SPRAT1 is a low resolution (R ∼ 300) long-slit spectrograph operating in the optical range 400 – 800 nm. It employs a linear layout with deployable optics and can image a 7.5 × 1.8 arcmin field during target acquisition. SPRAT has successfully operated on the robotic 2-metre Liverpool Telescope (LT)<sup>2</sup> on La Palma since late 2014, with >1000 calibration arc spectra and acquisition images taken since installation. Reliable autonomous acquisition without human intervention requires stricter stability criteria to reliably locate a target object in a long-slit spectrograph. We describe methods used to characterise the mechanical repeatability in deployment of the slit and optical components using calibration arcs and standard star spectra, together with acquisition field images. The effect of the instrument orientation and annual temperature variations on the accuracy in locating a target in the imaging plane is characterised together with longer term drifts. The characterisation is compared with the initial design goals of the instrument and used to calculate correction coefficients.
The preferred programming languages and operating systems used in writing and running astrometric software have changed over time. The Python language is now well supported by the scientific community which provides open-source standard libraries for astronomical calculation including Astropy,<sup>1</sup> SciPy<sup>2</sup> and NumPy.<sup>3</sup> We surveyed available open source astrometric libraries and compare ICRS coordinate to observation transforms using recent releases of C source code and Python wrappers from the IAU Standard of Fundamental Astronomy<sup>4</sup> (SOFA), against those using the US Naval Observatory Vector Astrometry Software<sup>5 </sup>(NOVAS). The selection of an underlying operating system with long term support is also an important aspect of maintaining a working telescope control system. The installation and operation of the libraries under both Linux Ubuntu LTS (Long Term Support) and Windows 10 are explored.
The Liverpool Telescope has been in fully autonomous operation since 2004. The supporting data archive facility has largely been untouched. The data provision service has not been an issue although some modernisation of the system is desirable. This project is timely. Not only does it suit the upgrade of the current LT data archive, it is in line with the design phase of the New Robotic Telescope which will be online in the early-2020s; and with the development of a new data archive facility for a range of telescopes at the National Astronomical Research Institute of Thailand. The Newton Fund enabled us to collaborate in designing a new versatile generic system that serves all purposes. In the end, we conclude that a single system would not meet the needs of all parties and only adopt similar front-ends while the back-ends are bespoke to our respective systems and data-flows.
The utility of a high-throughput, low resolution, optical long-slit spectrograph has been demonstrated with the recent deployment of the SPRAT and LOTUS spectrographs on the 2.0m Liverpool Telescope. In this paper we briefly explore some example science use cases for a more generic spectrograph. Our eventual aim is to a produce an adaptable and compact modular instrument design suitable for general deployment to other robotic or manual 1.5 - 3.0m class telescopes. We find that the wide variety of science goals mean that a single design may not be appropriate, however by developing a common optical/mechanical core to which standard optical elements are added we may be able to accommodate them.
The Liverpool Telescope is a fully robotic 2-metre telescope located at the Observatorio del Roque de los Muchachos on the Canary Island of La Palma. The telescope began routine science operations in 2004, and currently seven simultaneously mounted instruments support a broad science programme, with a focus on transient followup and other time domain topics well suited to the characteristics of robotic observing. Work has begun on a successor facility with the working title ‘Liverpool Telescope 2’. We are entering a new era of time domain astronomy with new discovery facilities across the electromagnetic spectrum, and the next generation of optical survey facilities such as LSST are set to revolutionise the field of transient science in particular. The fully robotic Liverpool Telescope 2 will have a 4-metre aperture and an improved response time, and will be designed to meet the challenges of this new era. Following a conceptual design phase, we are about to begin the detailed design which will lead towards the start of construction in 2018, for first light ∼2022. In this paper we provide an overview of the facility and an update on progress.
The Liverpool Telescope automated spectral data reduction pipelines perform both removal of instrumental signatures and provide wavelength calibrated data products promptly after observation. Unique science drivers for each of three instruments led to novel hardware solutions which required reassessment of some of the conventional CCD reduction recipes. For example, we describe the derivation of bias and dark corrections on detectors with neither overscan or shutter. In the context of spectroscopy we compare the quality of at fielding resulting from different algorithmic combinations of dispersed and non-dispersed sky and lamp flats in the case of spectra suffering from 2D spatial distortions.
We describe the development of a low cost, low resolution (R ~ 350), high throughput, long slit spectrograph covering visible (4000-8000) wavelengths. The spectrograph has been developed for fully robotic operation with
the Liverpool Telescope (La Palma). The primary aim is to provide rapid spectral classification of faint (V ∼ 20)
transient objects detected by projects such as Gaia, iPTF (intermediate Palomar Transient Factory), LOFAR,
and a variety of high energy satellites. The design employs a volume phase holographic (VPH) transmission grating as the dispersive element combined with a prism pair (grism) in a linear optical path. One of two peak spectral sensitivities are selectable by rotating the grism. The VPH and prism combination and entrance slit are deployable, and when removed from the beam allow the collimator/camera pair to re-image the target field onto the detector. This mode of operation provides automatic acquisition of the target onto the slit prior to spectrographic observation through World Coordinate System fitting. The selection and characterisation of optical components to maximise photon throughput is described together with performance predictions.