G-CLEF: GMT-Consortium Large Earth Finder

The GMT-Consortium Large Earth Finder (G-CLEF) is an instrument that is being designed to exceed the state-of-the-art radial velocity (RV) precision achievable with the current generation of stellar velocimeters. It is simultaneously being designed to enable a wide range of scientific programs, prominently by operating to blue wavelengths (< 350nm). G-CLEF will be the first light facility instrument on the Giant Magellan Telescope (GMT) when the GMT is commissioned in 2023. G-CLEF is a fiber-fed, vacuum-enclosed spectrograph with an asymmetric white pupil echelle design. (Szentgyorgyi et al., 2018)

The KASI OATG is working on Flexure Control Camera (FCC), Calibration Lightsource Subsystem (CLS) and Dichroic Mirror Assembly (DMA) of the G-CLEF. The G-CLEF FCC is included as a part in the G-CLEF Front End Assembly (GCFEA), which monitors the field images focused on a fiber mirror to control the flexure and the focus errors within the GCFEA. The five optical components constituting the FCC are aligned on a common optical bench. The order of the optical train is: a collimator, neutral density filters, a focus analyzer, a reimaging camera barrel, and a detector module. The collimator receives the beam reflected by the fiber mirror and consists of a triplet lens. The neutral density filters are located just after the collimator to make it possible a broad range star brightness as a target or a guide. The tent prism focus analyzer is positioned at a pupil produced by the collimator and is used to measure a focus offset. The reimaging camera barrel includes two pairs of doublet lenses to focus the beam onto the CCD focal plane. The detector module is composed of a linear translator and a field de-rotator. (Oh et al., 2018)

The FCC optics on the optical bench
The FCC mounted on the GCIP assembly

The function of the CLS is to feed two separate optical calibration fibers from various types of calibration light sources to the G CLEF spectrograph for calibration. The CLS consists of three parts: the source part, the fiber moving part and the support electronics part. The source part contains five light source modules and two spare module spaces. The fiber moving part has two calibration fiber heads mounted on each of the linear stage separately. Each source module has its own collimating lens that collimates light from the source into the fiber head in the fiber moving part. The focusing lens in the fiber head produces a source image on the calibration fiber. The two fiber heads can move independently.

Calibration Light Source Subsystem

Participating institutions

KASI OATG, Smithsonian Astrophysical Observatory (SAO)/Harvard-Smithsonian Center for Astrophysics (CfA), Carnegie Observatories

Presentation and publications

KASI CfLAT Optical Astronomical Technology Group 2018