The binary HD 300933/4 is a probableVV Cephei-type star[11] with a compositespectrum similar to that ofV381 Cephei (HR 8164), but with weakeremission lines ofFe II,S II, andNi II[4] (the "II" indicates that theelements are in their singlyionized state inspectroscopic notation[12]). A detailed analysis of the pair was first conducted in 1970, which yielded anabsolute magnitude of −5.3 and −2.5 in theV band for HD 300933 and HD 300934, respectively, albeit this was calculated using a distance smaller than modern estimates, at 2,500 parsecs (8,200 light-years).[4] With an updated value of3100 pc, itsKS band absolute magnitude is gauged at −10.8.[7]
HD 300933 displaysinfrared emissions that imply the existence ofcircumstellar dust at a temperature of 600 K (327 °C; 620 °F). Despite this, the system shows no signs ofultravioletextinction orreddening, meaning that the light path from the B star does not cross thewind from the supergiant component. This is thought to be either due to aninclined orbit or an unfavorable orbital phase when it was observed in 1987.[11]
The star is thought to be among thelargest stars, though its precise size is highly uncertain; a radius of 806R☉ can be calculated from theluminosity andeffective temperature provided by Healy et al. (2023),[8] whereas Messineo et al. (2019) gives a much smaller estimate of 462R☉[9] (though they use a far smaller distance of 1574 or 1585 pc, which is inconsistent with theGaia EDR3parallax of0.3216±0.0315 mas[1]).
^abHøg, E.; et al. (February 2000). "The Tycho-2 Catalogue of the 2.5 Million Brightest Stars".Astronomy and Astrophysics.355 (1):L27 –L30.Bibcode:2000A&A...355L..27H.
^abCutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)".CDS/ADC Collection of Electronic Catalogues.2246: II/246.Bibcode:2003yCat.2246....0C.
