The interpretation of protoplanetary disc wind diagnostic lines from
  X-ray photoevaporation and analytical MHD models
  High resolution spectra of typical wind diagnostics ([OI] 6300 \r{A} and
other forbidden emission lines) can often be decomposed into multiple
components: high-velocity components with blueshifts up to several 100 km/s are
usually attributed to fast jets, while narrow (NLVC) and broad (BLVC)
low-velocity components are believed to trace slower disc winds. Under the
assumption that the line-broadening is dominated by Keplerian rotation, several
studies have found that the BLVCs should trace gas launched between 0.05 and
0.5 au and correlations between the properties of BLVCs and NLVCs have been
interpreted as evidence for the emission tracing an extended MHD wind and not a
photoevaporative wind. We calculated synthetic line profiles obtained from
detailed photoionisation calculations of an X-ray photoevaporation model and a
simple MHD wind model and analyzed the emission regions of different diagnostic
lines and the resulting spectral profiles. The photoevaporation model
reproduces most of the observed NLVCs but not the BLVCs or HVCs. The MHD model
is able to reproduce all components but produces Keplerian double peaks at
average inclinations that are rarely observed. The combination of MHD and
photoevaporative winds could solve this problem. Our results suggest that the
Gaussian decomposition does not allow for a clear distinction of flux from
different wind regions and that the line broadening is often dominated by the
velocity gradient in the outflow rather than by Keplerian rotation. We show
that observed correlations between BLVC and NLVC do not necessarily imply a
common origin in an extended MHD wind.
