NGC 2346

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NGC 2346
Observational Data
Designation NGC 2346
V651 Mon
Right ascension 07h 09m 22.5217s[1][2]
Declination -00° 48′ 23.611″[1][2]
Constellation Monoceros
Type of object Planetary nebula
Dimensions 0.910'×0.910'[1][3]
Magnitude Apparent Mag: +11.58[1][4]
Absolute Mag: +2.34[5]
Distance from Earth 2,300 ly[6]
Radial velocity 47.00 km/s[1][7]
Proper motion RA: -2.146 mas/year[1][2]
Dec: -1.219 mas/year[1][2]
Parallax 0.6861±0.0431 mas[1][2]

NGC 2346 (V651 Mon) is a planetary nebula in the constellation of Monoceros.[8] The nebula is unusual for having a very small binary system at its centre that has an orbital period of only 16 days.[6] NGC 2346 was discovered in 1795 by William Herschel.[9] The nebula is sometimes called the "Butterfly nebula," though this more commonly refers to NGC 6302.

The nebula is thought to lie about 2,300 light years away.[6] It has an apparent diameter of 0.910 arcminutes which corresponds to a physical size of roughly one third of a light year across. The nebula is a bipolar planetary nebula meaning it has two large protrusions or lobes pointing in opposite directions. large clumps of material as well as a toriodal structure have been observed in the nebula.[10]

Binary star system

The stars at the nebula's core orbit each other every 15.99 days with a separation estimated between 0.159-0.167 AU or 34.2-35.7 solar radii.[11] The binary system has a combined apparent magnitude of +11.[9] The first star in the system is a A5V subdwarf star with a mass 1.8 times that of the Sun and a luminosity 18 times larger.[10] It has a surface temperature of 8,000 kelvin, making it slightly hotter than the Sun's surface. The other star is thought to be a white dwarf star with a surface temperature in excess of 100,000 kelvin.

The two stars form a variable star, thought to be caused by dust surrounding the stars' occasionally dimming their light.[9] Early photographic plates of the stars suggest their light was steady from 1899 until 1981 when it suddenly dropped, reducing the apparent magnitude of the two stars to +15. It then regularly varied between +15 and +11 with its usual period of 16 days. It is thought to be because the brighter of the two stars would periodically be hidden by a cloud in front of the nebula, estimated at perhaps 12 to 30 million miles across.[9] This lasted until 1985 when the star's brightness recovered. In 1996 the star experienced another such dimming though to be caused for similar reasons that lasted for around 400 days. Yet another such dimming occurred in 2004.


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 NGC 2346. Simbad Astronomical Database. Retrieved on 2019-08-25.
  2. 2.0 2.1 2.2 2.3 2.4 Gaia Colaboration. VizieR Online Data Catalog: Gaia DR2 (Gaia Collaboration, 2018). (2018). VizieR Online Data Catalog. bibcode: 2018yCat.1345....0G
  3. Stanghellini, L.; Shaw, R. A.; Villaver, E. (2008). "The Magellanic Cloud Calibration of the Galactic Planetary Nebula Distance Scale". The Astrophysical Journal 689 (1): 194-202. doi:10.1086/592395. Bibcode2008ApJ...689..194S.  arXiv:0807.1129
  4. Høg, E.; Fabricius, C.; Makarov, V. V. et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics 355: L27-L30. Bibcode2000A&A...355L..27H. 
  5. From direct calculation using distance of 2,300 ly and apparent magnitude of +11.58.
  6. 6.0 6.1 6.2 NGC 2346. (1999-10-07). Retrieved on 2019-08-25.
  7. Barbier-Brossat, M.; Petit, M.; Figon, P. (1994). "Third bibliographic catalogue of stellar radial velocities". Astronomy and Astrophysics Supplementary Series 108: 603-609. Bibcode1994A&AS..108..603B. 
  8. NGC 2346: A Butterfly-Shaped Planetary Nebula. (2001-10-28). Retrieved on 2019-08-25.
  9. 9.0 9.1 9.2 9.3 Bob King (2016-03-02). NGC 2346: A Cosmic Butterfly Plays Peekaboo. Retrieved on 2019-08-25.
  10. 10.0 10.1 Manchado, L.; Stanghellini, E.; Villaver, E. et al. (2015). "High resolution imaging of NGC 2346 with GSAOI/GeMS: disentangling the planetary nebula molecular structure to understand its origin and evolution". The Astrophysical Journal 808 (2). doi:10.1088/0004-637X/808/2/115. Bibcode2015ApJ...808..115M.  arXiv:1506.03712
  11. Kato, T.; Nogami, D.; Baba, H. (2001). "The 1996-1997 Fading of V651 Mon, the Binary Central Star of the Planetary Nebula NGC 2346". Publications of the Astronomical Society of Japan 53 (5): 901–904. doi:10.1093/pasj/53.5.901.  arXiv:astro-ph/0112304