NGC 40 explained

NGC 40
Type:Planetary
Epoch:J2000
Ra:[1]
Dist Pc:1,619[2]
Appmag V:11.6[3]
Size V:38 × 35
Constellation:Cepheus
Names:Bow-Tie Nebula, Caldwell 2, PN G120.0+09.8

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 small, hot star.[4] Radiation from the star causes the shed outer layer to heat to about 10,000 degrees Celsius and become visible as a planetary nebula. The nebula is about one light-year across. 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.

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.[5]

The central star of NGC 40 has a Henry Draper Catalogue designation of HD 826.[6] It has a spectral type of [WC8], indicating a spectrum similar to that of a carbon-rich Wolf–Rayet star.[7] The central star has a bolometric luminosity of about and radius of . The star appears to have an effective temperature of about, but the temperature of the source ionizing the nebula is only about . One proposed explanation to this contradiction is that the star was previously cooler, but has experienced a late thermal pulse which re-ignited fusion and caused its temperature to increase.[6]

External links

Notes and References

  1. NGC 40 . 2006-12-22.
  2. 2021AJ....161..147B . Estimating Distances from Parallaxes. V. Geometric and Photogeometric Distances to 1.47 Billion Stars in Gaia Early Data Release 3 . Bailer-Jones . C. A. L. . Rybizki . J. . Fouesneau . M. . Demleitner . M. . Andrae . R. . The Astronomical Journal . 2021 . 161 . 3 . 147 . 10.3847/1538-3881/abd806 . 2012.05220 . 228063812 . free .
  3. Book: O'Meara , Stephen James . Deep Sky Companions: The Caldwell Objects . Sky Publishing Corporation . 2002 . 22–23 . 978-0-933346-97-0 .
  4. Web site: Chandra X-Ray Observatory. 2007-06-05.
  5. 10.1093/mnras/stac1761. Adjusting the bow-tie: A morpho-kinematic study of NGC 40 . 2022 . Rodríguez-González . J. B. . Toalá . J. A. . Sabin . L. . Ramos-Larios . G. . Guerrero . M. A. . López . J. A. . Estrada-Dorado . S. . Monthly Notices of the Royal Astronomical Society . 515 . 2 . 1557–1567 . free . 2206.13368 .
  6. 2019MNRAS.485.3360T . Hidden IR structures in NGC 40: Signpost of an ancient born-again event . Toalá . J. A. . Ramos-Larios . G. . Guerrero . M. A. . Todt . H. . Monthly Notices of the Royal Astronomical Society . 2019 . 485 . 3 . 3360 . 10.1093/mnras/stz624 . free . 1902.11219 .
  7. 10.1051/0004-6361/202141916. Planetary nebulae in Gaia EDR3: Central star identification, properties, and binarity. 2021. González-Santamaría. I.. Manteiga. M.. Manchado. A.. Ulla. A.. Dafonte. C.. López Varela. P.. Astronomy & Astrophysics. 656. A51. 2109.12114. 2021A&A...656A..51G. 237940344.

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