Last modified on 14 August 2018, at 14:45

Sigma Draconis

Sigma Draconis
Observational Data
Designation HD 185144
HIP 96100
Right ascension 19h 32m 21.5899s[1]
Declination +69° 39′ 40.236″[1]
Constellation Draco
Type of object Red dwarf
Magnitude Apparent Mag: +4.68[1]
Absolute Mag: +5.87[2]
Astrometry
Distance from Earth 18.8 ly[3]
Radial velocity 26.78±0.08 km/s[1]
Proper motion RA: 597.482 mas/yr[1]
Dec.: -1,738.313 mas/yr[1]
Parallax 173.77±0.18 mas[1]

Sigma Draconis is a nearby star located in the constellation of Draco. The star is one of the closest to our Sun, at only 18.8 light years away. Even though it is an orange class K star, because of its relative close distance the star is visible to the unaided eye under very dark skies, with an apparent magnitude of 4.68.[1]

Sigma Draconis' traditional name is Alsafi, which is derived from the Arabic word athafi (or Athafiyy), meaning "the cooking tripods". This is in reference to the tripods desert nomads used for cooking in the open-air.[4]

Sigma Draconis is an orange-red dwarf star on the main sequence of spectral class K0 V. The star has some 89 percent of our Sun's mass, and some 79 percent of its diameter, but is only 39 percent as luminous.[5] The star's metallicity is only some 56 to 59 percent that of out Sun, based on the abundance of iron.

So far all searches using radial velocity techniques, conducted by the Lick Planet Search, to locate substellar companions around Sigma Draconis have failed to find any brown dwarf or large gas giant very near to the star. For an Earth-like world to have liquid water on its surface, the orbit would need to be around 0.62 AU, somewhat less than the orbit of Venus. At this time such a world is about impossible to detect.

Currently Sigma Draconis is considered a high priority target for the both the future NASA's Terrestrial Planet Finder and the ESA's Darwin probe when they are launched around 2015. These probes will search for rocky worlds in the habitable zone of Sigma Draconis and other stars.

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Sigma Draconis from the SIMBAD Astronomical Database
  2. From definition of absolute magnitude, using apparent magnitude (+4.68) and distance (18.8 ly) given here.
  3. Calculated from given parallax of 173.77 mas.
  4. Allen, Richard Hinkley (1963). Star Names, Their Lore and Meaning. New York: Dover. ISBN 0-486-21079-0. Avaliable online at: penelope.uchicago.edu
  5. Pasinetti Fracassini, L., Pastori, L., Covino, S. and Pozzi, A. (2001). Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) -Third edition -Comments and statistics. Astronomy and Astrophysics, 367(2), pp.521-524. Bibcode:2001A&A...367..521P