Deneb

Coordinates: Sky map 20h 41m 25.9s, +45° 16′ 49″
Source: Wikipedia, the free encyclopedia.
This article is about the star. For other uses, see Deneb (disambiguation).
Deneb
Location of Deneb
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Pronunciation
 /ˈdɛnɛb/, /ˈdɛnəb/[1]
Right ascension 20h 41m 25.9s[2]
Declination +45° 16′ 49″[2]
Apparent magnitude (V) 1.25[3] (1.21–1.29[4])
Characteristics
Spectral type A2 Ia[5]
U−B color index −0.23[3]
B−V color index +0.09[3]
Variable type Alpha Cygni[4]
Distance
2,615±215 ly
(802±66[7] pc)
Absolute magnitude (MV)−8.38[7]
Details
Rotational velocity
(v sin i)		20±2 km/s
HR 7924, SAO
 49941
Database references
SIMBADdata

Deneb (/ˈdɛnɛb/) is a first-magnitude star in the constellation of Cygnus. Deneb is one of the vertices of the asterism known as the Summer Triangle and the "head" of the Northern Cross. It is the brightest star in Cygnus and the 19th brightest star in the night sky, with an average apparent magnitude of +1.25. A blue-white supergiant, Deneb rivals Rigel as the most luminous first-magnitude star. However, its distance, and hence luminosity, is poorly known; its luminosity is somewhere between 55,000 and 196,000 times that of the Sun. Its Bayer designation is α Cygni, which is Latinised to Alpha Cygni, abbreviated to Alpha Cyg or α Cyg.

Nomenclature

Deneb is the brighest star in the constellation of Cygnus (top)

α Cygni (Latinised to Alpha Cygni) is the star's designation given by Johann Bayer in 1603. The traditional name Deneb is derived from the Arabic word for "tail", from the phrase ذنب الدجاجة Dhanab al-Dajājah, or "tail of the hen".[8] The IAU Working Group on Star Names has recognised the name Deneb for this star, and it is entered in their Catalog of Star Names.[9]

Denebadigege was used in the

Alfonsine Tables,[10] other variants include Deneb Adige, Denebedigege and Arided. This latter name was derived from Al Ridhādh, a name for the constellation. Johann Bayer called it Arrioph, derived from Aridf and Al Ridf, 'the hindmost' or Gallina. German poet and author Philippus Caesius termed it Os rosae, or Rosemund in German, or Uropygium – the parson's nose.[8]
The names Arided and Aridif have fallen out of use.

An older traditional name is Arided /ˈærɪdɛd/, from the Arabic ar-ridf 'the one sitting behind the rider' (or just 'the follower'), perhaps referring to the other major stars of Cygnus, which were called al-fawāris 'the riders'.[11]

Observation

The Summer Triangle

The 19th

northern hemisphere.[13] It never dips below the horizon at or above 45° north latitude, just grazing the northern horizon at its lowest point at such locations as Minneapolis, Montréal and Turin. In the southern hemisphere, Deneb is not visible south of 45° parallel south, so it just barely rises above the horizon in South Africa, southern Australia, and northern New Zealand
during the southern winter.

Deneb is located at the tip of the Northern Cross asterism made up of the brightest stars in Cygnus, the others being Albireo (Beta Cygni), Gamma Cygni, Delta Cygni, and Epsilon Cygni.[13] It also lies at one vertex of the prominent and widely spaced asterism called the Summer Triangle, shared with the first-magnitude stars Vega in the constellation Lyra and Altair in Aquila.[14][15] This outline of stars is the approximate shape of a right triangle, with Deneb located at one of the acute angles.

The

calcium H and K lines showed a stationary core, which indicated the variable velocity was instead being caused by motion of the star's atmosphere. This variation ranged from +6 to −9 km/s around the star's mean radial velocity.[18] Other, similar supergiants were found to have variable velocities, with this star being a typical member.[17]

Pole star

Due to the

Alderamin.[20]

Preceded by
Pole Star
 Succeeded by
Alderamin
 		8700 AD to 11000 AD Delta Cygni

Physical characteristics

Deneb's adopted distance from the Earth is around 802 parsecs (2,620 ly).[7] This is derived by a variety of different methods, including spectral luminosity classes, atmospheric modelling, stellar evolution models, assumed membership of the Cygnus OB7 association, and direct measurement of angular diameter. These methods give different distances, and all have significant margins of error. The original derivation of a parallax using measurements from the astrometric satellite Hipparcos gave an uncertain result of 1.01 ± 0.57 mas[21][22] that was consistent with this distance. However, a more recent reanalysis gives the much larger parallax whose distance is barely half the current accepted value.[2] One 2008 calculation using the Hipparcos data puts the most likely distance at 475 parsecs (1,550 ly), with an uncertainty of around 15%.[23] The controversy over whether the direct Hipparcos measurements can be ignored in favour of a wide range of indirect stellar models and interstellar distance scales is similar to the better known situation with the Pleiades.[2]

Deneb's absolute magnitude is estimated as −8.4, placing it among the visually brightest stars known, with an estimated luminosity of nearly 200,000 L☉. This is towards the upper end of values published over the past few decades, which vary between 55,000 L☉ and 196,000 L☉, while the distance based on the Hipparcos parallax corresponds to closer to 40,000 L☉.[24][25][26]

Deneb is the most luminous first magnitude star, that is, stars with a brighter apparent magnitude than 1.5. Deneb is also the most distant of the 30

largest white 'A' spectral type stars known
.

