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Date and Time of the Query: 2019-06-20 T14:12:24 PDT
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For refcode 1990A&AS...84...47T:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1990A&AS...84...47T Comparisons between 21 cm data from Effelsberg and Greenbank W. G. Tifft, and W K. Huchtmeier Max-Planck-Institut fur Radioastronomie, Auf dem Hugel 69, 5300 Bonn 1, F.R.G. Steward Observatory, University of Arizona, Tucson, Arizona 85721, U.S.A. Received July 5, accepted December 2Z 1989 Abstract -- Comparison of 2l cm data from the Effelsberg 100-m and NRAO Greenbank 91-m telescopes are used to find the limiting precision for redshift measurement. At signal-to-noise levels of 10 or above random uncertainty actually achieved in a single redshift measurement is demonstrated to be 0.85 km s^-1^ at a bandwidth of 6.25 MHz. Uncertainty in other bands scale, as the square root of the bandwidth relative to 6.25 MHz. Random error is also found to be independent of which telescope or software is used as long as the s/n is large. At low s/n the choice of software will affect precision. Substantial systematic errors are shown to be present in some existing system or software, due to errors in specifying the location of the center frequency. Such errors can easily be eliminated with standardized intercomparisons. Some small residual systematic shifts, amounting to a few tenths of a km s^-1^, are suspected and remain unexplained pending further study. Effects of telescope pointing errors on redshifts are calibrated by comparing offset measurements. A clear correlation exists between profile shape changes and redshift differences as pointing is varied. An unavoidable minimum redshift scatter of about 0.1 km s^-1^ is shown to arise from the basic limits on telescope pointing. Profile widths, however, are very insensitive to pointing error. Overall, basic comparisons over time or between systems can be made at the 0.1 k, s^-1^ level. Key words: galaxies - redshifts - radio-lines: 21 cm radio telescopes.
Retrieve 120 NED objects in this reference.
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