Hipparcos distances of Ophiuchus and Lupus cloud complexes

TL;DR

This paper accurately determines the distances to the Ophiuchus and Lupus molecular clouds using combined extinction maps and stellar parallaxes, providing high-precision measurements and insights into their structure.

Contribution

It introduces a maximum-likelihood method to estimate cloud distances and orientations, improving precision over previous techniques.

Findings

Ophiuchus is at 119 +/- 6 pc

Lupus is at 155 +/- 8 pc

Cloud streamers are closer than the core in Ophiuchus

Abstract

We combine extinction maps from the Two Micron All Sky Survey (2MASS) with Hipparcos and Tycho parallaxes to obtain reliable and high-precision estimates of the distance to the Ophiuchus and Lupus dark complexes. Our analysis, based on a rigorous maximum-likelihood approach, shows that the rho-Ophiuchi cloud is located at (119 +/- 6) pc and the Lupus complex is located at (155 +/- 8) pc; in addition, we are able to put constraints on the thickness of the clouds and on their orientation on the sky (both these effects are not included in the error estimate quoted above). For Ophiuchus, we find some evidence that the streamers are closer to us than the core. The method applied in this paper is currently limited to nearby molecular clouds, but it will find many natural applications in the GAIA-era, when it will be possible to pin down the distance and three-dimensional structure of virtually every molecular cloud in the Galaxy.