NGC 6781

NGC 6781
Emission nebula
Planetary nebula
NGC 6781 from the La Silla Observatory
Observation data: J2000 epoch
Right ascension19h 18m 28.085s[1]
Declination+06° 32′ 19.29″[1]
Distance1,500 ly   (460[2] pc)
Apparent magnitude (V)11.4[3]
Apparent dimensions (V)1′.9 × 1′.8[3]
ConstellationAquila
Physical characteristics
Radius0.44[2] ly
DesignationsIRAS 19160+0626, NGC 6781[4]
See also: Lists of nebulae

NGC 6781, also known as the Snowglobe Nebula,[5] is a planetary nebula located in the equatorial constellation of Aquila, about 2.5° east-northeast of the 5th magnitude star 19 Aquilae.[3] It was discovered July 30, 1788 by the Anglo-German astronomer William Herschel.[6] The nebula lies at a distance of 1,500 ly from the Sun.[2] It has a visual magnitude of 11.4 and spans an angular size of 1.9 × 1.8 arcminutes.[3]

The bipolar dust shell of this nebula is believed to be barrel-shaped and is being viewed from nearly pole-on.[7] It has an outer angular radius of 61″; equivalent to a physical radius of 0.44 ly (0.135 pc). The total mass of gas ejected as the central star passed through its last asymptotic giant branch (AGB) thermal pulse event is 0.41 M☉, while the estimated dust mass is 1.53 M☉.[2]

The magnitude 16.88 central star of the planetary nebula is a white dwarf with a spectral type of DAO. It has an M-type co-moving companion at a projected separation of under 5,000 AU.[8] The white dwarf progenitor star had an estimated initial mass of ~2.5 M☉. It left the AGB and entered the cooling stage around 9,400 years ago.[2]

  1. ^ a b Cite error: The named reference Kerber_et_al_2003 was invoked but never defined (see the help page).
  2. ^ a b c d e Cite error: The named reference Otsuka_et_al_2017 was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference O'Meara2007 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference simbad was invoked but never defined (see the help page).
  5. ^ Stoyan, Ronald; Schurig, Stephan (2014). interstellarum Deep Sky Atlas. Erlangen: Cambridge University Press; Oculum-Verlag GmbH. ISBN 978-1-107-50338-0. OCLC 920437579.
  6. ^ Cite error: The named reference Seligman was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Phillips_et_al_2011 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference González-Santamaría_et_al_2021 was invoked but never defined (see the help page).