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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.
| Studies of the local interstellar medium. VIII - Morphology and kinematics of the diffuse interstellar clouds toward Orion
Interstellar clouds in the direction of the Orion association show onlypositive velocities for target stars within 190 pc of the sun, and bothpositive and negative velocities for more distant target stars,confirming an earlier prediction by Cowie, Songaila, and York (1979).The nearby positive velocity cloud, designated here as Orion-Lepus 70(OL 70), is a standard diffuse interstellar cloud: it is subject to theambient galactic radiation field, with properties consistent with Tabout equal to 100 K and n about equal to 3/cu cm. Combined with acolumn density log N(H) = 19.8-20.0/sq cm, these values imply a cloudthickness of about 7 pc. The kinematics of OL 70 are consistent witheither an origin as part of the expanding Loop I superbubble shell, oras part of Lindbald's expanding ring, or a synthesis of the two models.The negative velocity interstellar components seen in stars at d notless than 200 pc are caused by interstellar matter accelerated by theexpanding Ori-Eri superbubble. Relatively dense interstellar gas atpositive LSR velocities is also found within the Orion association, sothat it is difficult to pick out OL 70 components in the spectra of thedistant stars.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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Observation and Astrometry data
| Constellation: | Orion |
| Right ascension: | 05h37m37.18s |
| Declination: | -08°12'01.4" |
| Apparent magnitude: | 7.702 |
| Distance: | 289.855 parsecs |
| Proper motion RA: | -4.2 |
| Proper motion Dec: | 1.2 |
| B-T magnitude: | 7.942 |
| V-T magnitude: | 7.722 |
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