HDW 2 (Hartl-Dengl-Weinberger 2, also identified as Sharpless 200 (Sh2-200) and PNG 138.1+04.1) is an ancient planetary nebula with a binary central star according to Weidmann and Gamen (Astronomy & Astrophysics, 526, A6, 2011).  This nebula was first discovered by the astronomer Stewart Sharpless in 1959 who included it in his catalogue of HII regions under the name of Sh2-200. His catalogue was compiled after analyzing photographic plates taken at the Palomar Observatory. The misidentification of HDW 2 (or Sh2-200) arose from the criteria of assembling the catalogue, which compared the separate red and blue photographic plates of the same region. If a nebula was more prominently visible on the red plate, it was deduced that it was more likely to be an ionized nebula. The other criteria were the presence of bright stars in the vicinity which might be the source of ionization. (Astrodon Imaging)

In 1983, Sh2-200 was included in the HDW catalogue of possible planetary nebulae by the astronomers Herbert Hartl, Johann Dengel and Ronald Weinberger. However, it wasn't confirmed to be a true genuine planetary nebula until 2017 when spectra were taken as part of professional observations.

In 1987, further narrowband observations by Herbert Hartl and Ronald Weinberger detected a large faint outer halo extending further than the central shell (Astronomy & Astrophysics, 519, 1987).  A feature not fully appreciated or clearly defined in the scientific literature is something known as ISM [interstellar medium]-type haloes. These are a type of structure that represent ambient interstellar gas in the vicinity of the planetary nebula but not physically related to it. Despite being very old and highly evolved, low surface brightness planetary nebulae such as HDW 2 contain very hot and energetic central stars, which are the remnant cores of the progenitor star that died and ejected its outer gaseous layers. The energy output of some planetary nebula central stars is so prodigious that it is capable of ionizing unrelated gas in the surrounding vicinity causing it to glow. The most popular example of this phenomenon is the large halo around NGC 3242.  (Hanson Astronomy)

Imaged over several nights:  Oct 14-15, 18, 20-21, 26-28; Nov 1, 18 and 20, 2022.