Tim Hardy

Progress on Altair: The Gemini North Adaptive Optics System

The Gemini Adaptive Optics System, (Altair), under construction at the National Research Council of Canadas Herzberg Institute of Astrophysics is unique among AO systems. Altair is designed with its deformable mirror (DM) conjugate to high altitude. We summarize construction progress. We then describe Altair in more detail. Both the Wavefront sensor foreoptics and control system are unconventional, because the guide star footprint on an altitude-conjugated DM moves as the guide star position varies. During a typical nodding sequence, where the telescope moves 10 arcseconds between exposures, this footprint moves by half an actuator and/or WFS lenslet. The advantages of altitude conjugation include increased isoplanatic patch size, which improves sky coverage, and improved uniformity of the corrected field. Altitude conjugation also reduces focal anisoplanatism with laser beacons. Although the initial installation of Altair will use natural guide stars, it will be fully ready to use a laser guide star (LGS). The infrastructure of Gemini observatory provides a variety of wavefront sensors and nested control loops that together permit some unique design concepts for Altair.

FLAMINGOS-2: the facility near-infrared wide-field imager and multi-object spectrograph for Gemini

Stephen Eikenberry, Reba Bandyopadhyay, J. Greg Bennett, Aaron Bessoff, Matt Branch, Miguel Charcos, Richard Corley, Curtis Dewitt, John-David Eriksen, Richard Elston, Skip Frommeyer, Anthony Gonzalez, Kevin Hanna, Michael Herlevich, David Hon, Jeff Julian, Roger Julian, Nestor Lasso, Antonio Marin-Franch, Jose Marti, Charlie Murphey, S. Nicholas Raines, William Rambold, David Rashkin, Craig Warner Department of Astronomy, University of Florida, Gainesville, FL 32611

Inuksuit: robotic astronomical site-testing stations in the Canadian High Arctic

Coastal mountains at Canadas northern tip possess many of the desirable properties that make the Antarctic glacial plateau attractive for astronomy: they are cold, high, dry, and in continuous darkness for several months in winter. Satellite images suggest that they should also benefit from clear skies for a fraction of time comparable to the best mid-latitude sites, and conventional site-selection criteria point to good seeing. In order to confirm these conditions, we are testing three mountain sites on northwestern Ellesmere Island, in Nunavut. On each we have installed a compact, autonomous site-testing station consisting of a meteorological station, a simple optical/near-infrared camera for sensing cloud cover, and - at one site - a more advanced all-sky viewing camera. The systems were deployed by helicopter and run on batteries recharged by wind (a compact methanol fuel cell is under study as a supplementary power source). Effective two-way communications via the Iridium satellite network allows a limited number of highly compressed images to be transferred. The full-winter dataset is stored at the site on flash-drives, thus requiring a return visit to retrieve, but day-to-day station performance can be assessed using telemetry and a computer model. Based on site-testing results, the plan is to select one site for the addition of a seeing monitor and a small but scientifically productive telescope.

FLAMINGOS-2 OIWFS

An On-Instrument Wavefront Sensor (OIWFS) designed, built and tested by the National Research Council of Canada (NRC) for the FLoridA Multi-object Imaging Near-IR Grism Observational Spectrometer (FLAMINGOS) is described. The University of Florida is building the FLAMINGOS-2 IR spectrograph for the Gemini Observatory as a near copy of the original multi-telescope FLAMINGOS instrument. NRC/HIA was subcontracted to build the OIWFS based on the Gemini Multi-Object Spectrograph (GMOS) design. The FLAMINGOS-2 OIWFS patrols the bulk of the FLAMINGOS-2 field-of-view and will accept the Gemini f/16 input beam as well as the f/30 beam from the Gemini Multi-Conjugate Adaptive Optics (MCAO) system. The portion of the probe arm that enters the FLAMINGOS-2 field-of-view is cooled, to avoid contaminating the infrared images. The OIWFS uses the same CCD and CCD controller as was used on GMOS (e2v CCD39 and ARC GENII). Mechanically, the OIWFS is a modified version of the GMOS OIWFS. It comprises two stacked rotational stages, each operating on a single bearing. The top stage supports an optics package, which includes a lenslet array, pickoff arm and CCD. The optical design uses a four subaperture Shack-Hartmann lenslet array. The mechanism is controlled using EPICS based software that includes GUI engineering screens. Test results showing the OIWFS to be fully compliant with design specifications are presented.

The infrared imaging spectrograph (IRIS) for TMT: electronics-cable architecture

The InfraRed Imaging Spectrograph (IRIS) is a first-light instrument for the Thirty Meter Telescope (TMT). It combines a diffraction limited imager and an integral field spectrograph. This paper focuses on the electrical system of IRIS. With an instrument of the size and complexity of IRIS we face several electrical challenges. Many of the major controllers must be located directly on the cryostat to reduce cable lengths, and others require multiple bulkheads and must pass through a large cable wrap. Cooling and vibration due to the rotation of the instrument are also major challenges. We will present our selection of cables and connectors for both room temperature and cryogenic environments, packaging in the various cabinets and enclosures, and techniques for complex bulkheads including for large detectors at the cryostat wall.

