2 Choosing constant stars

The diagram on p.465 in the HIPPARCOS Catalogue vol. 1 (ESA SP-1200, 1997) illustrates that the fraction of variable stars is quite variable over the HR-diagram. In the giant branch the fraction is up to 100% and reduces to 10% on the main sequence. As a first step we binned a part of the HR-diagram according to spectral types (B, A, F, and G), luminosity classes (II and III, IV, and V), and the brightness at 4, 6, 8 and 10mag(V) with an interval of $\pm$0.5magnitudes. For each bin we interrogated the SIMBAD database for stars observed by HIPPARCOS and which appear to be unsuspicious, i.e. to have no GCVS name, no suffixes to the spectral type, no peculiarities which might indicate photometric variability, etc. The result of this interrogation was a list of 12500 stars. Furthermore we excluded those stars found to be variable by HIPPARCOS and stars with less than 60 data points. From the remainder we randomly selected half and hence reduced our list of candidate constant stars to 4863. As a next step we extracted the photometric data from the HIPPARCOS EPOCH PHOTOMETRY archive or from ESA 1997 CD-ROM 2, where the file hip_ep.dat contains the HIPPARCOS EPOCH PHOTOMETRY ANNEX. A software tool extracted automatically the photometric data of the stars under consideration and removed bad data points as indicated by a different to zero quality flag (Field HT4 in the file).