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An Observational Test on the Origin of Magnetic Fields in Chemically Peculiar Stars of the Upper Main Sequence

The presence of strong magnetic fields is detected in about 5 to 10% of the chemically peculiar stars in the upper main sequence. The origin and evolution of these fields in the CP stars are not yet explained. It is not yet clear in which phase of stellar evolution fields of the order of 1000 G, i.e., stronger than in normal B and A-type stars are emerging. Open clusters are ideal laboratories for resolving these issues since their age can be determined. In an observational project we have performed CCD photometry of a relatively young and rich open cluster NGC 6705. We have used Maitzen's Deltaa photometric system which measures the flux depression at lambda 5200 AA as diagnostic tool for detection of magnetic CP stars. Observations were obtained on the 1-m Austro-Croatian telescope at Hvar, Croatia, which recently has become operational. More than 400 stars, members of the cluster were detected in this intermedium-band system. Results will be discussed in the framework of the current theoretical models of the origin of the magnetic fields in CP stars.

open cluster; CCD photometry; CP2 stars; Lambda Boo stars

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