HD 84810, also known asl Carinae (l Car), is astar in the southernconstellation ofCarina. Itsapparent magnitude varies from about 3.4 to 4.1, making it readily visible to the naked eye and one of the brightest members of Carina. Based uponparallax measurements, it is approximately 1,600light-years (490parsecs) fromEarth.[1]
From the characteristics of itsspectrum, l Carinae has astellar classification of G5 Iab/Ib.[3] This indicates the star has reached a stage in itsevolution where it has expanded to become asupergiant with 169 times the radius of the Sun.[9] As this is a massive star with 8.7 times the mass of the Sun,[7] it rapidly burns through its supply of nuclear fuel and has become a supergiant in roughly17-19 million years, after spending15–17 million years as amain sequence star.[11]
l Carinae is classified as aCepheidvariable star and its brightness varies over an amplitude range of 0.725 in magnitude with a long period of 35.560 days. This unusually long period makes it essential for calibrating theperiod-luminosity relation for Cepheid variables; additionally, it is one of the nearest Cepheid variables, making it relatively easy to observe.[7] Theradial velocity of the star likewise varies by 39 km/s during each pulsation cycle.[13] Its radius varies by about 40 R☉ as it pulsates, reaching maximum size as its brightness is decreasing towards minimum.[7]
It has a compact circumstellar envelope that can be discerned usinginterferometry. The envelope has been resolved at an infrared wavelength of 10μm, showing a radius of 10–100 AU at a mean temperature of 100 K. The material for this envelope was supplied by mass ejected from the central star.[11]
The period of l Carinae is calculated to be slowly increasing and it is thought to be crossing theinstability strip for the third time, cooling as it evolves towards ared supergiant after ablue loop.[7]
^abcSamus, 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: B/GCVS.Bibcode:2009yCat....102025S.
^abMadore, B. F. (June 1975), "Photoelectric UBV photometry of Cepheids in the Magellanic Clouds and in the southern Milky Way",Astrophysical Journal Supplement Series,29:219–284,Bibcode:1975ApJS...29..219M,doi:10.1086/190342.
^Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick (eds.), "The Revision of the General Catalogue of Radial Velocities",Determination of Radial Velocities and Their Applications, Proceedings from IAU Symposium No. 30,30, University of Toronto:International Astronomical Union: 57,Bibcode:1967IAUS...30...57E.
^Fouqué, P.; Arriagada, P.; Storm, J.; Barnes, T. G.; Nardetto, N.; Mérand, A.; Kervella, P.; Gieren, W.; Bersier, D.; Benedict, G. F.; McArthur, B. E. (2007). "A new calibration of Galactic Cepheid period-luminosity relations from B to K bands, and a comparison to LMC relations".Astronomy and Astrophysics.476 (1):73–81.arXiv:0709.3255.Bibcode:2007A&A...476...73F.doi:10.1051/0004-6361:20078187.S2CID17687829.
^abLuck, R. E. (September 1979), "The chemical compositions of nine southern supergiant stars",Astrophysical Journal, Part 1,232:797–806,Bibcode:1979ApJ...232..797L,doi:10.1086/157340.
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