2000ApJ...535..293P

We report new observations of Na I and Ca II interstellar absorption in a nearby (230±30 pc) southern high-latitude filament obtained at a spectroscopic resolution of ∼0.32 km.s^–1 using HD 22252 as the background probe. Complex absorption is present for both species with total column densities of N(Ca II)∼1.3x10¹² cm^–2 and N(Na I)>7x10¹² cm^–2. Over a velocity range of 25 km.s^–1 we find 11 Ca II velocity components loosely grouped into three velocity aggregates. Unusually narrow Ca II absorption is present with b-values in the range 0.25-0.5 km.s^–1; such small values are rarely discovered. Each of these narrow Ca II components has an associated broader component at a slightly shifted velocity. Finally, there are two Ca II clouds with large b-values (∼5 km.s^–1) but no detectable Na I that flank the three aggregates. At our particular intercept we may be observing the filament edge-on and seeing cold interior condensations each with a warm outer shell–all contained within a further exterior envelope of ionized gas. We estimate that a typical interior condensation will have a linear dimension d in the range 10⁴<d<6x10⁴ AU and a pressure nT of 1.5<nT<9x10⁴ cm^–3 K, but with large uncertainties. This result is consistent with the picture of small and relatively dense cloud cores expanding into the local bubble.