  The LIGO HET Response (LIGHETR) project is an enterprise to follow up optical
transients (OT) discovered as gravitational wave merger sources by the
LIGO/Virgo collaboration (LVC). Early spectroscopy has the potential to
constrain crucial parameters such as the aspect angle. The LIGHETR
collaboration also includes the capacity to model the spectroscopic evolution
of mergers to facilitate a real-time direct comparison of models with our data.
The principal facility is the Hobby-Eberly Telescope. LIGHETR uses the
massively-replicated VIRUS array of spectrographs to search for associated OTs
and obtain early blue spectra and in a complementary role, the low-resolution
LRS-2 spectrograph is used to obtain spectra of viable candidates as well as a
densely-sampled series of spectra of true counterparts. Once an OT is
identified, the anticipated cadence of spectra would match or considerably
exceed anything achieved for GW170817 = AT2017gfo for which there were no
spectra in the first 12 hours and thereafter only roughly once daily. We
describe special HET-specific software written to facilitate the program and
attempts to determine the flux limits to undetected sources. We also describe
our campaign to follow up OT candidates during the third observational campaign
of the LIGO and Virgo Scientific Collaborations. We obtained VIRUS spectroscopy
of candidate galaxy hosts for 5 LVC gravitational wave events and LRS-2 spectra
of one candidate for the OT associated with S190901ap. We identified that
candidate, ZTF19abvionh = AT2019pip, as a possible Wolf-Rayet star in an
otherwise unrecognized nearby dwarf galaxy.
