Multiwavelength photometry of Sh 2-138 YSOs

The data comprise of optical and near-infrared (NIR) photometric and spectroscopic observations from the 2-m Himalayan Chandra} Telescope, radio observations from the Giant Metrewave Radio Telescope (GMRT), and archival data covering radio through NIR wavelengths. A total of 10 Class I and 54 Class II young stellar objects (YSOs) are identified in a 4.6-arcminx4.6-arcmin area of the Sh 2-138 region.

Five compact ionized clumps, with four lacking of any optical or NIR counterparts, are identified using the 1280MHz radio map, and correspond to sources with spectral type earlier than B0.5. Free-free emission spectral energy distribution fitting of the central compact HII region yields an electron density of ~2250+/-400cm^-3^. With the aid of a wide range of spectra, from 0.5-15{mu}m, the central brightest source - previously hypothesized to be the main ionizing source - is characterized as a Herbig Be type star.