Hipparcos distance estimates of the Ophiuchus and the Lupus cloud complexes

¹ Space Telescope European Coordination Facility/ESO, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany e-mail: mlombard@eso.org
² University of Milan, Department of Physics, via Celoria 16, 20133 Milan, Italy
³ Harvard-Smithsonian Center for Astrophysics, Mail Stop 42, 60 Garden Street, Cambridge, MA 02138, USA
⁴ Calar Alto Observatory – Centro Astronómico Hispano Alemán, C/Jesús Durbán Remón 2-2, 04004 Almeria, Spain

Received: 20 November 2007
Accepted: 16 January 2008

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 ρ -Ophiuchi cloud is located at and the Lupus complex is located at ; 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.