A new determination of the local distribution of interstellar NaI

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 250pc 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 (n_H < 0.01 cm(-3) ) with a radius of at least 70pc in most directions, more than 50% larger in volume than previously determined from NaI absorption data. Additionally, the well-known low-density interstellar tunnel in the direction of the star beta 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 170pc. Finally, we note the absence of dense neutral gas out to a distance of at least 100pc in the direction of galactic longitude {l^II} = 135(deg) .