Local Bubble. Extinction within 55 pc?

TL;DR

This study maps the local interstellar medium's extinction within 55 parsecs using Hipparcos data, revealing the shape and boundary of the Local Bubble through spatial extinction distribution analysis.

Contribution

It introduces a method combining Hipparcos parallaxes, B-V photometry, and spectral classification to map extinction and delineate the Local Bubble's boundary.

Findings

Northern quadrants show higher extinction up to 0.2 mag.

Southern quadrants exhibit lower extinction around 0.05 mag.

The boundary of the low-extinction region is coherent over several degrees.

Abstract

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