AAS 205th Meeting, 9-13 January 2005
Session 78 Galactic Astronomy with the Arecibo L-band Feed Array
Special Session, Tuesday, January 11, 2005, 10:00-11:30am, Pacific Salon 1

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[78.07] GALFA Hardware and Calibration Techniques

C. Heiles, J. Goldston, J. Mock, A. Parsons, S. Stanimirovic, D. Werthimer (UC Berkeley)

We have built a special-purpose spectrometer for GALFA observations. For each polarization on each beam, meaning 14 independent incidences, we obtain two spectra. One is the primary HI data spectrum, which has about 8000 channels over 7 MHz bandwidth and for HI provides velocity resolution about 0.18 km/s with coverage about 1500 km/s. The other is the calibration spectrum, which has 512 channels over 100 MHz and is used to evaluate and remove Arecibo's baseline ripple, which is caused by multiple reflections between the primary and secondary surfaces.

We briefly describe two new techniques for removing instrumental effects from the 7 MHz HI spectra. One is ``least squares frequency switching'', which uses four or more local oscillator frequencies to evaluate the reference spectrum using a least squares technique. The other removes baseline ripple from the 7 MHz HI spectrum using Fourier techniques and the 100 MHz calibration spectrum.

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