We present the design and science case for the Liverpool Telescope's fourth-generation polarimeter; MOPTOP: a Multicolour OPTimised Optical Polarimeter which is optimised for sensitivity and bi-colour observations. We introduce an optimised polarimeter which is as far as possible limited only by the photon counting efficiency of the detectors. Using a combination of CMOS cameras, a continuously rotating half-wave plate and a wire grid polarising beamsplitter, we predict we can accurately measure the polarisation of sources to ~ 1% at ~19th magnitude in 10 minutes on a 2 metre telescope. For brighter sources we anticipate much low systematics (⪅ 0.1%) than our current polarimeter. The design also gives the ability to measure polarization and photometric variability on timescales as short as a few seconds. Overall the instrument will allow accurate measurements of the intra-nightly variability of the polarisation of sources such as gamma-ray bursts and blazars (AGN orientated with the jet pointing toward the observer), allowing the constraint of magnetic field models revealing more information about the formation, ejection and collimation of jets.
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.
Scientific-CMOS (sCMOS) cameras can combine low noise with high readout speeds and do not suffer the charge multiplication noise that effectively reduces the quantum efficiency of electron multiplying CCDs by a factor 2. As such they have strong potential in fast photometry and polarimetry instrumentation. In this paper we describe the results of laboratory experiments using a pair of commercial off the shelf sCMOS cameras based around a 4 transistor per pixel architecture. In particular using a both stable and a pulsed light sources we evaluate the timing precision that may be obtained when the cameras readouts are synchronized either in software or electronically. We find that software synchronization can introduce an error of ~ 200-msec. With electronic synchronization any error is below the limit (~ 50-msec) of our simple measurement technique.
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.
IO:I is a new instrument that has recently been commissioned for the Liverpool Telescope, extending current imaging capabilities beyond the optical and into the near-infrared. Cost has been minimized by the use of a previously decommissioned instrument’s cryostat as the base for a prototype and retrofitting it with Teledyne’s 1.7-μm cutoff Hawaii-2RG HgCdTe detector, SIDECAR ASIC controller, and JADE2 interface card. The mechanical, electronic, and cryogenic aspects of the cryostat retrofitting process will be reviewed together with a description of the software/hardware setup. This is followed by a discussion of the results derived from characterization tests, including measurements of read noise, conversion gain, full well depth, and linearity. The paper closes with a brief overview of the autonomous data reduction process and the presentation of results from photometric testing conducted on on-sky, pipeline processed data.
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.
Some modern CCD designs provide a dummy readout amplifier that is designed to be operated with the same clock and bias signals as the true amplifier in order to provide a measurement of clock induced and other common-mode noise signals in the true amplifier readout. In general the dummy output signal is subtracted electronically from the true output signal in a differential input preamplifier before digitization. Here we report on an alternative approach where both signals are digitized and the subtraction done in software. We present the results of testing this method of operation using the ARC SDSU generation III CCD controllers and an e2v CCD231 device and find it works well, allowing a noise figure of ~ 2:2 electrons to be reached in the presence of significantly higher (~ 6 electrons) pickup noise. In addition we test the effectiveness of using unused (but still genuine) readout amplifiers on the detector to provide a pseudo-dummy output, which we also find effective in cancelling common mode noise. This provides the option of implementing noise reduction on CCDs that are not equipped with dummy outputs at the expense of overall readout speed.
The robotic 2m Liverpool Telescope, based on the Canary island of La Palma, has a diverse instrument suite and a strong track record in time domain science, with highlights including early time photometry and spectra of supernovae, measurements of the polarization of gamma-ray burst afterglows, and high cadence light curves of transiting extrasolar planets. In the next decade the time domain will become an increasingly prominent part of the astronomical agenda with new facilities such as LSST, SKA, CTA and Gaia, and promised detections of astrophysical gravitational wave and neutrino sources opening new windows on the transient universe. To capitalise on this exciting new era we intend to build Liverpool Telescope 2: a new robotic facility on La Palma dedicated to time domain science. The next generation of survey facilities will discover large numbers of new transient sources, but there will be a pressing need for follow-up observations for scientific exploitation, in particular spectroscopic follow-up. Liverpool Telescope 2 will have a 4-metre aperture, enabling optical/infrared spectroscopy of faint objects. Robotic telescopes are capable of rapid reaction to unpredictable phenomena, and for fast-fading transients like gamma-ray burst afterglows. This rapid reaction enables observations which would be impossible on less agile telescopes of much larger aperture. We intend Liverpool Telescope 2 to have a world-leading response time, with the aim that we will be taking data with a few tens of seconds of receipt of a trigger from a ground- or space-based transient detection facility. We outline here our scientific goals and present the results of our preliminary optical design studies.
The Small Telescopes Installed at the Liverpool Telescope (STILT) project has been in operation since March 2009, collecting data with three wide field unfiltered cameras: SkycamA, SkycamT and SkycamZ. To process the data, a pipeline was developed to automate source extraction, catalogue cross-matching, photometric calibration and database storage. In this paper, modifications and further developments to this pipeline will be discussed, including a complete refactor of the pipeline's codebase into Python, migration of the back-end database technology from MySQL to PostgreSQL, and changing the catalogue used for source cross-matching from USNO-B1 to APASS. In addition to this, details will be given relating to the development of a preliminary front-end to the source extracted database which will allow a user to perform common queries such as cone searches and light curve comparisons of catalogue and non-catalogue matched objects. Some next steps and future ideas for the project will also be presented.
