A Search for Weak Ultraviolet Interstellar Absorption Features in IUE Spectra of rho Ophiuchi and zeta Ophiuchi

Abstract

We have applied procedures designed to reduce substantially the non-random, so-called "fixed-pattern" noise present in IUE spectra to archival long-wavelength light-dispersion spectra of rho Ophiuchi and zeta Ophiuchi. Substantial elimination of the fixed-pattern noise via flat fielding can yield 2-sigma equivalent width limits of 5-10 mA from the sum of a small number (< 5) of well exposed archival spectra, and increases confidence in the reality of any weak features found. Examination of complete long-wavelength ( 2200-3250 A) spectra of these two stars has revealed, in addition to many known strong absorption lines, several lines of Fe I and Si I which had not previously been reported, as well as a small number of opssible unidentified lines. We also present substantially improved upper limits to the equivalent widths of a number of other weak lines; limits an order of mganitude smaller, now achievable with the HST GHRS, should produce detections of some of these. (SECTION: Interstellar Medium and Nebulae)