TYCHO background determination and monitoring

Abstract

Attention is given to the method of background determination in the Tycho photon counts. A part of the data from the first eight months is used to study the periodical and aperiodical behavior of the background and provide statistics on the usability of Tycho data. The scientific value of the Tycho mission is directly correlated to the amount of low background data, because the faint stars, which are the most interesting, can only be detected in these data stretches. The method of background determination as well as a careful definition of the usage of a local background is shown to improve the background error and thus the detection efficiency.