HIGH SIGNAL-TO-NOISE RATIO OBSERVATIONS OF WEAK INTERSTELLAR ABSORPTION-LINES TOWARDS ZETA-OPHIUCHI WITH THE GODDARD HIGH-RESOLUTION SPECTROGRAPH ABOARD THE HUBBLE-SPACE-TELESCOPE

We present an atlas and tabulation of weak interstellar absorption lin es in the ultraviolet spectrum of zeta Ophiuchi in four selected wavel ength regions observed with the Goddard High Resolution Spectrograph a board the Hubble Space Telescope. The signal-to-noise ratio ranges fro m 150 to nearly 400, and the spectral resolving power exceeds 20 000, allowing 2 sigma detections of features as weak as W-lambda=0.8 m Angs trom. We report positive measurements of two lines of OH, and weak det ections of P I, Tl II, and N V. Upper limits of W-lambda<1 m Angstrom are found for the molecules H2O, HCl, SiO, NO+, and CH2. Similar limit s are found for heavy elements Te II, Co II, and Sb II. Three lines ar e present in our spectrum for which we have no identifications. They a re found at wavelengths of lambda=1229.84, 1313.98, and 1314.23 Angstr om. However, none of the features reported by previous authors as unid entified absorption lines in the wavelength regions we have observed a re present in our data. (C) 1996 American Astronomical Society.