Detection of Interstellar Lithium

We have observed the 6708 A absorption line doublet of interstellar 7Li in the spectrum of Oph, using a Pepsios high-resolution optical spectrometer. The lithium feature has a radial velocity of -14.9 t 0.6 km -1 with respect to the Sun and an equivalent width of 0.68 t 0.09 mA. Within our detection limit, essentially no 6Li is seen, so that 7Li/6Li > 7. Using the observed Ca ii to Ca I ratio, we calculate N(Li ii) and find that, with respect to hydrogen, the lithium (and sodium) are depleted in the Oph cloud to about one-sixth their solar-system values. Subject headings:abundances - interstellar matter - spectrophotometry