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Astron. Astrophys. 350, 659-671 (1999)

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2. Observations

The observations were carried out with the IRAM 30-m telescope at Pico Veleta (near Granada, Spain) during several runs in September, October and November 1997. Table 1 summarizes the observed molecular species, the transitions, their rest frequencies and some observing parameters, such as the HPBW, the typical system temperature ([FORMULA]) and the integration time ([FORMULA]; ON+OFF source). The main beam efficiency varies from 0.75 (at 90 GHz) to 0.37 (at 230 GHz) according with the values reported by Wild (1995). The observations were made by position switching. Pointing was checked every hour by observing nearby planets or continuum sources and it was found to be accurate to within 3". As spectrometers, an autocorrelator split into three parts was used to allow simultaneous observations of three different transitions. This has provided a resolution in the ranges between 0.10 and 0.14 km s-1 at 1.3 mm, between 0.14 and 0.17 km s-1 at 2 mm and 0.10-0.11 km s-1 at 3 mm. When necessary, the spectra were smoothed to a lower velocity resolution (up to 0.86 km s-1). Moreover, also a 1 MHz filter bank, split into three parts of 2 [FORMULA] 256 and 512 channels, was used to allow simultaneous observations. It provided a velocity resolution of 2.60-3.48 km s-1 (1.3 mm), 1.77-2.30 km s-1 (2 mm) and 1.24-1.38 km s-1 (3 mm). The spectra were calibrated with the standard chopper wheel method and are reported here in units of main-beam brightness temperature ([FORMULA]).


Table 1. List of molecular species, transitions and observing parameters

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© European Southern Observatory (ESO) 1999

Online publication: October 4, 1999