The ESO Extremely Large Telescope (ELT) has been in construction since 2014. In parallel with the construction of the telescope, ESO has entered into agreements with consortia in the ESO member states to build the first instruments for that telescope. To meet the telescope science goals, the ambitious instrument plan includes two instruments for first light: an optical to near-infrared integral field spectrograph with a dedicated adaptive optics system (HARMONI) and a near-infrared camera with simple spectrograph (MICADO) behind a multi-conjugate adaptive optics module (MAORY). The next instrument will be a mid-infrared imager and spectrograph (METIS). Plans to follow this first suite of instruments include a high-resolution spectrograph (HIRES) and a multi-object spectrograph (MOSAIC). Technology development is underway to prepare for building the ELT Planetary Camera and Spectrograph. An overview of the telescope and its instruments is given.
MICADO will enable the ELT to perform diffraction limited near-infrared observations at first light. The instrument’s capabilities focus on imaging (including astrometric and high contrast) as well as single object spectroscopy. This contribution looks at how requirements from the observing modes have driven the instrument design and functionality. Using examples from specific science cases, and making use of the data simulation tool, an outline is presented of what we can expect the instrument to achieve.
In this paper we will report on the status of the instrumentation project for the European Southern Observatory's Extremely Large Telescope (ELT). Three instruments are in the construction phase: HARMONI, MICADO and METIS. The multi-conjugate adaptive optics system for MICADO, MAORY, is also under development. Preliminary Design Reviews of all of these systems are planned to be completed by mid-2019. The construction of a laser tomographic module for HARMONI is part of "Phase 2" of the ELT: the design has been advanced to Preliminary Design level in order to define the interface to the HARMONI spectrograph. Preparations for the next instruments have also been proceeding in parallel with the development of these instruments. Conceptual design studies for the multi-object spectrograph MOSAIC, and for the high resolution spectrograph HIRES have been completed and reviewed. We present the current design of each of these instruments and will summarise the work ongoing at ESO related to their development.
A suite of seven instruments and associated AO systems have been planned as the "E-ELT Instrumentation Roadmap". Following the E-ELT project approval in December 2014, rapid progress has been made in organising and signing the agreements for construction with European universities and institutes. Three instruments (HARMONI, MICADO and METIS) and one MCAO module (MAORY) have now been approved for construction. In addition, Phase-A studies have begun for the next two instruments - a multi-object spectrograph and high-resolution spectrograph. Technology development is also ongoing in preparation for the final instrument in the roadmap, the planetary camera and spectrograph. We present a summary of the status and capabilities of this first set of instruments for the E-ELT.
MICADO will equip the E-ELT with a first light capability for diffraction limited imaging at near-infrared wavelengths. The instrument’s observing modes focus on various flavours of imaging, including astrometric, high contrast, and time resolved. There is also a single object spectroscopic mode optimised for wavelength coverage at moderately high resolution. This contribution provides an overview of the key functionality of the instrument, outlining the scientific rationale for its observing modes. The interface between MICADO and the adaptive optics system MAORY that feeds it is summarised. The design of the instrument is discussed, focusing on the optics and mechanisms inside the cryostat, together with a brief overview of the other key sub-systems.
MAORY is one of the four instruments for the E-ELT approved for construction. It is an adaptive optics module offering two compensation modes: multi-conjugate and single-conjugate adaptive optics. The project has recently entered its phase B. A system-level overview of the current status of the project is given in this paper.
ESO has a very active on-going AO WFS detector development program to not only meet the needs of the current crop of instruments for the VLT, but also has been actively involved in gathering requirements, planning, and developing detectors and controllers/cameras for the instruments in design and being proposed for the E-ELT.
This paper provides an overall summary of the AO WFS Detector requirements of the E-ELT instruments currently in design and telescope focal units. This is followed by a description of the many interesting detector, controller, and camera developments underway at ESO to meet these needs; a) the rationale behind and plan to upgrade the 240x240 pixels, 2000fps, “zero noise”, L3Vision CCD220 sensor based AONGC camera; b) status of the LGSD/NGSD High QE, 3e- RoN, fast 700fps, 1760x1680 pixels, Visible CMOS Imager and camera development; c) status of and development plans for the Selex SAPHIRA NIR eAPD and controller.
Most of the instruments and detector/camera developments are described in more detail in other papers at this conference.