Developing an infrared APD array camera for near-infrared wavefront sensing

We will be upgrading the MMT Observatory’s (MMTO) Adaptive Optics (AO) system with a novel Pyramid Wavefront Sensor (PWFS). Our camera will utilize Leonardo’s SAPHIRA, a low-read-noise electron Avalanche Photodiode (eAPD) array. By observing natural guide stars in the near-infrared, we will improve the sky coverage at the MMTO by an order of magnitude. We have developed a compact cryostat that utilizes Sunpower’s CryoTel MT cryocooler to reduce the SAPHIRA’s dark current and thermal background radiation. Our camera’s cooling performance and cryocooler induced vibrations have been quantified and the results are presented here. Upon characterizing the laboratory performance of our camera at various reverse-bias voltages, this instrument will be integrated with MMTO’s adaptive optics system. The successful implementation of this wavefront sensor will pave the way for future applications using this technology in AO systems of extremely large telescopes.

Hamamatsu CCD upgrade for the Gemini multi-object spectrographs GMOS-S and GMOS-N: results from the 2017 GMOS-N upgrade and project completion summary

The installation of fully-depleted Hamamatsu CCDs in GMOS-N in February/March 2017 marked the conclusion of the CCD upgrade project for the two Gemini Multi-Object Spectrographs. The corresponding upgrade for GMOS-S was completed in June/July 2014, so that both GMOS instruments are now operated with a detector array of three fully-depleted Hamamatsu CCDs. We present results from the commissioning of the GMOS-N Hamamatsu CCDs and discuss their on-sky performance. We provide a comparison of the GMOS-N and GMOSS detector parameters and summarize the main observing and data reduction strategies that apply to both detector arrays.

Upgrading the MMT AO system with a near-infrared Pyramid wavefront sensor

There are long existing limitations of the sky coverage of astronomical Adaptive Optics (AO) systems that use natural guide stars (NGSs) as reference sources. In this work, we present numerical simulations and lab test results of an optical NGS pyramid wavefront sensor (PWFS) for the MMT AO system. The potential increase of sky coverage benefits from the gain in sensitivity of the PWFS in a closed-loop NIR AO system compared with the optical Shack-Hartmann wavefront sensor (SHWFS). The upgraded MMT AO WFS system will use IR avalanche photodiode (APD) array with extremely low readout noise (at sub-electron level), run at a high frame rate (over 1kHz), and cover the wavelength range from 0.85-1.8 μm. This upgraded system will access a larger portion of the sky by looking at fainter, redder reference stars. We use ”yao” simulation to show the expected limiting magnitude gain of NIR PWFS compared with the existing optical SHWFS. The sky coverage will increase by 11 times at the Galactic plane and by 6 times at the North Galactic Pole when compared to traditional optical WFSs. This novel WFS will also enable observations of the dust obscured plane of the Galaxy, where the optical light of most stars is more extincted. We demonstrate the basic lab test with a set of double roof prisms. We evaluate the overall performance of the PWFS on our lab AO bench, present captured micro-pupil images and do wavefront reconstruction. We will upgrade to SAPHIRA and pyramid prism for later lab test. We plan to implement this system at MMT and carry out on-sky tests in Spring 2019.

NFIRAOS adaptive optics for the Thirty Meter Telescope

NFIRAOS (Narrow-Field InfraRed Adaptive Optics System) will be the first-light multi-conjugate adaptive optics system for the Thirty Meter Telescope (TMT). NFIRAOS houses all of its opto-mechanical sub-systems within an optics enclosure cooled to precisely -30°C in order to improve sensitivity in the near-infrared. It supports up to three client science instruments, including the first-light InfraRed Imaging Spectrograph (IRIS). Powering NFIRAOS is a Real Time Controller that will process the signals from six laser wavefront sensors, one natural guide star pyramid WFS, up to three low-order on-instrument WFS and up to four guide windows on the client instrument’s science detector in order to correct for atmospheric turbulence, windshake, optical errors and plate-scale distortion. NFIRAOS is currently preparing for its final design review in late June 2018 at NRC Herzberg in Victoria, British Columbia in partnership with Canadian industry and TMT.

Acquisition and Dithering with the TMT IRIS On-Instrument Wavefront Sensor System

IRIS is a first-light facility instrument for the TMT that operates as a client of the NFIRAOS MCAO system. IRIS is a collaboration between TMT, Caltech, the University of California, NAOJ and NRC Herzberg. IRIS contains three OnInstrument WaveFront Sensors (OIWFS) probes which together with On-Detector Guide Windows (ODGW) on the IRIS imager, pick off light from natural guide stars over a two arcminute diameter field of regard. Here, we present typical use cases for the OIWFS and ODGW including acquisition, dithering, and tracking non-sidereal targets while highlighting design choices that allow these operations to be performed in the minimal amount of time while achieving the required performance. We conclude with some potential changes that will be explored early in the final design phase.