Astronomy and Astrophysics, volume 346, 785-797 (1999/6-3)
Mapping the contours of the Local Bubble: preliminary results.
SFEIR D.M., LALLEMENT R., CRIFO F. and WELSH B.Y.
Abstract (from CDS):
We present preliminary results from a long-term program of mapping the neutral absorption characteristics of the local interstellar medium, taking advantage of Hipparcos stellar distances. Equivalent widths of the NaI D-line doublet at 5890Å are presented for the lines-of-sight towards some 143 new target stars lying within 300pc of the Sun. Using these data which were obtained at the Observatoire de Haute Provence, together with previously published NaI absorption measurements towards a further 313 nearby targets, we present absorption maps of the distribution of neutral gas in the local interstellar medium as viewed from 3 different galactic projections. In particular, these maps reveal the Local Bubble region as a low neutral density interstellar cavity in the galactic plane with radii between 65-250pc that is surrounded by a (dense) neutral gas boundary (or ``wall''). We have compared our iso-column contours with the contours derived by Snowden et al. (1998ApJ...493..715S
) using ROSAT soft X-ray emission data. Consistency in the global dimensions derived for both sets of contours is found for the case of a million degree hot LB plasma of emissivity 0.0023cm–6
.pc with an electron density of 0.005cm–2
. We have detected only one relatively dense accumulation of cold, neutral gas within 60pc of the Sun that surrounds the star δ Cyg, and note that the nearest molecular cloud complex of MBM 12 probably resides at the very edge of the Local Bubble at a distance of ∼90pc. Our observations may also explain the very different physical properties of the columns of interstellar gas in the line-of-sight to the two hot stars ε CMa and β CMa as being due to their locations with respect to the Bubble contours. Finally, in the meridian plane the LB cavity is found to be elongated perpendicularly to the Gould's Belt plane, possibly being ``squeezed'' by the expanding shells of the Sco-Cen and Perseus-Taurus OB associations.
ISM: bubbles - ISM: structure - Galaxy: solar neighbourhood
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<Available at CDS (J/A+A/346/785): table1.dat table2.dat tables.ps tables.tex>
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