Journal Article

A distance estimate based on angular expansion for the planetary nebula NGC 6881

Lizette Guzmán-Ramírez, Yolanda Gómez, Laurent Loinard and Daniel Tafoya

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 414, issue 4, pages 3129-3133
Published in print July 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18609.x
A distance estimate based on angular expansion for the planetary nebula NGC 6881

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In this paper, we report on high angular resolution radio observations of the planetary nebula NGC 6881 obtained with the Very Large Array (VLA) at a wavelength of 6 cm. The emission appears to be the superposition of a roundish core and a point-symmetric bipolar structure elongated along a position angle of about 145°. This is strongly reminiscent of the morphology seen in Hα and [N ii] images. A comparison between VLA observations obtained in 1984 and 1994 clearly reveals the expansion of the core of the nebula, at a rate of 2.1 ± 0.7 mas yr−1. Assuming that the expansion velocity in the plane of the sky (determined from these measurements) and the expansion velocity along the line of sight (estimated from optical spectroscopy available in the literature) are equal, we find a distance to NGC 6881 of 1.6 ± 0.5 ± 0.3 kpc, where the first error reflects the uncertainty on the expansion and the second error comes from the potential difference between pattern and material speeds. This distance is compatible with (but does not necessarily imply) an association of NGC 6881 with the nearby H ii region Sh 2-109 and, more generally, the Cygnus star-forming region.

Keywords: techniques: interferometric; astrometry; stars: late-type; planetary nebulae: general; planetary nebulae: individual: NGC 6881; (PN G74.5+02.1); radio continuum: general

Journal Article.  3379 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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