7.2. 12.5μ imaging of Sgr A West with the Keck Telescope

Abstract

We have used the 10-meter Keck I telescope and the camera mode of the long wavelength spectrometer to observe the central region of the Galaxy at 12.5 μm. The 96×70 As:Si array used had a scale of 0.114 arcsec per pixel. The filter was centered at 12.5 μm and had a bandwidth of about 1 μm. The array was flat-fielded using sky flats from the background. We observed the central 20×20 arcsec region (about 1pc × 1pc) by using a mosaic pattern of the 11×8 arcsec array in approximately half-array steps. The position of the array was determined after the fact by using structure in the flux in the overlap regions. The accuracy of the positioning was better than 0.1 arcsec. The resultant spatial resolution of the final map was about 0.7 arcsec FWHM based on the size of IRS 7 and IRS 3. The demonstrated diffraction limit of the phased Keck telescope at 12.5 microns is just over 0.3 arcsec FWHM, so that the final resolution is a result of atmospheric seeing and chopper smear. The final map is shown in Figure 1. The map is similar, but of much higher angular resolution, to the 12.5 μm map of Gezari (1992, The Center, Bulge and Disk of the Galaxy, ed. Blitz, Dordrecht: Kluwer, 23).