Spitzer Observations of the Massive Star-forming Complex S254-S258: Structure and Evolution

We present Spitzer IRAC, NOAO 2.1 m Flamingos, Keck NIRC, and FCRAO SEQUOIA observations of the massive star-forming complex S254-S258, covering an area of 25^' × 20^'. Using a combination of the IRAC and NIR data, we identify and classify the young stellar objects (YSOs) 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 YSOs are found in clusters surrounded by isolated YSOs in a low-density distributed population. The ratio of clustered to total YSOs 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 H II 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 H II region S256. The cluster G192.54-0.15, located inside H II region S254 has a V_LSR of 17 km s⁻¹ 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 V_LSR between 5 and 9 km s⁻¹. The arc-shaped structure of the molecular cloud following the border of the H II regions and the high column density in the border of the H II regions support the idea that the material has been swept up by the expansion of the H II regions.