1 Introduction

The first paper of this series (Moro & Munari 2000, Paper I), devoted to the Asiago Database on Photometric Systems (ADPS), presented a compilation of basic information and reference data for ultraviolet, optical and infrared photometric systems, for both the ground-based and space varieties. In Paper I, 167 photometric systems were censed in extenso and other 34 were briefly noted. Only data from the literature were used, with all information traceable back to the original source.

The literature survey in Paper I proved how poorly documented the majority of the systems was and, even when data were provided, it was usually difficult to interpret unambiguously their meaning, or to inter-compare them, because of the highly heterogeneous methods and conventions adopted by different authors. Even basic concepts such as wavelength and width of a band came in so many varieties that common grounds could be established, from literature data, only for a thin minority of the systems (see discussion under System Description in Sect. 2 of Paper I). The situation with band and reddening parameters is worth some statistics. Out of 201 censed systems, (a) 24% had no wavelength or width information or they were in clear conflict with published band transmission curves, (b) 28% had poor information, typically just the mean or peak wavelength, (c) 44% had decent information (mainly systems with square bands or interference filters), and only for (e) 4% the available information included effective wavelengths for more than one spectral type (just 2% in the case of effective widths). The situation with reddening parameters is even more depressing. Again, out of the 201 censed systems, reddening information was (i) completely missing for 78% of them, (ii) poorly known for 15% (typically $A(\lambda )/E_{B-V}$ for just one or two bands), (iii) satisfactory for 4%, and (iv) complete for only 3% of them.

It appears therefore mandatory to establish a common set of parameters for all photometric systems, and to calibrate them via homogeneous synthetic photometry algorithms and a common sample of input spectra. The availability of the same extensive set of homogeneous parameters would support a proper use of the systems, an easier inter-comparison among them and the appreciation of their legacy when attempting the design of a new one.

A first step in such an homogeneous documentation of existing photometric systems is the derivation of band and reddening parameters for all the photometric systems with known transmission curves. The band parameters derived in this paper include various types of wavelengths, widths and moments for a set of normal and peculiar input spectra, as well as polynomial fits of their behavior with blackbody temperature. Reddening parameters include the Cardelli et al. (1989) a(x) and b(x) coefficients, $A(\lambda )/A(V)$ and $A(\lambda )/E_{B-V}$ for various types of source spectra and extinction laws (R_V=5.0, 3.1 and 2.1), and polynomial fits to the behavior of effective wavelength and width.

All our work is based on synthetic photometry. It is by far the only viable mean to document so many systems on homogeneous grounds. However, it cannot entirely substitute detailed individual characterization of photometric systems based on careful analysis of published observations (when available in large enough number and accuracy). Such individual analysis, by iteratively working on the color differences recorded between known stars, can even lead to a revision of published band profiles (cf. Bessell 2000 revision of the Hipparcos/Tycho band profiles published in the ESA's Hipparcos Catalogue). A detailed characterization based on actual observations has been so far successfully attempted only for very few systems and its application to the >200 censed in the ADPS is vastly out of the scope and possibilities of the present series of papers.

Finally, when compiling Paper I we tried to be as complete as possible for the optical and ultraviolet regions ( $\lambda \leq 1~\mu$m). In the infrared the completeness was known to be lower. To improve the completeness of ADPS, further 12 infrared and additional 5 optical systems are now included, bringing the total number of photometric systems censed by ADPS to 218. The new 17 systems are briefly noted in Sect. 4.

Figure 1: The set of spectra of normal stars used in the computations of this paper.

Figure 2: The set of peculiar spectra used in the computation of equivalent wavelengths and widths. Note the logarithmic scale for the ordinates, used to expand the dynamical range of the plot so to emphasize visibility of weak features. Some guidance to line identification is provided.