Andrew McGrath

Starbug: enabling the smart focal plane

We propose a new robotic system for positioning payloads such as pickoff mirrors, fibres or deployable IFUs on telescope focal planes. Based on a combination of concepts used in existing fibre positioning systems, the proposed system retains the advantages of each type of existing positioner, while eliminating many of the disadvantages. It employs micro-robotic actuators to independently and simultaneously position an arbitrary number of small payloads accurately on an arbitrarily large field plate and offers a cost-effective and multiply-redundant design for payload positioning systems suitable for use at Cassegrain or Nasmyth foci of large telescopes. Operation in cryogenic environments, positioning accuracies of a few microns, simultaneous movement of arbitrary numbers of positioners and the removal of many movement constraints are some of the advantages offered. We demonstrate a prototype positioner for the system.

The Science Case for PILOT I: Summary and Overview

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. Conditions at Dome C are known to be exceptional for astronomy. The seeing (above ∼30 m height), coherence time, and isoplanatic angle are all twice as good as at typical mid-latitude sites, while the water-vapour column, and the atmosphere and telescope thermal emission are all an order of magnitude better. These conditions enable a unique scientific capability for PILOT, which is addressed in this series of papers. The current paper presents an overview of the optical and instrumentation suite for PILOT and its expected performance, a summary of the key science goals and observational approach for the facility, a discussion of the synergies between the science goals for PILOT and other telescopes, and a discussion of the future of Antarctic astronomy. Paper II and Paper III present details of the science projects divided, respectively, between the distant Universe (i.e. studies of first light, and the assembly and evolution of structure) and the nearby Universe (i.e. studies of Local Group galaxies, the Milky Way, and the Solar System).

It's alive! Performance and control of prototype Starbug actuators

As part of the Starbug development, a range of actuator technologies have been prototyped and trialled in the quest to develop this novel focal plane positioning system. The Starbug concept is a robotic positioning system that deploys multiple payloads, such as pickoff optics, optical fibres and other possible devices to micron level accuracy over a flat or curved focal plane. The development is aimed at addressing some of the limitations of other positioning systems to provide a reliable, cost effective way of positioning multiple payloads in ambient and cryogenic environments. In this paper we identify the specification and required characteristics of the micro-robotic actuators as applied to the MOMSI instrument concept, present descriptions of some of the prototypes along with the results from characterisation and performance tests. These tests were undertaken at various orientations and temperatures as well as using different actuator concepts.

The MOMFOS fiber positioner

The Anglo-Australian Observatory has undertaken a design study for a ≈1000 fibre positioner for the prime focus of the Giant Segmented Mirror Telescope (GSMT) as part of the MOMFOS (Multi-Object Multi-Fibre Optical Spectrograph) instrument. To our knowledge this is the first design study funded for a prime focus instrument for an ELT. It offers a particularly elegant and efficient solution for wide-field multiobject spectroscopy on extremely large telescopes (>30m) for the acquisition of large scale high-redshift surveys (12), density coverage (≈2.5 million galaxies) and limiting magnitude (R≤26.5). Closely based on the innovative Echidna positioner under construction for Subarus FMOS system, the MOMFOS positioner uses piezoelectric microrobotic actuators able to position accurately all 1000 fibres simultaneously. The FMOS-Echidna design is extended to include a novel position feedback system offering radical benefits in cost and speed. We present positioning results for a design capable of a higher packing density than that developed for FMOS-Echidna, providing ≈1000 fibres across the 175 mm diameter field of view (20 arcmin).

Deployable payloads with Starbug

We explore the range of wide field multi-object instrument concepts taking advantage of the unique capabilities of the Starbug focal plane positioning concept. Advances to familiar instrument concepts, such as fiber positioners and deployable fiber-fed IFUs, are discussed along with image relays and deployable active sensors. We conceive deployable payloads as components of systems more traditionally regarded as part of telescope systems rather than instruments - such as adaptive optics and ADCs. Also presented are some of the opportunities offered by the truly unique capabilities of Starbug, such as microtracking to apply intra-field distortion correction during the course of an observation.

2dF grows up: Echidna for the AAT

We present the concept design of a new fibre positioner and spectrograph system for the Anglo-Australian Telescope, as a proposed enhancement to the Anglo-Australian Observatorys well-known 2dF facility. A four-fold multiplex enhancement is accomplished by replacing the 400-fibre 2dF fibre positioning robot with a 1600-fibre Echidna unit, feeding three clones of the AAOmega optical spectrograph. Such a facility has the capability of a redshift 1 survey of a large fraction of the southern sky, collecting five to ten thousand spectra per night for a million-galaxy survey.

Ukidna: the RAVE machine

The Anglo-Australian Observatory is currently designing a new fibre positioner for the UK Schmidt Telescope. The instrument will have 2250 fibres, positioned with sub-arcsecond accuracy across a six degree field of view, and will have a reconfiguration time of one minute. The instrument is to enable the RAVE survey of high precision abundances and velocities for up to 50 million stars. The design is largely adapted from the AAOs FMOS-Echidna fibre positioner for Subaru. New design challenges for Ukidna include the enormous number of fibres, the large focal surface, and the field curvature of the Schmidt telescope. These features are mostly shared with the expected needs of future prime-focus multi-fibre systems on 8-30m class telescopes. We present details and performance of the multi-actuator design.

Role of Surface Capping Molecule Polarity on the Optical Properties of Solution Synthesized Germanium Nanocrystals

The role surface capping molecules play in dictating the optical properties of semiconductor nanocrystals (NCs) is becoming increasingly evident. In this paper the role of surface capping molecule polarity on the optical properties of germanium NCs (Ge NCs) is explored. Capping molecules are split into two groups: nonpolar and polar. The NCs are fully characterized structurally and optically to establish the link between observed optical properties and surface capping molecules. Ge NC optical properties altered by surface capping molecule polarity include emission maximum, emission lifetime, quantum yield, and Stokes shift. For Ge NCs, this work also allows rational tuning of their optical properties through changes to surface capping molecule polarity, leading to improvements in emerging Ge based bioimaging and optoelectronic devices.

Running PILOT: operational challenges and plans for an Antarctic Observatory

We highlight the operational challenges and planned solutions faced by an optical observatory taking advantage of the superior astronomical observing potential of the Antarctic plateau. Unique operational aspects of an Antarctic optical observatory arise from its remoteness, the polar environment and the unusual observing cycle afforded by long continuous periods of darkness and daylight. PILOT is planned to be run with remote observing via satellite communications, and must overcome both limited physical access and data transfer. Commissioning and lifetime operations must deal with extended logistics chains, continual wintertime darkness, extremely low temperatures and frost accumulation amidst other challenging issues considered in the PILOT operational plan, and discussed in this presentation.

A new look for Gemini: rapid-cured composites for an exchangeable top-end

The Gemini-sponsored WFMOS Feasibility Study investigated a wide-field, prime focus installation for the Gemini telescopes. As constructed, the Gemini design allows for multiple, interchangeable telescope top-ends, although this capability has never been implemented. Constrained by a particularly challenging top-end mass budget, we proposed a new top end specific to WFMOS, employing a carbon fiber reinforced plastic structure. An innovative, out-of-autoclave manufacturing process using balanced pressure and liquid heating and cooling enables high-specification, large CFRP structures to be constructed suitable for incorporation as fundamental parts of telescope structures. Advantages include low weight, enhanced overall telescope stiffness, and cost-effective construction with on-site final assembly. We describe the manufacturing process and the proposed top-end structure, as well as highlighting the advantages of this type of structure and material for large and extremely large telescopes in general.