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Contents Page: Volume 14, Number 1

Driftscan Surveys in the 21cm Line with the Arecibo and Nançay Telescopes

F. H. Briggs
Kapteyn Astronomical Institute
E. Sorar
University of Pittsburgh
R. C. Kraan-Korteweg
DAEC, Observatoire de Paris, Meudon
W. van Driel
USN, Observatoire de Paris, Meudon


Driftscan methods are highly efficient, stable techniques for conducting extragalactic surveys in the 21cm line of neutral hydrogen. Holding the telescope still while the beam scans the sky at the sidereal rate produces exceptionally stable spectral baselines, increased stability for RFI signals, and excellent diagnostic information about system performance. Data can be processed naturally and efficiently by grouping long sequences of spectra into an image format, thereby allowing thousands of individual spectra to be calibrated, inspected and manipulated as a single data structure with standard tools that already exist in astronomical software. The behavior of spectral standing waves (multi-path effects) can be appraised and excised in this environment, making observations possible while the Sun is up. The method is illustrated with survey data from Arecibo and Nançay.

Keywords: methods: data analysis - techniques: image processing - telescopes
surveys - galaxies: distances and redshifts - radio lines: galaxies

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