Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...281..603c&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 281, no. 2, p. 603-612
Astronomy and Astrophysics
Astrophysics
23
Astronomical Spectroscopy, Charge Coupled Devices, Faint Objects, Image Processing, Spectroscopic Telescopes, Astronomical Photography, Background Noise, Error Analysis, Signal To Noise Ratios
Scientific paper
After a review of the sources of noise in faint object low resolution spectroscopy, we discuss the limitations in the signal to noise (S/N) ratio due to the flat-fielding errors and sky line sampling residuals after sky subtraction. These errors became rapidly dominant with high flux, and limit the S/N at very low resolution. In order to partly cancel these difficulties, we propose a new observing mode for faint object spectroscopy, called 'Va-et-Vient'spectroscopy. Thanks to multiple back-and-forth shifts of charge on the CCD, synchronized with the telescope shifts, the object and a close reference sky are integrated in the same physical conditions on the CCD through the spectrograph. This method enables us to stay in a photon noise regime on long sky background noise limited exposures. A laboratory experiment has been developed to test the feasibility of the method and has been fully exploited. The results are presented in the paper, as well as some preliminary comments on tests obtained on the European Southern Observatory (ESO) NTT to evaluate the merit of this approach for the next generation of very large telescopes. A gain of one to two magnitudes, compared with limited actual performances, should be achieved with the new generation of very large telescopes.
Altieri Bruno
Beigbeder Francis
Cuillandre Jean Charles
Duplin J. P.
Fort Bernard
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