Unveiling the star formation history of the Upper Scorpius association through its kinematics

Abstract

Stellar associations can be discerned as overdensities of sources not only in the physical space but also in the velocity space. The common motion of their members, gradually eroded by the galactic tidal field, is partially reminiscent of the initial kinematic structure. Using recent data from Gaia EDR3, combined with radial velocities from GALAH and APOGEE, we traced back the present positions of stars belonging to Upper Scorpius, a subgroup of Scorpius-Centaurus, the nearest OB association. About one half of the subgroup (the “clustered” population) appears composed of many smaller entities, which were in a more compact configuration in the past. The presence of a kinematic duality is reflected into an age spread between this younger clustered population and an older diffuse population, in turn confirmed by a different fraction fD of disc-bearing stars (fD = 0.24 ± 0.02 versus fD = 0.10 ± 0.01). Star formation in Upper Scorpius appears to have lasted more than 10 Myr and proceeded in small groups that, after a few Myr, dissolve in the field of the older population but retain for some time memory of their initial structure. The difference of ages inferred through isochrones and kinematics, in this regard, could provide a powerful tool to quantify the timescale of gas removal.

Chronostar. II. Kinematic age and substructure of the Scorpius-Centaurus OB2 association

“…This is a complex component in the C model, consistent with the growing observational evidence for multiple populations in USCO (e.g. Kerr et al 2021;González et al 2021;Squicciarini et al 2021). It likely consists of multiple populations that have not been recovered within this model due to the limitations of the input catalog to the fit.…”

“…By contrast, Wright & Mamajek (2018) argue that USCO is an outcome of multiple bursts of star formation and thus has a real, substantial age spread. Simi-larly, Squicciarini et al (2021) claim that star formation in USCO must have lasted more than 10 Myr.…”

“…Gaia data (Gaia Collaboration et al 2018) is available on https://gea.esac.esa.int/archive/. Radial velocity measurements are taken from the GALAH DR3 survey (Buder et al 2021), RAVE DR6 list (Steinmetz et al 2020), APOGEE DR16 list (Ahumada et al 2020(Ahumada et al ), Žerjal et al (2021, and a compiled table in the Banyan Σ paper (Gagné et al 2018) -all references from their table are listed below Table C1. Equivalent widths of lithium are taken from Wheeler et al (2021), Rizzuto et al (2015, Žerjal et al (2019) and Žerjal et al (2021).…”

“…Traceback efforts for Sco-Cen have thus far yielded conflicting results. Recently, Squicciarini et al (2021) traced back the celestial coordinates of the Upper Scorpius members on the basis of their present day proper motions and found 8 distinct kinematic subgroups divided into dense and diffuse populations. An analysis using Gaia DR1 data (Gaia Collaboration et al 2016b, ∼400 stars) by Wright & Mamajek (2018) found no evidence that the three Sco-Cen subgroups were more compact in the past, but did confirm that the stars are gravitationally unbound and have a nonisotropic velocity dispersion.…”

Results from The COPAINS Pilot Survey: four new brown dwarfs and a high companion detection rate for accelerating stars

“…The masses for all the stars in the sample were also revised, using the Manifold Age Determination for Young Stars ( , Squicciarini & Bonavita in preparation; see Squicciarini et al 2021, for a description of the tool) and the updated values of the stellar ages. M retrieved and cross-matched photometry from Gaia EDR3 (Gaia Collaboration et al 2021) and 2MASS (Skrutskie et al 2006) for all our targets and then applied a correction for interstellar extinction by integrating along the line of sight the 3D extinction map by (Leike et al 2020); the derived A(G) were turned into the photometric band of interest using a total-to-selective absorption ratio R=3.16 and extinction coefficients A λ from Wang & Chen (2019).…”