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NML Cygni
CygOB2 med.jpg
H-Alpha light image of Cygnus OB2, the stellar association in which NML Cygni is located
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 20h 46m 25.6s
Declination +40° 06′ 59.4″
Apparent magnitude (V) 16.60
Spectral type M6I[1]
B−V color index 2.0
Variable type Semiregular
Proper motion (μ) RA: -1.55[2] mas/yr
Dec.: -4.59[2] mas/yr
Parallax (π) 0.620[2] ± 0.047[2] mas
Distance 1.61k[2] pc
Mass 25–40[2] M
Radius 1,650[2] R
Luminosity 270,000[2] L
Other designations
V* V1489 Cyg, RAFGL 2650, IRC +40448
Database references

NML Cygni or V1489 Cygni is a red hypergiant star[2] and one of the largest stars currently known with a radius about 1,650 times the Sun's,[3] equal to 7.67 astronomical units. Its distance from Earth is estimated to be around 1.6 kpc, or about 5,300 light-years.[3]

NML Cygni is a part of the Cygnus OB2 association, one of the closest massive associations to the Sun spanning nearly 2° on the sky, or ∼30 pc in radius at the distance of 1.74 ± 0.2 kpc.[4]


The diameter of NML Cygni, at 1,650 times that of the sun, is about 2,295,000,000 kilometres (1.426×109 mi). If placed at the center of the Solar System, its surface would extend beyond the orbit of Jupiter, filling over half the gap between Jupiter and Saturn's orbit. It contains a volume approximately 4.5 billion times that of the Sun. The bolometric luminosity (Lbol) for this star is near 3 × 105 L. Its bolometric magnitude (Mbol) is around −9.0. It is one of the most luminous cool hypergiant stars.[4] It is also a semiregular variable star with a period of around 940 days.[4]

This star is evolved and a number of heavy elements and molecules have been detected in its atmosphere, particularly oxygen, hydroxyl, and water. It has a dusty environment surrounding it,[2][4] and it exhibits a bean-shaped asymmetric nebula that is coincident with the distribution of its H2O|H2O vapor masers.[5]

NML Cygni has an estimated mass loss rate of 2×10−4 Mper year,[6][7] one of the highest known for any star. The annual parallax of this star is measured to be around 0.62 milli-arc-seconds.[2] From the observations, it is estimated that this star has two discrete optically thick envelopes of dust and molecules. The optical depth of the inner shell is found to be 1.9, while that of the outer one is 0.33.[8] These dust envelopes are formed due to the strong post-main sequence wind velocity, 23 km/s, and the high mass loss.

Because of its position on the outskirts of the massive Cygnus OB2 association, the detectable effects of NML Cygni's radiation on the surrounding dust and gas are limited to the region away from the central hot stars of the association.[4]

Observational history[edit]

NML Cygni was discovered in 1965, by Neugebauer, Martz, and Leighton which described two extremely red luminous stars, their colour being described as consistent with a black body temperature of 1,000K.[9] The name NML comes from the names of these three discoverers.[10] The second star was briefly referred to as NML Tauri[11] but is now known as IK Tauri,[12] an M9 Mira variable. NML Cygni has since also been given the designation V1489 Cygni on account of the small semi-regular brightness variations,[13] but is still most commonly referred to as NML Cygni.

Its composition began to be revealed with the discovery of OH masers (1612 MHz) in 1968 (Wilson and Barrett).[14] The presence of molecules like H2O, SiO, CO, HCN, CS, SO, SO2, and H2S was also revealed in the later years.[6]

See also[edit]


  1. ^ Monnier, J. D.; Millan‐Gabet, R.; Tuthill, P. G.; Traub, W. A.; Carleton, N. P.; Coude Du Foresto, V.; Danchi, W. C.; Lacasse, M. G.; Morel, S.; Perrin, G.; Porro, I. L.; Schloerb, F. P.; Townes, C. H. (2004). "High‐Resolution Imaging of Dust Shells by Using Keck Aperture Masking and the IOTA Interferometer". The Astrophysical Journal 605: 436. arXiv:astro-ph/0401363. Bibcode:2004ApJ...605..436M. doi:10.1086/382218.  edit
  2. ^ a b c d e f g h i j k Zhang, B.; Reid, M. J.; Menten, K. M.; Zheng, X. W.; Brunthaler, A. (2012). "The distance and size of the red hypergiant NML Cygni from VLBA and VLA astrometry". Astronomy & Astrophysics 544: A42. arXiv:1207.1850. Bibcode:2012A&A...544A..42Z. doi:10.1051/0004-6361/201219587.  edit
  3. ^ a b Michael Thomas Schuster (2007). Investigating the Circumstellar Environments of the Cool Hypergiants. ProQuest. p. 57. ISBN 978-0-549-32782-0. Retrieved 27 August 2012. 
  4. ^ a b c d e Schuster, M. T.; Marengo, M.; Hora, J. L.; Fazio, G. G.; Humphreys, R. M.; Gehrz, R. D.; Hinz, P. M.; Kenworthy, M. A.; Hoffmann, W. F. (2009). "Imaging the Cool Hypergiant NML Cygni's Dusty Circumstellar Envelope with Adaptive Optics". The Astrophysical Journal 699 (2): 1423. arXiv:0904.4690. Bibcode:2009ApJ...699.1423S. doi:10.1088/0004-637X/699/2/1423.  edit
  5. ^ Schuster, M. T.; Humphreys, R. M.; Marengo, M. (2006). "The Circumstellar Environments of NML Cygni and the Cool Hypergiants". The Astronomical Journal 131: 603. arXiv:astro-ph/0510010. Bibcode:2006AJ....131..603S. doi:10.1086/498395.  edit
  6. ^ a b Kevin Marvel (19 December 1996). "NML Cygni". The Circumstellar Environment of Evolved Stars As Revealed by Studies of Circumstellar Water Masers. Universal-Publishers. pp. 182–212. ISBN 978-1-58112-061-5. Retrieved 23 August 2012. 
  7. ^ "Combined Array for Research in Millimeter-wave Astronomy". Retrieved August 27, 2012. 
  8. ^ W. C. DanchiI, W. H. Green, D. D. S. Hale, K. McEleroy, J. D. Monnier, P. G. Tuthill, C. H. Townes (July 2001). "Proper Motions of Dust Shells Surrounding NML Cygni". The Astrophysical Journal 555: 405. doi:10.1086/322237. 
  9. ^ Bibcode1965ApJ...142..399N
  10. ^ J. B. Hearnshaw (2 May 1996). "New infrared sources and their interpretation". The Measurement of Starlight: Two Centuries of Astronomical Photometry. Cambridge University Press. p. 278. ISBN 978-0-521-40393-1. Retrieved 23 August 2012. 
  11. ^ Pesch, P. (1967). "Objective-Prism Spectra of Some Very Red Stars". The Astrophysical Journal 147: 381. doi:10.1086/149015.  edit
  12. ^ Bibcode1968IBVS..311....1K
  13. ^ Bibcode1975IBVS.1068....1K
  14. ^ Bibcode1987MNRAS.225..491C

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/NML_Cygni — Please support Wikipedia.
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Tue, 01 Apr 2014 17:19:03 -0700

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