Completed 21cm Multibeam Receiver being hoisted up
to the Parkes focus cabin.
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Дата изменения: Unknown Дата индексирования: Sun Feb 3 11:21:44 2013 Кодировка: Поисковые слова: vela satellite |
Completed 21cm Multibeam Receiver being hoisted up
to the Parkes focus cabin.
The receiver was funded to conduct the HIPASS ("HI Parkes All-Sky Survey" ) and ZOA (Zone of Avoidance) HI surveys. It is now available, in 64 MHz mode and in pulsar mode, for normal National Facility use. Narrow band 4, 8 and 16 MHz filters are available.
| Parameter | Beam 1 | Beams 2-7 | Beams 8-13 |
|---|---|---|---|
| Frequency Range | 1.23-1.53 GHz | 1.22-1.52 GHz | 1.22-1.52 GHz |
| Polarisations | 2 orthogonal linear | 2 orthogonal linear | 2 orthogonal linear |
| Average System Temperature (K) (Elev=55o) | 21 K | 21 K | 21 K |
| FWHP beamwidth | 14.0 arcmin | 14.1 arcmin | 14.5 arcmin |
| FWHP beam ellipticity (radial) | 0.00 | 0.03 | 0.06 |
| Efficiency | 1.36 Jy K-1 | 1.45 Jy K-1 | 1.72 Jy K-1 |
| Average System Temperature (Jy) (Elev=55o) | 29 Jy | 30 Jy | 36 Jy |
| Average Cal Temperature (Jy) | 1.6 Jy | 1.8 Jy | 2.0 Jy |
| Coma lobe | none | -17 dB | -14 dB |
Notes
(1) System temperature reaches a minimum at an elevation of about 55o. At extreme elevations (30o and 90o), temperatures are about 2 K higher. Temperatures are measured at a frequency of 1394.5 MHz over a bandwidth of 64 MHz.
(2) The flux density scale is based on Hydra A for which a value of 40.6 Jy at 1394.5 MHz is assumed (after accounting for an 8% beam dilution; Reynolds, private communication).
The above diagram shows the configuration of the feed system as projected onto the sky when the feed angle is 0o and the telescope is observing on the northern meridian. North is to the top, east to the left. The available range of feed angles range from -60o to +60o. When the feed angle is 0o, beam 3 is closest to the lift leg which lies on the downhill side of the prime focus cabin.
Normally, the multibeam receiver is used to map extended areas. Typically the feed angle is set to 15o to the scanning angle. The scanning rate is usually around 1o min-1. Scans are normally made in "stepped" mode, where the parallactic angle is only correct at mid-scan. This is to avoid problems with the changing bandpass as the receiver rotates. However, full parallactification may be enabled if required.
| Bandwidth | |||
|---|---|---|---|
| Parameter | 64 MHz | 8 MHz | 4 MHz |
| Number of beams | 13 | 7 | 7 |
| Number of polarisations/beam | 2 | 2,4 | 2,4 |
| Maximum number of channels/polarisation | 1024 | 2048 | 2048 |
| Corresponding channel separation (kHz) | 62.5 | 3.91 | 1.95 |
| Frequency resolution (kHz) | 75.6 | 4.73 | 2.36 |
| Velocity resolution (km s-1) | 16.0 | 1.00 | 0.50 |
| ..with Tukey 25% smoothing (km s-1) | 18.0 | 1.12 | 0.56 |
| ..with Hanning smoothing (km s-1) | 26.4 | 1.65 | 0.82 |
| ..with Tukey 25% + Hanning smoothing (km s-1) | 27.0 | 1.69 | 0.85 |
Notes
(1) Tukey 25% smoothing is recommended in 64 MHz mode to suppress ringing from Galactic HI. LiveData is able to perform this.
(2) The FWHM (50%) resolutions are 1.21, 1.36, 2.00 and 2.05 times the channel
spacing for sinc, Tukey 25%, Hanning and combined Tukey+Hanning weighting,
respectively. For the 20% level, multiply the channel spacing by 1.64, 1.88,
2.88 and 2.90, respectively.
(3) Limited capablility is available for XY/YX cross-correlation and cross-correlation between beams. Contact Warwick Wilson (wwilson@atnf.csiro.au) for details.