The binary HD 300933/4 is a probable VV Cephei-type star[11] with a composite spectrum similar to that of V381 Cephei (HR 8164), but with weaker emission lines of Fe II, S II, and Ni II[4] (the "II" indicates that the elements are in their singly ionized state in spectroscopic notation[12]). A detailed analysis of the pair was first conducted in 1970, which yielded an absolute magnitude of −5.3 and −2.5 in the V 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 of 3100 pc, its KS band absolute magnitude is gauged at −10.8.[7]
HD 300933 displays infrared emissions that imply the existence of circumstellar dust at a temperature of 600 K (327 °C; 620 °F). Despite this, the system shows no signs of ultravioletextinction or reddening, meaning that the light path from the B star does not cross the wind from the supergiant component. This is thought to be either due to an inclined orbit or an unfavorable orbital phase when it was observed in 1987.[11]
The star is thought to be among the largest stars, though its precise size is highly uncertain; a radius of 806 R☉ can be calculated from the luminosity and effective temperature provided by Healy et al. (2023),[8] whereas Messineo et al. (2019) gives a much smaller estimate of 462 R☉[9] (though they use a far smaller distance of 1574 or 1585 pc, which is inconsistent with the Gaia EDR3parallax of 0.3216±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.