The Multi-Conjugate Adaptive Optics module for the European Extremely Large Telescope has been designed to achieve uniform compensation of the atmospheric turbulence effects on a wide field of view in the near infrared. The design realized in the Phase A of the project is undergoing major revision in order to define a robust baseline in view of the next phases of the project. An overview of the on-going activities is presented.
We present the status of the instrumentation programme for the European Extremely Large Telescope. The
instrumentation planning is governed by the E-ELT Instrument Roadmap, which synthesises the scientific, technical and
managerial influences on the instrument programme into a staged development plan. Preparations for the start of the
design and build phases of the first light instruments and their adaptive optics systems are well underway and are
summarised here. In parallel, the process for development of the next three instruments has begun. Recent work on the
instrument interface to the telescope is described.
ESO has a very active on-going detector development program to not only meet the needs of the current crop of instruments for the VLT, but is also actively involved in gathering requirements and developing detectors for the challenging instruments being proposed and in design for the E-ELT. This paper provides an overall summary of the detector requirements of the various E-ELT instruments and the many interesting detector developments ESO is involved in to meet these needs. Most of these instruments and detector developments are described in more detail in other papers at this conference.
KMOS is a multi-object near-infrared integral field spectrograph built by a consortium of UK and German institutes for
the ESO Paranal Observatory. We report on the on-sky performance verification of KMOS measured during three
commissioning runs on the ESO VLT in 2012/13 and some of the early science results.
We present plans for instrumentation on the European Extremely Large Telescope. ESO is working with its community
of astronomers and instrument builders to develop the E-ELT Instrumentation Roadmap. The roadmap is a timeline of
the steps towards the full instrument programme, from specification of the scientific requirements, via a technology
development phase, to selection of the instrument concepts. Key goals are to be flexibile to new ideas and to ensure the
timely, on-budget delivery of instruments that meet the community's scientific needs. The result is an exciting
programme of seven instruments planned over the first decade of the telescope construction phase.
The ESO instrumentation programme now encompasses both an on-going programme for La-Silla Paranal observatory
and a new programme for construction of the instruments for the E-ELT. The scale and ambition of the combined
programme will present a future challenge for the European instrument-building community and for ESO as managing
organisation. The current status and plans are summarised.
KMOS is a multi-object near-infrared integral field spectrograph being built by a consortium of UK and German
institutes. We report on the final integration and test phases of KMOS, and its performance verification, prior to
commissioning on the ESO VLT later this year.
During the last year a modified baseline design for the E-ELT has been developed. The aim of this revision was both to
achieve a significant cost saving and to reduce risk on major items. The primary mirror diameter was slightly reduced to
39 m and the total height of the telescope also decreased accordingly. This paper describes the work performed by ESO
and a variety of contractors to review the EELT design to match the modified baseline. Detailed design and construction
planning, as well as detailed cost estimates were updated for the 39-metre baseline design. In June 2011, ESO Council
formally endorsed this modified design as the E-ELT revised baseline.
The design drivers and balancing cost factors will be described along with the risk reduction measures taken during this
phase. This will culminate in the design which has been agreed as being ready to move forward to construction once
approval from ESO Council has been achieved.
During the last two and half years ten phase-A instrument studies for the E-ELT have been launched by ESO and carried
out by consortia of institutes in the ESO member states and Chile. These studies have been undertaken in parallel with
the phase B of the E-ELT telescope. This effort has pursued two main goals: to prove the feasibility and performance of
a set of instruments to meet the project science goals and to identify and incorporate in the telescope design those
features that satisfy best the needs of the future hosts, i.e., the science instruments. To succeed on this goal it is crucial to
identify such needs as early as possible in the design process.
This concurrent approach definitively benefits both the instruments concept design and the telescope development, but
implies as well a number of difficult tasks. This paper compiles, from a system-engineering point of view, the benefits
and difficulties as well as the lesson learned during this concurrent process. In addition, the main outcomes of the
process, in terms of telescope-instruments interfaces definition and requirements from the instruments to the telescope
and vice-versa, are reported.
In this paper we present a brief status report on the conceptual designs of the instruments and adaptive optics modules
that have been studied for the European Extremely Large Telescope (E-ELT). In parallel with the design study for the
42-m telescope, ESO launched 8 studies devoted to the proposed instruments and 2 for post-focal adaptive optics
systems. The studies were carried out in consortia of ESO member state institutes or, in two cases, by ESO in
collaboration with external institutes. All studies have now been successfully completed. The result is a powerful set of
facility instruments which promise to deliver the scientific goals of the telescope.
