"Va et Vient" (back and forth) spectroscopy with CCDs: a new approach to faint object spectroscopy on very large telescopes

Jean Pierre Picat; Jean-Charles Cuillandre; Bernard Pierre Fort; G. Soucail

doi:10.1117/12.176775

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1 June 1994 "Va et Vient" (back and forth) spectroscopy with CCDs: a new approach to faint object spectroscopy on very large telescopes

Jean Pierre Picat, Jean-Charles Cuillandre, Bernard Pierre Fort, G. Soucail

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Proceedings Volume 2198, Instrumentation in Astronomy VIII; (1994) https://doi.org/10.1117/12.176775
Event: 1994 Symposium on Astronomical Telescopes and Instrumentation for the 21st Century, 1994, Kailua, Kona, HI, United States

Abstract

The signal to noise ratio of very faint object spectroscopy is discussed in the context of the gain in limiting magnitude attainable on very large telescopes at low spectral resolution. It is shown that if the multiplicative errors resulting from the sky subtraction are not corrected, deeper spectroscopy will not be obtained by increasing the telescope size. A new CCD observing technique, which we call `Va et Vient' spectroscopy, is described in detail. This is a beam switching method where the elementary exposures are short enough to freeze the sky temporal fluctuations, and where the CCD is read only after a series of a few dozen of exposures. During the integration, the signals from the object field and the reference sky are separated by shifting the charges onto the CCD along the columns. Analytical evaluations are confirmed by laboratory tests and show that this technique is photon noise limited even at high flux and thus can lead to deeper spectroscopy. We give estimates of the results that can be achieved with the new generation of very large telescopes.

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Jean Pierre Picat, Jean-Charles Cuillandre, Bernard Pierre Fort, and G. Soucail ""Va et Vient" (back and forth) spectroscopy with CCDs: a new approach to faint object spectroscopy on very large telescopes", Proc. SPIE 2198, Instrumentation in Astronomy VIII, (1 June 1994); https://doi.org/10.1117/12.176775

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