NGC 40

NGC 40 (also known as the Bow-Tie Nebula and Caldwell 2) is a planetary nebula discovered by William Herschel on November 25, 1788, and is composed of hot gas around a dying star. The star has ejected its outer layer which has left behind a smaller, hot star with a temperature on the surface of about 50,000 degrees Celsius.[3] Radiation from the star causes the shed outer layer to heat to about 10,000 degrees Celsius,[3] and is about one light-year across.[3] About 30,000 years from now, scientists theorize that NGC 40 will fade away, leaving only a white dwarf star approximately the size of Earth.[3]

For the Bow Tie Nebula in Centaurus, see Boomerang Nebula.
NGC 40
Emission nebula
Planetary nebula
PanSTARRS false-color image of NGC 40, using the red r-band image as blue
Observation data: J2000 epoch
Right ascension00h 13m 01.015s[1]
Declination+72° 31′ 19.085″[1]
Distance~3,500[2] ly   (~1,000[2] pc)
Apparent magnitude (V)10.7,[1] 11.6[2]
Apparent dimensions (V)38″ × 35″[2]
ConstellationCepheus
DesignationsBow-Tie Nebula, Caldwell 2

Morphologically, the shape of NGC 40 resembles a barrel with the long axis pointing towards the north-northeast. There are two additional pairs of lobes around the poles, which correspond to additional ejections from the star.[4]

Currently the central star of NGC 40 has a spectral type of [WC8], indicating a spectrum similar to that of a carbon-rich Wolf–Rayet star.[5]

  • HST
    HST
  • Image of NGC 40 by Amateur Astronomer
    Image of NGC 40 by Amateur Astronomer
  • Optical image from the WIYN telescope telescope
    Optical image from the WIYN telescope telescope

References
  1. "NGC 40". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-12-22.
  2. O'Meara, Stephen James (2002). Deep Sky Companions: The Caldwell Objects. Sky Publishing Corporation. pp. 22–23. ISBN 978-0-933346-97-0.
  3. "Chandra X-Ray Observatory". Retrieved 2007-06-05.
  4. Rodríguez-González, J. B.; Toalá, J. A.; Sabin, L.; Ramos-Larios, G.; Guerrero, M. A.; López, J. A.; Estrada-Dorado, S. (2022). "Adjusting the bow-tie: A morpho-kinematic study of NGC 40". Monthly Notices of the Royal Astronomical Society. 515 (2): 1557–1567. arXiv:2206.13368. doi:10.1093/mnras/stac1761.
  5. González-Santamaría, I.; Manteiga, M.; Manchado, A.; Ulla, A.; Dafonte, C.; López Varela, P. (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.

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