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Probing the inner halo and IVC gas through the Local Interstellar Chimney
We present an absorption study of the interstellar gas at high positivegalactic latitudes in the direction close to the axis of the LocalChimney (LC), which is an extension of the rarefied local cavity thatreaches out from the galactic disk to a z-distance of at least 250 pcinto the lower halo region. Our study includes high-resolution (R 1.7 km s-1) spectral observations of the interstellar NaI andCaII absorption lines seen towards 6 early-type stars with distancesranging from 225 to 500 pc contained within a radius of6° along the sight-line (l = 160°, b= +55°). These visible data are supplemented withfar-ultraviolet absorption measurements of the interstellar sight-linestowards two hot white dwarf stars, RE J1043+490 (d = 230 pc) and REJ1059+512 (d = 315 pc), taken with the NASA Far UltravioletSpectroscopic Explorer (FUSE) satellite.Our observations reveal interstellar gas clouds with velocities in the-20 to -60 km s-1 range that appear to be falling towards thegalactic disk. In particular, we have detected absorption with avelocity of V_helio -55 km s-1 towards two sight-lines(HD 89501 and HD 88545) that can be associated with an intermediatevelocity (IV) cloud called the IV Arch. Our observations place aprobable z-distance to this IVC of 275-320 pc, this being much nearerthan previously thought.The far UV spectra of the two hot white dwarfs show only a few (10)interstellar absorption lines, which is indicative of the very lowdensity phase of the interstellar gas contained within the LC region. Wehave derived relative elemental abundance ratios for C, N, O, Si, Ar andFe for these two sight-lines and find that the abundance patterns arevery similar to those found for other sight-lines in the local cavity.The high ionization line of OVIłambda1032 Å has beendetected towards RE J1043+490 with a column density of 7 ×1012 cm-2, which is consistent with the averagespace density of this ion recently found in the Local Bubble region.Finally, we (tentatively) propose a possible connection between theformation of the Gould Belt, the Local Bubble cavity, the Local Chimneyand the overlying IV Arch clouds.
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