In the new era of Extremely Large Telescopes (ELTs) currently under construction, challenging requirements drive spectrograph designs towards techniques that efficiently use a facility's light collection power. Operating in the single-mode (SM) regime, close to the diffraction limit, reduces the footprint of the instrument compared to a conventional high-resolving power spectrograph. The custom built injection fiber system with 3D-printed microlenses on top of it for the replicable high-resolution exoplanet and asteroseismology spectrograph (RHEA) at Subaru in combination with extreme adaptive optics of SCExAO, proved its high efficiency in a lab environment, manifesting up to ~77% of the theoretical predicted performance.
RHEA is a compact high-resolution single-mode spectrograph that can easily be produced in larger quantities as budgets allow. The instrument will be housed in a temperature-stabilized vacuum chamber which is surrounded by several layers of thermal shielding. The optical design employs cost-effective commercially available compo- nents, a cooled CMOS detector, and a double-fiber input which permits simultaneous wavelength calibration.
RHEA is a single-mode ´echelle spectrograph designed to be a replicable and cost effective method of undertaking precision radial velocity measurements. The instrument has a novel fiber feed with an integral field unit injecting into a grid of single-mode fibers reformatted to form a pseudo-slit, increasing throughput and enabling highspatial resolution observations when operating behind Subaru and the SCExAO adaptive optics system. The past 18 months have seen a replacement cable constructed for the instrument to address modal noise caused by closely packed fibers with similar path lengths. Here we detail the cable fabrication procedure, design improvements, increased precision in meeting the required sub-micron optical tolerances, throughput gains, and known remaining issues.
The RHEA Spectrograph is a single-mode echelle spectrograph designed to be a replicable and cost effective method of undertaking precision radial velocity measurements. Two versions of RHEA currently exist, one located at the Australian National University in Canberra, Australia (450 - 600nm wavelength range), and another located at the Subaru Telescope in Hawaii, USA (600 - 800 nm wavelength range). Both instruments have a novel fibre feed consisting of an integral field unit injecting light into a 2D grid of single mode fibres. This grid of fibres is then reformatted into a 1D array at the input of the spectrograph (consisting of the science fibres and a reference fibre capable of receiving a white-light or xenon reference source for simultaneous calibration). The use of single mode fibres frees RHEA from the issue of modal noise and significantly reduces the size of the optics used. In addition to increasing the overall light throughput of the system, the integral field unit allows for cutting edge science goals to be achieved when operating behind the 8.2m Subaru Telescope and the SCExAO adaptive optics system. These include, but are not limited to: resolved stellar photospheres; resolved protoplanetary disk structures; resolved Mira shocks, dust and winds; and sub-arcsecond companions. We present details and results of early tests of RHEA@Subaru and progress towards the stated science goals.
The Replicable High-resolution Exoplanet and Asteroseismology (RHEA) spectrograph is being developed to serve as a basis for multiple copies across a network of small robotic telescopes. The spectrograph operates at the diffraction-limit by using a single-mode fiber input, resulting in a compact and modal-noise-free unit. The optical design is mainly based on off-the-shelf available components and comprises a near-Littrow configuration with prism cross-disperser. The échelle format covers a wavelength range of 430-650 nm at R=75,000 resolving power. In this paper we briefly summarize the current status of the instrument and present preliminary results from the first on-sky demonstration of the prototype using a fully automated 16" telescope, where we observe stable and semi-variable stars up to V=3.5 magnitude. Future steps to enhance the efficiency and passive stability of RHEA are discussed in detail. For example, we show the concept of using a multi-fiber injection unit, akin to a photonic lantern, which not only enables increased throughput but also offers simultaneous wavelength calibration.
SCExAO is the premier high-contrast imaging platform for the Subaru Telescope. It offers high Strehl ratios at near-IR wavelengths (y-K band) with stable pointing and coronagraphs with extremely small inner working angles, optimized for imaging faint companions very close to the host. In the visible, it has several interferometric imagers which offer polarimetric and spectroscopic capabilities. A recent addition is the RHEA spectrograph enabling spatially resolved high resolution spectroscopy of the surfaces of giant stars, for example. New capabilities on the horizon include post-coronagraphic spectroscopy, spectral differential imaging, nulling interferometry as well as an integral field spectrograph and an MKID array. Here we present the new modules of SCExAO, give an overview of the current commissioning status of each of the modules and present preliminary results.