A new determination of the optical K(z) relation for QSOs is presented, derived from multiwavelength photometry of 25 low-redshift QSOs. The relation deviates strongly from the simple picture of single power law spectra as an overall description, but also from previous empirical determinations based on composite spectra. The deviations are particularly significant at low redshifts where K(z) dr...

We examine the X-ray luminosity scaling relations of 31 nearby galaxy clusters from the Representative XMM-Newton Cluster Structure Survey (REXCESS). The objects are selected only in X-ray luminosity, optimally sampling the cluster luminosity function. Temperatures range from 2 to 9 keV, and there is no bias toward any particular morphological type. To reduce measurement scatter we extract pert...

We present improved visual and near-infrared empirical mass-luminosity relations for very low mass stars (M<0.6 M). These relations make use of all stellar masses in this range known with better than 10% accuracy, most of which are new determinations with 0.2 to 5% accuracy from our own programme, presented in a companion paper. As predicted by stellar structure models, the metallicity dispersi...

Using the empirical relations between the central galaxy luminosity and the halo mass, and between the total luminosity of galaxies in a halo and the halo mass, we construct the galaxy luminosity function (LF). To the luminosity of the central galaxy in a halo of a given mass we assign log-normal scatter with the mean and the dispersion of the luminosity directly calibrated against the observat...

We study a sample of about 1400 disk M dwarfs that are found in 148 fields observed with the Wide Field Camera 2 (WFC2) on the Hubble Space Telescope and 162 fields observed with pre-repair Planetary Camera 1 (PC1), of which 95 of the WFC2 fields are newly analyzed. The method of maximum likelihood is applied to derive the luminosity function and the Galactic disk parameters. At first, we use a...