FORS1 SKY BRIGHTNESS

QC1 ASCII DATA

(*) The data available do not cover Period 67 and 68 (April 2001-March 2002) due to an operational break.

General

Since Period 65 (April-September 2000), the value of the sky brightness of Paranal is constantly monitored using FORS1. Preliminar results from measurements obtained during sunspot maximum are reported and discussed in A&A 400, 1183 (2003). The sky brightness is measured from the reduced SCIENCE images by running a code created by F. Patat (ESO) and described in in A&A 401, 797 (2003). The code has been integrated in the DFO system to obtain automatically, for each reduced science image, the sky brightness measurements as part of the QC process. Images are scan to select those best suited for a reliable sky brightness measurement. In this phase, the image sky background is evaluated automatically and those images affected by a very noisy backgrounds, by enhanced objects crowding, by saturation problems and by reflections or ghost images are filtered out. The measured sky brightness values (in instrumental magnitudes/arcsec sq.) were then calibrated on-the-fly using the photometric zeropoints of the day, and corrected for the atmospheric extinction and for the instrument color-terms using the closest in time values logged in the QC1 database. Corrections for the contributions of the zodiacal light and of the moon are also applied.

Since 2005-11-15 we use instead the zeropoints obtained for photometric nights within the last 3 months. Also the corrections for zodiacal light and moon light are provided, but not applied.

The final values are then automatically ingested in the sky brightness QC1 database. Here, only calibrated sky brightness values in the UBVRI passbands are trended. Both raw and calibrated sky brightness values are available in the QC1 database.

Related Publications

UBVRI night sky brightness during sunspot maximum at ESO-Paranal
F.Patat, 2003, A&A 400, 1183-1198 (pdf | ps)

A robust algorithm for sky background computation in CCD images
F.Patat, 2003, A&A 401, 797 (pdf | ps)

Night sky brightness during sunspot maximum at Paranal
F.Patat, 2004, The Messenger 115, 18 (pdf)

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