# # Program information file # PROGRAM_ID 2023A048 PROGRAM_TITLE IRTF Spectroscopy of LVK O4 Transients PROGRAM_INV1 Melissa Butner PROGRAM_INV2 Allyn Smith PROGRAM_INV3 Matthew Wiesner PROGRAM_INV4 Douglas Tucker PROGRAM_INV5 PROGRAM_SCICAT extra-galactic PROGRAM_ABSTRACT_BEG The August 2017 discovery of the optical counterpart of a binary neutron star merger -- a kilonova -- was one of the highlights of observational astrophysics of the early 21st Century. The merger was first detected, by the LIGO/Virgo Collaboration [LVC], via the merger's gravitational wave signal [GW170817]. LVC observing season O3 concluded in March 2020 and resulted in a catalog of 90 events, including the first black hole-neutron star merger. After a period of downtime for maintenance and upgrades, the LVC is preparing for observing season O4, which should begin in March 2023. Our team proposes to use the NASA/IRTF 3.0m SpeX instrument for NIR spectroscopic follow-up of spectroscopically confirmed kilonovae deriving from kilonova search & discovery programs in order to characterize their near-infrared properties. Here, we propose to obtain NIR follow-up spectra of some fraction of the roughly 50 percent of LVC O4 kilonovae that are anticipated to be bright enough for suitable IRTF SpeX spectroscopy [K<18]. We need more observations of more kilonovae both to help improve models and to identify any variations in this newly observed class of object. It is believed that spectra with a S/N=10 or higher would be sufficient to measure and model the NIR features and to analyze their variations within the population of kilonovae. We believe we can reach that S/N with some identified kilonovae using 3600 sec integration time. The proposed program would provide data on the evolution of the NIR spectrum of new kilonovae, aiding in the modeling of each new kilonova in particular and in the exploration of any population variations within the NIR properties of this newly discovered class of transients in general. PROGRAM_ABSTRACT_END