A SEARCH FOR INTERSTELLAR C-3 IN THE TRANSLUCENT CLOUD TOWARD HD-147889

As part of an effort to search for new interstellar molecules at optic al and near-UV wavelengths, we have obtained high S/N (approximate to 500) echelle CCD spectra of the well-studied translucent sight line to ward HD 147889 in the rho Oph dark cloud complex. These observations s how that HD 147889 is actually a double-lined spectroscopic binary con sisting of two B2 IV-V components with rotational (v sin i) velocities of about 30 and 70 km s(-1), an orbital period of about 5 days, and a radial velocity semiamplitude of about 70 km s(-1). The presence and movement of the weak stellar features in the spectrum of HD 147889 may account for some of the discrepancies in previous interstellar absorp tion-line studies of this object. Despite this potential stellar confu sion, we have tentatively identified an interstellar absorption featur e at the wavelength (4051.6 Angstrom) expected for an unresolved blend of the strongest Q-branch lines arising from the ground vibrational s tate of the C-3 A(1)II-X(1) Sigma electronic transition. Assuming a cl oud temperature of 40 K, the strength of this feature would correspond to a C-3 column density of 4 x 10(12) cm(-2) toward HD 147889. This v alue of N(C-3) is about a factor of 5 smaller than that predicted by t he van Dishoeck & Black (1989) model of the HD 147889 cloud.