NGC 6781

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

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

The bipolar dust shell of this nebula is believed to be barrel-shaped and is being viewed from nearly pole-on. 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☉.

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. 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.

References

  1. 1 2 Kerber, F.; et al. (September 2003). "Galactic Planetary Nebulae and their central stars. I. An accurate and homogeneous set of coordinates". Astronomy and Astrophysics. 408 (3): 1029–1035. Bibcode:2003A&A...408.1029K. doi:10.1051/0004-6361:20031046.
  2. 1 2 3 4 5 Otsuka, Masaaki; et al. (August 2017). "The Herschel Planetary Nebula Survey (HerPlaNS): A Comprehensive Dusty Photoionization Model of NGC6781". The Astrophysical Journal Supplement Series. 231 (2): 29. arXiv:1707.06565. Bibcode:2017ApJS..231...22O. doi:10.3847/1538-4365/aa8175. PMC 5619666. PMID 28966408. 22.
  3. 1 2 3 4 O'Meara, Steve (2007). Herschel 400 Observing Guide. Cambridge University Press. p. 249. ISBN 9780521858939.
  4. ↑ "NGC 6781". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2007-04-18.
  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. ↑ O'Meara, Stephen James (2011). Deep-Sky Companions: The Secret Deep. Cambridge University Press. ISBN 978-0-521-19876-9.
  7. ↑ Seligman, Courtney. "NGC Objects: NGC 6750 - 6799". Celestial Atlas. Retrieved 2021-01-07.
  8. ↑ Phillips, J. P.; et al. (July 2011). "Optical and mid-infrared observations of the planetary nebula NGC 6781". Monthly Notices of the Royal Astronomical Society. 415 (1): 513–524. arXiv:1106.3706. Bibcode:2011MNRAS.415..513P. doi:10.1111/j.1365-2966.2011.18722.x. S2CID 119269567.
  9. ↑ González-Santamaría, I.; et al. (2021). "Planetary nebulae in Gaia EDR3: Central star identification, properties, and binarity". Astronomy & Astrophysics. 656: A51. arXiv:2109.12114. Bibcode:2021A&A...656A..51G. doi:10.1051/0004-6361/202141916. S2CID 237940344.