Gamma Cygni

From Wikipedia, the free encyclopedia
Jump to: navigation, search
For other uses of "Sadr", see Sadr (disambiguation).
Gamma Cygni
Diagram showing star positions and boundaries of the Cygnus constellation and its surroundings
Cercle rouge 100%.svg

Location of γ Cygni (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Cygnus
Right ascension 20h 22m 13.70184s[1]
Declination +40° 15′ 24.0450″[1]
Apparent magnitude (V) 2.23[2]
Characteristics
Spectral type F8 Iab[3]
U−B color index +0.54[2]
B−V color index +0.67[2]
Variable type Pulsating
Astrometry
Radial velocity (Rv) -7.5[4] km/s
Proper motion (μ) RA: +2.39[1] mas/yr
Dec.: -0.91[1] mas/yr
Parallax (π) 1.78 ± 0.27[1] mas
Distance approx. 1,800 ly
(approx. 560 pc)
Absolute magnitude (MV) -6.12
Details
Mass 12.11 ± 0.71[5] M
Radius 150 ± 80[3] R
Luminosity (bolometric) 33,023[5] L
Surface gravity (log g) 1.02 ± 0.10[6] cgs
Temperature 5790 ± 100[6] K
Rotational velocity (v sin i) 15[7] km/s
Age 1.2 × 107[6] years
Other designations
Sadr, Sadir, Sador, 37 Cyg, HR 7796, BD +39°4159, HD 194093, SAO 49528, FK5 765, HIP 100453.
Database references
SIMBAD data

Gamma Cygni (γ Cyg, γ Cygni) is the Bayer designation for a star in the northern constellation Cygnus, forming the intersection of an asterism of five stars called the Northern Cross. It has the traditional name Sadr (also spelled Sadir or Sador), which name comes from the Arabic word صدر şadr, "chest", the same word which gave rise to the star Schedar (Alpha Cassiopeiae). In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Sadr al Dedjadjet, (صدرألدجاجة-şadr aldajaaja), which was translated into Latin as Pectus Gallinǣ, meaning the hen's chest.[8]

In Chinese, 天津 (Tiān Jīn), meaning Celestial Ford, refers to an asterism consisting of γ Cygni, δ Cygni, 30 Cygni, α Cygni, ν Cygni, τ Cygni, υ Cygni, ζ Cygni and ε Cygni.[9] Consequently, γ Cygni itself is known as 天津一 (Tiān Jīn yī, English: the First Star of Celestial Ford.).[10]

Properties[edit]

With an apparent visual magnitude of 2.23,[2] this is among the brighter stars visible in the night sky. Parallax measurements give a distance estimate of 1,800 light years (560 parsecs), with a 15% margin of error.[1] The stellar classification of this star is F8 Iab, indicating that it has reached the supergiant stage of its stellar evolution. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[11]

IC1318 and neighboring regions. Image by Erik Larsen.

Compared to the Sun this is an enormous star, with 12 times the Sun's mass and about 150 times the Sun's radius.[5] It is emitting over 33,000 times as much energy as the Sun, at an effective temperature of 6,100 K in its outer envelope.[5] This temperature is what gives the star the characteristic yellow-white hue of an F-type star. Massive stars such as this consume their nuclear fuel much more rapidly than the Sun, so the estimated age of this star is only about 12 million years old[6]

The spectrum of this star shows some unusual dynamic features, including variations in radial velocity of up to 2 km/s, occurring on a time scale of 100 days or more. Indeed, on the Hertzsprung–Russell diagram, Gamma Cygni lies close to the instability strip and its spectrum is markedly like that of a Cepheid variable.[3] This star is surrounded by a diffuse nebula called IC1318, or the Gamma Cygni region.

References[edit]

  1. ^ a b c d e f van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Johnson, H. L. et al. (1966), UBVRIJKL photometry of the bright stars, Communications of the Lunar and Planetary Laboratory 4 (99), Bibcode:1966CoLPL...4...99J 
  3. ^ a b c Gray, David F. (November 2010), Photospheric Variations of the Supergiant γ Cyg, The Astronomical Journal 140 (5): 1329–1336, Bibcode:2010AJ....140.1329G, doi:10.1088/0004-6256/140/5/1329 
  4. ^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E 
  5. ^ a b c d Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), Masses and luminosities of O- and B-type stars and red supergiants, Astronomische Nachrichten 331 (4): 349, arXiv:1003.2335, Bibcode:2010AN....331..349H, doi:10.1002/asna.200911355 
  6. ^ a b c d Lyubimkov, Leonid S. et al. (February 2010), Accurate fundamental parameters for A-, F- and G-type Supergiants in the solar neighbourhood, Monthly Notices of the Royal Astronomical Society 402 (2): 1369–1379, arXiv:0911.1335, Bibcode:2010MNRAS.402.1369L, doi:10.1111/j.1365-2966.2009.15979.x 
  7. ^ Bernacca, P. L.; Perinotto, M. (1970). "A catalogue of stellar rotational velocities". Contributi Osservatorio Astronomico di Padova in Asiago 239 (1). Bibcode:1970CoAsi.239....1B. 
  8. ^ Knobel, E. B. (June 1895), Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket, Monthly Notices of the Royal Astronomical Society 55: 429, Bibcode:1895MNRAS..55..429K, doi:10.1093/mnras/55.8.429 
  9. ^ (Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  10. ^ (Chinese) 香港太空館 - 研究資源 - 亮星中英對照表, Hong Kong Space Museum. Accessed on line November 23, 2010.
  11. ^ Garrison, R. F. (December 1993), Anchor Points for the MK System of Spectral Classification, Bulletin of the American Astronomical Society 25: 1319, Bibcode:1993AAS...183.1710G, retrieved 2012-02-04 

External links[edit]