT PROTOPLANETARY DUST NEAR MAIN SEQUENCE STARS

Ramiro de la Reza
Observatorio Nacional- CNPq
Rio de Janeiro


The recent discovery of four "51 Peg" type planets, with masses between
0.6 to 3.8 Mjup located very near (within 0.1 AU) their MS stars, leave
us to think that dust rings with very short radii could exist around stars
evolving to the MS. These dust rings would be parts of protoplanetary disks
that will later aggregate to form eventual planets. Thermal balance 
relations between the star's radiation and the dust reemission enable us to
predict radiation fluxes at 2.2 microns. For hypothetical A0,F0 and G0 MS
stars located at 20 pc from us, large observable fluxes are obtained, at 
least for corresponding A0,F0 dust rings with radii between 4 to 2 AU 
(corresponding to 0.2" and 0.1" respectively) and for dust masses equal to 
half Earth and Jupiter masses. Because at 2.2 microns there is practically 
no excess ring radiation respect to the considered stars photospheric 
radiation field, the ring can only be visualized by masking the star in an 
Off-Axis situation. To our knowledge this "hot" dust has never been imaged 
in "Beta Pic" or "Vega" type objects due to the mentioned interfering 
radiation.
This gives to SOAR at ~2 microns where its performance is at its best, in a 
coronagraphic and off-axis combination, a unique place. This study can be 
complemented with observations at 10 microns with GEMINI in order to detect 
farther rings in the protoplanetary disk.

Required PSF; (0.2" -0.1"), very low scattered light.
S/N required for resolution element; >100.
Typical exposure time for this S/N & Lunar phase; long,dark,any(IR).
Anticipated photometric dynamic range required; very high > 10**4.
Tip/Tilt feasible; yes.
Anticipated number of separate pointing to complete program; we would want to
survey many objects.
Can this program execute in a queue; ?
Required instruments(spectral R,filters,wavelength range); coronagraph, 
IR imagers with small pixel scales, Off-axis system.
Why can this program execute on the Blanco 4m ?;inadequate imaging performance.
Other complementary telescopes ?; Yes, the GEMINI at 10 microns for some stars.