1 Introduction

Until quite recently atmospheric modelling was divided between planetary atmospheres, which required low temperature data (20 K to max. 500 K), and stellar atmospheres which required high temperature data (1000 K to 7000 K). Two sets of collision-induced absorption (CIA) data have been produced in the past, with the aim to assist the planetary and the stellar efforts. These data have been based on two slightly different inputs, suitable for the task at hand. Whereas the low temperature data were almost "exact'', i.e. matched closely all laboratory results, the input they were based on was not suitable for computing CIA spectra at very high temperatures. As a result, the two sets were not "compatible'' to be inter- or extrapolated into each other. They were meant to be used for either one task, or the other.

In 1995 two new kind of objects, on the border between the traditional regions of stars and planets, were discovered: the first brown dwarf (Nakajima et al. 1995) and the first "hot jupiter'' extra-solar planet (Mayor & Queloz 1995). As a consequence, the need emerged for analysing spectra at intermediate temperatures between 400 K and 1000 K.

Collision-induced absorption due to hydrogen pairs has been recognised, for many years, to play an important role in the radiative transfer of atmospheres of the outer planets (Conrath et al. 1989; Hanel et al. 1992; Trafton 1995), and it also plays a decisive role as a dominant opacity source in Saturn's largest moon Titan (Samuelson et al. 1997). In recent years, interest has increased concerning the impact of CIA on stellar atmospheres of cool stars as well (Borysow 1994; Borysow et al. 1997; Borysow & Jørgensen 1999). Here, CIA is very important for the infrared energy balance. Therefore the missing data now have been computed by the means described below, and have been placed on the Internet, at www.astro.ku.dk/aborysow/programs. The low- and the high temperature part of the new data (i.e. those below and above 400 K) will be described in Sects. 2, 3, respectively.

The theory of collision-induced absorption in general is described in detail in the extensive monograph by Frommhold (1993) and will not be summarized in this paper.