SIMBAD references

The "Vienna Atomic Line Data Base" (VALD) consists of a set of critically evaluated lists of astrophysically important atomic transition parameters and supporting extraction software. VALD contains about 600000 entries and is one of the largest collections of accurate and homogeneous data for atomic transitions presently available. It also includes specific tools for extracting data for spectrum synthesis and model atmosphere calculations. The different accuracies of data available in the literature made it necessary to introduce a ranking system and to provide a flexible method for extracting the best possible set of atomic line parameters for a given transition from all the available sources. The data base is presently restricted to spectral lines which are relevant for stars in which the LTE approximation is sufficient and molecular lines do not have to be taken into account. The provision was made that these requirements should not restrict the general design of VALD and the possibility of future expansion. In this paper we describe the structure of VALD, the available data sets and specific retrieval tools. The electronic-mail interface (VALD-EMS) created to allow remote access to VALD is also described. Both users and producers of atomic data are invited to explore the database, and to collaborate in improving and extending its contents.