Astronomy:Lambda Andromedae

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Short description: Binary star system in the constellation of Andromeda
Lambda Andromedae
Location of λ Andromedae (circled)
Observation data
Equinox J2000.0]] (ICRS)
Constellation Andromeda
Right ascension  23h 37m 33.84278s[1]
Declination +46° 27′ 29.3447″[1]
Apparent magnitude (V) 3.65 - 4.05[2]
Characteristics
Evolutionary stage subgiant[3]
Spectral type G8 IV[3]
U−B color index +0.688[4]
B−V color index +0.996[4]
Variable type RS CVn[2]
Astrometry
Radial velocity (Rv)+6.8[5] km/s
Proper motion (μ) RA: 159.606(101)[1] mas/yr
Dec.: −421.822(97)[1] mas/yr
Parallax (π)38.5736 ± 0.1179[1] mas
Distance84.6 ± 0.3 ly
(25.92 ± 0.08 pc)
Absolute magnitude (MV)1.91[6]
Orbit[7]
PrimaryA
CompanionB
Period (P)20.520394(41) days
Semi-major axis (a)≥(1.8536±0.0021)×106 km
Eccentricity (e)0.0607±0.0012
Periastron epoch (T)2459696.372±0.056 BJD
Argument of periapsis (ω)
(primary)		336.8±1.0°
Semi-amplitude (K1)
(primary)		6.5815±0.0076 km/s
Details
A
Mass1.47±0.44[7] M☉
Radius7.787±0.053[8] R☉
Luminosity28.8[8] L☉
Surface gravity (log g)2.75±0.25[9] cgs
Temperature4,633[7] K
Metallicity [Fe/H]−0.56[10] dex
Rotation54.41±0.30[7] days
Rotational velocity (v sin i)7.3[11] km/s
B
Mass0.086–0.115[7] M☉
Other designations
Udkadua, λ And, 16 Andromedae, BD+45°4283, FK5 890, GJ 9832, HD 222107, HIP 116584, HR 8961, SAO 53204, PPM 64456, LTT 16964, NLTT 57442[12]
Database references
SIMBADdata

Lambda Andromedae, Latinized from λ Andromedae, also named Udkadua,[13] is a binary star system in the northern constellation of Andromeda. At an estimated distance of approximately 84.6 light-years (25.9 parsecs) from Earth,[1] it has an apparent visual magnitude of around +3.8.[4] This is bright enough to be seen with the naked eye. The system is drifting further away from the Sun with a radial velocity of +6.8 km/s.[5]

Naming

λ Andromedae in optical light

This star represented the heel of the ancient Sumerian constellation Udkadua, "the storm demon with the gaping mouth". The IAU Working Group on Star Names approved the name Udkadua for this star on 8 May 2025 and it is now so entered in the IAU Catalog of Star Names.[13]

In traditional Arabic astronomy, the stars ι Andromedae, κ Andromedae, and λ Andromedae were known as Kaff al-Musalsala, the hand of the chained woman (i.e. Andromeda), and as Ra’s al-Nāqa, the head of the she-camel.[14]

In Chinese, 螣蛇 (Téng Shé), meaning Flying Serpent, refers to an asterism consisting of λ Andromedae, α Lacertae, 4 Lacertae, π2 Cygni, π1 Cygni, HD 206267, ε Cephei, β Lacertae, σ Cassiopeiae, ρ Cassiopeiae, τ Cassiopeiae, AR Cassiopeiae, 9 Lacertae, 3 Andromedae, 7 Andromedae, 8 Andromedae, κ Andromedae, ι Andromedae, and ψ Andromedae. Consequently, the Chinese name for λ Andromedae itself is 螣蛇十九 (Téng Shé shíjiǔ, English: the Nineteenth Star of Flying Serpent).[15]

Properties

A light curve for Lambda Andromedae, plotted from Hipparcos data[16]

Lambda Andromedae is a single-lined spectroscopic binary with an orbital period of 20.52 days.[7] The spectrum of the primary matches a stellar classification of G8 IV, meaning that it is an evolved star that is in the subgiant 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 its outer envelope at an effective temperature of 4,800 K,[9] giving it the characteristic yellow hue of a G-type star.

