V399 Carinae has long been suspected to be variable.[18] A 1981 study of yellow supergiants fit observations to a Cepheid-like light curve with a period of 58.8 days, although the luminosity and spectral type do not place the star near the Cepheid instability strip.[15] It was listed in the General Catalogue of Variable Stars as a possible δ Cep variable.[19] Further observations refined the period to 47.25 days.[6] The Hipparcos catalogue classified V399 Car as a semiregular variable with a period of 88 days and a mean amplitude of only 0.04 magnitudes.[20] An automated classification from Hipparos photometry suggested it is an α Cygni variable.[21] The observed brightness varies from magnitude +4.63 to +4.72.[2]
V399 Carinae lies amongst the stars of the open cluster IC 2581, by far the brightest member of the cluster. It is about 7,500 light years from Earth assuming it is a member of IC 2581, which is given a 62.9% probability.[22] Its angular diameter has been estimated at 0.954±0.09 milliarcseconds,[23] which, at the estimated distance of 2009 parsecs,[1] gives it a radius 206 times the solar radius.[8]
^ abcWatson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25. 25: 47. Bibcode:2006SASS...25...47W.
^ abSchild, R. E.; Garrison, R. F.; Hiltner, W. A. (1983). "UBV photometry for southern OB stars". Astrophysical Journal Supplement Series. 51: 321. Bibcode:1983ApJS...51..321S. doi:10.1086/190852.
^ abcBerdnikov, L. N.; Turner, D. G. (1997). "Photoelectric VIc and New Elements for V399 Carinae = HR 4110". Information Bulletin on Variable Stars. 4456: 1. Bibcode:1997IBVS.4456....1B.
^Rest, A.; Prieto, J. L.; Walborn, N. R.; Smith, N.; Bianco, F. B.; Chornock, R.; Welch, D. L.; Howell, D. A.; Huber, M. E.; Foley, R. J.; Fong, W.; Sinnott, B.; Bond, H. E.; Smith, R. C.; Toledo, I.; Minniti, D.; Mandel, K. (2012). "Light echoes reveal an unexpectedly cool η Carinae during its nineteenth-century Great Eruption". Nature. 482 (7385): 375–8. arXiv:1112.2210. Bibcode:2012Natur.482..375R. doi:10.1038/nature10775. PMID22337057. S2CID205227548.
^Luck, R. Earle (1994). "Open cluster chemical composition. 1: Later type stars in eight clusters". Astrophysical Journal Supplement Series. 91: 309. Bibcode:1994ApJS...91..309L. doi:10.1086/191940.
^Kostjuk, N. D. (2004). "VizieR Online Data Catalog: HD-DM-GC-HR-HIP-Bayer-Flamsteed Cross Index (Kostjuk, 2002)". VizieR On-line Data Catalog: IV/27A. Originally Published in: Institute of Astronomy of Russian Academy of Sciences (2002). 4027. Bibcode:2004yCat.4027....0K.
^Kholopov, P. N.; Samus, N. N.; Kazarovets, E. V.; Perova, N. B. (1985). "The 67th Name-List of Variable Stars". Information Bulletin on Variable Stars. 2681: 1. Bibcode:1985IBVS.2681....1K.
^Perryman, M. A. C.; Lindegren, L.; Kovalevsky, J.; Hoeg, E.; Bastian, U.; Bernacca, P. L.; Crézé, M.; Donati, F.; Grenon, M.; Grewing, M.; Van Leeuwen, F.; Van Der Marel, H.; Mignard, F.; Murray, C. A.; Le Poole, R. S.; Schrijver, H.; Turon, C.; Arenou, F.; Froeschlé, M.; Petersen, C. S. (1997). "The HIPPARCOS Catalogue". Astronomy and Astrophysics. 323: L49. Bibcode:1997A&A...323L..49P.