Local Bubble. Extinction within 55 pc?
  In the mapping of the local ISM it is of some interest to know where the
first indications of the boundary of the Local Bubble can be measured. The
Hipparcos distances combined to B-V photometry and some sort of spectral
classification permit mapping of the spatial extinction distribution.
Photometry is available for almost the complete Hipparcos sample and Michigan
Classification is available for brighter stars south of delta = +5 deg (1900).
For the northern and fainter stars spectral types, e.g. the HD types, are given
but a luminosity class is often missing. The B-V photometry and the parallax
do, however, permit a dwarf/giant separation due to the value of the slope of
the reddening vector compared to the gradient of the main sequence in a color
magnitude diagram, in the form: B-V vs. M_V+A_V = V+5(1+log(pi)), together with
the rather shallow extinction present in the Hipparcos sample. We present the
distribution of median A_V(l, b) for stars with Hipparcos 2 distances less than
55 pc. The northern part of the first and second quadrant has most extinction,
up to 0.2 mag and the southern part of the third and fourth quadrant the
slightest extinction, 0.05 mag. The boundary of the extinction minimum appears
rather coherent on an angular resolution of a few degrees