The aims of the individual studies were broad: to explore the scientific capabilities required to meet the E-ELT science
goals, to examine the technical feasibility of the instrument, to understand the requirements placed on the telescope
design and to develop a delivery plan. From the perspective of the observatory, these are key inputs to the development
of the proposal for the first generation E-ELT instrument suite along with the highest priority science goals and
budgetary and technical constraints. We discuss the lessons learned and some of the key results of the process.
KMOS is a near-infrared multi-object integral-field spectrometer which is one of a suite of second-generation
instruments under construction for the VLT. The instrument is being built by a consortium of UK and German
institutes working in partnership with ESO and is now in the manufacture, integration and test phase. In this paper
we present an overview of recent progress with the design and build of KMOS and present the first results from the
subsystem test and integration.
X-shooter is the first second-generation instrument newly commissioned a the VLT. It is a high efficiency single
target intermediate resolution spectrograph covering the range 300 - 2500 nm in a single shot. We summarize
the main characteristics of the instrument and present its performances as measured during commissioning and
the first months of science operations.
The European Southern Observatory (ESO) is conducting a phase B study of a European Extremely Large Telescope (E-ELT).
The baseline concept foresees a 42m primary, 5 mirror adaptive telescope with two of the mirrors giving the
possibility of very fast correction of the atmospheric turbulence. In parallel to the telescope study, ESO is coordinating
8 studies of instruments and 2 of post-focus Adaptive Optics systems, carried out in collaboration with Institutes in the
member states. Scope of the studies, to be completed by 1Q 2010, is to demonstrate that the high priority scientific goals of
the E-ELT project can be achieved with feasible and affordable instruments. The main observing modes being considered
are: NIR wide field imaging and spectroscopy to the diffraction limit or with partial correction of the atmospheric seeing;
high spectral resolution, high stability visible spectroscopy; high contrast, diffraction limited imaging and spectroscopy; DL
mid-infrared imaging and spectroscopy. The status of the 8 current studies is presented.
Multi-object instruments provide an increasing challenge for pick-off technology (the means by which objects are selected in the focal plane and fed to sub-instruments such as integral field spectrographs). We have developed a technology demonstrator for a new pick-off system. The performance requirements for the demonstrator have been driven by the outline requirements for possible ELT instruments and the science requirements based on an ELT science case. The goals for the pick-off include that the system should capable of positioning upwards of one hundred pick-off mirrors to an accuracy better than 5 microns. Additionally, the system should be able to achieve this for a curved focal surface -- in this instance with a radius of curvature of 2m.
This paper presents the first experimental results from one of the approaches adopted within the Smart Focal Plane project -- that of a Planetary Positioning System. This pick-and place system is so called because it uniquely uses a combination of three rotation stages to place a magnetically mounted pick-off mirror at any position and orientation on the focal surface. A fixed angular offset between the two principal rotation stages ensures that the pick-off mirror is always placed precisely perpendicular to the curved focal plane. The pick-off mirror is gripped and released by a planar micromechanical mechanism which is lowered and raised by a coil-actuated linear stage.
One of the highlights of the European ELT Science Case book is the study of resolved stellar populations, potentially out to the Virgo Cluster of galaxies. A European ELT would enable such studies in a wide range of unexplored, distant environments, in terms of both galaxy morphology and metallicity. As part of a small study, a revised science case has been used to shape the conceptual design of a multi-object, multi-field spectrometer and imager (MOMSI). Here we present an overview of some key science drivers, and how to achieve these with elements such as multiplex, AO-correction, pick-off technology and spectral resolution.
KMOS is a near-infrared multi-object integral field spectrometer which has been selected as one of a suite of second-generation instruments to be constructed for the ESO VLT in Chile. The instrument will be built by a consortium of UK and German institutes working in partnership with ESO and is currently at the end of its preliminary design phase. We present the design status of KMOS and discuss the most novel technical aspects and the compliance with the technical specification.
