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Based on observations at the European Southern Observatory at the 15 m Swedish ESO Submillimetre telescope, SEST, and at the the 1.52 m telescope which is operated under the ESO-ON agreement.

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Appendix A is only available in electronic form at http://www.edpsciences.org

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The Digitized Sky Surveys were produced at the Space Telescope Science Institute under US Government grant NAG W-2166.

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The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope.

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