Observations of the planetary nebula RWT 152 with OSIRIS/GTC

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. RWT 152 is one of the few known planetary nebulae with an sdO central star. We present subarcsecond red tunable filter Hα imaging and intermediate-resolution, long-slit spectroscopy of RWT 152 obtained with OSIRIS/GTC (Optical System for Imaging and low-Intermediate-Resolution Integrated Spectroscopy/Gran Telescopio Canarias) with the goal of analysing its properties. The Hα image reveals a bipolar nebula with a bright equatorial region and multiple bubbles in the main lobes. A faint circular halo surrounds the main nebula. The nebular spectra reveal a very low excitation nebula with weak emission lines from H+, He+and double-ionized metals, and absence of emission lines from neutral and single-ionized metals, except for an extremely faint [N II] λ6584 emission line. These spectra may be explained if RWT 152 is a density-bounded planetary nebula. Low nebular chemical abundances of S, O, Ar, N and Ne are obtained in RWT 152, which, together with the derived high peculiar velocity (~ 92-131 km s-1), indicate that this object is a halo planetary nebula. The available data are consistent with RWT 152 evolving from a low-mass progenitor (~1 M⊙) formed in a metal-poor environment.