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It bore the traditional name Alsafi, derived from the ArabicAth?fi, itself erroneously transcribed from the Arabic plural Ath?fiyy, by which the nomads designated the tripods of their open-air kitchens. It was the name of an association of this star, Tau Draconis and Upsilon Draconis. According to a 1971 NASA memorandum, Ath?fi or Alsafi were the title for three stars: Sigma Draconis as Alsafi, Tau Draconis as Ath?fi I and Upsilon Draconis as Ath?fi II. In 2016, the IAU organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN approved the name Alsafi for Sigma Draconis on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.
The radius of Sigma Draconis has been directly measured using interferometry with the CHARA array, which yields a result of 77.6% of the Sun's radius. It has 85% of the Sun's mass, but the luminosity of this star is only 41% that of the Sun. The projected rotation rate (v sin i) is relatively low at 1.4 km/s. It is considered a slightly metal-poor star, meaning that it has a lower proportion of elements with masses greater than helium when compared to the Sun.
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 (as of 1992). The total variability is among the lowest of all stars that have been measured by the Hipparcos spacecraft.
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.
The unconfirmed Sigma Draconis planetary system
^Kepler's Third Law, assuming a circular orbit gives . The mass of the star (ignoring the comparatively insignificant mass of the planet as the star Sigma Draconis has approximately 25,000 times more mass than the unconfirmed planet) and period of planet's orbit are known from the paper, so the semimajor axis can be calculated using .
^" - ? - ?" [Hong Kong Space Museum - Research Resources - Bright Star Chinese-English Table] (in Chinese). Hong Kong Space Museum. Archived from the original on 2008-10-25. Retrieved 2010.
^Johnson, H. L.; Morgan, W. W. (1953). "Fundamental stellar photometry for standards of spectral type on the revised system of the Yerkes spectral atlas". Astrophysical Journal. 117: 313. Bibcode:1953ApJ...117..313J. doi:10.1086/145697.
^Agnew, Matthew T.; et al. (2019). "Predicting multiple planet stability and habitable zone companions in the TESS era". Monthly Notices of the Royal Astronomical Society. 485 (4): 4703-4725. arXiv:1901.11297. Bibcode:2019MNRAS.485.4703A. doi:10.1093/mnras/stz345. S2CID119028049. -- A random example of Kepler's 3rd law equation rearranged to change the subject to the orbital radius, and it being used in that rearranged state thereafter. See in the paper section 3.1, under the title "Numerical approach".