Radio Recombination Lines

Recombination lines at radio wavelengths have been - and still are - a pow­ erful tool for modern astronomy. For more than thirty years they have allowed astronomers to probe the gases from which stars form. They have even been detected in the Sun. In addition, observations of these spectral lines facilitate basic research into the atom, in forms and environments that can only exist in the huge dimensions and extreme conditions of cosmic laboratories. We intend this book to serve as a tourist's guide to the world of Radio Recombination Lines. It contains three divisions: a history of their discovery, the physics of how they form and how their voyage to us influences their spectral profiles, and a description of their many astronomical contributions to date. The appendix includes supplementary calculations that may be useful to some astronomers. This material also includes tables of line frequencies from 12 MHz to 30THz (AlOJLm) as well as FORTRAN computer code to calculate the fine structure components of the lines, to evaluate radial matrix integrals, and to calculate the departure coefficients of hydrogen in a cosmic environment. It also describes how to convert observational to astrophysical units. The text includes extensive references to the literature to assist readers who want more details.

Inhalt

Preface. 1: Introduction. 1.1. The Cosmos as a Laboratory. 1.2. Spectral Lines in Astronomy. 1.3. The Bohr Atom. 1.4. 2: RRLs and Atomic Physics. 2.1. The First Surprising Results: The Absence of Stark Broadening. 2.2. The Broadening of Radio Recombination Lines. 2.3. Intensity of Radio Recombination Lines. 2.4. The Range of RRL Studies. 2.5. How Many Atomic Levels Can Exist? 2.6. Summary. 3: RRLs: Tools for Astronomers. 3.1. Physical Conditions in H II Regions. 3.2. Ionized Hydrogen and Helium in the Atmosphere. 3.3. Exploration of the Cold ISM by RRLs. 3.4. RRLs from Stars and Stellar Envelopes. RRLs from Extragalactic Objects. A: Constants: A.1. Miscellaneous Constants. A.2. Rydberg Constants. B: Tables of Line Frequencies. B.1. Frequencies Below 100 GHz. B.2. Frequencies Above 100 GHz. A.3. FORTRAN Code for Fine-Structure frequencies. C: Supplemental Calculations. C.1. Early Estimates of Stark Broadening. C.2. Refinements to the Bohr Model. D: Hydrogen Oscillator Strengths. D.1. Population of Atomic Sublevels. D.2. Calculation of Oscillator Strengths. D.3. Radial Matrix Integrals Code. E: Departure Coefficients. E.1. FORTRAN Code for Calculating bn Values. F: Observational Units. F.1. What Radio Telescopes Measure. F.2. How Radio Telescopes Measure. Author Index. References. Index.