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