The ``Monochromatic Density Diagnostic'' Technique: First Detection of Multiple Density Components in the Chromosphere of alpha Tauri

Abstract

Emission line profiles of the red giant alpha Tau, obtained by Carpenter et al. (1991) using the echelle and medium dispersion gratings of the Goddard High Resolution Spectrograph are re-examined. Ratios of monochromatic flux densities of lines of the C II) 2s² 2p(2)P⁰ goes to 2s2p² (4)P multiple near 2325 A, well-known diagnostics of electron densities in the chromospheres of cool evolved stars, change systematically with relative wavelength across the line profiles. With the justifiable assumption that these lines are optically thin, this implies that the electron density varies sytematically across the lines profiles. This is the first time that traditional electron density diagostic line ratios have been successfully applied to monochromatic line flux densities in cool stars. this work clearly demonstrates the power of very high signal-to-noise, high-resolution spectra in the UV. The monochromatic density diagonstic technique holds promise as a powerful tool for studying flows in a variety of astrophysical objects, including the Sun. The paper concludes with a compliation of ions from the boron and aluminum sequences for which this technique can be expected to produce valuable results using astronomical data from the GHRS and solar data from instruments on the Solar and Heliospheric Observatory (SOHO).