Sigma Draconis

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Sigma Draconis
Observation data
Epoch J2000      Equinox J2000
Constellation Draco
Right ascension 19h 32m 21.59026s[1]
Declination +69° 39′ 40.2354″[1]
Apparent magnitude (V) 4.674[2]
Characteristics
Spectral type G9 V[3][4]
U−B color index +0.386[2]
B−V color index +0.791[2]
Variable type None
Astrometry
Radial velocity (Rv) 26.7[5] km/s
Proper motion (μ) RA: 598.07[1] mas/yr
Dec.: −1738.40[1] mas/yr
Parallax (π) 173.77 ± 0.18[1] mas
Distance 18.77 ± 0.02 ly
(5.755 ± 0.006 pc)
Absolute magnitude (MV) 5.87
Details
Mass 0.87[6] M☉
Radius 0.778 ± 0.008[7] R☉
Luminosity 0.428 ± 0.013[7] L☉
Surface gravity (log g) 4.60[6] cgs
Temperature 5,299 ± 32[7] K
Metallicity [Fe/H] −0.20[7] dex
Rotational velocity (v sin i) 1.4[8] km/s
Age 4.7[9] Gyr
Other designations
σ Draconis, 61 Draconis, HD 185144, HR 7462, BD+69°1053, GCTP 4607.00, GJ 764, LHS 477, and HIP 96100.[5]
Database references
SIMBAD data
ARICNS data

Sigma Draconis (σ Dra, σ Draconis) is a 4.7-magnitude star located at a distance of 18.8 light-years in the constellation Draco. Its traditional name is Alsafi.[10]

Name

Sigma Draconis, the Bayer designation for this star, was established in 1603 as part of the Uranometria, a star catalogue produced by German celestial cartographer Johann Bayer. The proper name Alsafi was derived from Arabic Athāfi, erroneously transcribed from the Arabic plural Athāfiyy, by which the nomads designated the tripods of their open-air kitchens. It was the name of an association of this star, τ Dra and υ Dra.[10] According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Athāfi or Alsafi were the title for three stars: σ Dra as Alsafi, τ Dra as Athāfi I and υ Dra as Athāfi II.[11]

In Chinese, 天廚 (Tiān Chú), meaning Celestial Kitchen, refers to an asterism consisting of σ Draconis, δ Draconis, ε Draconis, ρ Draconis, 64 Draconis and π Draconis.[12] Consequently, σ Draconis itself is known as 天廚二 (Tiān Chú èr, English: the Second Star of Celestial Kitchen.)[13]

Properties

The star is a main sequence dwarf of spectral type K0 V, which has long served as a K0 V spectral standard star.[14][15][16] Its classification as K0 V defines one of the rare anchor points of the Morgan–Keenan system[17] that have remained unchanged since the original 1943 MKK Atlas. The radius has been directly measured using interferometry with the CHARA Array, which yields a result of 77.8% of the Sun's radius.[7] It has 87% of the Sun's mass, but the luminosity of this star is only 43% that of the Sun.[6][7] The projected rotation rate (v sin i) is relatively low at 1.4 km/s.[8] It is considered a slightly metal-poor star, meaning that it has a lower proportion of isotopes with masses more than helium when compared to the Sun.[18]

The temperature, luminosity and surface activity appear to vary slightly in a manner very similar to the sunspot cycle, although the full length of the cycle has not yet been determined.[19] The total variability is among the lowest of all stars that have been measured by the Hipparcos spacecraft.[18]

The star made its perihelion passage about 46,725 years ago, when it came within 16.55 ly (5.075 pc).[20] The components of Sigma Draconis's space velocity are U=+36, V=+40 and W=-10 km/s. This gives the star an unusually large orbital eccentricity about the Milky Way galaxy of 0.30 (compared to 0.06 for the Sun.) The mean galactocentric distance for the orbit is 10.3 kiloparsecs (about 34,000 light-years).[18]

As of 2013, no Jupiter-size or larger companion had been detected about the star and there was no indication of excess infrared radiation that would be evidence of circumstellar matter (such as a debris disk).[8][21]

Planet search

Between 2004 and 2013, extensive radial velocity measurements were gathered on Sigma Draconis using the High Resolution Echelle Spectrometer on the Keck Observatory. The Keck/HIRES data indicated a possible period of about 300 days and a likely alias period of 2800 days. Adding data taken with the Automated Planet Finder at the Lick Observatory strengthened and narrowed the 300-day period while reducing the significance of the 2800-day period. The combined analysis suggests there may be a Uranus-mass planet on a 308-day orbit, though the authors do not yet consider the discovery to be publishable as they have not yet attempted to rule out other, non-planetary explanations for the velocity variations.[22]

The unconfirmed Sigma Draconis planetary system[22]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b (unconfirmed) ≳12 M⊕ 0.814[nb 1] 308 ~0 — —

See also

Notes

  1. ↑ Kepler's Third Law, assuming a circular orbit - \begin{smallmatrix}\frac{4 \pi^2}{T^2} = \frac{G M}{R^3}\end{smallmatrix} Mass and the Period are known from paper[22] so equation can be written with semimajor axis as the subject - \begin{smallmatrix}R = \sqrt[3]{\frac{GMT^2}{4\pi^2}}\end{smallmatrix}.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 2.2 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ 5.0 5.1 Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ 6.0 6.1 6.2 Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 8.0 8.1 8.2 Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ 10.0 10.1 Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ (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.
  13. ↑ (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.
  14. ↑ Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas H.L. Johnson & W.W. Morgan, 1953, Astrophysical Journal, 117, 313
  15. ↑ Spectral Classification W.W. Morgan & P.C. Keenan, 1973, Annual Review of Astronomy and Astrophysics, 11, 29
  16. ↑ The Perkins Catalog of Revised MK Types for the Cooler Stars, P.C. Keenan & R.C McNeil, "Astrophysical Journal Supplement Series" 71 (October 1989), pp. 245–266.
  17. ↑ MK ANCHOR POINTS, Robert F. Garrison
  18. ↑ 18.0 18.1 18.2 Lua error in package.lua at line 80: module 'strict' not found.
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ 22.0 22.1 22.2 Lua error in package.lua at line 80: module 'strict' not found.

External links

  • Lua error in package.lua at line 80: module 'strict' not found.
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