The Astrophysical Journal, 706:614–622, 2009 November 20 doi:10.1088/0004-637X/706/1/614 C 2009. The American Astronomical Society. All rights reserved. Printed in the U.S.A. RUBIDIUM IN THE INTERSTELLAR MEDIUM Kyle M. Walker1,5, S. R. Federman1,5, David C. Knauth2,3,6, and David L. Lambert4 1 Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606, USA;
[email protected],
[email protected] 2 Franklin High School, Reisterstown, MD 21136, USA;
[email protected] 3 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA 4 W. J. McDonald Observatory, University of Texas at Austin, Austin, TX 78712, USA;
[email protected] Received 2009 January 2; accepted 2009 October 6; published 2009 November 3 ABSTRACT We present observations of interstellar rubidium toward o Per, ζ Per, AE Aur, HD 147889, χ Oph, ζ Oph, and 20 Aql. Theory suggests that stable 85Rb and long-lived 87Rb are produced predominantly by high-mass stars, through a combination of the weak s- and r-processes. The 85Rb/87Rb ratio was determined from measurements of the Rb i line at 7800 Å and was compared to the solar system meteoritic ratio of 2.59. Within 1σ uncertainties, all directions except HD 147889 have Rb isotope ratios consistent with the solar system value. The ratio toward HD 147889 is much lower than the meteoritic value and similar to that toward ρ Oph A; both lines of sight probe the Rho Ophiuchus Molecular Cloud. The earlier result was attributed to a deficit of r-processed 85Rb.