The G 305 Star-Forming Region. Ii. Irregular Variable Stars

Abstract We present a catalog of 167 newly discovered, irregular variables spanning a ∼7 deg 2 area that encompasses the G 305 star-forming complex, one of the most luminous giant H ii regions in the Galaxy. We aim to unveil and characterize the young stellar object (YSO) population of the region by analyzing the K s -band variability and JHK s infrared colors from the VISTA Variables in the Vía Láctea survey. Additionally, SDSS-IV APOGEE-2 infrared spectra of selected objects are analyzed. The sample shows relatively high amplitudes (0.661 mag < Δ K S < 3.521 mag). Most of them resemble sources with outbursts with amplitude >1 mag and duration longer than a few days, typically at least a year, known as eruptive variables . About 60% are likely to be Class II/flat/I objects. This is also confirmed by the spectral index α when available. From the analysis of APOGEE-2 near-infrared spectra of sources in the region, another 122 stars are classified as YSOs and display some infrared variability. The measured effective temperature T eff peak is around 4000 K, and they are slightly supersolar in metal abundance. The modal radial velocity is approximately −41 km s −1 . Combining available catalogs of YSOs in the region with our data, we investigate the spatial distributions of 700 YSOs. They are clearly concentrated within the central cavity formed by the massive clusters Danks 1 and 2. The calculated surface density for the entire catalog is 0.025 YSOs pc −2 , while the central cavity contains 10 times more objects per area (0.238 YSOs pc −2 ).