A Potassium Line Shape Study At Stellar Atmospheric Temperatures Of Brown Dwarfs

\begin{wrapfigure}{r}{0pt} \includegraphics[scale=0.3]{K_Ar_ISMS.eps} \end{wrapfigure} There is considerable ambiguity in the collisional broadening mechanism for the resonance doublets of alkali metals, e.g., potassium near 0.77 $\mu$m. The presence of alkali metals within stellar atmospheres of brown dwarfs calls for accurate modeling on the effect of collisional broadening to better interpolate the spectra measured by space telescopes. We present an easy approach to generate potassium vapor in the laboratory at conditions similar to the effective surface temperatures ($\sim$1000 K) of brown dwarfs. High-temperature potassium/argon mixtures are produced in a shock tube via shock-heating seeded potassium chloride salts. This seeding approach is effective over 1100 - 1900 K and is very safe, compared with the handling of highly reactive potassium samples. The absorption line shapes of both K I resonance doublets (D1: 770 nm; D2: 767 nm) are studied with argon as the collisional partner. The measured spectra are well-modeled with Voigt profiles, and the measured broadening parameters, i.e., argon broadening coefficients and pressure shift coefficients, are well-fit with power-law relationships in the range of test temperatures