Astronomy:NGC 6781
| Emission nebula | |
|---|---|
| Planetary nebula | |
 NGC 6781 from the La Silla Observatory | |
| Observation data: J2000 epoch | |
| Right ascension | 19h 18m 28.085s[1] |
| Declination | +06° 32′ 19.29″[1] |
| Distance | 1,500 ly (460[2] pc) |
| Apparent magnitude (V) | 11.4[3] |
| Apparent dimensions (V) | 1′.9 × 1′.8[3] |
| Constellation | Aquila |
| Physical characteristics | |
| Radius | 0.44[2] ly |
| Designations | IRAS 19160+0626, NGC 6781[4] |
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 astronomical unit|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]
References
- ↑ 1.0 1.1 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. doi:10.1051/0004-6361:20031046. Bibcode: 2003A&A...408.1029K.
- ↑ 2.0 2.1 2.2 2.3 2.4 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. doi:10.3847/1538-4365/aa8175. 22. PMID 28966408. Bibcode: 2017ApJS..231...22O.
- ↑ 3.0 3.1 3.2 3.3 O'Meara, Steve (2007). Herschel 400 Observing Guide. Cambridge University Press. p. 249. ISBN 9780521858939. https://books.google.com/books?id=Nyh9fAC_tpIC&pg=PA249.
- ↑ "NGC 6781". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+6781.
- ↑ Stoyan, Ronald; Schurig, Stephan (2014). interstellarum Deep Sky Atlas. Erlangen: Cambridge University Press; Oculum-Verlag GmbH. ISBN 978-1-107-50338-0. OCLC 920437579. http://www.deep-sky-atlas.com/.
- ↑ Seligman, Courtney. "NGC Objects: NGC 6750 - 6799". Celestial Atlas. https://cseligman.com/text/atlas/ngc67a.htm.
- ↑ 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. doi:10.1111/j.1365-2966.2011.18722.x. Bibcode: 2011MNRAS.415..513P.
- ↑ González-Santamaría, I. et al. (2021). "Planetary nebulae in Gaia EDR3: Central star identification, properties, and binarity". Astronomy & Astrophysics 656: A51. doi:10.1051/0004-6361/202141916. Bibcode: 2021A&A...656A..51G.
External links
- NGC 6781 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
Coordinates: 
19h 18m 28s, +06° 32′ 19.3″
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