We show that sampling effects in the initial mass function are very important in the low-mass cluster case. To this aim, we compute photoionization models ionized by realistic clusters made up of various combinations of individual stars and clusters built with a synthesis model. We discuss the differences in the position on diagnostic diagrams

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Scattering of light from an anisotropic source produces linear polarization in spectral lines and in the continuum. In the outer layers of a stellar atmosphere the anisotropy of the radiation field is typically dominated by the radiation escaping away, but local horizontal fluctuations of the physical conditions may also contribute, distorting the

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The last years saw numerous detections of substructure in the Galactic halo, largely due to wide area surveys like the Sloan Digital Sky Survey (SDSS) or the Two Micron All Sky Survey (2MASS). The analysis of SDSS data revealed the `Field of Streams' which encompasses, among other features, the broad and extended Sagittarius tidal stream as well as

The Sloan Digitized Sky Survey (SDSS) and the proposed Sloan Extension for Galactic Understanding and Evolution (SEGUE) offer a unprecedented stellar database with which to explore the properties of the thin disk, thick disk, and halo of the Galaxy. To make full use of the information contained in the available spectra and photometry, we require