P. E. Clegg

In-orbit performance of the ISO long-wavelength spectrometer

The long wavelength spectrometer on-board the European Space Agency IR Space Observatory (ISO) uses a grating and one of two Fabry-Perot interferometers to make medium and high resolution spectroscopic observations in the 43-196.9 micrometers wavelength range. The instrument has been in continuous use since the launch of ISO in November 1995. In this paper we describe the calibration of the instrument and its performance, both spectroscopic and photometric, over the two years of instrument operations.

Millimeter and submillimeter observations of 3C 273

The first detection of 3C 273 (1226 + 023) at wavelengths of 107, 240, and 400 microns together with contemporary measurements at 800 microns, 1.1, 1.9, 3.3, and 8.9 mm, is reported. These observations show that the continuum spectrum of 3C 273 can be extrapolated smoothly from the submillimeter to the infrared with a constant spectral index. There is no evidence of thermal emission from dust. It is shown that the spectrum is consistent with optically thin synchrotron emission from a relativistic beam at a small angle to the line of sight.

Calibration and performance of the LWS

The status of calibration and performance of the ISO Long-Wavelength Spectrometer eleven months after launch is described. The strategy followed for the calibration observations and first results are summarized. The overall performance of the instrument essentially fulfills the expectations; certain changes in sensitivity of the detectors are reported. Some improvements in the way observations are executed, which resulted from the in-flight experience, are explained.

Millimeter-wave observations of flat spectrum radio sources

Measurements at wavelengths between 0.4 and 2.0 mm of a sample of 26 compact, flat spectrum radio sources are presented. These observations extend the known radio spectra of this class of sources to higher frequencies and show that most of these sources are still flat at short millimeter wavelengths. The spectral shapes are consistent with an inhomogeneous synchrotron model (with some degree of relativistic beaming); however, the lack of concurrent multifrequency data prevents more definite conclusions at this stage.

Long-term performance of doped Ge:Ga photoconductors in the space environment

The long wavelength spectrometer on board the ESA IR Space Observatory employs doped geranium photoconductors to perform spectroscopy in the 43 to 197 micrometers waveband. The instrument has been in continuous on orbit operation for over two years - longer than any other experiment in this waveband. Invaluable data have been gathered on the long term performance of a beryllium doped germanium detector and both stressed and unstressed gallium doped germanium detectors in the presence of ionizing radiation in the form of cosmic rays and charged particles trapped in the Earths magnetic fields. In this paper we report on the in-orbit performance of the detectors and in particular on the long term behavior of the dark current and responsivity.