Jonathan Lawrence

Infrared and Submillimeter Atmospheric Characteristics of High Antarctic Plateau Sites

The best ground-based astronomical sites in terms of telescope sensitivity at infrared and submillimeter wavelengths are located on the Antarctic Plateau, where high atmospheric transparency and low sky emission are obtained because of the extremely cold and dry air; these benefits are well characterized at the South Pole station. The relative advantages offered by three potentially superior sites, Dome C, Dome F, and Dome A, located higher on the Antarctic Plateau, are quantified here through the development of atmospheric models using the line-by-line radiative transfer model code. In the near- to mid-infrared, sensitivity gains relative to the South Pole of up to a factor of 10 are predicted at Dome A, and a factor of 2 for Dome C. In the mid- to far-infrared, sensitivity gains relative to the South Pole up to a factor of 100 are predicted for Dome A and 10 for Dome C. These values correspond to even larger gains (up to 3 orders of magnitude) compared to the best mid-latitude sites, such as Mauna Kea and the Chajnantor Plateau.

The Dark Energy Spectrometer (DESpec): A Multi-Fiber Spectroscopic Upgrade of the Dark Energy Camera and Survey for the Blanco Telescope

We describe an initiative to build and use the Dark Energy Spectrometer (DESpec), a wide-field spectroscopic survey instrument for the Blanco 4 meter telescope at Cerro Tololo InterAmerican Observatory (CTIO) in Chile. A new system with about 4000 robotically positioned optical fibers will be interchangeable with the CCD imager of the existing Dark Energy Camera (DECam), accessing a field of view of 3.8 square degrees in a single exposure. The proposed instrument will be operated by CTIO and available for use by the astronomy community. Our collaboration proposes to use DESpec to conduct a wide, deep spectroscopic survey to study Dark Energy. In a survey of about 350 nights, the DESpec collaboration proposes to obtain spectroscopic redshifts for about 8 million galaxies over 5000 square degrees selected from the Dark Energy Survey (DES). This Dark Energy Spectroscopic Survey will advance our knowledge of cosmic expansion and structure growth significantly beyond that obtainable with imaging-only surveys. Since it adds a spectroscopic third dimension to the same sky as DES, DESpec will enable increasingly precise techniques to discriminate among alternative explanations of cosmic acceleration, such as Dark Energy and Modified Gravity.

The Science Case for PILOT III: the Nearby Universe

PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed 2.5-m optical/ infrared telescope to be located at Dome C on the Antarctic plateau. The atmospheric conditions at Dome C deliver a high sensitivity, high photometric precision, wide-field, high spatial resolution, and high-cadence imaging capability to the PILOT telescope. These capabilities enable a unique scientific potential for PILOT, which is addressed in this series of papers. The current paper presents a series of projects dealing with the nearby Universe that have been identified as key science drivers for the PILOT facility. Several projects are proposed that examine stellar populations in nearby galaxies and stellar clusters in order to gain insight into the formation and evolution processes of galaxies and stars. A series of projects will investigate the molecular phase of the Galaxy and explore the ecology of star formation, and investigate the formation processes of stellar and planetary systems. Three projects in the field of exoplanet science are proposed: a search for free-floating low-mass planets and dwarfs, a program of follow-up observations of gravitational microlensing events, and a study of infrared light-curves for previously discovered exoplanets. Three projects are also proposed in the field of planetary and space science: optical and near-infrared studies aimed at characterising planetary atmospheres, a study of coronal mass ejections from the Sun, and a monitoring program searching for small-scale Low Earth Orbit satellite debris items.

Proposed instrumentation for PILOT

PILOT (the Pathfinder for an International Large Optical Telescope) is a proposed Australian/European optical/infrared telescope for Dome C on the Antarctic Plateau, with target first light in 2012. The proposed telescope is 2.4m diameter, with overall focal ratio f/10, and a 1 degree field-of-view. In median seeing conditions, it delivers 0.3 FWHM wide-field image quality, from 0.7-2.5 microns. In the best quartile of conditions, it delivers diffraction-limited imaging down to 1 micron, or even less with lucky imaging. The areas where PILOT offers the greatest advantages are (a) very high resolution optical imaging, (b) high resolution wide-field optical imaging, and (c) all wide-field thermal infrared imaging. The proposed first generation instrumentation consists of (a) a fast, low-noise camera for diffraction-limited optical lucky imaging; (b) a gigapixel optical camera for seeing-limited imaging over a 1 degree field; (c) a 4K x 4K near-infrared (1-5 micron) camera with both wide-field and diffraction-limited modes; and (d) a double-beamed midinfrared (7-40 micron) camera.

The MANIFEST prototyping design study

MANIFEST is a facility multi-object fibre system for the Giant Magellan Telescope, which uses ‘Starbug’ fibre positioning robots. MANIFEST, when coupled to the telescope’s planned seeing-limited instruments, GMACS, and G-CLEF, offers access to: larger fields of view; higher multiplex gains; versatile reformatting of the focal plane via IFUs; image-slicers; and in some cases higher spatial and spectral resolution. The Prototyping Design Study phase for MANIFEST, nearing completion, has focused on developing a working prototype of a Starbugs system, called TAIPAN, for the UK Schmidt Telescope, which will conduct a stellar and galaxy survey of the Southern sky. The Prototyping Design Study has also included work on the GMT instrument interfaces. In this paper, we outline the instrument design features of TAIPAN, highlight the modifications that will be necessary for the MANIFEST implementation, and provide an update on the MANIFEST/instrument interfaces.

