Discovery of Extended Structures around Two Evolved Planetary Nebulae M 2-55 and Abell 2

We report a multi-wavelength study of two evolved planetary nebulae (PNs) M 2-55 and Abell 2. Deep optical narrow-band images ([O III], H?, and [N II]) of M 2-55 reveal two pairs of bipolar lobes and a new faint arc-like structure. This arc-shaped filament around M 2-55 appears 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 larger than their main nebulae seen in the visible. We also present a mid-resolution optical spectrum of M 2-55, 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.

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