Discovery of extended structures around two evolved planetary nebulae M2-55 and Abell 2

Abstract

We report a multi-wavelength study of two evolved planetary nebulae (PNs)M2-55 and Abell 2. Deep optical narrow-band images ([O III], Hα, and [N II]) of M2-55 reveal two pairs of bipolar lobes and a new faint arc-like structure. This arc-shaped filament around M2-55 appears as a well-defined boundary from southwest to southeast, strongly suggesting that this nebula is in interaction with its surrounding interstellar medium. From the imaging data of Wide-field Infrared Survey Explorer (WISE) all-sky survey, we discovered extensive mid-infrared halos around these PNs, which are approximately twice the size of their main nebulae seen in the visible.We also present a mid-resolution optical spectrum of M2-55, which shows that it is a high-excitation evolved PN with a low electron density of 250 cm^-3. Furthermore, we investigate the properties of these nebulae from their spectral energy distributions (SEDs) by means of archival data.