Thomas Gauron

Hectospec, the mmt's 300 optical fiber-fed spectrograph

ABSTRACT The Hectospec is a 300 optical fiber fed spectrograph commissioned at the MMT in the spring of 2004. In the configuration pioneered by the Autofib instrument at the Anglo‐Australian Telescope, Hectospec’s fiber probes are arranged in a radial “fisherman on the pond” geometry and held in position with small magnets. A pair of high‐speed, six‐axis robots move the 300 fiber buttons between observing configurations within ∼300 s, and to an accuracy of ∼25 μm. The optical fibers run for 26 m between the MMT’s focal surface and the bench spectrograph, operating at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textc...

A prototype phasing camera for the Giant Magellan Telescope

Achieving the diffraction limit with the adaptive optics system of the 25m Giant Magellan Telescope will require that the 7 pairs of mirror segments be in phase. Phasing the GMT is made difficult because of the 30-40cm gaps between the primary mirror segments. These large gaps result in atmospheric induced phase errors making optical phasing difficult at visible wavelengths. The large gaps between the borosilicate mirror segments also make an edge sensing system prone to thermally induced instability. We describe an optical method that uses twelve 1.5-m square subapertures that span the segment boundaries. The light from each subaperture is mapped onto a MEMS mirror segment and then a lenslet array which are used to stabilize the atmospherically induced image motion. Centroids for stabilization are measured at 700nm. The piston error is measured from the fringes visible in each of the 12 stabilized images at 2.2 microns. By dispersing the fringes we can resolve 2π phase ambiguities. We are constructing a prototype camera to be deployed at the 6.5m Magellan Clay telescope.

The GMT-Consortium Large Earth Finder (G-CLEF): an optical Echelle spectrograph for the Giant Magellan Telescope (GMT)

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 3500Å to 9500Å. 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.

The G-CLEF spectrograph optical design

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph, which has been selected as a first light instrument for the Giant Magellan Telescope (GMT) currently under construction at the Las Campanas Observatory. We designed G-CLEF as a general-purpose echelle spectrograph with a precision radial velocity (PRV) capability goal of 0.1 m/s, which will enable it to detect/measure the mass of an Earth-sized planet orbiting a Solar-type star in its habitable zone. This goal imposes challenging requirements on all aspects of the instrument and some of those are best incorporated directly into the optical design process. In this paper we describe the preliminary optical design of the G-CLEF instrument and briefly describe some novel solutions we have introduced into the asymmetric white pupil echelle configuration.

The opto-mechanical design of the GMT-consortium large earth finder (G-CLEF)

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.

Two decades of Chandra high-resolution camera operations: lessons learned and future prospects

We summarize nearly two decades of successful operation of the Chandra High Resolution Camera (HRC). The HRC is a pair of cesium–iodide (CsI) coated microchannel plate X-ray detectors launched in July, 1999, one optimized for widefield imaging (HRC-I) and a second as a readout for X-ray transmission gratings (HRC-S). We discuss the temporal evolution of the performance of the flight instrument, the impact of extended exposure to the charged particle environment of high Earth orbit, and lessons learned from nineteen years of flight operations. We also describe our investigation of new algorithms to remove more efficiently the charged particle background from the science data, as we prepare for another decade of operation.

The preliminary design of the G-CLEF spectrograph instrument device control system

The Giant Magellan Telescope (GMT)-Consortium Large Earth Finder (G-CLEF) is a fiber-fed, precision radial velocity optical echelle spectrograph. The preliminary software design incorporates a hierarchical, multi-level state machine. At the lowest level, the state machine utilizes GMT-provided frameworks to communicate with the hardware. At higher levels of abstraction, the design makes extensive use of State Chart Extensible Markup Language (SCXML) representations to define the operation of the instrument. The functionality of the design can be validated by executing these representations. The incorporation of an interpreter to directly execute the SCXML as a component of the control system is being investigated. The approaches used to develop the preliminary software design concept are described, the use and utility of SCXML for instrument control is discussed, and the application of the preliminary design to a subset of G-CLEF subsystems is demonstrated.

