Program: GN-2019B-Q-218

The discovery and study of the optical source SSS17a/AT2017gfo associated with the binary neutron star merger GW170817 has forever changed the field of astronomy and provided confirmation of Binary Neutron Star mergers (BNS) as the source of r-process elements (Coulter et al. 2017, Smartt et al. 2017, Abbott et al. 2017 for a summary of the campaign). While the primary evidence for this is the rapidly decaying light curve (1.5 mag/day) consistent with the radioactive decay of a kilonova, our collaboration was the only group that was also able to identify spectroscopic features of light r-process elements, specifically Cesium and Tellurium, indicative of a blue or low opacity kilonova (Smartt et al 2017). What we see spectroscopically is likely to vary from object to object depending strongly on the angle with respect to the merger axis and on the opacity along the line of sight and on how the opacity evolves in time (Metzger 2017). While we only observed light r-process elements, the heavy r-process elements could be visible with orientation or function of time and additional events need to be followed-up photometrically and spectroscopically. To advance our understanding of kilonova and r-process elements, we need optical and near-infrared spectra as a function of time as these are not axisymmetric objects. Advanced LIGO (aLIGO) and Advance Virgo (AdVirgo) are on schedule to begin the third year long observing run (O3) in April 2019 followed by another LIGO shutdown period for improvements. The sensitivities to BNS are improved such that they can detect the gravitational waves from an event in a search volume of 2 to 3 times over the brief period in O2 when GW170817 was discovered (Abbott et al. 2018). The rate of BNS is still poorly understood, but the range expected by the LIGO/Virgo Consortium is between 1 and 50 per year (Abbott et al. 2018) and the median 0.9 Credible Region is very well suited to the combined survey power of Pan-STARRS1 and Pan-STARRS2. This proposal is for 24 hours TOO queue time for follow-up optical and near-infrared spectroscopy with GMOS and GNIRS on Gemini on 2-3 kilonova from aLIGO/AdVirgo alerts to complement CFHT u, UKIRT JHK and Pan-STARRS grizy photometry. The follow-up of other rare transients will be carried out as a secondary program.