Search for OH 18 cm Radio Emission from 1I/2017 U1 with the Green Bank Telescope

This paper reports the first OH 18 cm line observation of the first detected interstellar object 1I/2017 U1 (‘Oumuamua) using the Green Bank Telescope. We have observed the OH lines at 1665.402, 1667.359, and 1720.53 MHz frequencies with a spectral resolution of 357 Hz (approximately 0.06 km s−1). At the time of the observation, ‘Oumuamua was at topocentric distance and velocity of 1.07 au and 63.4 km s−1, respectively, or at heliocentric distance and velocity of 1.8 au and 39 km s−1, respectively. Based on a detailed data reduction and an analogy-based inversion, our final results confirm the asteroidal origin of ‘Oumuamua with an upper bound OH production of Q[OH] < 0.17 × 1028 s−1.