Characterization and Status of a Terahertz Telescope

The Receiver Lab Telescope (RLT) is a ground-based terahertz observatory, located at an altitude of 5525 m on Cerro Sairecabur, Chile. The RLT has been in operation since late 2002, producing the first well-calibrated astronomical data from the ground at frequencies above 1 THz. We discuss the status of this telescope after 18 months of operation and plans for the upcoming observing season. There are many practical challenges to operating a telescope at these frequencies, including difficulties in determining the pointing, measuring the telescope beam and efficiency, and calibrating data, resulting from high receiver noise, receiver gain instabilities, and low atmospheric transmission. We present some of the techniques we have employed for the RLT, including the use of atmospheric absorption lines in the place of continuum measurements for efficiency and beam measurements, and the utility of a Fourier-transform spectrometer for producing reliable data calibration.