We present the serendipitous discovery of a young stellar cluster in the Galactic disk at l =12 ^ { \circ } .
Using Keck/NIRSPEC , we obtained high– and low–resolution spectroscopy of several stars in the cluster , and we identified one red supergiant and two blue supergiants .
The radial velocity of the red supergiant provides a kinematic cluster distance of 4.7 \pm 0.4 kpc , implying luminosities of the stars consistent with their spectral types .
Together with the known Wolf–Rayet star located 2 \farcm 4 from the cluster center , the presence of the red supergiant and the blue supergiants suggests a cluster age of 6 - 8 Myr , and an initial mass of \gtrsim 2000 M _ { \odot } .
Several stars in the cluster are coincident with X–ray sources , including the blue supergiants and the Wolf–Rayet star .
This is indicative of a high binary fraction , and is reminiscent of the massive young cluster Westerlund 1 .
The cluster is coincident with two supernova remnants , SNR G12.72 - 0.0 and G12.82 - 0.02 , and the highly magnetized pulsar associated with the TeV \gamma –ray source HESS J1813 - 178 .
The mixture of spectral types suggests that the progenitors of these objects had initial masses of 20 - 30 M _ { \odot } .