Revealing Ionization Conditions of Sz 102 with Spatially Resolved [Ne
  III] Microjets
  Forbidden neon emission lines from small-scale microjets can probe
high-energy processes in low-mass young stellar systems. We obtained spatially
resolved [Ne III] spectra of the microjets from the classical T Tauri Star Sz
102 using the Hubble Space Telescope Imaging Spectrograph (HST/STIS) at a
spatial resolution of ~0".1. The blueshifted and redshifted [Ne III] emission
both peak in intensity within ~0".1 of the star and gradually decay along the
flow outward to ~0".24. The spatial distribution and extent of the [Ne III]
microjet is consistent with a jet that is ionized close to the base and
subsequently recombines on a longer timescale than the flow time. Ca II H and K
lines are also detected from the redshifted microjet with a line full-width at
half-maximum of ~170 km/s, consistent with those of other forbidden emission
lines, atop a 300-km/s wide stellar component. The launching radius of the Sz
102 jet, inferred from the observed line centroids and the range of inclination
angles and stellar masses from the literature, is on the order of ~0.03 au. The
possible proximity of the launching region to the star allows immediate
ionization without distance dilution from the circumstellar ionization sources,
most likely keV X-ray flares generated by magnetic reconnection events in the
star-disk system, to sustain the observed [Ne III] flux.
