An O2 If*/WN6 star caught in the act in a compact H ii region in the starburst cluster NGC 3603

In this paper, we report on the discovery of an O2 If*/WN6 star probably still partially embedded in its parental cocoon in the starburst cluster NGC 3603. From the observed size of the associated compact H ii region, it has been possible to derive a probable dynamic age of no more than 600 000 yr. Using the computed visual extinction value A(V) similar to 6.0 +/- 0.2 mag, an absolute visual magnitude M-V = -5.7 mag has been obtained. For the assumed heliocentric distance of 7.6 kpc, this results in a bolometric luminosity of 8 x 10(5) L-circle dot. Also, from the V magnitude and the V - I colour of the new star, and from previous models for the massive star population of NGC 3603, we estimate the mass of the binary (O2 If*/WN6 + O3 If) and the single star (O2 If*/WN6). For the binary, we find that the initial masses of each component possibly exceed 80 and 40 M-circle dot, respectively, while for the single star the initial mass of MTT 58 is possibly in excess of 100 M-circle dot.