BALLOON-BORNE FAR-INFRARED FABRY-PEROT SPECTROMETER FOR ASTROPHYSICALOBSERVATIONS

The balloon-borne cryogenic far-infrared spectrometer (FIS) described in this paper is a liquid-helium cooled direct-detection spectrometer which covers the wavelength range from 140 mu m to 220 mu m. The spect ral resolution R is about 2000. FIS is based on two scanning Fabry-Per ot interferometers (SFPs) whose reflector gaps can be varied continuou sly over more than 200 mu m by the magnetic force of superconducting c oils. FIS has been developed to measure far-infrared emission lines fr om star-forming regions. The most prominent among these are the 157 mu m [CII] line and the 205 mu m [NII] line. In order to perform the cal ibration of FIS during the flight preparation at the balloon-launch fa cility of CNES in Aire sur 1'Adour (France), we have devised a new met hod of calibration of FIS which is performed exclusively with the help of an evacuable absorption cell. In-flight tests in the stratosphere have confirmed that all components of the instrument work. This test p ermitted us to estimate the system noise equivalent power (NEPsys). It is in the expected range of about 10(-14) W/H-1/2 at the wavelength, of 157 pm and of about 2 x 10(-14) W/Hz(1/2) at 205 mu m wavelength. ( C) 1998 Elsevier Science B.V. All rights reserved.