Spitzer observations of the Massive star forming complex S254-S258: structure and evolution

TL;DR

This study uses multi-wavelength observations to analyze the structure, star formation activity, and evolution of the S254-S258 complex, revealing new clusters, YSO classifications, and cloud dynamics influenced by HII region expansion.

Contribution

It provides the first detailed classification of YSOs and identification of new clusters in the S254-S258 complex, linking molecular cloud structure with star formation processes.

Findings

Detected 510 YSOs with IR-excess, including 87 Class I and 165 Class II sources.

Identified six new star clusters, including one around the ionizing star of S255.

Molecular cloud structure shows evidence of material swept up by expanding HII regions.

Abstract

We present Spitzer-IRAC, NOAO 2.1meter-Flamingos, Keck-NIRC, and FCRAO-SEQUOIA observations of the massive star forming complex S254-S258, covering an area of 25x20 arc-minutes. Using a combination of the IRAC and NIR data, we identify and classify the young stellar objects (YSO) in the complex. We detect 510 sources with near or mid IR-excess, and we classify 87 Class I, and 165 Class II sources. The YSO are found in clusters surrounded by isolated YSO in a low-density distributed population. The ratio of clustered to total YSO is 0.8. We identify six new clusters in the complex. One of them, G192.63-00, is located around the ionizing star of the HII region S255. We hypothesize that the ionizing star of S255 was formed in this cluster. We also detect a southern component of the cluster in HII region S256. The cluster G192.54-0.15, located inside HII region S254 has a VLSR of 17 km/s with respect to the main cloud, and we conclude that it is located in the background of the complex. The structure of the molecular cloud is examined using 12CO and 13CO, as well as a near-IR extinction map. The main body of the molecular cloud has VLSR between 5 and 9 km/s. The arc-shaped structure of the molecular cloud, following the border of the HII regions, and the high column density in the border of the HII regions support the idea that the material has been swept up by the expansion of the HII regions.