# # Program information file # PROGRAM_ID 2023B024 PROGRAM_TITLE IRTF Observations of Kilonovae in the Fourth LIGO/Virgo Observing Run PROGRAM_INV1 Victoria Villar PROGRAM_INV2 Conor Ransome PROGRAM_INV3 Karthik Yadavalli PROGRAM_INV4 Kaylee de Soto PROGRAM_INV5 Edo Berger PROGRAM_SCICAT extra-galactic PROGRAM_ABSTRACT_BEG We propose to use SpeX on IRTF to observe two EM counterparts to neutron star mergers observed during LIGO/Virgo's fourth observing run, which will begin in May 2023 and will last for 18 months. A kilonova refers to the thermal explosion following a neutron star merger that results from the radioactive decay of newly synthesized, heavy ['r-process'] elements. The NIR emission of kilonova is of particular interest, due to the expected signatures of the heaviest elements [lanthanides and actinides] at these wavelengths. With an increased sensitivity, LIGO/Virgo is expected to discovery between 2-20 KNe during the fourth observing run. Here, we will target the brightest events [with K-band magnitude<20.5] which will also have the tightest localizations. We request three observations of three potential events, spread across 3-6 nights, depending on observability. Our ultimate aim is to take the earliest NIR spectrum of a localized kilonova and to uncover the intrinsic diversity of these newly discovered events. PROGRAM_ABSTRACT_END