# # Program information file # PROGRAM_ID 2023B061 PROGRAM_TITLE Rapid SpeX and `Opihi Follow-up of a New Kilonova PROGRAM_INV1 Jason Hinkle PROGRAM_INV2 Benjamin Shappee PROGRAM_INV3 Mark Huber PROGRAM_INV4 Willem Hoogendam PROGRAM_INV5 Ellen Lee PROGRAM_SCICAT extra-galactic PROGRAM_ABSTRACT_BEG In September 2015, a new window into the universe was opened with the discovery of the first gravitational wave source. Only two years later, multi-messenger astrophysics took a critical step forward with the discovery of GW170817 and corresponding electromagnetic counterparts, the short gamma-ray burst GRB 170817A and the optical/NIR kilonova SSS17a. Kilonovae are powered by low mass outflows with velocities of order 10% the speed of light. Despite theoretical predictions, SSS17a showed an early-time [< 1 d] hot, blue spectrum before fading and cooling over a timescale of several days. Interestingly, no kilonova models can self-consistently reproduce the observed spectra of SSS17a. Clearly with only one known object, many questions remain on the diversity of kilonova and their underlying physics. LIGO/Virgo/Kagra will begin their O4 campaign in May 2023, and transient surveys are poised to rapidly detect electromagnetic counterparts of GW triggers. Here we propose to obtain a NIR spectroscopic time series with SpeX and optical light curve with `Opihi on IRTF of a newly-discovered kilonova, beginning within a day of discovery and continuing for a week thereafter. These spectra will allow us to measure broad lines of r-process elements and further constrain kilonova models as models predict significant differences in the red/NIR spectral shape. SpeX in PRISM mode is well-suited to obtain moderate S/N spectra of a kilonova as they are intrinsically faint objects with strong red/NIR emission. PROGRAM_ABSTRACT_END