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7.10.4 Examples

  Fig. 13 shows the extractions of two orders near the middle of Fig. 11, but taken from a combination of more exposures than those shown in the figure. The line of sight to $\zeta$ Ori has interstellar absorption lines from two conspicuous velocity components, one at a heliocentric velocity of about 0 km s-1 and another at 24 km s-1. The upper panel shows absorptions by these two components in the 5-0 R(3) line of the Lyman band system of H2, situated between two telluric absorption lines of atomic oxygen in excited fine-structure states at 1040.942 and 1041.688Å. The double-humped, broad feature in the middle is unidentified. In the lower panel, the fully saturated, broad features are caused by absorption from singly-ionized carbon in the ground fine-structure level (left) and an excited level (right). Other features (the conspicuous double ones) are produced by hydrogen molecules in the J = 0 and 1 rotational states (the 5-0 R(0)and R(1) lines at 1036.546 and 1037.146Å, respectively).