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The local distribution of NA I interstellar gas
We present high-resolution absorption measurements (lambda/Delta lambdaapproximately 75,000) of the interstellar Na I D lines at 5890 A toward80 southern hemisphere early-type stars located in the localinterstellar medium (LISM). Combining these results with other sodiummeasurements taken from the literature, we produce galactic maps of thedistribution of neutral sodium column density for a total of 293 starsgenerally lying within approximately 250 pc of the Sun. These mapsreveal the approximate shape of the mid-plane contours of the rarefiedregion of interstellar space termed the Local Bubble. Its shape is seenas highly asymmetric, with a radius ranging from 30 to 300 pc, and withan average radius of 60 pc. Similar plots of the Galactic mid-planedistribution of sources emitting extreme ultraviolet radiation show thatthey also trace out similar contours of the Local Bubble derived from NaI absorption measurements. We conclude that the Local Bubble absorptioninterface can be represented by a hydrogen column density,NuETA = 2 x 1019 cm-2, which explainsboth the local distribution of Na I absorption and the observed galacticdistribution of extreme ultraviolet sources. The derived mid-planecontours of the Bubble generally reproduce the large-scale featurescarved out in the interstellar medium by several nearby galactic shellstructures.
| On the distance to Chain A
High dispersion spectroscopic observations of nine A-type stars and oneF-type star in the Na I D and/or Ca II H and K lines are presented. Moststars lie toward the high-velocity complex Chain A. These spectra arecompared with 21-cm H I emission profiles of the same lines of sight. Nooptical high- or intermediate-velocity components are detected. A lowerlimit for the height of Chain A above the galactic plane of z about 200pc can be deduced. The detections of interstellar Ca II in the spectraof halo RR Lyrae stars in the literature are shown to be in doubt.
| The distance to the high-velocity clouds - Mass infall and galactic disk formation
The high-velocity neutral hydrogen complex C in optical (Ca K)absorption against stars at distances of 1-2 kpc has been detected,confirming a previous tentative detection and placing an upper limit onthe distance to this complex. A similar (though as yet more uncertain)limit is placed to the distance to complex A. No complex is detected inabsorption against any nearby star, effectively ruling out models inwhich the clouds are formed by supershells in the local disk. If thesedistances are representative of the bulk of the high-velocity clouds,the local mass infall rate is 6 x 10 to the -9th solar mass/sq pc/yr,which would supply the disk column density in 10 billion yr. The cloudslie above the bulk of the disk, and it is shown how they may be used tomeasure the pressure of the halo and to place an upper bound on themetagalactic UV flux.
| Photographic magnitudes of stars brighter than 7m.75 between +75° and +80° declination (Errata: 11 270)
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| Yerkes actinometry. Zone +73deg to +90deg.
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