A key instrument for an Extremely Large Telescope (ELT) is likely to be multi-object spectrometer which observes at least 100 discrete sources with diffraction limited spatial resolution and moderate spectral resolution in the wavelength region from 1.0 to 2.5 μm. Such an instrument has been chosen as the principal driver for the Smart Focal Planes technology development project which has brought together 14 companies and institutes in Europe and Australia. An overview of a new ELT instrument concept based upon beam manipulators (including novel 'starbug' miniature robots) is presented; supported by a summary of scientific goals and systems requirements. Progress made on specific support technology studies is also presented, including work on image slicer replication and cryogenic reconfigurable slits.
A prototype cryogenic 'pick-off' arm for selecting a small field from the focal plane of a large telescope has been built and tested against a set of scientific requirements representative of those for proposed multi-integral-field spectrographs. In this paper, we present the design of the arm and the results of the cryogenic testing. Since the proposed instruments will require tens of arms, perhaps hundreds, we have also considered the industrialisation of the manufacture and assembly of the arms. We briefly discuss this aspect of the design and the possibilities for future instrumentation on Extremely Large Telescopes.
We describe the design of a 2nd generation instrument for the ESO VLT which will deliver a unique multiple deployable integral field capability in the near-infrared (1-2.5μm). The science drivers for the instrument are presented and linked to the functional specification. The baseline instrument concept is described with emphasis on technological innovations. Detailed discussions of specific technologies, and ongoing prototype studies, are described in separate papers.
UIST is a facility class near-infrared instrument recently commissioned at the UK Infrared Telescope (UKIRT). UIST provides a comprehensive imaging and spectroscopic facility with spatial resolution limited only by the delivered tip-tilt corrected seeing. In addition to long slit spectroscopic modes, UIST includes the first deployable cryogenic integral field unit in a common user instrument. We will present results obtained during the commissioning period in late 2002. These include measurements of the image quality and the sensitivities of the different observing modes of the instrument. We also discuss the use of an instrument-specific telescope pointing-model developed for UIST to allow the instrument to meet the stringent flexure requirements arising from the choice of 0.06arcsec/pixel and 0.12arcsec/pixel plate scales. We pay particular attention to the performance of the image slicing integral field unit (IFU). We will present astronomical results from the first year of UIST operations, during which time UIST carried out diverse programmes, from mineralogical studies of Mars to measuring the mass of the black hole at the centre of the most distant quasar.
Smart Focal Planes are devices that enable the efficient sampling of a telescope's focal plane to feed spectroscopic and imaging instruments. Examples are integral field units (fiber and image slicers), cryogenic beam manipulators, and MOEMS (micro-opto-electromechanical systems) such as miniature slit shutters. These technologies are critical in making best use of the current 8m class telescopes for key science goals such as spectroscopic surveys of high redshift galaxies, and will be even more important for Extremely Large Telescope (ELT) instruments. In fact, the density of pixels in an ELT focal plane with several milliarcsecond resolution will mean that sub-sampling of the field will be needed even for imaging. We have proposed a joint European project to develop these technologies, building on expertise from partners in the UK, France, the Netherlands, Spain, Germany and others, and led by the UK. We describe the current status of these technologies, showing how they will contribute to the feasibility and performance of proposed instruments for ELTs, and concentrating on capabilities within Europe. We then outline the proposed future developments, highlighting the technical challenges, such as the difficulties of manufacturing and verifying complex image slicers with thousands of optical surfaces, and building highly reliable cryogenic mechanisms such as pick-off arms, beam steering mirrors and reconfigurble slit mechanisms.
