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3. Observations

3.1. SiO 43 GHz observations

Observations at the 43 GHz SiO (v=1 and 2, J=1-0) transitions were made using the Parkes radio telescope during the period September 16-21, 1993. At 43 GHz the inner 16.7 m of the 64 m reflector is effectively used and, with an aperture efficiency of 34%, the telescope sensitivity is tex2html_wrap_inline2564. The beam size at 43 GHz is tex2html_wrap_inline2566. Telescope pointing errors are less than tex2html_wrap_inline2568 (rms) in right ascension and declination.

We used the CSIRO 43 GHz maser superheterodyne receiver, giving typical system temperatures in the range tex2html_wrap_inline2570 (SSB). All observations were made in horizontal linear polarization. The instantaneous bandwidth of the maser RF amplifier was about 100 MHz, precluding simultaneous observations of the v=1 and v=2 transitions.

Measured fluxes were corrected for atmospheric attenuation using the form tex2html_wrap_inline2576, where Z is the telescope zenith angle and tex2html_wrap_inline2580, the vertical attenuation, was taken as 0.1. During the first few days of the observations the weather was unstable with clouds and occasional rain showers making the calibration uncertain. Apart from the data taken during unstable weather conditions, we estimate that the flux values are accurate to tex2html_wrap_inline2582.

Spectra were obtained using a 1024-channel autocorrelator configured to give a velocity coverage of tex2html_wrap_inline2584, and a resolution before smoothing of tex2html_wrap_inline2586. Off-line Hanning smoothing was subsequently applied, resulting in a resolution of tex2html_wrap_inline2588. Low-order baseline corrections have been applied to the spectra.

3.2. SiO 86 GHz observations

The 86 GHz SiO (v=1, J=2-1) observations were performed on various occasions between 1991 and 1995 using the 15m Swedish-ESO Submillimetre Telescope (SEST) and the Onsala Space Observatory 20 m telescope.

The beamwidth of the SEST is tex2html_wrap_inline2596 at 86 GHz, and the pointing accuracy is estimated to be better than tex2html_wrap_inline2598 (rms). The telescope was used in a dual beam switch mode with the source alternately placed in the two beams, a method that yields very flat baselines. The beam separation was about tex2html_wrap_inline2600. The aperture efficiency of the telescope at 86 GHz is 62%, which gives a conversion factor of tex2html_wrap_inline2602.

The receiver was a dual (linear) polarization Schottky receiver with a typical system temperature above the atmosphere of tex2html_wrap_inline2604 (SSB). Only the horizontally polarized receiver was used. Calibration was done with a standard chopper wheel method and the flux values are estimated to be accurate to tex2html_wrap_inline2582.

Spectra were taken with an acousto optical spectrometer (AOS) with a bandwidth of 86 MHz (resulting in a velocity coverage of tex2html_wrap_inline2608), a channel separation of 43 kHz, and a resolution of 80 kHz. The spectra were subsequently smoothed by adding the spectrometer channels together four by four, resulting in a velocity resolution of about tex2html_wrap_inline2610.

The Onsala 20 m telescope has a beamwidth of tex2html_wrap_inline2612 at 86 GHz, and the pointing accuracy is estimated to be better than tex2html_wrap_inline2598 (rms). The telescope was used in a dual beam switch mode with a beam separation of about tex2html_wrap_inline2600. The aperture efficiency of the telescope at 86 GHz is 0.5, which gives a conversion factor of tex2html_wrap_inline2618.

The receiver was a horizontally, linearly polarized SIS receiver with a typical system temperature above the atmosphere of tex2html_wrap_inline2604 (SSB). Calibration was done with a standard chopper wheel method and the flux values are estimated to be accurate to tex2html_wrap_inline2582.

Spectra were taken with a multichannel filterbank with a bandwidth of 64 MHz, resulting in a velocity coverage of tex2html_wrap_inline2624, and a channel separation of 250 kHz, which corresponds to a velocity resolution of tex2html_wrap_inline2626.


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