GRB jets contain rapidly moving electrons which will spiral around magnetic field lines. This causes them to
emit polarized synchrotron emission. We have built a series of polarimeters (RINGO and RINGO2) to investigate
this by measuring the polarization of optical light from GRBs at a certain single wavelength. The instruments
are mounted on the Liverpool Telescope, which is a fully robotic (i.e. unmanned) telescope on La Palma which
reacts to triggers from satellites such as the NASA SWIFT mission. This has had great success, with the first
ever detections of early time optical polarization being made. In addition, the first measurements of the change
in optical polarization from a GRB as the jet expands have recently been obtained.
In this paper we describe the design and construction of RINGO3. This will be a multi-colour instrument
that can observe simultaneously at three wavelengths. By doing so we will be able to unambiguously identify
where in the burst the polarized emission is coming from. This will allow us to distinguish between three
possibilities: (1) Magnetic instabilities generated in the shock front, (2) Line of sight effects and (3) Large-scale
magnetic fields present throughout the relativistic outflow. The instrument design combines a rapidly rotating
polaroid, specially designed polarization insensitive dichroic mirrors and three electron multiplying CCD cameras
to provide simultaneous wavelength coverage with a time resolution of 1 second.
The Liverpool Telescope has undergone a major revision of operations model, improving the facility's flexibility and
rapid response to targets of opportunity. We switched from a "full service" model where observers submitted requests to
the Support Astronomer for checking and uploading into the scheduler database to a direct access model where observers
personally load sequences directly into the database at any time, including during the night. A new data model describing
the observing specifications has been developed over two years for the back-end operations infrastructure and has been
invisible to users until early 2010 when the new graphical user interface was deployed to all observers. The development
project has been a success, defined as providing new flexible operating modes to users without incurring any downtime
at the change over or interruption to the ongoing monitoring projects in which the observatory specializes. Devolving
responsibility for data entry to users does not necessarily simplify the role of observatory staff. Ceding that absolute
hands-on control by experienced staff complicates the support task because staff no longer have advance personal
knowledge of everything the telescope is doing. In certain cases software utilities and controls can be developed to
simplify tasks for both observers and operations staff.
We describe the design and construction of a new novel optical polarimeter (RINGO2) for the Liverpool Telescope.
The instrument is designed for rapid (< 3 minute) followup observations of Gamma Ray Bursts in order to
measure the early time polarization and time evolution on timescales of ~ 1 - 10000 seconds. By using a fast
rotating Polaroid whose rotation is synchronized to control the readout of an electron multiplying CCD eight
times per revolution, we can rebin our data in the time domain after acquisition with little noise penalty, thereby
allowing us to explore the polarization evolution of these rapidly variable objects for the first time.
The commercially-available Boltwood Cloud Sensor couples a sky-facing non-imaging thermopile operating in the 8-14
micron range with an ambient air thermometer, to determine the relative sky temperature, and thus indicate the presence
of cloud. A Boltwood sensor was installed on the Liverpool Telescope's weather mast on La Palma in the Canary
Islands in September 2006 in order to investigate its response to both thick and thin cloud at both low and high (cirrus)
levels. An additional aim was to investigate the detectability of calima (Saharan dust) that is occasionally blown over
the islands. In this paper we present the results of our investigations, presenting correlations between the observed
temperature differential and photometricity as determined from the observation of photometric standard stars, and give
some useful "rules-of-thumb" for others considering using such devices.
We describe the design and construction of a novel optical ring-polarimeter (RINGO) for the Liverpool Telescope. The instrument is designed for rapid (< 5 minutes) followup observations of Gamma Ray Bursts in order to measure the early time polarization and its evolution for the first time. Sensitivity calculations and data reduction procedures are described, and the results of on-sky commissioning presented. The instrument is now on the telescope and in routine use during GRB followup.
The Liverpool Telescope is a 2.0 metre robotic telescope that is operating unattended at the Observatorio del Roque de Los Muchachos, Spain. This paper gives an overview of the design and implementation of the telescope and its instrumentation and presents a snapshot of the current performance during the commissioning process. Science observations are under way, and we give brief highlights from a number of programmes that have been enabled by the robotic nature of the telescope.
Since the Faulkes Telescopes are to be used by a wide variety of audiences, both powerful engineering level and simple graphical interfaces exist giving complete remote and robotic control of the telescope over the internet. Security is extremely important to protect the health of both humans and equipment. Data integrity must also be carefully guarded for images being delivered directly into the classroom. The adopted network architecture is described along with the variety of security and intrusion detection software. We use a combination of SSL, proxies, IPSec, and both Linux iptables and Cisco IOS firewalls to ensure only authenticated and safe commands are sent to the telescopes. With an eye to a possible future global network of robotic telescopes, the system implemented is capable of scaling linearly to any moderate (of order ten) number of telescopes.