Naveen Pai

First light results from the High Efficiency and Resolution Multi-Element Spectrograph at the Anglo-Australian Telescope

Abstract. The High Efficiency and Resolution Multi Element Spectrograph, HERMES, is a facility-class optical spectrograph for the Anglo-Australian Telescope (AAT). It is designed primarily for Galactic Archaeology, the first major attempt to create a detailed understanding of galaxy formation and evolution by studying the history of our own galaxy, the Milky Way. The goal of the GALAH survey is to reconstruct the mass assembly history of the Milky Way through a detailed chemical abundance study of one million stars. The spectrograph is based at the AAT and is fed by the existing 2dF robotic fiber positioning system. The spectrograph uses volume phase holographic gratings to achieve a spectral resolving power of 28,000 in standard mode and also provides a high-resolution mode ranging between 40,000 and 50,000 using a slit mask. The GALAH survey requires an SNR greater than 100 for a star brightness of V=14 in an exposure time of one hour. The total spectral coverage of the four channels is about 100 nm between 370 and 1000 nm for up to 392 simultaneous targets within the 2-degree field of view. HERMES has been commissioned over three runs, during bright time in October, November, and December 2013, in parallel with the beginning of the GALAH pilot survey, which started in November 2013. We present the first-light results from the commissioning run and the beginning of the GALAH survey, including performance results such as throughput and resolution, as well as instrument reliability.

Integrating the HERMES spectrograph for the AAT

The High Efficiency and Resolution Multi Element Spectrograph, HERMES is an optical spectrograph designed primarily for the GALAH, Galactic Archeology Survey, the first major attempt to create a detailed understanding of galaxy formation and evolution by studying the history of our own galaxy, the Milky Way1. The goal of the GALAH survey is to reconstruct the mass assembly history of the of the Milky way, through a detailed spatially tagged abundance study of one million stars in the Milky Way. The spectrograph will be based at the Anglo Australian Telescope (AAT) and be fed with the existing 2dF robotic fibre positioning system. The spectrograph uses VPH-gratings to achieve a spectral resolving power of 28,000 in standard mode and also provides a high resolution mode ranging between 40,000 to 50,000 using a slit mask. The GALAH survey requires a SNR greater than 100 aiming for a star brightness of V=14. The total spectral coverage of the four channels is about 100nm between 370 and 1000nm for up to 392 simultaneous targets within the 2 degree field of view. Current efforts are focused on manufacturing and integration. The delivery date of spectrograph at the telescope is scheduled for 2013. A performance prediction is presented and a complete overview of the status of the HERMES spectrograph is given. This paper details the following specific topics: The approach to AIT, the manufacturing and integration of the large mechanical frame, the opto-mechanical slit assembly, collimator optics and cameras, VPH gratings, cryostats, fibre cable assembly, instrument control hardware and software, data reduction.

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.

TAIPAN instrument fibre positioner and Starbug robots: engineering overview

TAIPAN will conduct a stellar and galaxy survey of the Southern sky. The TAIPAN positioner is being developed as a prototype for the MANIFEST instrument on the GMT. The design for TAIPAN incorporates 150 optical fibres (with an upgrade path to 300) situated within independently controlled robotic positioners known as Starbugs. Starbugs allow precise parallel positioning of individual fibres, thus significantly reducing instrument configuration time and increasing the amount of observing time. Presented is an engineering overview of the UKST upgrade of the completely new Instrument Spider Assembly utilized to support the Starbug Fibre Positioning Robot and current status of the Starbug itself.

TAIPAN fibre feed and spectrograph: engineering overview

TAIPAN will conduct a stellar and galaxy survey of the Southern sky. The TAIPAN positioner is being developed as a prototype for the MANIFEST instrument on the GMT. The TAIPAN Spectrograph is an AAO designed all-refractive 2-arm design that delivers a spectral resolution of R>2000 over the wavelength range 370-870 nm. It is fed by a custom fibre cable from the TAIPAN Starbugs positioner. The design for TAIPAN incorporates 150 optical fibres (with an upgrade path to 300). Presented is an engineering overview of the UKST Fibre Cable design used to support Starbugs, the custom slit design, and the overall design and build plan for the TAIPAN Spectrograph.

AESOP: the 4MOST fiber positioner

The Australian Astronomical Observatory’s (AAO’s) AESOP project is part of the 4 metre Multi-Object Spectrograph Telescope (4MOST) system for the VISTA telescope. It includes the 2436-fiber positioner, space frame and electronics enclosures. The AESOP concept and the role of the AAO in the 4MOST project have been described in previous SPIE proceedings. Prototype tests, which were completed early in 2017 demonstrated that the instrument requirements are satisfied by the design. The project final design stage has recently been completed. In this paper, key features of the AESOP positioning system design, along with the techniques developed to overcome key mechanical, electronic, and software engineering challenges are described. The major performance requirement for AESOP is that all 2436 science fiber cores and 12 guide fiber bundles are to be re-positioned to an accuracy of 10 µm within 1 minute. With a fast prime-focus focal-ratio, a close tolerance on the axial position of the fiber tips must be held so efficiency does not suffer from de-focus losses. Positioning accuracy is controlled with the metrology cameras installed on the telescope, which measures the positions of the fiber tips to an accuracy of a few µm and allows iterative positioning until all fiber tips are within tolerance. Maintaining co-planarity of the fiber tips requires accurate control in the assembly of several components that contribute to such errors. Assembly jigs have been developed and proven adequate for this purpose. Attaining high reliability in an assembly with many small components of disparate materials bonded together, including piezo ceramics, carbon fiber reinforced plastic, hardened steel, and electrical circuit boards, has entailed careful selection and application of cements and tightly controlled soldering for electrical connections.

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.

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.

Wide-field multi-object spectroscopy with MANIFEST

MANIFEST is a multi-object fibre facility for the Giant Magellan Telescope that uses ‘Starbug’ robots to accurately position fibre units across the telescope’s focal plane. MANIFEST, when coupled to the telescope’s planned seeinglimited instruments, offers access to larger fields of view; higher multiplex gains; versatile focal plane reformatting of the focal plane via integral-field-units; image-slicers; and in some cases higher spatial and spectral resolution. The TAIPAN instrument on the UK Schmidt Telescope is now close to science verification which will demonstrate the feasibility of the Starbug concept. We are now moving into the conceptual development phase for MANIFEST, with a focus on developing interfaces for the telescope and for the instruments.

Performance of the first production-ready actuators for the 4MOST-AESOP fiber positioner

In this paper we present recent progress on the Australian Astronomical Observatory’s AESOP2 fiber positioner for 4MOST (on VISTA). As an evolution of the Echidna “spine” technology used for FMOS (on Subaru), AESOP has challenging requirements to position 2,448 fibers in parallel, within 1 minute, to an accuracy of < 10 um RMS. AESOP successfully passed ESO’s official final design review and manufacturing has commenced. We present performance results from the first batch of newly-manufactured positioners and also report on how the AESOP project is tracking in terms of schedule, budget and risk.