Two new evolved bipolar planetary nebulae in the solar neighbourhood

Abstract

We present AAO/UKST Hα+[N II] narrow-band imagery and low- and medium-resolution optical spectroscopy of RCW 24 and RCW 69. These nebulae were previously classified as H II regions, but we now show them to be two of the largest and nearest bipolar Type I PNe yet discovered. Distances were estimated using extinction - distance and kinematic methods, and via a new Ha surface brightness - radius relation. The adopted distances are 1.0 ± 0.3 kpc for RCW 24 and 1.3 ± 0.2 kpc for RCW 69. Both objects have enhanced nitrogen abundances, with log N/O ≃ +0.44 for RCW 24, and log N/O = +0.33 for RCW 69. Systemic velocities and |z| distances are VLSR = +5 km s -1 and |z| ∼ 23 pc for RCW 24, and VLSR = -33 km s-1 and only |z| ∼ 7 pc for RCW 69. Both PNe originated from massive progenitors (>2.0-2.5 M⊙), as deduced from their chemical abundances, large ionized masses, small |z| distances, low peculiar velocities and relatively hot central stars. These two objects form an important addition to the small sample of evolved bipolar PNe in the solar neighbourhood. © 2006 RAS.