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Astron. Astrophys. 335, 1070-1076 (1998)

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3. Observations

The transitions which we observed were taken from the list of Coudert & Hougen (1990). These are listed in Table 1 together with their quantum numbers are their tunneling state [FORMULA].

The observations have been made using the NRAO 12 m telescope 1 on Kitt Peak (beam width [FORMULA] at the search frequencies), the IRAM 30 m telescope on Pico Veleta (beam: 30"), and the MPIfR 100 m telescope in Effelsberg (beam: 38"). For all measurements we employed the position switching mode. The focus and pointing corrections were based on continuum scans through nearby continuum sources. The 100 m data were calibrated using continuum measurements of 3C 48, assuming a flux density of 1.1 Jy (Ott et al. 1994). The data observed with the 30 m and 12 m telescopes were calibrated using a chopper wheel method. All temperatures are given on a main-beam brightness temperature scale.

At the MPIfR 100 m telescope, a K-band maser was used. The system noise corrected for absorption in the earth's atmosphere and telescope efficiency is [FORMULA]. The spectrometer was a 1024 channel autocorrelator with a channel separation of 50 or 100 kHz, corresponding to a velocity resolution of 0.6 or 1.2 km s-1. For the perihelion observations of Hale-Bopp, we used the same ephemeris and observing procedures as described in Bird et al. (1997).

At the NRAO 12 m telescope, a dual channel, single sideband, SIS receiver with typical system temperatures of 250 K was used. As spectrometers we placed either half of a 1024 channel hybrid spectrometer on each of the two receiver channels. The channel separation was 97 kHz (i.e [FORMULA]1.2 km s-1). Only for the dark cloud L134N, we used a higher resolution of 24 kHz (0.3 km s-1).

At the IRAM 30 m telescope two single channel SIS receivers were used. As backends we used filterbanks with a channel separation of 1 MHz (3.6 km s-1).

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© European Southern Observatory (ESO) 1998

Online publication: June 26, 1998