Plans for a European Extremely Large Telescope are quite well advanced. However examination of instrument designs has thus far been directed only at covering the anticipated science requirements and has had little impact on telescope design considerations. Nevertheless, the provision of a suitable environment for instruments is a critical part of the design of all large telescopes. We illustrate this point with examples from recent experience. A Work Package, part of a proposed Design Study for a European ELT under the European Union's Framework Programme 6 (FP6), will explore this issue, while also developing designs for a scientifically credible instrument suite. For three instruments mechanical and optical design studies will be carried out in sufficient detail clearly to identify design drivers for the telescope. These are a wide-field seeing limited or ground-layer AO-corrected (GLAO) optical/NIR spectrometer, WFSPEC; an MCAO-corrected O/NIR Multi-Object Multi-field Spectrometer-Imager, MOMSI, which offers particularly daunting challenges; and a mid-infrared high-resolution AO-corrected Imager-Spectrometer instrument, MIDIR. Five instrument designs will be examined in less detail: an extreme-AO (XAO) corrected coronagraphic imager-spectrometer known as Planet Finder (the goal of which is the detection and characterization of terrestrial exo-planets); a very high resolution spectrometer, HISPEC; a high time-resolution instrument, HITRI, intended to allow photometry, polarimetry and phase-resolved spectroscopy of faint rapidly varying objects; a fast-response broad-band multi-function instrument known as GRB-catcher; and a sub-millimeter imager, SCUBA-3. A separate small study will seek innovative designs not included in the main suite. Another will initiate the program by examining the requirements of atmospheric dispersion correction (ADC) for 30 to 100-m diffraction-limited telescopes, which may require active sensing and, possibly, "adaptive" correction on atmospheric turbulence timescales. All these studies -- except that of SCUBA3 -- will require support from Adaptive Optics studies, as most instruments will be utterly dependent on AO: close communication between instrument and AO groups is essential, here and in general.
The UIST instrument is a 1-5μm Imager Spectrometer for the UKIRT telescope. The instrument has a high spatial resolution, and is designed to critically sample image sizes of 0.24arcsec. The instrument weighs 750kg and measures approximately 1100x1000x700mm. The flexure specification for the instrument is to maintain the image at the slit within 10% of the narrowest slit width, which is 44μm wide. However combined flexure of the instrument and its supporting structure is expected to be many times more than this. To meet the UIST flexure requirements we propose use of an instrument specific component in the telescope pointing model, to correct for repeatable flexure. Two designs for mounting regimes are presented, together with flexure test results and a discussion of the use of a simple pointing correction. The first, flexible, truss design did not meet requirements and was replaced with a rigid truss system. The paper describes some lessons learned during the development of the UIST mounting scheme, which can be applied in other instrument designs.
We present the results of a detailed technical study of the use of image slicers for multiple integral field spectroscopy at infrared wavelengths. Our solution uses independently controlled robotic arms to relay selected portions of the focal plane to fixed positions where they are dissected using a set of advanced image slicers. We discuss the technical requirements of this approach and describe a feasibility study to examine the risks and technical challenges.
We present here details of the manufacture of a deployable image
slicing IFU for UIST (a new imager spectrometer for UKIRT). We also
present the alignment methods developed and used to achieve optimal
transmission and give results for laboratory testing of the IFU at
cryogenic temperatures in its operational configuration in UIST.
These tests covered transmission, scattered light, alignment of exit pupils and the spatial and spectral PSFs. The calibration and
automatic data reduction methods which produce spectra (in the form
of an x, y, λ data-cube) aligned in wavelength and the two spatial dimensions for all the observed pixels will be described.
We present her the opto-mechanical design of an image slicer with reference to designs for a deployable IFU for UIST and two mid-IR IFUs for NGST. Particular attention is paid to how the design achieves a number of goals required of an IFU working in an astronomical IR instrument.
High-quality, efficient calibration instruments is a pre- requisite for the modern observatory. Each of the Gemini telescopes will be equipped with identical facility calibration units (GCALs) designed to provide wavelength and flat-field calibrations for the suite of instruments. The broad range of instrumentation planned for the telescopes heavily constrains the design of GCAL. Short calibration exposures are required over wavelengths from 0.3micrometers to 5micrometers , field sizes up to 7 arcminutes and spectral resolution from R-5 to 50,000. The output from GCAL must mimic the f-16 beam of the telescope and provide a uniform illumination of the focal plane. The calibration units are mounted on the Gemini Instrument Support Structure, two meters from the focal pane, necessitating the use of large optical components. We will discuss the opto-mechanical design of the Gemini calibration unit, with reference to those feature which allow these stringent requirements to be met. A novel reflector/diffuser unit replaces the integration sphere more normally found in calibration systems. The efficiency of this system is an order of magnitude greater than for an integration sphere. A system of two off-axis mirrors reproduces the telescope pupil and provides the 7 foot focal plane. The results of laboratory test of the uniformity and throughput of the GCAL will be presented.