Veloce Rosso: Australia's new precision radial velocity spectrograph

Veloce is an ultra-stable fibre-fed R4 echelle spectrograph for the 3.9 m Anglo-Australian Telescope. The first channel to be commissioned, Veloce ‘Rosso’, utilises multiple low-cost design innovations to obtain Doppler velocities for sun-like and M-dwarf stars at <1 ms -1 precision. The spectrograph has an asymmetric white-pupil format with a 100-mm beam diameter, delivering R>75,000 spectra over a 580-930 nm range for the Rosso channel. Simultaneous calibration is provided by a single-mode pulsed laser frequency comb in tandem with a traditional arc lamp. A bundle of 19 object fibres ensures full sampling of stellar targets from the AAT site. Veloce is housed in dual environmental enclosures that maintain positive air pressure at a stability of ±0.3 mbar, with a thermal stability of ±0.01 K on the optical bench. We present a technical overview and early performance data from Australias next major spectroscopic machine.

VELOCE’s novel IFU-fitted fibre feed

VELOCE is an IFU fibre feed and spectrograph for the AAT that is replacing CYCLOPS2. It is being constructed by the AAO and ANU. In this paper we discuss the design and engineering of the IFU/fibre feed components of the cable. We discuss the mode scrambling gain obtained with octagonal core fibres and how these octagonal core fibres should be spliced to regular circular core fibres to ensure maximum throughput for the cable using specialised splicing techniques. In addition we also describe a new approach to manufacturing a precision 1D/2D array of optical fibres for some applications in IFU manufacture and slit manufacture using 3D printed fused silica substrates, allowing for a cheap substitute to expensive lithographic etching in silicon at the expense of positional accuracy. We also discuss the Menlo Systems laser comb which employs endlessly-singlemode fibre to eliminate modal noise associated with multimode fibre transmission to provide the VELOCE spectrograph with a stable and repeatable source of wavelength calibration lines.

PRAXIS: an OH suppression optimised near infrared spectrograph

The problem of atmospheric emission from OH molecules is a long standing problem for near-infrared astronomy. PRAXIS is a unique spectrograph which is fed by fibres that remove the OH background and is optimised specifically to benefit from OH-Suppression. The OH suppression is achieved with fibre Bragg gratings, which were tested successfully on the GNOSIS instrument. PRAXIS uses the same fibre Bragg gratings as GNOSIS in its first implementation, and will exploit new, cheaper and more efficient, multicore fibre Bragg gratings in the second implementation. The OH lines are suppressed by a factor of ∼ 1000, and the expected increase in the signal-to-noise in the interline regions compared to GNOSIS is a factor of ∼ 9 with the GNOSIS gratings and a factor of ∼ 17 with the new gratings. PRAXIS will enable the full exploitation of OH suppression for the first time, which was not achieved by GNOSIS (a retrofit to an existing instrument that was not OH-Suppression optimised) due to high thermal emission, low spectrograph transmission and detector noise. PRAXIS has extremely low thermal emission, through the cooling of all significantly emitting parts, including the fore-optics, the fibre Bragg gratings, a long length of fibre, and the fibre slit, and an optical design that minimises leaks of thermal emission from outside the spectrograph. PRAXIS has low detector noise through the use of a Hawaii-2RG detector, and a high throughput through a efficient VPH based spectrograph. PRAXIS will determine the absolute level of the interline continuum and enable observations of individual objects via an IFU. In this paper we give a status update and report on acceptance tests.

GHOST optical fiber system

The Gemini High-Resolution Optical SpecTrograph (GHOST) is the newest instrument being developed for the Gemini telescopes, in a collaboration between the Australian Astronomical Observatory (AAO), the Herzberg Institute for Astrophysics, National Research Council (HIA-NRC) in Canada, and the Australian National University. This paper describes the design of the fiber optic system, developed by AAO. This system links the GHOST multi-object positioner, mounted on Geminis Cassegrain focus, with the HIA-NRC developed spectrograph, located in the pier lab, 20 meters below the main observatory floor. The GHOST optical cable consists of 62 fibers, Polymicro FBP53/74/94P (53 μm core, 94 μm polyimide buffer), packed into 8 furcation tubes. The optical fibers are held inside the furcation tubes by friction, with between one and twelve fibers in each of the individual tubes. The furcation tubes are mechanically secured to manifold and anchor assemblies by bonding to integral Kevlar yarn within the tubing. The cable includes an interlock switch, linked to the telescope control system, to halt all telescope motions if the cable becomes overstressed. Fibers are terminated by two integral field units (IFU1 and IFU2), guiding and science slits and a calibration light entry port. Mode scrambling is achieved by mechanical agitation in two orthogonal directions, with adjustable frequency and amplitude of up to 10 Hz and 50 mm, respectively.

TAIPAN: the AAO's first Starbug positioner and spectrograph (Conference Presentation)

The AAO’s TAIPAN instrument is a multi-object fibre positioner and spectrograph installed on the 1.2m UK-Schmidt telescope at Siding Spring Observatory. The positioner, a prototype for the MANIFEST positioner on the Giant Magellan Telescope, uses independently controlled Starbug robots to position a maximum of 300 optical fibres on a 32cm glass field plate (for a 6 degree field of view), to an accuracy of 5 microns (0.3 arcsec). The Starbug technology allows multi-object spectroscopy to be carried out with a minimum of overhead between observations, significantly decreasing field configuration time. Over the next 5 years the TAIPAN instrument will be used for two southern-hemisphere surveys: Taipan, a spectroscopic survey of 1x10^6 galaxies at z<0.3, and FunnelWeb, a stellar survey complete to Gaia G=12.5. In this paper we present an overview of the operational TAIPAN instrument: its design, construction and integration, and discuss the 2017 commissioning campaign and science verification results obtained in early 2018.