The system consists of a single primary star (designated Mu Draconis A, officially named Alrakis/ælˈreɪkɪs/ from the traditional name of the system),[8][9] a secondary binary pair (Mu Draconis B) and a further single star (C). B's two components are designated Mu Draconis Ba and Bb.
Mu Draconis A and Ba are nearly identical F-type main-sequence stars, with masses of 1.35 M☉ and 1.30 M☉, respectively.[7] Both have the spectral class of F5V, and have similar apparent magnitude, at 5.66 and 5.69, respectively.[3] The secondary, Mu Draconis B, has a drifting radial velocity, and is itself a spectroscopic binary with an orbital period of 2,270 days.[10] The distance between both stars is 2 arcseconds, so a telescope with a diameter of at least 6 centimetres is necessary to see them separate. The smaller component, Mu Draconis Bb, has a mass of 0.2 M☉. Mu Draconis C is a 14th magnitude common-proper-motion companion 13.2" away from the bright pair, with a mass of 0.29 M☉.[7]
Nomenclature
μ Draconis in optical light
μ Draconis (Latinised to Mu Draconis) is the star's Bayer designation. The designations of the three constituents as Mu Draconis A, B and C, and those of B's components - Mu Draconis Ba and Bb - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[11]
It is also known by the name Arrakis (or Errakis), which is derived from the name given to it by Arabian stargazers, الراقص al-rāqiṣ "the trotting (camel)" (lit. "the dancing one").[12][13]
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[15] It approved the name Alrakis for the component Mu Draconis A on February 1, 2017, and it is now so included in the List of IAU-approved Star Names.[9]
^Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN978-1-931559-44-7.
^Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
^Kunitzsch, P.; Smart, T. (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, MA: Sky Pub. p. 35. ISBN978-1-931559-44-7.
