Search for OH 18-cm radio emission from 1I/2017 U1 with the Green Bank telescope

TL;DR

This study reports the first search for OH 18-cm radio emission from interstellar object 1I/2017 U1 (`Oumuamua) using the Green Bank Telescope, setting upper limits on its OH production rate.

Contribution

It provides the first observational constraints on OH emission from `Oumuamua, supporting its asteroidal origin with a new upper limit on OH production.

Findings

No OH emission detected from `Oumuamua.

Upper bound on OH production rate is Q[OH] < 0.17 x 10^{28} s^{-1}.

Supports the asteroid-like nature of `Oumuamua.

Abstract

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 MHz, 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 (as discussed in Meech et al., 2017) with an upper bound of OH production of Q[OH] < 0.17 x 10^{28} s^{-1}.