A multiwavelength census of stellar contents in the young cluster NGC 1624

作者：Jose Jessy^*; Pandey A K; Ogura K; Ojha D K; Bhatt B C; Samal M R; Chauhan N; Sahu D K; Rawat P S

来源：Monthly Notices of the Royal Astronomical Society, 2011, 411(4): 2530-2548.

DOI：10.1111/j.1365-2966.2010.17860.x

• stars: formation
• stars: luminosity function
• mass function
• stars: pre-main-sequence
• open clusters and associations: individual: NGC 1624

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 similar to 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 similar to 20 per cent. However, this should be considered as a lower limit. These YSOs are found to have an age spread of similar to 5 Myr with a median age of similar to 2-3 Myr and a mass range of similar to 0.1-3.0 M-circle dot. 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 similar to B0.5V. From the optical data, the slope of the mass MF) Gamma, in the mass range 1.2 < M/M-circle dot < 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-circle dot < 27 yield Gamma = -1.31 +/- 0.15. Thus the MF agrees fairly with the Salpeter value. The slope of the K-band luminosity KLF) for the cluster is found to be 0.30 +/- 0.06, which is in agreement with the values obtained for other young clusters.

• 出版日期2011-3