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Astron. Astrophys. 318, 931-946 (1997)

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2. Observational procedures

Observations of W3 were carried out using all configurations of the Very Large Array. Continuum observations using two polarizations, each with 50 MHz bandwidth, were made at 6 cm (frequencies of 4885 and 4835 MHz), 2 cm (frequencies 14965 and 14915 MHz) and 1.3 cm (frequencies of 22485 and 22435 MHz). In the D configuration (16 and 21 July 1988), the C configuration (3, 17, and 21 September 1989), and the B configuration (29 April 1989), all three continuum bands were observed. In the A configuration (23 January 1989), only 6 cm and 2 cm observations were made. All available antennas of the array were used. Total on source times (for all configurations) were 599 minutes for 6 cm, 650 minutes for 2 cm, and 372 minutes for 1.3 cm. The data for each frequency band and array configuration were independently edited and calibrated using the NRAO Astronomical Image Processing System (AIPS) software. The calibration source 3C 48 was used as the absolute flux density standard (S = 5.4 Jy at 6 cm, 1.7 Jy at 2 cm, and 1.1 Jy at 1.3 cm). Both 3C84 and 0224+671 were employed as phase reference sources. The u-v data sets for each frequency and each array configuration were calibrated separately, and then the data for all array configurations for a given frequency were combined into one data set. These data were then self-calibrated, Fourier inverted using natural weighting of the u-v data, and then CLEANed in the standard manner.

Also, on 21 September 1989, VLA observations were made toward W3 in the H66 [FORMULA] line at a rest frequency of 22369.020 MHz. Thirty-one spectral channels with width 0.4 MHz (5.4 km s-1) covered a 12.5 MHz band (168 km s-1). Bandpass and phase calibration were determined using the strong source 3C84. The absolute flux density standard used was 3C48. Hanning smoothing was applied to the data on-line. The u-v data were calibrated, Fourier inverted using natural weighting, and CLEANed in the standard manner. No self-calibration was applied. Continuum subtraction was performed in the image plane, using spectral channels at the ends of the bandpass where no line emission was found. A total of 270 minutes of on-source time was observed, using all antennas of the array. The VLA was in the C configuration.

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© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998
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