WeDe 1

WeDe 1
Image of WeDe 1.
Basic Information
Right ascension	05h 59m 24.8669398728s
Declination	+10° 41' 40.411774572"
Constellation	Orion
Type Of Nebula	Planetary
Other Designations	PN G197.4-06.4, PK 197-06, PK 197-06 1, WeDe 1

WeDe 1, also known as WDHS 1 or Weinberger-Dengel-Hartl-Sabbadin 1, is a planetary nebula located in the constellation Orion. It was reported in 1983 by astronomers Ronald Weinberger, J. Dengel, H. Hartl, and F. Sabbadin in the paper A newly discovered nearby planetary nebula of old age, published in The Astrophysical Journal, volume 265, pages 249–257. The object is also catalogued as PN G197.4−06.4 and PK 197−06.1. Its large angular size and very low surface brightness make it an exceptionally difficult planetary nebula to observe visually. Modern observing sources give an extent of approximately 22 × 17 arcminutes, while the original discovery paper reported an angular dimension of 17 × 14 arcminutes.

Discovery

The planetary nebula was discovered and reported by a team of European astronomers consisting of Ronald Weinberger, J. Dengel, H. Hartl, and F. Sabbadin. The discovery was published in 1983 under the title A newly discovered nearby planetary nebula of old age. The catalogue designation WeDe is derived from the surnames Weinberger and Dengel, while the alternative designation WDHS incorporates Weinberger, Dengel, Hartl, and Sabbadin. The object is identified in modern astronomical databases as PN G197.4−06.4. SIMBAD associates the nebula with the central star WD 0556+106 and Gaia DR3 3341996555048041856.

Characteristics

WeDe 1 is considered an old and highly evolved planetary nebula. The original discovery paper described it as being in a very late evolutionary stage and possibly among the most evolved planetary nebulae known at the time. The authors reported a red surface brightness of approximately 23.6 mag arcsec−2 and estimated a mean linear diameter of about 1.44 pc using the distance available at the time. Its large angular diameter and extremely low surface brightness make the nebula difficult to detect. Observational reports describe the object as exceptionally faint, with its visibility depending strongly on the observing conditions, optical filters, aperture, and imaging technique. SIMBAD gives the J2000 optical position as approximately right ascension 05h 59m 24.87s and declination +10° 41′ 40.4″. The object lies several degrees north of Betelgeuse in the constellation Orion. It is also located in the general vicinity of the open cluster NGC 2141, although the nebula should not be described as physically associated with that cluster without further evidence. The nebula is particularly prominent in narrow-band observations of low-ionization emission. Observational compilations indicate that its red emission is dominated by [N II] rather than Hα, which helps explain why observations through different filters can produce markedly different appearances.

Central star

The central star of WeDe 1 is WD 0556+106, also identified in modern catalogues with Gaia DR3 3341996555048041856. The original 1983 study measured the central star at approximately B = 17.1 mag and estimated an effective temperature of at least 52,000 K, consistent with a hot stellar remnant capable of ionizing the surrounding nebular gas. The hot central star provides the ionizing radiation responsible for the emission from the surrounding nebular gas. Photometric studies have also examined the central star for possible companions; a faint wide companion was reported, although the authors considered it likely to be an unrelated optical companion rather than a physically bound system.