A peculiar planetary nebula candidate in a globular cluster in the Fornax dwarf spheroidal galaxy

Abstract

Context. Until now, only one planetary nebula (PN) has been known in the Fornax dwarf spheroidal galaxy. Aims. The discovery of a second PN candidate, associated with one of the 5 globular clusters in the Fornax dwarf, is reported. Methods. Spectra of the globular cluster H5, obtained with the UVES echelle spectrograph on the ESO Very Large Telescope, show [O iii] line emission at a radial velocity consistent with membership of the Fornax dwarf. A possible counterpart of the [Oiii] emission is identified in archival images from the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. The source of the emission is located about 1. 5 (less than one core radius) southwest of the centre of the cluster. Results. The emission line source is identified as a likely PN, albeit with several peculiar properties. No Hβ, Hei, orHe ii line emission is detected and the [O iii]/Hβ ratio is >25 (2σ). The expansion velocity inferred from the [O iii] 5007 Å line is Ve ≈ 55 km s−1, which is large for a PN. The diameter measured on the HST images is about 0. 23 or 0.15 pc at the distance of the Fornax dSph. Conclusions. This object doubles the number of known PNe in Fornax, and is only the 5th PN associated with an old GC for which direct imaging is available. It may be a member of the rare class of extremely H-deficient PNe, the second such case found in a GC.