SIMBAD references

We present a high S/N ratio optical spectrum of the bright quasar HS 1700+6416. These data usefully complement the UV HST data from Vogel & Reimers (1995). We analyse the metal line systems using photo-ionization models allowing for inhomogeneities in the gas. The models are able to reproduce within a factor of two the large N(HeI)/N(HI) ratio together with the mean column densities of the heavy element species observed in the z∼2 systems. The density contrast between low and high density regions is of the order of 30. Although the [O/C] abundance ratio seems slighly larger than solar, firm conclusion should await higher spectral resolution data. A break at the He II ionization limit of a factor of ten is acceptable in the ionizing spectrum. Abundances are found to be about 0.08Z_☉. This together with other determinations from the literature indicates that there is evolution in the metal content of metal line systems with redshift: [Mg/H] is slightly below solar at z∼0.7 and [C/H]∼10^–2-10^–1 at z∼2. We detect an associated C IV system at z_abs=2.7126 in which there is some evidence for the presence of Ne VIII, probably Ne VI, Ne VII, and possibly Si XII.