NGC 6781

NGC 6781 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.[5] 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]

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]

The bipolar dust shell of this nebula is believed to be barrel-shaped and is being viewed from nearly pole-on.[6] 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.[7] 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. 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. 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. 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. Seligman, Courtney. "NGC Objects: NGC 6750 - 6799". Celestial Atlas. Retrieved 2021-01-07.
  6. 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.
  7. 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.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.