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
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.
Key words: stars: AGB and post-AGB / planetary nebulae: general / planetary nebulae: individual: NGC 6302
© ESO, 2007