Abstract: On Astrophysical Spectroscopy’s Atomic Data Needs.

In the last 25 years the quality of data obtained from astronomical spectrographs has drastically improved due to the wide spread use of electronic detectors, especially Charge Coupled Devices (CCDs) whose quantum efficiencies are approaching unity throughout much of the optical region. The typical signal-to-noise ratio (S/N) for a high dispersion spectrogram has increased from about 25 with photographic plates to between 100 and 300 with CCDs. Several reduction and analysis problems which were usually ignored at S/N = 25 now have to be considered in detail, for example, scattered light in the spectrograph. Further, spectrum synthesis techniques are becoming more the norm especially for the best understood types of stars.

We examine the data needs from the perspective of spectrum synthesis and consider gf values, line damping parameters, hyperfine structure, and isotopic shifts. Proper interpretation of stellar spectra requires good quality atomic data. This is equally true for the sharp-lined stars and those with moderate rotational velocities, although the latter lack the resolution of the former. Astrophysical gf values can be important supplements to laboratory and theoretical values in obtaining the thousands of accurate and precise gf values needed to synthesize the optical region spectra of stars hotter than the Sun. Telluric spectra, which our atmosphere superimposes upon the stellar, and specialized types of analyses such as those of interstellar lines and magnetic fields have their own data needs.