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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.
| Radial-velocity measurements. V - Ground support of the HIPPARCOS satellite observation program
The paper presents data on 1070 radial velocity measurements of starsdistributed in 39 fields measuring 4 deg x 4 deg. The PPO series ofFehrenbach et al. (1987) and Duflot et al. (1990) is continued using theFehrenbach objective prism method.
| The local interstellar medium and soft local X-ray radiation
The nature of the soft local X-ray radiation is discussed. The questionof whether the radiation originates from a local bubble, a number ofnonlocal bubbles, or the Galactic corona is examined. Attention is givento Rosat findings and to the known characteristics of the Dracomolecular cloud, the Hercules H I shell, and the Hercules field.
| Interstellar NA I D line studies of stars towards the Draco nebula
This study presents new high-dispersion CCD spectra of sodium for eightprogram stars located in the direction of the high-latitude Dracomolecular cloud (DMC). The derived lower distance limit of 180 pc abovethe Galactic plane was evaluated from nondetection of interstellarabsorption lines of sodium at the Draco velocity in sight lines of B8-F0type stars. This result is in agreement with former distance estimatesfrom star counts as well as from UBV photometric extinctionmeasurements. The existence of the most negative velocity components inspectra of the most distant stars suggests a more speculative distanceestimate of 400-600 pc for the DMC. The present determination of a lowerdistance limit to the DMC from an interstellar absorption-line studysupplements the few existing optical determinations of firm (upper)distance limits to other high-latitude molecular clouds.
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