We present results on the integration and testing of an imaging spectrometer for the 1-5micrometers wavelength band. UIST offers high angular resolution imaging and spectroscopy and has been designed to exploit the best performance of the UK IR Telescope. In addition to imaging with 0.24arcsec and 0.12arcsec resolution, long-slit and cross-dispersed spectroscopy, UIST has an integral field mode using a reflective image slicer. An image rotator allows the slits and the rectangular field of view of the IFU to be oriented at any position angle on the sky. The UIST optical design relies on refractive optics with the spectroscopy provided by both replicated and direct-ruled grisms. The lenses are mounted in mechanical modules which also contain the mechanisms, such as the filter and slit wheels. The integration of the opto-mechanical system will be discussed. The high tolerances on positioning the optical components to be used under cryogenic conditions are achieved by mechanical alignment on an optical bench which is an integral part of the instrument. Initial tests of the cryogenic performance of the optics will be presented. The UIST detector is an 1024 by 1024 InSb 'ALADDIN' array from the Raytheon IR Center of Excellence. The array controller is modified from 'EDICT', a VME processor based system which was developed at the UK ATC to control the mid-IR arrays used in the MICHELLE spectrometer. Progress on the integration of the UIST detector and controller will be discussed.
The design of any modern astronomical telescope requires close interaction between the science requirements, the optical and mechanical design of the telescope and its instrumentation. In addition new, large aperture, telescopes will need to have adaptive optics as an integral part of the concept. This paper discusses optical concepts for the telescope and instruments, highlighting technology challenges.
An imaging spectrometer is being designed to take advantage of recent improvements in the image quality achieved at the UK Infrared Telescope. The realization of near-diffraction limited imaging at two microns brings with it the possibility of significant improvements in sensitivity to IR observations. UIST will provide a versatile facility for high spatial resolution imaging and spectroscopy in the 1-5 micrometers wavelength range. We will present the opto-mechanical design of this new instrument, highlighting the innovative features. These include provision of multiple pixel scales within the camera and polarimetry via a Wollaston prism. One of the most challenging areas of the design is the inclusion of a cryogenic integral field unit for area spectroscopy over a 5 inch field. The spectroscopic modes include cross- dispersed spectroscopy over the complete 1-2.5 micrometers wavelength ranges and moderate resolution long slit or area spectroscopy over the complete 1-5 micrometers range. A higher resolution mode will also the included. This will allow USTI to take advantage of the very low backgrounds to be found between OH sky lines. The instruments will incorporate a 1024 X 1024 Indium Antimonide array from SBRC. The development of the IR array controller for UIST will also be discussed.
Reliable calibration of astronomical data from large telescopes is an essential factor in obtaining high sensitivity observations for both the astronomer at the telescope and the archive researcher. A dedicated calibration unit provides an efficient and predictable method of observing calibration frames. Such a facility is being designed for the Gemini telescopes. It is required to calibrate instruments with wavelengths from the UV to the infrared, covering a broad range of both spectral and spatial resolution. We present the design of this calibration unit and the predicted performance with the 'first-light' Gemini instruments.
We present data on the image quality achieved with the near IR array spectrometer cooled grating spectrometer 4 (CGS4) on the UK IR telescope (UKIRT) on Mauna Kea. A design spot size of 30 micrometers was specified for CGS4, to maintain acceptable image quality with both the 58 by 62 pixel array with which it is currently equipped and the 256 by 256 array which CGS4 was also designed to accommodate. Details are given of the design, construction and alignment method which allow linear tolerances of 50 micrometers and angular tolerances of 25 mrad to be met and maintained at cryogenic temperatures. The instrumental flexure is also discussed. Both laboratory spectra and those taken at the telescope illustrate that design spot sizes of 30 micrometers have been achieved in the near IR. It will be demonstrated that the theoretical resolution of the instrument is attained for resolving powers from approximately 200 to 20,000.
First light with the advanced cooled grating spectrometer (CGS4) was achieved at the United Kingdom Infrared Telescope on February 4, 1991 following successful delivery of the instrument from the Royal Observatory, Edinburgh. We discuss the performance of CGS4 and summarize our experience in maintaining optimum array sensitivity. CGS4 is unique in that both the data acquisition and reduction can be almost completely automated, and the key elements of the software and their impact on observing are described. We discuss how various aspects of CGS4 such as the reproducibility of flat fields relate to the ability to provide users with flat-fielded, sky-subtracted spectra almost in real-time. We also discuss the problems of the variability of OH line emission and atmospheric transmission and describe the sky subtraction techniques which we have been using both at the telescope and in post observing analysis.