2011MNRAS.411.2530J

We present a comprehensive multiwavelength analysis of the young cluster NGC 1624 associated with the H II region Sh2-212 using optical UBVRI photometry, optical spectroscopy and GMRT radio continuum mapping along with the near-infrared (NIR) JHK archival data. From optical observations of the massive stars, reddening E(B-V) and distance to the cluster are estimated to be 0.76-1.00 mag and 6.0±0.8 kpc, respectively. The present analysis yields a spectral class of O6.5V for the main ionizing source of the region, and the maximum post-main-sequence age of the cluster is estimated as ∼4 Myr. Detailed physical properties of the young stellar objects (YSOs) in the region are analysed using a combination of optical/NIR colour-colour and colour-magnitude diagrams. The distribution of YSOs in the (J-H)/(H-K) NIR colour-colour diagram shows that a majority of them have A_V≤ 4 mag. However, a few YSOs show A_V values higher than 4 mag. Based on the NIR excess characteristics, we identified 120 probable candidate YSOs in this region, which yield a disc frequency of ∼20 per cent. However, this should be considered as a lower limit. These YSOs are found to have an age spread of ∼5 Myr with a median age of ∼2-3 Myr and a mass range of ∼0.1-3.0 M_☉. A significant number of YSOs are located close to the cluster centre and we detect an enhanced density of reddened YSOs located/projected close to the molecular clumps detected by [Deharveng et al.] at the periphery of NGC 1624. This indicates that the YSOs located within the cluster core are relatively older in comparison to those located/projected near the clumps. From the radio continuum flux, the spectral class of the ionizing source of the ultracompact H II (UCH II) region at the periphery of Sh2-212 is estimated to be ∼B0.5V. From the optical data, the slope of the mass function (MF) Γ, in the mass range 1.2 ≤M/M_☉< 27, can be represented by a single power law with a slope -1.18±0.10, whereas the NIR data in the mass range 0.65 ≤M/M_☉< 27 yield Γ=-1.31±0.15. Thus the MF agrees fairly with the Salpeter value. The slope of the K-band luminosity function (KLF) for the cluster is found to be 0.30 ± 0.06, which is in agreement with the values obtained for other young clusters.