Low-mass star formation and subclustering in the H II regions RCW 32, 33, and 27 of the Vela Molecular Ridge

Abstract

Context. Most stars born in clusters and recent results suggest that star formation (SF) preferentially occurs in subclusters. Studying the morphology and SF history of young clusters is crucial to understanding early cluster formation processes. Aims. We aim to identify the embedded population of young stellar objects (YSOs) down to the low mass stars in the M-type regime, in the three H II regions RCW 33, RCW 32 and RCW 27 located in the northwestern region of the Vela Molecular Ridge. Our aim is to characterise their properties, such as morphology and extent of the clusters in the three H II regions, derive stellar ages and the connection of the SF history with the environment. Methods. Through public photometric surveys such as Gaia, VPHAS, 2MASS and Spitzer/GLIMPSE, we identify YSOs with classical techniques aimed at detecting IR, Hα and UV excesses, as signature of circumstellar disks and accretion. In addition, we implement a method to distinguish main sequence (MS) stars and giants in the M-type regime, by comparing the reddening derived in several optical/IR color-color diagrams, assuming suitable theoretical models. Since this diagnostic is sensitive to stellar gravity, the procedure allows us to identify also pre-main sequence (PMS) stars. Results. Using the classical membership criteria, we find a large population of YSOs showing signatures of circumstellar disks with or without accretion. In addition, with the new technique of M-type star selection, we find a rich population of young M-type stars with a spatial distribution strongly correlated to the more massive population. We find evidence of three young clusters, with different morphology, for which we estimate the individual distances by using TGAS Gaia data of the brighter subsample. In addition, we identify field stars falling in the same region, by securely classifying them as giants and foreground MS stars. Conclusions. We identify the embedded population of YSOs, down to about 0.1 M , associated with the three H II regions RCW 33, RCW 32 and RCW 27 and the three clusters Vela T2, Cr 197 and Vela T1, respectively. All the three clusters are located at a similar distance but show very different morphologies. Our results suggest a decreasing SF rate in Vela T2 and triggered SF in Cr 197 and Vela T1.

A ring in a shell: the large-scale 6D structure of the Vela OB2 complex

“…8). The Vela Molecular Ridge contains a string of HII regions at distances of 800 pc to 2 kpc Rodgers et al (1960); May et al (1988); Pettersson & Reipurth (1994); Neckel & Staude (1995); Prisinzano et al (2018), which are not related to the Vela OB2 complex. They are visible as bright compact regions in Fig.…”

The New EXor Outburst of ESO-Hα 99 Observed by Gaia ATLAS and TESS

“…It appears that RCW 27 is a particularly fertile star-forming region. Pettersson & Reipurth (1994) carried out a large survey for Hα emission stars towards RCW 27, 32, and 33, many of which have subsequently been identified as T Tauri stars, e.g., by Prizinzano et al (2018). One of these young emission-line stars is ESO-Hα 99, the object of this paper.…”

Investigation of rocket effect in bright-rimmed clouds using Gaia EDR3

“…BRC 55: For BRC 55, in the Hii region RCW 27, the massive source responsible for ionizing BRC 55 is HD 73882, which has RUWE = 2.068. Therefore, we obtained the astrometric parameters of the members of RCW 27 (Prisinzano et al 2018) from Gaia EDR3 and used the median PM of the cluster members as the reference PM to estimate θpm.…”