New constraints on the nature and origin of the Leading Arm of the
  Magellanic Stream
  We present a new precision measurement of gas-phase abundances of S, O, N,
Si, Fe, P, Al, Ca as well as molecular hydrogen (H_2) in the Leading Arm
(region II, LAII) of the Magellanic Stream (MS) towards the Seyfert galaxy NGC
3783. The results are based on high-quality archival ultraviolet/optical/radio
data from various different instruments (HST/STIS, FUSE, AAT, GBT, GB140ft,
ATCA). Our study updates previous results from lower-resolution data and
provides for the first time a self-consistent component model of the complex
multi-phase absorber, delivering important constraints on the nature and origin
of LAII. We derive a uniform, moderate alpha abundance in the two main absorber
groups at +245 and +190 km s^-1 of alpha/H = 0.30 pm 0.05 solar, a low nitrogen
abundance of N/H = 0.05 pm 0.01 solar, and a high dust content with substantial
dust depletion values for Si, Fe, Al, and Ca. These alpha, N, and dust
abundances in LAII are similar to those observed in the Small Magellanic Cloud
(SMC). From the analysis of the H_2 absorption, we determine a high thermal
pressure of P/k = 1680 K cm^-3 in LAII, in line with the idea that LAII is
located in the inner Milky Way halo at a z-height of <20 kpc where it
hydrodynamically interacts with the ambient hot coronal gas. Our study supports
a scenario, in which LAII stems from the break-up of a metal- and dust-enriched
progenitor cloud that was recently (200-500 Myr ago) stripped from the SMC.