This is an RS 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 in chromospheric activity. 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 the ROSAT satellite, is 2.95×1030 erg/s.[9] A magnetic field with an average strength of 21 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 with Doppler imaging.[7]

The secondary has a very low mass of about 0.1 M☉. It is most likely an L-type brown dwarf.[7]

Evolution

Many different spectral classes have been published for λ Andromedae, ranging from G6 to K1. Most sources give a luminosity class of III (giant) or IV (subgiant).[18] Analysis of the physical properties of the star, including its temperature, luminosity, magnetic field, and stellar wind, show that it has recently experienced the first dredge-up and has begun to ascend the red giant branch although it still has a hot corona and is classified as a subgiant by some definitions.[9][3]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  2. ↑ 2.0 2.1 Samus, N. N. 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. 
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Ó 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, doi:10.1093/mnras/staa3468, Bibcode: 2021MNRAS.500.3438O. 
  4. ↑ 4.0 4.1 4.2 Jennens, P. A.; Helfer, H. L. (September 1975), "A new photometric metal abundance and luminosity calibration for field G and K giants.", Monthly Notices of the Royal Astronomical Society 172 (3): 667–679, doi:10.1093/mnras/172.3.667, Bibcode: 1975MNRAS.172..667J. 
  5. ↑ 5.0 5.1 Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Carnegie Institute Washington D.C. Publication (Washington: Carnegie Institution of Washington), Bibcode: 1953GCRV..C......0W. 
  6. ↑ 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. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 Adebali, Ö; Strassmeier, K. G.; Ilyin, I. V.; Weber, M.; Gruner, D.; Kővári, Zs (2025-03-01), "First Doppler image and starspot-corrected orbit for λ Andromedae - A multifaceted activity analysis" (in en), Astronomy & Astrophysics 695: A89, doi:10.1051/0004-6361/202453073, ISSN 0004-6361, Bibcode: 2025A&A...695A..89A. 
  8. ↑ 8.0 8.1 8.2 Martinez, Arturo O.; Baron, Fabien R.; Monnier, John D.; Roettenbacher, Rachael M.; Parks, J. Robert (2021), "Dynamical Surface Imaging of λ Andromedae", The Astrophysical Journal 916 (1): 60, doi:10.3847/1538-4357/ac06a5, Bibcode: 2021ApJ...916...60M. 
  9. ↑ 9.0 9.1 9.2 9.3 Drake, Jeremy J. et al. (November 2011), "Close to the dredge: precise X-Ray C and N abundances in λ Andromeda and its precocious red giant branch mixing problem", The Astronomical Journal 142 (5): 144, doi:10.1088/0004-6256/142/5/144, Bibcode: 2011AJ....142..144D. 
  10. ↑ Mallik, Sushma V. (December 1999), "Lithium abundance and mass", Astronomy and Astrophysics 352: 495–507, Bibcode: 1999A&A...352..495M. 
  11. ↑ Massarotti, Alessandro et al. (January 2008), "Rotational and radial velocities for a sample of 761 HIPPARCOS giants and the role of binarity", The Astronomical Journal 135 (1): 209–231, doi:10.1088/0004-6256/135/1/209, Bibcode: 2008AJ....135..209M. 
  12. ↑ "lam And". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=lam+And. 
  13. ↑ 13.0 13.1 "IAU Catalog of Star Names". https://exopla.net/star-names/modern-iau-star-names/. 
  14. ↑ "Kaffalmusalsala (كفّ المسلسة)". IAU Working Group on Star Names. https://xing.fmi.uni-jena.de/mediawiki/index.php/Kaffalmusalsala. 
    "al-Nāqa (الناقة)". IAU Working Group on Star Names. https://xing.fmi.uni-jena.de/mediawiki/index.php/Al-Naqa. 
  15. ↑ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 7 日
  16. ↑ /ftp/cats/more/HIP/cdroms/cats, Strasbourg astronomical Data Center, https://cdsarc.cds.unistra.fr/viz-bin/ftp-index?/ftp/cats/more/HIP/cdroms/cats, retrieved 15 October 2022. 
  17. ↑ 17.0 17.1 Frasca, A. et al. (February 2008), "Spots, plages, and flares on λ Andromedae and II Pegasi", Astronomy and Astrophysics 479 (2): 557–565, doi:10.1051/0004-6361:20077915, Bibcode: 2008A&A...479..557F. 
  18. ↑ 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. 



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