BUSCA: First Results of Simultaneous Photometry at the Calar Alto Observatory

After the pre-Calar Alto tests from September 1998 to January 2000 at Hoher List Observatory, BUSCA (``Bonn University Simultaneous CAmera'', Reif et al., 1999) had its ``First Light'' at the 2.2m telescope at Calar Alto in April 2000. We were able to integrate BUSCA into the Calar Alto environment, the new auto-guiding unit, the instrument control and data acquisition. The BUSCA optics did perform as expected even at sub-arcsec seeing. At the end of 2000 the thinned 4K×4K 15μ CCD-Chip for the UV-channel will be available. We expect that BUSCA will become a regular instrument at the 2.2m telescope in the observing period autumn 2001. We present as a first scientific result a metallicity calibration of red giant branch stars with the BUSCA Strömgren system. With this calibration we are able to detect CN variations in giant stars, which were observed by spectroscopy previously. Observing many globular clusters will help us to solve the question whether these variations are triggered by primordial abundance variations or by evolutionary mixing processes. The poster shows the current status of the instrumentation project and presents the first results of the April run. Reif, K., Bagschik, K., de Boer, K.S., Schmoll, J., Müller, Ph., Poschmann, H., Klink, G., Kohley, R., Heber, U., Mebold, U., 1999, SPIE Vol. 3649, 109-120 (or , http://www.astro.uni-bonn.de/ěrb? ?ccd/busca/ei99/busca.html)