Molecular line intensity calculations are not a straightforward task. We present a description of the basics for including molecular lines in synthetic spectra and of the input data needed. We aim both at describing ways in which molecular lines are computed in the context of photospheres of F–G–K stars, and to present a new online available version of our code for spectrum synthesis of cool stars. We apply calculations to molecular bands in the ultraviolet, visible, and near-infrared main features, and comparisons with spectra of reference stars are shown. We provide user-friendly tools for the free use of the code Pfant. The code is available at http://trevisanj.github.io/PFANT.

Luminous water maser emission in the 616–523 line at 22GHz has been detected from two dozen galaxies. In all cases the emission is confined to the nucleus and has been found only in AGN, in particular, in Type 2 Seyferts and LINERs. I argue that most of the observed megamaser sources are powered by X-ray irradiation of dense gas by the central engine. After briefly reviewing the physics of these X-Ray Dissociation Regions, I discuss in detail the observations of the maser disk in NGC 4258, its implications, and compare alternative models for the maser emission. I then discuss the observations of the other sources that have been imaged with VLBI to date, and how they do or do not fit into the framework of a thin, rotating disk, as in NGC 4258. Finally, I briefly discuss future prospects, especially the possibility of detecting other water maser transitions.