obtain the best match to the observed spectrum. Ideally we would like to measure the Rb isotope ratio, $^{85}$Rb/$^{87}$Rb, but @lambert76 were unable to measure accurate ratios in Arcturus even when using data with superior spectral resolution and signal-to-noise ratio (S/N) due to the presence of hyperfine structure and the small isotopic shift. While our tests confirmed that we could not measure accurate Rb isotope ratios, we verify the finding by @tomkin99 that the derived Rb abundances are not sensitive to the assumed isotope ratio. Using the @kurucz84 solar atlas, we measured an abundance log $\epsilon$(Rb) = 2.58 using a model atmosphere with [$T_{\rm eff}$]{}/$\log g$/$\xi_t$ = 5770/4.44/0.85. Our derived solar Rb abundance is in very good agreement with the @grevesse98 value, log $\epsilon$(Rb) = 2.60.

The subordinate Rb[i]{} line near 7947 Å is weaker by a factor of 2 and is roughly 2% deep relative to the continuum. We detect this line in all our spectra and preliminary analyses suggest that the abundances derived from this line agree with those from the 7800 Å line (see Figure \[fig:7947a\]). However, we prefer to restrict our results to the 7800 Å line since the 7947 Å region is more crowded, i.e., 