The ultraviolet absorption spectrum of the Z = 2.72 QSO HS 1700+6416. 1: Results on heavy-element absorption systems

Astronomy and Astrophysics – Astronomy

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Absorption Spectra, Abundance, Heavy Elements, Lyman Spectra, Quasars, Ultraviolet Absorption, Ultraviolet Spectra, Visible Spectrum, Carbon, Faint Object Camera, Hubble Space Telescope, Lyman Alpha Radiation, Oxygen, Photoionization, Radio Astronomy, Red Shift, Spectrographs

Scientific paper

We present the analysis of ultraviolet and optical spectra of the bright, high-redshift quasar HS 1700+6416. Ultraviolet observations in the range from 1150 to 3280 A were obtained with the Faint Object Spectrograph (FOS) onboard the Hubble Space Telescope (HST) at a resolution of R = 1300. The identification of the numerous absorption lines provides evidence for 15 heavy-element absorption systems, among them 7 Lyman Limit systems (LLS) clearly visible from their Lyman edges in the HST data. The entire spectrum is a superposition of absorption lines by hydrogen, helium and heavy-elements in 7 LLS, at least 8 heavy-element absorption systems and the interstellar medium as well as Lyman lines arising in the more numerous Ly-alpha clouds. Prominent absorption by several ionization stages of C, N and O is detected in almost all heavy-element absorption systems when the corresponding resonance lines fall in the observed wavelength range. The blending problem as a result of the high absorption line density and the low spectral resolution severely affects the quantitative analysis of the data. In order to derive column densities a spectrum synthesis program has been developed. Column densities measurements have been used to constrain photoionization models in order to derive physical parameters of the absorber systems. On the basis of our analysis, all heavy-element absorption systems (with the exception of the system at z = 1.1572) show enhanced oxygen and nitrogen abundances relative to carbon. No correlation of any of the physical parameters with redshift is obvious, but the relative oxygen overabundance (O/C) seem to increase with decreasing carbon abundance (C/H). Normalized and calculated spectra along with the line identifications are shown.

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