2009ApJ...698..509K

We report here on a new determination of the interstellar ⁸⁵Rb/⁸⁷Rb isotopic ratio for diffuse gas along the line of sight toward HD169454. We have detected no contribution of ⁸⁷Rb in the Rb I absorption line at 7800 Å in this cloud. We deduce a lower limit of ⁸⁵Rb/⁸⁷Rb>2.4 (95% C.L.). This new value differs significantly from the only other reported local interstellar value of 1.21±0.30(1σ) along a different line of sight, and is marginally consistent with the solar value of 2.43. We discuss the implications of this new isotopic ratio in the context of the various relevant models for the nucleosynthesis of heavy elements. We suggest that material in this cloud may be depleted in the main s-process component.