The massive expanding molecular torus in the planetary nebula NGC 6302

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 –1 transitions of ¹²CO and ¹³CO at arcsecond resolution. These data are analysed in combination with observations of both the –1 and –2 transitions of ¹²CO and ¹³CO made with JCMT.

Results. The ¹²CO and ¹³CO emission match the dark lane seen in absorption in the Hα image of the object and trace an expanding torus of material. The CO indicates a mass of the torus of ~  . The torus is expanding with a velocity of ~8 km s^-1, centred at . 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 . 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 month.