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Astron. Astrophys. 345, 949-964 (1999)

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2. Observations and data reduction

2.1. Plateau de Bure interferometer

The interferometric observations were carried out between December 1996 and March 1997 using the IRAM 1 five element array at Plateau de Bure, France (Guilloteau et al. 1992). The five 15 m antennas were equipped with 82-116 GHz and 210-245 GHz SIS receivers operating simultaneously with double-sideband (DSB) temperatures of 35 K at 3 mm and 50 K at 1.3 mm. The receivers were tuned single side-band at 3.5 mm and double side-band at 1.3 mm. The facility correlator was centred at 86.650 GHz in the lower side-band at 3.5 mm and at 220.595 GHz in the upper side-band at 1.3 mm. We show the frequency set-up of the correlator and list the detected spectral lines in Table 1. The six units in the correlator were placed in such a way that a frequency range free of lines could be used to measure the continuum flux. The spectral resolution of the correlator is about twice the channel spacings given in Table 1. Source visibilities were phase calibrated by means of interspersed observations (every 20 minutes) of nearby point sources.


[TABLE]

Table 1. Frequency set-up for detected molecular lines with the PdBI. DSB tuning at 1.3 mm was used.
Notes:
a) the effective spectral resolution is about twice the nominal channel spacing
b) the 1.3 mm continuum was obtained by averaging one 80 MHz and two 160 MHz bandwidths in the lower side band


The bandpass calibration was carried out in the antenna-based manner. The flux of the primary calibrators was bootstrapped from IRAM monitoring measurements and used to derive the absolute flux density scale. Table 2 gives a list of the main parameters for our PdBI observations.


[TABLE]

Table 2. Instrumental parameters for the IRAM PdBI observations


The calibration and data reduction were made using the standard IRAM/GAG software. Continuum subtraction was performed in the U-V plane by using the integral over the line-free channels of the 160 MHz units. Finally, channel maps were produced for all the lines. The conversion factor from flux to brightness temperature in the synthesised beam is [FORMULA] K (Jy/beam)-1 at 3.5 mm and [FORMULA] K (Jy/beam)-1 at 1.3 mm.

2.2. James Clerk Maxwell Telescope - SCUBA

The submillimetre observations were carried out with the Submillimetre Common-User Bolometer Array (SCUBA) (Holland et al. 1999) on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. SCUBA consists of three millimetre-wave photometry pixels and two sub-millimetre arrays: a short-wavelength array containing 91 pixels and a long-wavelength array containing 37 pixels arranged in a close-packed hexagon. Both arrays have approximately the same field-of-view (2:03) and can be used simultaneously. The data were taken in August 1997 with fully sampled maps generated at 3" sampling at 850, 450, 750 and 350 µm using the "jiggle" observing mode and photometry (single-pixel) observations taken at 1.35 and 2.0 mm. Azimuth chopping of 2´ was used for the map data and 1´ for the photometry data. Uranus was used for calibration (Orton et al. 1986). The zenith atmospheric opacity at 850 µm ranged from 0.36 to 0.40 during the observations. Integration times and beam sizes at these wavelengths are detailed in Table 3. The data were reduced using the SCUBA User Reduction Facility (SURF) (Jenness & Lightfoot 1998) with the outer ring of bolometers being used for sky removal as detailed in Jenness et al. (1998).


[TABLE]

Table 3. Approximate JCMT beam-sizes (full-width half maximum) at the observed wavelengths. These values do not include the error beams that appear at high frequencies. The table also includes the total integration time observed in each mode and frequency (including the time spent nodding)


2.3. United Kingdom infrared telescope

Mid-infrared images of IRAS 20126+4104 have been obtained using MAX, the mid-IR imager developed by the Max-Planck-Institut für Astronomie (MPIA) for the United Kingdom Infrared Telescope (UKIRT) (Robberto & Herbst 1998). The camera is equipped with a Rockwell International 128[FORMULA]128 SiAs BIB array optimised for high-background applications. The all-reflective camera optics provide a scale of 0.27 arcsec/pixel, corresponding to a field of view of 35"[FORMULA]35".

Observations were performed under excellent weather conditions on the night of 29th August 1996, taking full advantage of the newly installed top-ring and the hexapod secondary mirror mount with tip-tilt adaptive control developed at the MPIA. Tip-tilt correction allows MAX to routinely attain diffraction limited conditions (0:0054 at 10 µm on UKIRT) on hour-long intergration times.

We used a N-band filter with effective wavelength [FORMULA]=10.2 µm, half-width bandpass [FORMULA]=5.2 µm, and a Q-band filter with [FORMULA]=19.9 µm and [FORMULA]=1.9 µm. Airmass was [FORMULA]1.6. Our data acquisition strategy was the usual chopping and beam switching techniques. On both filters, the integration time per single frame was 10.24 msec. Chopping at [FORMULA]2.2 Hz, we took 20 single frames per chop position. After 100 single frames on source, the telescope was pointed to the offset beam to correct for non-uniform illumination effects introduced by chopping. This cycle was repeated 4 times in the N band and 3 times in the Q bands, providing a total on-source integration time of 163.84 sec and 122.88 sec, respectively.

Photometric calibration was obtained observing at various airmasses a set of red giant stars included in a list of faint ISO-PHOT calibrators, namely BS 6913 (spectral type K1III), BS 7648 (sp. type K5III) and BS 7635 (sp. type M0III).

No attempt was made to determine the absolute position in right ascension and declination of the images. For the morphology of the region, which will become clear in the following, we assume that the position of the 10 and 20 µm peaks coincides with that of the 1.3 mm continuum peak.

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© European Southern Observatory (ESO) 1999

Online publication: April 28, 1999
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