Departamento de Física – ICEx – UFMG, Caixa Postal 702, 30.123-970 Belo Horizonte, Brazil e-mail: [falves;franco]@fisica.ufmg.br
Accepted: 27 March 2007
Aims.We seek an accurate distance to the Pipe nebula.
Methods.The B-band linear polarimetry collected for stars from the Hipparcos catalogue is used to investigate the dependence of the measured interstellar polarization as a function of the star's trigonometric parallax.
Results.The linear polarization obtained for 82 Hipparcos stars in the general direction of the Pipe nebula are presented and analysed. The distribution of the obtained position angles suggests the existence of two polarizing components. One of them has low average column density and seems to be closer than ~70 pc to the Sun, while the other component has a higher column density and seems to belong to a very extended interstellar structure. The obtained parallax-polarization diagram indicates a low degree of polarization for stars with 8 mas, while a steep rise in polarization is observed for stars with 7 mas, corresponding to a distance of approximately 140 pc.
Conclusions.Our analysis suggests a distance of 145 ± 16 pc to de Pipe nebula, meaning that this cloud is part of the Ophiuchus dark cloud complex. There is evidence that the largest filament of the Pipe nebula has collapsed along the magnetic field lines, indicating that magnetic pressure plays an important role in the evolution of this cloud.
Key words: ISM: clouds / ISM: individual objects: Pipe nebula / stars: distances / stars: individual objects: Hipparcos / techniques: polarimetric
© ESO, 2007