2 The Database

The 167 systems included in the ADPS are listed in Table 1, in order of publication year. The systems are documented by individual figures that conform to the common layout.

The reference sources are given in square brackets for all the information provided with a given photometric system and are also listed in Table 2. No information is entered if not present in literature. The information provided with the systems surveyed in the ADPS are grouped into five main blocks:

System Code Name. This is formed from the system name generally used in the literature, the author(s) name(s) and the year of publication of the original paper introducing the system. A short sentence describing the system main usage or aim follows (normally as given by the authors themselves).

General Information. The authors of the system (not listed for space missions), the telescope and detector originally adopted, and the main reference article are given here. The main reference article is generally the one introducing the photometric system; however, some of these historical articles contain little information and in such cases a more recent, informative paper is taken instead.

System Description. Basic information like the filters used, the wavelength and width of the bands, the zero points and the flux calibrations are reported here. The literature is heterogeneous regarding these parameters, with values sometimes referring only to the filters, or to the filters+detector combination or also including the contribution of the telescope optics and atmosphere. So different quantities as $\lambda_{\rm peak}$ (peak transmission), $\lambda_{\rm c}$ (unspecified band "centre"), $\lambda_{\rm eff}$ (generally without specification of the energy distribution of the input source weighting the transmission profile) or $\lambda_0$ (again unspecified) are provided by the authors of the photometric systems as the wavelength of the bands. The situation is somewhat more confused when it comes to the width of the bands: the authors have used values ranging from the FWHM of a Gaussian approximation to the band, to something resembling the full width at zero transmission, or half of the total width at 50% transmission, or even unspecified concepts as "band-width'', "band-pass" or "half width". There are cases where the values given for the wavelength and width of the bands are missing or they disagree with the plotted and/or tabulated transmission profiles. In such cases we have computed on the transmission profiles two quantities and reported them in the ADPS with the aim of clarifying the situation: the WHM (width at half maximum: the full wavelength span between the points where the transmission reaches half of the maximum value) and $\lambda_{\rm c}$ (central lambda: the wavelength halfway between these half-maximum transmission points). In Paper II we plan to homogenise and standardise the situation regarding the wavelength and width of the bands for all systems with published transmission curves by means of synthetic photometry against the same set of observed and synthetic spectra. Finally, for some systems references are also provided to papers specifically devoted to the porting of the system to a different detector (like photographic plates or CCDs for systems originally designed for photo-multipliers).

System Analysis. This section deals with assorted information like the most frequently used colour indices and their aim (preserving as much as possible the terminology used by the original authors), reddening-free parameters, reddening ratios and transformation to other systems. Transformations are only to chronologically earlier systems in order to avoid duplication.

Transmission Curves. The last section is devoted to the presentation of the band transmission profiles both in graphical and tabular form. The transmission curves are not plotted and tabulated if they refer to square bands (essentially flat 1.0 transmission within the band and 0.0 outside), such as those provided by diaphragms placed on the focal plane of a spectrograph in front of a photo-multiplier tube or the square bands synthesised from fluxed digital spectra. When the transmission curves have been plotted but not tabulated by the authors, we have reconstructed them by measuring the plotted profile. In such a case, the reader is warned by a sentence like "As derived from Fig. Y of [XXX]".