  In the era of high resolution submillimeter interferometers, it will soon be
possible to observe the neutral circumstellar medium directly involved in gas
giant planet (GGP) formation at physical scales previously unattainable. In
order to explore possible signatures of gas giant planet formation via disk
instabilities, we have combined a 3D, non-local thermodynamic equilibrium (LTE)
radiative transfer code with a 3D, finite differences hydrodynamical code to
model molecular emission lines from the vicinity of a 1.4 M_J self-gravitating
proto-GGP. Here, we explore the properties of rotational transitions of the
commonly observed dense gas tracer, HCO+. Our main results are the following:
1. Very high lying HCO+ transitions (e.g. HCO+ J=7-6) can trace dense planet
forming clumps around circumstellar disks. Depending on the molecular
abundance, the proto-GGP may be directly imageable by the Atacama Large
Millimeter Array (ALMA). 2. HCO+ emission lines are heavily self-absorbed
through the proto-GGP's dense molecular core. This signature is nearly
ubiquitous, and only weakly dependent on assumed HCO+ abundances. The
self-absorption features are most pronounced at higher angular resolutions.
Dense clumps that are not self-gravitating only show minor self-absorption
features. 3. Line temperatures are highest through the proto-GGP at all assumed
abundances and inclination angles. Conversely, due to self-absorption in the
line, the velocity-integrated intensity may not be. High angular resolution
interferometers such as the Submillimeter Array (SMA) and ALMA may be able to
differentiate between competing theories of gas giant planet formation.
