Attaining m s⁻¹ level intrinsic Doppler precision with RHEA, a low-cost single-mode spectrograph

We present RHEA, a compact and inexpensive single-mode spectrograph which is built to exploit the capabilities of modest-sized telescopes in an economic way. The instrument is fed by up to seven optical waveguides with the aim of achieving an efficient and modal-noise-free unit, suitable for attaining extreme Doppler precision. The cross-dispersed layout features a wavelength coverage from 430–650 nm, with spectral resolution of R ∼75,000. When coupled to small telescopes using fast tip/tilt control, our instrument is well-suited to sensitive spectroscopy. Example science cases are accurate radial velocity studies of low to intermediate-mass giant stars with the purpose of searching for giant plants and using asteroseismology to simultaneously measure the host star parameters. In this paper we describe the final instrument design and present first results from testing the internal stability.