Monolithic CMOS detectors for use as x-ray imaging spectrometers

The Smithsonian Astrophysical Observatory (SAO) in collaboration with Stanford Research Institute (SRI) has been developing monolithic CMOS detectors for use as astronomical soft X-ray imaging spectrometers since 2008. The long term goal of this collaboration is to produce X-ray Active Pixel Sensor (APS) detectors with Fano limited performance over the 0.1-10keV band for “Facility Class” missions such as Lynx. Since CMOS x-ray imagers consume very little power; are inherently ”radiation hard”; have high levels of integration, and are capable of very high read rates they are ideal for “Small Satellite” missions as well. SAO/SRI CMOS imagers are presently being proposed for several, more immediate X-ray “Small Sat” real and concept missions. CMOS device fabrication provides the most rapid path forward towards advances in virtually all types of integrated circuits. The same techniques and infrastructure that has produced tremendous capabilities in microprocessors, RAM and FPGAs are now being applied to CMOS based imaging detectors CMOS imaging detectors have found their way into high end consumer cameras and in various (non X-ray) astronomical missions, e.g. the flight imaging detectors for the SoloHi mission, the WISPR imager on the Parker Solar Probe. SAO is presently investigating three different devices that each embody technology that would be highly desirable in an x-ray imaging spectrometer; these are: back thinned high sensitivity NMOS PPD devices; NMOS devices with stitchable reticles; and monolithic PMOS devices that collect photo-holes instead of photo electrons. The back-thinned, high sensitivity NMOS PPD devices, known as Big Minimal IIIs (BMIII) were specifically funded and designed for soft x-ray single photon counting. They embody a 1k by 1k array of 6 Transistor (6T) 16µm PPD pixels. Each pixel has a 135 μV/e sense node. The stitchable reticle devices, known as “Mk by Nk”, can be made seamlessly in any format which fits on a silicon wafer. They consist of an array of 6 Transistor (6T) 10μm PPD pixels (for these test devices M=N=1) with a sense node of 90 μV/e. A stichable reticle CMOS with a choice of format size would be ideal for large focal plane or for a narrow rectangular grating readout. The third device category is a small 256 by 256 16μm pixel PMOS device which collects holes instead of electrons with a 60μV/h+ sense node. SAO/SRI conventional NMOS CMOS devices known as the Big Minimal III (BigMinIII) have recently demonstrated the ability to detect and resolve X-rays with energies below 200eV. Even with this very good sub-1keV response, an NMOS astronomical instrument would still be fundamentally limited by charge collection, read and Random Telegraph Signal (RTS) noise particularly for soft, faint, extended sources and surveys. We have just for the first time performed very preliminary X-ray tests with monolithic FI PMOS devices. We present details of our new camera design and preliminary device performance with particular emphasis on those aspects of interest to single photon counting X-ray astronomy.

Precision thermal control of the GMT-Consortium Large Earth Finder (G-CLEF)

The GMT-Consortium Large Earth Finder (G-CLEF) will be part of the first generation instrumentation suite for the Giant Magellan Telescope (GMT). G-CLEF will be a general purpose optical passband echelle spectrograph with a precision radial velocity (PRV) capability of 10 cm/sec, a requirement necessary for the detection of Earth analogues. The instrument will be particularly sensitive to thermal effects and the necessary stability cannot be achieved through the use of low CTE materials alone. It is the combination of low CTE materials and exquisite thermal control which will enable the instrument to achieve its precision requirements. G-CLEF will complete its Critical Design phase in mid-2018. In this paper, we discuss the precision thermal control systems which enable milli-Kelvin-level stability of the spectrograph and its red and blue focal planes. The measurement electronics and thermal control strategies used in the spectrograph are described. Of particular importance is the development of a continuous LN2 flow cryo-cooler system used to maintain the focal planes at stable cryogenic operational temperatures. This system has been validated with a prototyping effort completed during the instrument’s design phase. We also review G-CLEF’s insulated enclosure which simultaneously maintains the spectrograph a stable temperature and limits the maximum thermal leakage into the telescope dome. This work has been supported by the GMTO Corporation, a non-profit organization operated on behalf of an international consortium of universities and institutions: Arizona State University, Astronomy Australia Ltd, the Australian National University, the Carnegie Institution for Science, Harvard University, the Korea Astronomy and Space Science Institute, the São Paulo Research Foundation, the Smithsonian Institution, the University of Texas at Austin, Texas AM University, the University of Arizona, and the University of Chicago.

The GMT-consortium large earth finder (G-CLEF): an optical echelle spectrograph for the Giant Magellan Telescope (GMT)

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 (< 3500Å). 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. We discuss several innovative structural, optical and control system features that differentiate G-CLEF from previous precision RV instruments.