The massive Class I eruptive variable V723 Carinae and its neighbour Car I-125

Near-IR observations from 1993 to 2014 of V723 Carinae confirm this to be a young eruptive variable embedded in the Car I PDR/dust cloud in NGC 3372. In 1993, it was fainter than 16.6 in JHK and went into outburst before 2003, reaching K ≃ 12.9 in 2004. Since then, V723 Car has suffered erratic flux variations of up to ΔK = 2 in time-scales of years. The variations are also evident into the mid-infrared. The H - K index shows correlation with K, though the ratio ΔK/Δ(H - K) differs from that expected from dust extinction. The 1.91 to 2.48 μm spectrum of V723 Car shows emission lines of H₂ and also Brγ, as well as 2.3-2.4 μm CO overtone bandheads. The system is extremely red (H - K ≥ 4), with mid- and far-IR colours of a Class I object. The fitted parameters of Robitaille et al.'s model to the 1.6-850 μm spectral energy distribution of V723 Car indicate a system composed of a 10 M_⊙ central star with a 5.6 × 10^-3 M_⊙ disc and a 1.6 × 10³ M_⊙ envelope with A_V ∼ 55 of extinction. The total luminosity of the system is about 4 × 10³ L_⊙. V723 Car is the most luminous, most massive, most deeply embedded, and possibly the youngest of all the young eruptive variables known. Evidence is provided of a 5000 au-long jet of shocked gas extending to opposite sides of the star. The infrared properties of a nearby 10 L_⊙ Class I young stellar object, Car I-125, are also described, with variations in K typical of Herbig Ae/Be stars. Its near-IR spectrum is featureless except for bright Brγ line emission.