On the distribution of interstellar matter around the sun

The Astronomical Journal1984Vol. 89, pp. 1022–1022

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Abstract

Available data on interstellar line or EUV continuum absorption attributable to the local (r equal to or less than 100 pc) interstellar medium are presented and analyzed as a whole for clues leading to a deeper understanding of the spatial distribution and physical properties of this material. By using these data in conjunction with upper limits provided by polarization and color excess surveys and relating everything to the neutral-hydrogen column density, it is shown that the data are consistent with a simple model that assumes the relatively pervasive presence of a tenuous (nH = 0.07 per cu cm), possibly warm (T = 1,000-10,000 K) gas extending uniformly out to considerable distances from the sun in most directions. The only region manifestly clear of this material lies in the 200 deg to 270 deg galactic longitude range in both high and low latitudes. Strong density discontinuities are clearly observable at r approximately 100-150 pc in the general directions of the Sco-Cen and Per associations and a weaker discontinuity much closer to the sun running along a ridge oriented parallel to the line connecting their centers. Beyond these fronts, the space density of interstellar matter must fall to very low values that extend out to several hundred parsecs or so from the sun. These results are not incompatible with H I, 21-cm, and soft X-ray all-sky surveys. The implication of these findings for the theory of the interstellar medium and EUV visibility is briefly discussed.

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Abstract

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