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The Keck Planet Finder (KPF) is a fiber-fed, high-resolution, high-stability spectrometer in development at the UC Berkeley Space Sciences Laboratory for the W.M. Keck Observatory. KPF is designed to characterize exoplanets via Doppler spectroscopy with a goal of a single measurement precision of 0.3 m s-1 or better, however its resolution and stability will enable a wide variety of astrophysical pursuits. Here we provide post-preliminary design review design updates for several subsystems, including: the main spectrometer, the fabrication of the Zerodur optical bench; the data reduction pipeline; fiber agitator; fiber cable design; fiber scrambler; VPH testing results and the exposure meter.

Precise wavelength calibration is a critical issue for high-resolution spectroscopic observations. The ideal calibration source should be able to provide a very stable and dense grid of evenly distributed spectral lines of constant intensity. A new method which satisfies all mentioned conditions has been developed by our group. The approach is to actively measure the exact position of a single spectral line of a Fabry-Perot etalon with very high precision with a wavelength-tuneable laser and compare it to an extremely stable wavelength standard. The ideal choice of standard is the D2 absorption line of Rubidium, which has been used as an optical frequency standard for decades. With this technique, the problem of stable wavelength calibration of spectrographs becomes a problem of how reliably we can measure and anchor one etalon line to the Rb transition. In this work we present our self-built module for Rb saturated absorption spectroscopy and discuss its stability., SPIE ANZCOP conference, Melbourne 2019

We report on the upgrade of the fiber link of FIES, the high-resolution echelle spectrograph at the Nordic Optical Telescope (NOT). In order to improve the radial velocity (RV) stability of FIES, we replaced the circular fibers by octagonal and rectangular ones to utilize their superior scrambling performance. Two additional fibers for a planned polarimetry mode were added during the upgrade. The injection optics and the telescope front-end were also replaced. The first on-sky RV measurements indicate that the influence of guiding errors is greatly suppressed, and the overall RV precision of FIES has significantly improved.

MAROON-X is a red-optical, high precision radial velocity spectrograph currently nearing completion and undergoing extensive performance testing at the University of Chicago. The instrument is scheduled to be installed at Gemini North in the first quarter of 2019. MAROON-X will be the only RV spectrograph on a large telescope with full access by the entire US community. In these proceedings we discuss the latest addition of the red wavelength arm and the two science grade detector systems, as well as the design and construction of the telescope front end. We also present results from ongoing RV stability tests in the lab. First results indicate that MAROON-X can be calibrated at the sub-m s−1 level, and perhaps even much better than that using a simultaneous reference approach.

The GMT-Consortium Large Earth Finder (G-CLEF) will be a cross-dispersed, optical band echelle spectrograph to be delivered as the first light scientific instrument for the Giant Magellan Telescope (GMT) in 2022. G-CLEF is vacuum enclosed and fiber-fed to enable precision radial velocity (PRV) measurements, especially for the detection and characterization of low-mass exoplanets orbiting solar-type stars. The passband of G-CLEF is broad, extending from 3500A to 9500A. This passband provides good sensitivity at blue wavelengths for stellar abundance studies and deep red response for observations of high-redshift phenomena. The design of G-CLEF incorporates several novel technical innovations. We give an overview of the innovative features of the current design. G-CLEF will be the first PRV spectrograph to have a composite optical bench so as to exploit that material’s extremely low coefficient of thermal expansion, high in-plane thermal conductivity and high stiffness-to-mass ratio. The spectrograph camera subsystem is divided into a red and a blue channel, split by a dichroic, so there are two independent refractive spectrograph cameras. The control system software is being developed in model-driven software context that has been adopted globally by the GMT. G-CLEF has been conceived and designed within a strict systems engineering framework. As a part of this process, we have developed a analytical toolset to assess the predicted performance of G-CLEF as it has evolved through design phases.

We report on the construction and testing of a vacuum-gap Fabry-Perot etalon calibrator for high precision radial velocity spectrographs. The etalon is referenced against hyper fine transitions of rubidium to provide a precise wavelength calibrator for MAROON-X, a new fiber-fed, red-optical, high-precision radial-velocity spectrograph currently under construction for one of the twin 6.5m Magellan Telescopes in Chile. We demonstrate a turnkey system, ready to be installed at any current and next generation radial velocity spectrograph that requires calibration over a wide spectral band-pass. Uncertainties in the position of one etalon line are at the 10 cm s -1 level in individual measurements taken at 4 Hz. Our long-term stability is mainly limited by aging effects of the spacer material Zerodur, which imprints a 12 cm s -1 daily drift. However, as the etalon position is traced by the rubidium reference with a precision of -1 for integration times longer than 10s, we can fully account for this effect at the RV data reduction level.

The GMT-Consortium Large Earth Finder (G-CLEF) is an echelle spectrograph with precision radial velocity (PRV) capability that will be a first light instrument for the Giant Magellan Telescope (GMT). G-CLEF has a PRV precision goal of 40 cm/sec (10 cm/s for multiple measurements) to enable detection of Earth-like exoplanets in the habitable zones of sun-like stars1. This precision is a primary driver of G-CLEF’s structural design. Extreme stability is necessary to minimize image motions at the CCD detectors. Minute changes in temperature, pressure, and acceleration environments cause structural deformations, inducing image motions which degrade PRV precision. The instrument’s structural design will ensure that the PRV goal is achieved under the environments G-CLEF will be subjected to as installed on the GMT azimuth platform, including: Millikelvin (0.001 °K) thermal soaks and gradients 10 millibar changes in ambient pressure Changes in acceleration due to instrument tip/tilt and telescope slewing Carbon fiber/cyanate composite was selected for the optical bench structure in order to meet performance goals. Low coefficient of thermal expansion (CTE) and high stiffness-to-weight are key features of the composite optical bench design. Manufacturability and serviceability of the instrument are also drivers of the design. In this paper, we discuss analyses leading to technical choices made to minimize G-CLEF’s sensitivity to changing environments. Finite element analysis (FEA) and image motion sensitivity studies were conducted to determine PRV performance under operational environments. We discuss the design of the optical bench structure to optimize stiffness-to-weight and minimize deformations due to inertial and pressure effects. We also discuss quasi-kinematic mounting of optical elements and assemblies, and optimization of these to ensure minimal image motion under thermal, pressure, and inertial loads expected during PRV observations.

