Chemical Composition of Young Stars in the Leading Arm of the Magellanic System

TL;DR

This study analyzes the chemical compositions of young stars in the Leading Arm of the Magellanic System, revealing their metallicities, velocities, and ages, and providing insights into their origins and the star formation history in this region.

Contribution

First detailed chemical abundance analysis of young stars in the Leading Arm, linking stellar metallicities with Magellanic Cloud origins and Galactic disk membership.

Findings

LA members have lower [Mg/H] than Galactic disk stars.

Most LA stars have metallicities similar to the LMC.

LA stars are young, around 50-70 Myr, indicating recent star formation.

Abstract

Chemical abundances of eight O- and B-type stars are determined from high-resolution spectra obtained with the MIKE instrument on the Magellan 6.5m Clay telescope. The sample is selected from 42 candidates of membership in the Leading Arm of the Magellanic System. Stellar parameters are measured by two independent grids of model atmospheres and analysis procedures, confirming the consistency of the stellar parameter results. Abundances of seven elements (He, C, N, O, Mg, Si, and S) are determined for the stars, as are their radial velocities and estimates of distances and ages. Among the seven B-type stars analyzed, the five that have radial velocities compatible with membership to the LA have an average [Mg/H] of $-0.42\pm0.16$, significantly lower than the average of the remaining two [Mg/H] = $-0.07\pm0.06$ that are kinematical members of the Galactic disk. Among the five LA members, four have individual [Mg/H] abundance compatible with that in the LMC. Within errors, we can not exclude the possibility that one of these stars has a [Mg/H] consistent with the more metal-poor, SMC-like material. The remaining fifth star has a [Mg/H] close to MW values. Distances to the LA members indicate that they are at the edge of the Galactic disk, while ages are of the order of $\sim 50-70$ Myr, lower than the dynamical age of the LA, suggesting a single star-forming episode in the LA. V$_{\rm LSR}$ the LA members decreases with decreasing Magellanic longitude, confirming the results of previous LA gas studies.