This star represented the heel of the ancientSumerian constellation Udkadua, "the storm demon with the gaping mouth". TheIAU Working Group on Star Names approved the name Udkadua for the primary component of the system. Lambda Andromedae A on 8 May 2025 and it is now so entered in the IAU Catalog of Star Names.[13]
In traditional Arabic astronomy, the starsι Andromedae,κ Andromedae, and λ Andromedae were known asKaff al-Musalsala, the hand of the chained woman (i.e. Andromeda), and asRa’s al-Nāqa, the head of the she-camel.[14]
Lambda Andromedae is a single-linedspectroscopic binary with an orbital period of 20.52 days.[7] Thespectrum of the primary matches astellar classification of G8 IV, meaning that it is anevolved star that is in thesubgiant stage.[3] The mass of this star is about 50% larger than that of the Sun,[7] but it has expanded to around seven times the Sun's radius. It is radiating over 28[8] times the luminosity of the Sun from itsouter envelope at aneffective temperature of 4,800 K,[9] giving it the characteristic yellow hue of a G-type star.
This is anRS Canum Venaticorum variable and its brightness varies by 0.225 magnitudes, reaching a maximum of 3.70, with a period of 53.952 days.[17] Such variability is theorized to occur because of tidal friction, which results inchromosphericactivity. However, the orbit of this system is nearly circular, so the cause of this system's variability remains uncertain.[17] The X-ray luminosity of this star, as measured by theROSAT satellite, is2.95×1030 erg/s.[9] Amagnetic field with an average strength of21 G has been detected on this star, which is stronger than the field on the Sun.[3]Starspots on the star's surface have been resolved withDoppler imaging.[7]
The secondary has a very low mass of about 0.1 M☉. It is most likely anL-typebrown dwarf.[7]
Many different spectral classes have been published for λ Andromedae, ranging from G6 to K1. Most sources give aluminosity class ofIII (giant) orIV (subgiant).[18] Analysis of the physical properties of the star, including its temperature, luminosity,magnetic field, andstellar wind, show that it has recently experienced thefirst dredge-up and has begun to ascend thered giant branch although it still has a hotcorona and is classified as a subgiant by some definitions.[9][3]
^abSamus, N. N.; Durlevich, O. V.; et al. (2009), "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)",VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S,1,Bibcode:2009yCat....102025S.
^abcdeÓ Fionnagáin, D.; Vidotto, A. A.; Petit, P.; Neiner, C.; Manchester IV, W.; Folsom, C. P.; Hallinan, G. (January 2021), "λ And: a post-main-sequence wind from a solar-mass star",Monthly Notices of the Royal Astronomical Society,500 (3):3438–3453,arXiv:2011.02406,Bibcode:2021MNRAS.500.3438O,doi:10.1093/mnras/staa3468.
^Elgarøy, Øystein; Engvold, Oddbjørn; Lund, Niels (March 1999), "The Wilson-Bappu effect of the MgII K line - dependence on stellar temperature, activity and metallicity",Astronomy and Astrophysics,343:222–228,Bibcode:1999A&A...343..222E.
^Skiff, B. A. (2014), "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009–2016)",VizieR On-line Data Catalog,Bibcode:2014yCat....1.2023S.
