The solar abundance of calcium and collision broadening of Cai- and Caii-Fraunhofer lines by hydrogen

✍ Scribed by H. Holweger

• Publisher: Springer
• Year: 1972
• Tongue: English
• Weight: 960 KB
• Volume: 25
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00155741

✦ Synopsis

An abundance analysis of the solar calcium spectrum is carried out using 46 lines with knownfivalues in the visible and near infrared spectral region. Resonance, forbidden and autoionizing lines are included. The solar abundance of calcium resulting from the 25 weaker, nearly dampingindependent lines only is log eca = 6.36 • 0.07, on the scale log e~ = 12. The great variety of transitions involved in the solar calcium spectrum, ranging from 0 eV lines of CaI to 7.5 eV lines of Cau and including autoionizing lines, are in reasonable agreement (Figure 1 b). Therefore notable non-LTE effects on their equivalent widths can be excluded.

Together with the sodium abundance log ez~ = 6.30 determined earlier, the solar abundance ratio Ca/Na = 1.15 is obtained with an accuracy of ~ 10%. Comparison with meteorites (carbonaceous chondrites I) shows that solar and meteoritic ratio agree within these limits.

The line broadening by collisions with hydrogen atoms is determined empirically from a comparison of weak and strong Fraunhofer lines of CaI and Call, thereby using the solar atmosphere as an absorption tube of comparatively well-known physical state. The damping half-widths 7J~ turn out to be larger than predicted from pure van der Waals interaction, the average enhancement factor being 3.0 for CaI and 1.7for Cau, independent of term properties to a first approximation. Regardless of the reason for this enhancement -inaccurate van der Waals theory or predominance of repulsive interactionthese results can be used in the spectroscopy of other stars.