A FABRY-PEROT IMAGER FOR NEAR-INFRARED ASTROPHYSICS AT THE COMMUNICATIONS-RESEARCH LABORATORY 1.5 METER TELESCOPE, AND IMAGING OF HYDROGEN RECOMBINATION LINES IN THE ORION NEBULA

We have developed a Fabry-Perot imager at the Nasmyth focus of the Com munications Research Laboratory (CRL) 1.5 m telescope. The field of vi ew of the camera is 4'.0 x 4'.0, which is the largest among near-infra red Fabry-Perot imagers. In order to make the velocity shift in the fi eld of view small, we chose a long focal length for the collimator (ap proximately 470 mm). The accurate parallelism of reflecting surfaces, 5 nm, is achieved by systems including a He-Ne laser and Si photodiode s. This gives an effective finesse of approximately 50. Wavelength cal ibration is carried out by using a Kr lamp. This calibration includes a correction for wavelength-dependent phase changes in the reflective coatings of the etalon. Using this Fabry-Perot imager, we obtained Brg amma and Pabeta images of the Orion Nebula, including the Bright Bar a nd a part of the Trapezium. From these images we obtained the distribu tion of extinction in this area. We found that there are regions with a tendency for the Brgamma/Pabeta intensity ratio to be larger at a pl ace with a larger Brgamma intensity. We conclude that in such regions dust grains exist within the ionized region, causing the extinction.