The G 305 Star-forming Region: II. Irregular variable stars

TL;DR

This study catalogs 167 irregular variable stars in the G 305 star-forming region, analyzing their infrared variability and spectra to identify young stellar objects and their spatial distribution.

Contribution

It provides the first detailed catalog of irregular variables in G 305, combining infrared variability data with spectroscopic analysis to characterize YSOs and their spatial clustering.

Findings

Most variables are eruptive with amplitudes >1 mag and long durations.

Approximately 60% are likely Class II/Flat/I YSOs based on spectral index.

YSOs are concentrated within the central cavity of the region.

Abstract

We present a catalog of 167 newly discovered, irregular variables spanning a $\sim$7 deg${^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 $K_{\rm s}$-band variability and $JHK_{\rm s}$ infrared colors from the {\it VISTA Variables in the V\'ia L\'actea} (VVV) survey. Additionally, SDSS-IV APOGEE-2 infrared spectra of selected objects are analyzed. The sample show relatively high amplitudes ($0.661<\Delta K_{\rm S} <3.521$ 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 {\it Eruptive Variables}. About 60% are likely to be Class II/Flat/I objects. This is also confirmed by the spectral index $\alpha$ when available. From the analysis of APOGEE-2 near-infrared spectra of sources in the region, another 122 stars are classified as YSOs, and displays some infrared variability. The measured effective temperature $T_{\rm eff}$ peak is around 4000K and they are slightly super-solar in metal abundance. The modal radial velocity is approximately $-$41 km/s. Combining available catalogs of YSOs in the region with our data, we investigate the spatial distributions of 700 YSOs. They are clearly concentrated within the central cavity formed by the massive clusters Danks 1 and 2. The calculated surface density for the entire catalog is 0.025 YSOs/pc$^{-2}$, while the central cavity contains 10 times more objects per area (0.238 YSOs/pc$^{-2}$).