New optical spectra of Ca ii and Na i toward HD 72127AB provide additional evidence for both spatial and temporal variations in the complex interstellar absorption along the two sight lines ; archival UV spectra yield information on the abundances , depletions , and physical conditions in the gas toward HD 72127A .
Similarities in the strengths of various tracers of interstellar material in the two lines of sight suggest that the total hydrogen column densities ( N \sim 2.5 \times 10 ^ { 20 } cm ^ { -2 } ) and the depletions and ionization in the main components at low LSR velocities also are similar .
Toward HD 72127A , the main components are relatively cool ( T \la 900 K ) , but with depletions resembling those found in warm , diffuse disc clouds ; the generally weaker components at higher velocities have much milder depletions , more like those found in halo clouds .
Several trace neutral species – Ca i , Cr i , and Fe i – are much stronger toward HD 72127B , however .
The column density of Cr i , for example , is about 30 times the value determined toward \zeta Oph ( the only previous detection of that species in the ISM ) .
Dielectronic recombination in warmer gas ( T \ga 5000 K ) may be largely responsible for the enhanced abundances of those trace neutral species toward HD 72127B .
If the main components toward HD 72127AB are associated with material in the Vela SNR , the differences in abundances and physical conditions occur on scales of about 1100 AU .