090323

We propose to complete the last virgul5% of high-quality observations for the eeHIFLUGCS galaxy cluster sample (16 of 376 clusters). The sample is based on ROSAT with completely and homogeneously redetermined fluxes as well as updated redshifts. For the already observed clusters we have also identified and amp amp amp gt 10 double/triple clusters and clusters dominated by AGN emission which then fall below the flux limit of 5e-12 erg/s/cm2. With the completed follow-up observations we will decrease the uncertainties in OmegaM by a factor of 2.8 compared to those obtained with the HIFLUGCS sample. If these virgul5% do not get observed the flux-limited sample drops by almost a factor of 3 to a disappointing 140 clusters. The observations will have long lasting legacy value for a range of astrophysical studies. [truncated! Please see actual data for full text]