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Institut de Radioastronomie Millimetrique (IRAM)

IRAM operates two Observatories which both offer unique scientific capabilities to their wide user communities. The 30m-telescope located at an altitude of nearly 3000m on the Pico Veleta in the Spanish Sierra Nevada has a surface accuracy and a pointing capability which allow to exploit the atmospheric windows at 3, 2, 1 mm. Occasionally the telescope is even used at 0.8 mm during particularly favourable atmospheric conditions.

While other telescopes exist in Europe that can observe in the 3mm-atmospheric window, e.g. the 100m-telescope in Germany, the Onsala telescope in Sweden, and the Metsahovi telescope in Finland, and while European groups operate (sub-)mm-telescopes like the SEST in Chile, the HHT in Arizona, and the JCMT in Hawaii, the IRAM 30m-telescope is by far the most sensitive in its wavelength range; it also offers unique observing capabilities through the simultaneous availability of several low-noise heterodyne receivers, a heterodyne array with currently 9 and soon 18 channels, and 37- and 117-channel bolometer arrays. The heterodyne receivers can be connected to a variety of analogue and digital backends that allow spectroscopic studies at different resolutions. The telescope is also equipped with a Mark IV VLBI terminal, and VLBI experiments at 3, 2, and 1.3mm wavelengths have successfully been carried out since several years. By combining the 30m-telescope with a 15m-diameter antenna on the Plateau de Bure Observatory, it has indeed been possible to detect for the first time fringes in a VLBI experiment at 1.3mm with a high signal/noise ratio.

The Plateau de Bure Interferometer started in 1990 as a 3-element array. It is located at 2550m altitude in the French Alps, near Gap. Since then, 3 more 15m-diameter antennas have been added, and today all 6 telescopes are equipped with low-noise heterodyne receivers for the 3mm and 1mm atmospheric windows. There is at present no other interferometer on the Earth that offers the same sensitivity at these wavelengths. With its maximum baseline of 408m (in east-west direction) it allows sub-arcsecond imaging at the shortest wavelengths.

The signals from the 6 antennas are processed in an IRAM developed digital correlator which allows a large variety of observing modes. A special virtue of this device is the possibility to phase up all 6 antennas for VLBI experiments. The first observations that demonstrate the enormous gain in sensitive by combining the Plateau de Bure array with the 30m-telescope and other telescopes in Europe and abroad have recently been performed and are presently awaiting correlation and analysis. In the near future it is planned to perform global VLBI experiments at 3mm wavelength together with the American VLBA, and in the longer term experiments that also use the ALMA antennas in Chile are envisaged. While the present generation of heterodyne receivers is already giving excellent results, a new generation of wider-band receivers for the 6 telescopes is under development. They will be accommodated in a single cryostat and will not only further improve the performance of the instrument in the currently available wavelength bands, but will provide a fuller coverage of the atmospheric windows at 3, 2, and 1mm.

In order to further increase the angular resolution of the instrument, work has been started to extend both the north-south and the east-west track. The latter one will be doubled, and in the longer term an even bigger extension can be envisaged.

The TNA contact for IRAM Pico Veleta is C. Thum

The TNA contact for IRAM Plateau de Bure is R. Neri

More information can be found on the IRAM Homepage.