Conceptual Design of a High-Resolution Ultra-Stable Spectrograph for GTC

A joint project has been proposed by the Chinese and Spanish astronomy communities, to develop a high-resolution, ultrastable spectrograph for the Gran Telescopio Canarias (GTC) at La Palma Being expected to conduct precise radial velocity (PRV) measurement with extreme precision of up to 10 cm s(-1), the instrument would promote the very high, present interest in the astronomical community to detect and characterize exoplanets. The project successfully passed the conceptual design review (CoDR) in 2019. The instrument is composed of a near-UV band spectrograph (UVS) and a visible band spectrograph (VIS). They provide a spectral resolving power of R >= 100,000 in the visible band (420 nm - 780 nm), and R >= 25,000 in the UV band (310 nm - 420 nm). The VIS subsystem will be enclosed in an ultra-stable environment in the Coude room for the stellar precise radial velocity (PRV) measurements. The UVS subsystem will be located near the Nasmyth focus to improve the total throughput at the wavelength shorter than 400 nm, to ensure various additional science cases ranging from stellar evolution to the measurement of fundamental constants. This paper gives an overview of the project background, science cases, and technical considerations during the conceptual design phase.