Properties of atomic lines in 51 Oph UV spectra

We analyzed the relative populations of atoms in excited fine-structure and metastable levels that are maintained by optical pumping and collisional excitation by electrons, and we found that most of the gas is situated at about 6 au from the star, has an electron volume density 10^5^<n(e)<3x10^6^cm^-3^, and a temperature T=8000K.

Our interpretations reveal that the gas is partly ionized, has a column density of neutral hydrogen equal to 10^21^cm^-2^, and has a composition similar to that of a mildly depleted interstellar medium or that of Jupiter-family comets. Compared to results for disks around some other stars, such as {beta} Pic and 49 Cet, we find surprisingly little neutral carbon. No molecular features were detected, which indicates that our line of sight misses the molecule-rich central plane of the disk.