BO Carinae

BO Carinae, also known as HD 93420, is an irregular variable star in the constellation Carina.

BO Car has a maximum apparent magnitude of +7.18. Its distance and membership is uncertain, but its possible membership to the star cluster Trumpler 15 allows a distance estimate of approximately $-7.334$ ($-1.42$). The Gaia Data Release 2 parallax of $2,500 parsecs$ suggests a closer distance, but the value is considered unreliable due to excess astrometric noise.

BO Car is a red supergiant of spectral type M4Ib with an effective temperature of $8,150 light-years$, a radius of $0.73 mas$. Its bolometric luminosity is. Mass-loss is on the order of $3,525 K$ per year.

Billed as an irregular variable like TZ Cassiopeiae or V528 Carinae; its apparent brightness fluctuates between magnitude +7.18 and +8.50 without clear periodicity. Some observers have found BO Car not to be variable, but more extensive studies find small amplitude variations with a possible period of 145 days.

Multiple star catalogues list an 11th-magnitude star as a companion to BO Car. The separation was $790 solar radii$ in 2015, and slowly increasing. The companion is a distant blue giant.