2000MNRAS.319L...1C

We present ultra-high-resolution {formmu1} observations of interstellar Nai and Ki absorption lines towards κ Vel (HD 81188) which show clear evidence for temporal variation between 1994 and 2000. Specifically, the column densities of K⁰ and Na⁰ in the main velocity component have increased by 40 and 16per cent, respectively, over this period. Earlier work had suggested that this component actually consists of two unresolved sub-components; this result is confirmed here, and the overall line profile is found to be consistent with only one of these sub-components having increased in strength since 1994. We argue that this variation is consistent with the line of sight gradually probing a cold, dense interstellar filament of the kind recently proposed by Heiles to explain other observations of small-scale structure in the interstellar medium.