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HD 156991


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An accurate determination of the distance to the Pipe nebula
Aims.We seek an accurate distance to the Pipe nebula. Methods: TheB-band linear polarimetry collected for stars from the Hipparcoscatalogue is used to investigate the dependence of the measuredinterstellar polarization as a function of the star's trigonometricparallax. Results: The linear polarization obtained for 82 Hipparcosstars in the general direction of the Pipe nebula are presented andanalysed. The distribution of the obtained position angles suggests theexistence of two polarizing components. One of them has low averagecolumn density and seems to be closer than ~70 pc to the Sun, while theother component has a higher column density and seems to belong to avery extended interstellar structure. The obtained parallax-polarizationdiagram indicates a low degree of polarization for stars withπH > 8 mas, while a steep rise in polarization isobserved for stars with πH ≈ 7 mas, corresponding to adistance of approximately 140 pc. Conclusions: Our analysis suggests adistance of 145 ± 16 pc to de Pipe nebula, meaning that thiscloud is part of the Ophiuchus dark cloud complex. There is evidencethat the largest filament of the Pipe nebula has collapsed along themagnetic field lines, indicating that magnetic pressure plays animportant role in the evolution of this cloud.Based on observations collected at Observatório do Pico dos Dias,operated by Laboratório Nacional de Astrofísica (LNA/MCT,Brazil). Tables 1 and 2 are only available in electronic form athttp://www.aanda.org

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Dades d'Observació i Astrometria

Constel·lació:Ophiucus
Ascensió Recta:17h21m31.61s
Declinació:-22°55'33.3"
Magnitud Aparent:8.685
Distancia:56.721 parsecs
Moviment propi RA:0.4
Moviment propi Dec:-31.8
B-T magnitude:9.43
V-T magnitude:8.747

Catàlegs i designacions:
Noms Propis   (Edit)
HD 1989HD 156991
TYCHO-2 2000TYC 6825-160-1
USNO-A2.0USNO-A2 0600-26290396
HIPHIP 84936

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