Astronomy & Astrophysics

A&A 473, 207-217 (2007)
DOI: 10.1051/0004-6361:20066973

The massive expanding molecular torus in the planetary nebula NGC 6302

N. Peretto¹, G. Fuller¹, A. Zijlstra¹, and N. Patel²

¹ School of Physics and Astronomy, University of Manchester, Sackville Street, PO Box 88, Manchester M60 1QD, UK
e-mail: nicolas.peretto@manchester.ac.uk
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS78, Cambridge, Massachusetts 02138, USA

(Received 19 December 2006 / Accepted 26 June 2007)

Abstract
Aims.We measure the mass and kinematics of the massive molecular torus in the the proto-typical butterfly planetary nebula NGC 6302. Determining the mass-loss history of the source is an important step in understanding the origin and formation of the wing-like morphology.
Methods. Using the SMA interferometer we have imaged both the continuum emission and the J=2-1 transitions of ¹²CO and ¹³CO at arcsecond resolution. These data are analysed in combination with observations of both the J=2-1 and J=3-2 transitions of ¹²CO and ¹³CO made with JCMT.
Results. The ¹²CO and ¹³CO emission match the dark lane seen in absorption in the H ${\alpha}$ image of the object and trace an expanding torus of material. The CO indicates a mass of the torus of ~2 $M_\odot \pm 1$ $M_\odot$ . The torus is expanding with a velocity of ~8 km s^-1, centred at $V_{\rm lsr}=-31.5\rm\,km\,s^$ . The size and expansion velocity of the torus indicates that it was ejected from ~7500 yr to 2900 yr ago, with a mass-loss rate of $5\times10^\,M_\odot\,\rm yr^$ . In addition we detect a ballistic component in the CO images which has a velocity gradient of 140 km s^-1 pc^-1.
Conclusions.The derived mass-loss history of the torus favours binary interaction as the cause of the ejection of the torus and we predict the existence of a companion with an orbital period $P\lesssim 1\,$ month.

Key words: stars: AGB and post-AGB -- planetary nebulae: general -- planetary nebulae: individual: NGC 6302

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