Star formation history of Canis Major OB1

Abstract

Aims. The Canis Major OB1 Association has an intriguing scenario of star formation, especially in the region called Canis Major R1 (CMa R1) traditionally assigned to a reflection nebula, but in reality an ionized region. This work is focused on the young stellar population associated to CMa R1, for which our previous results from ROSAT, optical and near-infrared data had revealed two stellar groups with different ages, suggesting a possible mixing of populations originated from distinct star-formation episodes. Methods. The X-ray data allow the detected sources to be characterized according to hardness ratios, light curves and spectra. Estimates of mass and age were obtained from the 2MASS catalogue, and used to define a complete subsample of stellar counterparts, for statistical purposes. Results. A catalogue of 387 XMM-Newton sources is provided, 78% being confirmed as members or probable members of the CMa R1 association. Flares (or similar events) were observed for 13 sources, and the spectra of 21 bright sources could be fitted by a thermal plasma model. Mean values of fits parameters were used to estimate X-ray luminosities. We found a minimum value of log(L X [erg/s]) = 29.43, indicating that our sample of low-mass stars (M ⋆ ≤ 0.5M ⊙ ), being faint X-ray emitters, is incomplete. Among the 250 objects selected as our complete subsample (defining our "best sample"), 171 are found to the East of the cloud, near Z CMa and dense molecular gas, 50% of them being young (< 5 Myr) and 30% being older (> 10 Myr). The opposite happens to the West, near GU CMa, in areas lacking molecular gas: among 79 objects, 30% are young and 50% are older. These findings confirm that a first episode of distributed star formation occurred in the whole studied region ∼10 Myr ago and dispersed the molecular gas, while a second, localized episode (< 5 Myr) took place in the regions where molecular gas is still present.

Searching for active low-mass stars in CMa star-forming region: multi-band photometry with T80S

“…To better understand the star formation scenario and the early evolutionary stages of the stars associated with CMa OB1/R1 we previously analyzed the X-ray sources detected by ROSAT and XMM-Newton satellites in the direction of the nebula Sh 2-296 (Gregorio- Hetem et al 2009;Santos-Silva et al 2018). The characterization of the X-ray sources was based on 2MASS data of their near-infrared counterparts for which mass and age were estimated.…”

“…1), there are 430 stars that are likely associated with the CMa R1 region. Among those previously known objects, 60 corresponds to B-or A-type stars (Claría 1974;Shevchenko et al 1999) and 370 are young low-mass stars candidates selected from XMM data (Santos-Silva et al 2018). However, 64 percent of them does not fulfill the parallax R.A. (J2000) Dec. (J2000)…”

“…Part of our sample was previously studied in order to search for disk-bearing stars among the candidates revealed by XMM-Newton data from Santos-Silva et al (2018), focusing on 205 X-ray sources exhibiting a single IR counterpart (Gregorio-Hetem et al 2016). The IR colors were compared to the criteria suggested by Koenig & Leisawitz (2014) to distinguish different PMS classes using WISE photometric bands (Wright et al 2010), according with the distribution of stars studied in Taurus by Rebull (2010).…”

“…CMa R1 has a mixing of young objects with ages ranging from 1 to 10 Myr, distributed on a large scale region (Gregorio-Hetem et al 2009). Based on X-ray observations in the direction of the Sh 2-296 nebula, Santos-Silva et al (2018) reported more than 300 low-mass young stars candidates. As noted by Fernandes et al (2015), among the T Tauri stars found by them around Sh 2-296, less than 10 percent show evidence of circumstellar disks.…”

Comparing the spatial and kinematic distribution of gas and young stars around the shell-like structure in the CMa OB1 association

“…The Canis Major OB1/R1 (henceforth CMa, for simplicity) is a nearby (d ∼ 1 kpc) OB Association with a complex star formation history. Our previous studies showed that the region contains young objects originated from different star-forming events (Gregorio- Hetem et al 2009;Santos-Silva et al 2018).…”