Deneb is a bluish-white star of

spectrum has served as one of the stable references by which other stars are classified.[5] Its mass is estimated at 19 M☉. Stellar winds causes matter to be lost at an average rate of 8±3×10−7 M☉ per year, 100,000 times the Sun's rate of mass loss or equivalent to about one Earth mass per 500 years.[28]

Evolutionary state

Deneb spent much of its early life as an

Wolf-Rayet stars before exploding in a type Ib or Ic supernova. Identifying whether Deneb is currently evolving towards a red supergiant or is currently evolving bluewards again would place valuable constraints on the classes of stars that explode as red supergiants and those that explode as hotter stars.[29]

Stars evolving red-wards for the first time are most likely fusing hydrogen in a shell around a helium core that has not yet grown hot enough to start fusion to carbon and oxygen. Convection has begun dredging up fusion products but these do not reach the surface. Post-red supergiant stars are expected to show those fusion products at the surface due to stronger convection during the red supergiant phase and due to loss of the obscuring outer layers of the star. Deneb is thought to be increasing its temperature after a period as a red supergiant, although current models do not exactly reproduce the surface elements showing in its spectrum.[29]

Variable star

A visual band light curve for Deneb, adapted from Yüce and Adelman (2019)[30]

Deneb is the prototype of the Alpha Cygni (α Cygni) variable stars,[31][30] whose small irregular amplitudes and rapid pulsations can cause its magnitude to vary anywhere between 1.21 and 1.29.[32] Its variable velocity discovered by Lee in 1910,[16] but it was not formally placed as a unique class of variable stars until the 1985 4th edition of the General Catalogue of Variable Stars.[33] The cause of the pulsations of Alpha Cygni variable stars are not fully understood, but their irregular nature seems to be due to beating of multiple pulsation periods. Analysis of radial velocities determined 16 different harmonic pulsation modes with periods ranging between 6.9 and 100.8 days.[34] A longer period of about 800 days probably also exists.[30]

Possible spectroscopic companion

Deneb has been reported as a possible single line spectroscopic binary with a period of about 850 days, where the spectral lines from the star suggest cyclical radial velocity changes.[34] Later investigations have found no evidence supporting the existence of a companion.[31]

Etymology and cultural significance

Wide-field view of the Summer Triangle and the Milky Way. Deneb is at the far left centre of the picture, at the end of the darker lane within the Milky Way.

Names similar to Deneb have been given to at least seven different stars, most notably Deneb Kaitos, the brightest star in the constellation of Cetus; Deneb Algedi, the brightest star in Capricornus; and Denebola, the second brightest star in Leo. All these stars are referring to the tail of the animals that their respective constellations represent.

In Chinese, 天津 (Tiān Jīn), meaning

Chinese name for Deneb itself is 天津四 (Tiān Jīn sì, English: the Fourth Star of the Celestial Ford).[36]

In the Chinese love story of

Qi Xi, Deneb marks the magpie bridge across the Milky Way, which allows the separated lovers Niu Lang (Altair) and Zhi Nü (Vega
) to be reunited on one special night of the year in late summer. In other versions of the story, Deneb is a fairy who acts as chaperone when the lovers meet.

Namesakes

Crater-class cargo ship named after the star. SS Deneb
was an Italian merchant vessel that bore this name from 1951 until she was scrapped in 1966.

See also

References

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    Bibcode:2009yCat....102025S
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  5. ^
    Bibcode:1993AAS...183.1710G. Archived from the original
    on 2019-06-25. Retrieved 2012-02-04.
  6. S2CID 119231169
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  7. ^
    S2CID 119225384
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  8. ^ a b Allen, Richard Hinckley (1963). Star Names: Their Lore and Meaning (Reprint ed.).
    ISBN 978-0-486-21079-7
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  9. ^ "IAU Catalog of Star Names". University of Rochester. Retrieved 28 July 2016.
  10. ^ Kunitzsch, Paul (1986). "The Star Catalogue Commonly Appended to the Alfonsine Tables".
    S2CID 118597258
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  11. ISBN 978-1-931559-44-7
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  12. ^ James, Andrew (2015-06-17). "The Constellations : Part 3 Culmination Times". Southern Astronomical Delights. Retrieved 2019-04-02.
  13. ^
    Bibcode:1937ASPL....3...23S
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  14. ^ Pasachoff, J. M. (2000). A Field Guide to Stars and Planets (4th ed.).
    ISBN 978-0-395-93431-9
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  15. ^ Upgren, A. R. (1998). Night Has a Thousand Eyes: A Naked-Eye Guide to the Sky, Its Science, and Lore.
    ISBN 978-0-306-45790-6
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    doi:10.1086/141741
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  19. University of Illinois
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  20. ^ Barlow, N. G. (2008). Mars: An introduction to its interior, surface and atmosphere.
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  25. ^ van de Kamp, P. (1953). "The Twenty Brightest Stars".
    doi:10.1086/126523
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  26. ^ Lamers, H. J. G. L. M.; Stalio, R.; Kondo, Y. (1978). "A study of mass loss from the mid-ultraviolet spectrum of α Cygni (A2 Ia), β Orionis (B8 Ia), and η Leonis (A0 Ib)".
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  36. ^ "香港太空館 - 研究資源 - 亮星中英對照表]". Hong Kong Space Museum (in Chinese). Archived from the original on 2008-10-25. Retrieved 2019-01-09.


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