The two components are designated Theta Serpentis A, officially namedAlya/ˈæliə/, the traditional name for the entire system)[12][13] also called Theta1 Serpentis, and B, also called Theta2 Serpentis.
θ Serpentis (Latinised toTheta Serpentis) is the system'sBayer designation;θ1 andθ2 Serpentis those of the brightest two components. The designations of the two constituents asTheta Serpentis AB andC, and those ofAB's components -Theta Serpentis A andB - derive from the convention used by the Washington Multiplicity Catalog (WMC) formultiple star systems, and adopted by theInternational Astronomical Union (IAU).[14]
The system bore the traditional nameAlya, orAlga, from theArabic الية’alyah "fat tail (of a sheep)".[15] In 2016, the IAU organized aWorking Group on Star Names (WGSN)[16] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entiremultiple systems.[17] It approved the nameAlya for the component Theta Serpentis A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[13]
In the catalogue of stars in theCalendarium ofAl Achsasi al Mouakket, this star was designatedDzaneb al Haiyet, which was translated intoLatin asCauda Serpentis, meaning 'the serpent's tail'.[18]
Both Theta1 Serpentis and Theta2 Serpentis areA-type main sequence stars.[4] As of 2019[update], these two stars are 22arcseconds apart on the sky along aposition angle of 106°, values that changed little since the first observations in 1755.[5] At the system's distance, the angular separation give aprojected separation of 900astronomical units, implying an orbital period in the order of 10,000 years.[6] θ1 has anapparent magnitude of +4.62 while the slightly dimmer θ2 has amagnitude of +4.98.[2] Both stars are similar to each other in all respects, havingluminosities of 24[8] and 13 timessolar,[3] masses of 2.0 and 1.8solar masses, radii of about twicesolar and effective temperatures of8,000 and7,600 K, respectively.[7][3]
The magnitude 6.71[22] star HD 175726[23] (Theta Serpentis C) is anoptical companion to the pair. As of 2007[update], it is separated by 421" from A and 405" from B.[5] It is not gravitationally bound to the pair since its distance to Earth is 87light-years, much closer than the AB pair. Itsproper motion is also discrepant with that of Theta Serpentis.[24] It is aG-type main-sequence star[25] with about the same mass and radius as the Sun.[26]
^abDavid, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets".The Astrophysical Journal.804 (2): 146.arXiv:1501.03154.Bibcode:2015ApJ...804..146D.doi:10.1088/0004-637X/804/2/146.
^Davis, George A. (1944). "The pronunciations, derivations, and meanings of a selected list of star names".Popular Astronomy.52: 8–30.Bibcode:1944PA.....52....8D.
^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, 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.
^Houk, N.; Swift, C. (1999). "Michigan catalogue of two-dimensional spectral types for the HD Stars".Michigan Spectral Survey.5.Bibcode:1999MSS...C05....0H.
