The birth of massive twins in M 17

We have imaged the ultra-compact H ii region M 17-UC1 at J, K, N, Q and 1.3 cm. A comparison with results from earlier epochs reveals an increase of the emitted flux both in the mid-infrared and radio continuum. Our N and Q images exhibit a second source of comparable strength 5′′ southwest of M 17-UC1. While M 17-UC1 is not visible at J, faint at K but very bright at 1.3 cm, the second southern source shows rather opposite characteristics, namely being very bright at infrared wavelengths but invisible in the radio continuum, probably due to self-absorption. The spectral energy distributions indicate that the sources are still surrounded by the remnants of their protostellar cocoons. The observed luminosities measured between 1.2 and 20.0 μm of about 103L for both sources leads to the conclusion that they represent the youngest population of early type stars in M 17. The projected linear distance of 8900 AU between M 17-UC1 and its southern companion qualifies them to be a likely binary star system of O or early B-type stars.