ABSTRACT
A near-infrared radial velocity (RV) survey focusing on the late-M dwarfs started in February 2019 within the framework of the Subaru Strategy Program (SSP). The InfraRed Doppler (IRD) instrument mainly consists of a high-resolution spectrometer and a laser frequency comb (LFC) system as a wavelength reference. Late-M dwarfs emit most of their energy in the near-infrared rather than in the visible. Therefore, to cover the bright absorption lines of M dwarfs, LFC provides a broadband spectrum from 970 nm to 1750 nm with a mode spacing of 12.5 GHz. It has advantages such as simple and robust frequency stabilization, an all-fiber optic configuration, and being observer friendly. The original comb spectrum just generated from highly nonlinear fibers undergoes optical processing such as spectral shaping, depolarization, and mode scrambling in multimode fiber utilization before it is input to the spectrometer. Using the IRD instrument, the IRD-SSP has made more than 100 nights of observations over the last three years. The LFC system operated stably without major trouble during this period, helping to maintain high RV accuracy. Despite the lack of direct maintenance for two and a half years due to Covid-19, the system has continued to operate without any interruption to the observations.