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph that has been selected as a first light instrument for the Giant Magellan Telescope (GMT) currently under construction at the Las Campanas Observatory in Chile’s Atacama desert region. We designed G-CLEF as a general-purpose echelle spectrograph with precision radial velocity (PRV) capability used for exoplanet detection. The radial velocity (RV) precision goal of GCLEF is 10 cm/sec, necessary for detection of Earth-sized planets orbiting stars like our Sun in the habitable zone. This goal imposes challenging stability requirements on the optical mounts and the overall spectrograph support structures. Stability in instruments of this type is typically affected by changes in temperature, orientation, and air pressure as well as vibrations caused by telescope tracking. For these reasons, we have chosen to enclose G-CLEF’s spectrograph in a thermally insulated, vibration isolated vacuum chamber and place it at a gravity invariant location on GMT’s azimuth platform. Additional design constraints posed by the GMT telescope include: a limited space envelope, a thermal emission ceiling, and a maximum weight allowance. Other factors, such as manufacturability, serviceability, available technology and budget are also significant design drivers. All of the previously listed considerations must be managed while ensuring that performance requirements are achieved. In this paper, we discuss the design of G-CLEF’s optical mounts and support structures including technical choices made to minimize the system’s sensitivity to thermal gradients. A more general treatment of the properties of G-CLEF can be found elsewhere in these proceedings1. We discuss the design of the vacuum chamber which houses the irregularly shaped optical bench and optics while conforming to a challenging space envelope on GMT’s azimuth platform. We also discuss the design of G-CLEF’s insulated enclosure and thermal control systems which maintain the spectrograph at milli-Kelvin level stability while simultaneously limiting the maximum thermal emission into the telescope dome environment. Finally, we discuss G-CLEF’s front-end assembly and fiber-feed system as well as other interface challenges presented by the telescope, enclosure and neighboring instrumentation.

The Echelon-Cross-Echelle Spectrograph (EXES) is one of the first generation instruments for the Stratospheric Observatory for Infrared Astronomy (SOFIA). The primary goal of EXES is to provide high-resolution, cross-dispersed spectroscopy, with resolutions of 50,000-100,000 and wavelength coverage of 0.5-1.5% between 4.5 μm and 28.3 μm. EXES will also have medium (R=5000-25000) and low (R=1500-4000) modes available, as well as a target acquisition imaging mode and a pupil-imaging mode for alignment testing. EXES is scheduled for commissioning flights in February 2014. It will be available to the public for shared-risk observations in SOFIA’s Cycle 2. Here we give an overview of the design and capabilities of EXES as well as its laboratory performance to date.

The Echelon-cross-Echelle Spectrograph (EXES) is one of the first generation instruments for the Stratospheric Observatory for Infrared Astronomy (SOFIA). It operates at high, medium, and low spectral resolution in the wavelength region 4.5 to 28.3 microns using a 1024x1024 Si:As detector array. From SOFIA, the high spectral resolution mode (R ≈ 100,000) will provide truly unique data given the improved atmospheric transmission. We are currently involved with system testing in preparation for our first ground-based telescope run to occur in Jan 2011 at the NASA IRTF 3m. We present the current status of EXES including lab results in our high and medium resolution modes, our plans for ground-based observing, and our expectations for operations on SOFIA.

CRIRES is a cryogenic, pre-dispersed, infrared Echelle spectrograph designed to provide a nominal resolving power ν/Δν of 105 between 1000 and 5000 nm for a nominal slit width of 0.2". The CRIRES installation at the Nasmyth focus A of the 8-m VLT UT1 (Antu) marks the completion of the original instrumentation plan for the VLT. A curvature sensing adaptive optics system feed is used to minimize slit losses and to provide 0.2" spatial resolution along the slit. A mosaic of four Aladdin InSb-arrays packaged on custom-fabricated ceramic boards has been developed. It provides for an effective 4096 × 512 pixel focal plane array to maximize the free spectral range covered in each exposure. Insertion of gas cells is possible in order to measure radial velocities with high precision. Measurement of circular and linear polarization in Zeeman sensitive lines for magnetic Doppler imaging is foreseen but not yet fully implemented. A cryogenic Wollaston prism on a kinematic mount is already incorporated. The retarder devices will be located close to the Unit Telescope focal plane. Here we briefly recall the major design features of CRIRES and describe the commissioning of the instrument including a report of extensive testing and a preview of astronomical results.

The University of Hawaii Wide-Field Imager (UHWFI) is a focal compressor designed to project the full half-degree field of the UH 2.2m telescope onto the refurbished 8K×8K CCD camera. The optics use Ohara glasses and are mounted in an oil-filled cell to minimize light losses and ghost images from the large number of internal surfaces. The UHWFI is equipped with a six-position filter wheel and a rotating sector shutter, both driven by stepper motors. The instrument is currently in the design phase and will be commissioned early in 2003.