NGC 6778
| Emission nebula | |
|---|---|
| Planetary nebula | |
 NGC 6778 (center) | |
| Observation data:J2000epoch | |
| Right ascension | 19h18m25.0s[1] |
| Declination | −01° 35′ 47″[1] |
| Distance | 10,300ly(3,150[2]pc) |
| Apparent magnitude(V) | 11.9[3] |
| Apparent diameter | 8.5″[4] |
| Constellation | Aquila |
| Designations | NGC6778 or 6785,[5]HD180871 |
NGC 6778is aplanetary nebula(PN) located about 10,300[1]light yearsaway from the Sun in theequatorialconstellationofAquila.It is positioned 5° to theSSWof the prominent starDelta Aquilae.This nebula was discovered by German astronomerAlbert Marthduring the period 1863–1865. English astronomerJohn Herschelmay have mistakenly catalogued it as NGC 6785, as nothing can be found now at the coordinates he gave for it. In theNew General Catalogueit was described as a "small, elongated, ill-defined disc".[3]
This planetary nebula displays a disrupted morphology, with a roughly S-shaped feature projecting out of an irregular shell, along with linearjet-like forms. The inner part contains a highly distortedellipticalring oriented along an east-west direction.[6]The nebula and ring have anangular sizeof8.5″and they are about 4,400 years old, while the jets are around 1,700 years old.[4]
At the center of the nebula is a closebinary starsystem with anorbital periodof just 3.68 hours, one of the shortest known among the binary central stars that form a planetary nebulae. Their proximity to each other provides strong evidence that they have passed through acommon-envelope(CE) phase earlier in theirevolution.[7]The pair may now consist of a primary star with0.6M☉,ared dwarfsecondary companion having0.3M☉,and asemimajor axisof only 0.005AU(1.1R☉).[6]
The surrounding nebula is inclined about 85° to the line of sight from the Earth. The torus of this nebula is notable for its high expansion velocity, measured at up to 60–70 km/s. It displays collimated outflows, possibly as a result of the CE behavior of the central stars or else a short-livedaccretion disk.The pair of jets are located along aposition angleof 15°,[7]showing fast outflow withradial velocitiesof around 100 km/s.[6]The nebula is notable for the rich amount of filamentary "low-ionizationstructures ", or LIS,[7]resembling the wispy structures ofnovaexplosions.[6]These too may be the result of the CE interaction.[7]
In addition to a higher than normalheliumabundance, the nebula displays unusually strong opticalrecombinationlinesfromheavier elements;one of the highest known among PNe. These may be the result of a very latethermal pulse,or "final flash", following the initial ejection of the stellar envelope that formed the nebula. The pulse would have ejected chemically-enriched material into the old nebula, changing its abundances.[8]
References
[edit]- ^abcPaturel, G.; et al. (December 2003), "HYPERLEDA. I. Identification and designation of galaxies",Astronomy and Astrophysics,412:45–55,Bibcode:2003A&A...412...45P,doi:10.1051/0004-6361:20031411.
- ^Stanghellini, Letizia; et al. (2008), "The Magellanic Cloud Calibration of the Galactic Planetary Nebula Distance Scale",The Astrophysical Journal,689(1): 194–202,arXiv:0807.1129,Bibcode:2008ApJ...689..194S,doi:10.1086/592395,S2CID119257242.
- ^abO'Meara, Stephen James (2011),Deep-Sky Companions: The Secret Deep,vol. 4, Cambridge University Press, p. 375,ISBN9781139500074.
- ^abTocknell, James; et al. (April 2014), "Constraints on common envelope magnetic fields from observations of jets in planetary nebulae",Monthly Notices of the Royal Astronomical Society,439(2): 2014–2024,arXiv:1308.5027,Bibcode:2014MNRAS.439.2014T,doi:10.1093/mnras/stu079.
- ^"NGC 6778".SIMBAD.Centre de données astronomiques de Strasbourg.Retrieved2019-07-08.
- ^abcdGuerrero, M. A.; Miranda, L. F. (March 2012), "NGC 6778: a disrupted planetary nebula around a binary central star",Astronomy & Astrophysics,539:9,arXiv:1201.2042,Bibcode:2012A&A...539A..47G,doi:10.1051/0004-6361/201117923,S2CID54979392,A47.
- ^abcdMiszalski, B.; et al. (July 2011), "Discovery of close binary central stars in the planetary nebulae NGC 6326 and NGC 6778",Astronomy & Astrophysics,531:5,arXiv:1105.5731,Bibcode:2011A&A...531A.158M,doi:10.1051/0004-6361/201117084,S2CID15010950,A158.
- ^Jones, D.; et al. (January 2016), "NGC 6778: strengthening the link between extreme abundance discrepancy factors and central star binarity in planetary nebulae",Monthly Notices of the Royal Astronomical Society,455(3): 3263–3272,arXiv:1510.07516,Bibcode:2016MNRAS.455.3263J,doi:10.1093/mnras/stv2519.
External links
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Media related toNGC 6778at Wikimedia Commons
