Abstract Near-infrared images and K-band spectroscopy of the massive star-forming region IRAS 23151+5912 are presented. The JHK' images reveal an embedded infrared cluster associated with infrared nebula, and the H2 (2.12 µm) narrow-band image provides for the first time evidence of outflow activity associated with the cluster. That the cluster is young can be shown by the high percentage of infrared excess sources and the outflow activity. We suggest an age of the cluster of ∼ 106 yr. Eight young stars are found in the bright nebular core around IRAS 23151+5912. By the color-magnitude diagrams of the cluster, we found five high-mass YSOs and four intermediate-mass YSOs in the cluster. Eight H2 emission features are discovered in the region with a scattered and non-axisymmetric distribution, indicating the existence of multiple outflows driven by the cluster. Diffuse H2 emission detected to the north and to the west of the cluster may result from UV leakage of the cluster. Brγ, H2, and CIV emission lines are found in the K-band spectrum of the brightest source, NIRS 19, indicating the presence of envelope, stellar wind, and shock in the circumstellar environment. We have estimated an O7--O9 spectral type for the central massive YSO (20 ∼ 30 M⊙ ), with an age of less than 1×106 yr.

Keywords infrared radiation --- stars: formation: --- ISM: individual: IRAS 23151 + 5912 --- ISM: jets and outflows

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