NGC 7027

NGC 7027
Emission nebula
Planetary nebula
Observation data: J2000 epoch
Right ascension 21h 7m 1.7s[1]
Declination +42° 14′ 11″[1]
Distance 3,000[2] ly
Apparent magnitude (V) 10[3]
Apparent dimensions (V) 14"
Constellation Cygnus
Physical characteristics
Radius 14,000 AU[2] ly

NGC 7027 is a very young and dense planetary nebula[4] located around 3,000 light-years (920 pc) away in the constellation Cygnus. It was discovered in 1878 by Édouard Stephan, using the 31 inch reflector at Marseille Observatory.[5] It is one of the smallest planetary nebulae, and by far the most extensively studied.[5]

NGC 7027 is one of the visually brightest planetary nebulae.[6] It is about 600 years old.[7]

It is unusually small, measuring only 0.2 by 0.1 light-years whereas the typical size for a planetary nebula is 1 light-year.[8] It has a very complex shape, consisting of an elliptical region of ionized gas[9] within a massive neutral cloud.[10] The inner structure is surrounded by a translucent shroud of gas and dust.[11] The nebula is shaped like a prolate ellipsoidal shell and contains a photodissociation region shaped like a "clover leaf".[9] NGC 7027 is expanding at 17 kilometers per second (11 mi/s).[10] The central regions of NGC 7027 have been found to emit X-rays, indicating very high temperatures.[9] Surrounding the ellipsoidal nebula are a series of faint, blue concentric shells.[12]

It is possible that the central white dwarf of NGC 7027 has an accretion disk that acts as a source of high temperatures.[13] The white dwarf is believed to have a mass approximately 0.7 times the mass of the Sun and is radiating at 7,700 times the Sun's luminosity.[6] NGC 7027 is currently in a short phase of planetary nebula evolution in which molecules in its envelope are being dissociated into their component atoms, and the atoms are being ionized.[14]

The expanding halo of NGC 7027 has a mass of about three times the mass of the Sun, and is about 100 times more massive than the ionized central region. This mass loss in NGC 7027 provided important evidence that stars a few times more massive than the Sun can avoid being destroyed in supernova explosions.[8]

NGC 7027 has a rich and highly ionized spectrum caused by its hot central star.[4] The nebula is rich in carbon, and is a very interesting object for the study of carbon chemistry in dense molecular material exposed to strong ultraviolet radiation.[15] The spectrum of NGC 7027 contains fewer spectral lines from neutral molecules than is usual for planetary nebulae. This is due to the destruction of neutral molecules by intense UV radiation.[16] The nebula contains ions of extremely high ionization potential.[17] NGC 7027 is a promising place to look for HeH+, a molecule which is believed to exist in interstellar space, but which has never been conclusively identified.[15] There is evidence for the presence of nanodiamond in NGC 7027.[18]

It was photographed by the Hubble Space Telescope in 1996. Prior to these observations, NGC 7027 was thought to be a proto-planetary nebula with the central star too cool to ionize any of the gas, but it is now known to be a planetary nebula in the earliest stage of its development.[8] The central star is believed to have been about 3–4 times the mass of the Sun.[4]

In a 6" telescope at around 50x it appears as a relatively bright bluish star. At magnifications around 180x a vaguely ursine shape has led to the epithet of the "Gummy Bear Nebula".[19] It is best viewed with the highest magnification possible.

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See also

References

  1. 1 2 "NASA/IPAC EXTRAGALACTIC DATABASE". Results for NGC 7027. Retrieved 2008-04-02.
  2. 1 2 "Staring into the Winds of Destruction: HST/NICMOS Images of the Planetary Nebula NGC 7027". Retrieved 2008-10-11.
  3. ↑ "NGC 7027". SEDS NGC Database. Retrieved 2008-10-11.
  4. 1 2 3 Salas, J. Bernard; Pottasch, S. R.; Beintema, D. A.; Wesselius, P. R. (2001). "The ISO-SWS spectrum of planetary nebula NGC 7027". Astronomy and Astrophysics. 367 (3): 949–958. Bibcode:2001A&A...367..949B. doi:10.1051/0004-6361:20000435.
  5. 1 2 O'Meara, Stephen James (2007). Hidden Treasures. p. 514. ISBN 0-521-83704-9.
  6. 1 2 Kaler, James B. (2002). The 100 Greatest Stars. New York: Springer-Verlag. p. 133. ISBN 0-387-95436-8.
  7. ↑ Waters, L. B. F. M.; Waelkens, C.; van der Hucht, Karel A. (1998-08-31). ISO's View on Stellar Evolution. p. 490. ISBN 978-0-7923-5152-8.
  8. 1 2 3 O'Meara, Stephen James (2007). Hidden Treasures. p. 516. ISBN 0-521-83704-9.
  9. 1 2 3 Kastner, Joel H.; Vrtilek, Saeqa D.; Soker, Noam (April 2001). "Discovery of Extended X-Ray Emission from the Planetary Nebula NGC 7027 by the Chandra X-Ray Observatory". The Astrophysical Journal. 550 (2): L189–L192. arXiv:astro-ph/0102468Freely accessible. Bibcode:2001ApJ...550L.189K. doi:10.1086/319651.
  10. 1 2 Masson, C. R. (January 1989). "The structure of NGC 7027 and a determination of its distance by measurement of proper motions". The Astrophysical Journal. 336: 294–303. Bibcode:1989ApJ...336..294M. doi:10.1086/167011.
  11. ↑ "NGC 7027". NOAO. Retrieved 2010-03-11.
  12. ↑ "Hubble Telescope Photo Reveals Stellar Death Process". 1996-01-16. Retrieved 2010-03-11.
  13. ↑ Gurzadi︠a︡n, Grigor Aramovich (1997). The physics and dynamics of planetary nebulae. Springer-Verlag. p. 464. ISBN 3-540-60965-2.
  14. ↑ "Hubble Captures the Shrouds of Dying Stars". 1998-03-18. Retrieved 2010-03-11.
  15. 1 2 Liu, X.-W.; Barlow, M. J.; Dalgarno, A.; Tennyson, J.; et al. (October 1997). "An ISO Long Wavelength Spectrometer detection of CH in NGC 7027 and an HeH^+ upper limit". Monthly Notices of the Royal Astronomical Society. 290 (4): L71–L75. Bibcode:1997MNRAS.290L..71L. doi:10.1093/mnras/290.4.l71.
  16. ↑ Kwok, Sun; Sandford, Scott (2008). Organic Matter in Space. United Kingdom: Cambridge University Press. p. 170. ISBN 978-0-521-88982-7.
  17. ↑ Gurzadi︠a︡n, Grigor Aramovich (1997). The physics and dynamics of planetary nebulae. Springer-Verlag. p. 45. ISBN 3-540-60965-2.
  18. ↑ Reddy, Francis (2006-01-17). "Seeing red with nanodiamonds". Astronomy.com. Retrieved 2010-03-11.
  19. ↑
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