High Signal-to-Noise Ratio Observations of Weak Interstellar Absorption Lines Towards XI Ophiuchi With the Goddard High-Resolution Spectrograph Aboard the Hubble Space Telescope
Abstract
We present an atlas and tabulation of weak interstellar absorption lines in the ultraviolet spectrum of ζ Ophiuchi in four selected wavelength regions observed with the Goddard High Resolution Spectrograph aboard the Hubble Space Telescope. The signal-to-noise ratio ranges from 150 to nearly 400, and the spectral resolving power exceeds 20 000, allowing 2σ detections of features as weak as Wλ=0.8 mÅ. We report positive measurements of two lines of OH, and weak detections of P I, Tl II, and N V. Upper limits of Wλ<1 mÅ are found for the molecules H2O, HCl, SiO, NO+, and CH2. Similar limits are found for heavy elements Te II, Co II, and Sb II. Three lines are present in our spectrum for which we have no identifications. They are found at wavelengths of λ=1229.84, 1313.98, and 1314.23 Å. However, none of the features reported by previous authors as unidentified absorption lines in the wavelength regions we have observed are present in our data.
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