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Astron. Astrophys. 333, 101-105 (1998)

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A new determination of the local distribution of interstellar Na I

B.Y. Welsh 1, F. Crifo 2 and R. Lallement 3

1 Experimental Astrophysics Group, Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
2 DASGAL and URA 335 du CNRS, Observatoire de Paris, F-92195 Meudon, France
3 Service d'Aeronomie du CNRS, B.P. 3, F-91371 Verrieres le Buisson, France

Received 29 September 1997 / Accepted 1 December 1997

Abstract

We present galactic maps of the distribution of neutral sodium absorption column density using the newly determined Hipparcos satellite distances for a total of 290 stars lying within 250 pc of the Sun. These maps now replace those originally presented in Welsh et al. (1994). The Local Bubble is now seen to be a neutral gas-free cavity ([FORMULA] [FORMULA] 0.01 cm-3) with a radius of at least 70 pc in most directions, more than 50% larger in volume than previously determined from Na I absorption data. Additionally, the well-known low-density interstellar tunnel in the direction of the star [FORMULA] CMa is almost twice as wide as previously thought, and the existence of a similarly tenuous interstellar feature has been identified in the galactic direction of Lupus-Norma extending to at least 170 pc. Finally, we note the absence of dense neutral gas out to a distance of at least 100 pc in the direction of galactic longitude [FORMULA] = [FORMULA].

Key words: ISM: clouds – ISM: atoms – solar neighbourhood

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© European Southern Observatory (ESO) 1998

Online publication: April 15, 1998
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