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The operational implementation of observing programs influences the scientific return of an Observatory. More than 15 years of observations with the VLT/Paranal Observatory allow us to assess the impact of science operations and program implementation. Bibliometric parameters are used to derive program productivities and citation rates and their relation to scheduling realizations (such as service and visitor mode), program types and service mode rank classes. In this contribution we present a set of performance indicators comparing specific program execution parameters. Results of this analysis help us to identify strengths and weaknesses of the adopted operational model, as well as possible improvements for an integrated VLT and ELT operations scheme in the next decade.

When ESO’s Very Large Telescope opened its first dome in April 1999 it was the first ground-based facility to offer to the scientific community access to an 8-10m class telescope with both classical and queue observing. The latter was considered to be the most promising way to ensure the observing flexibility necessary to execute the most demanding scientific programmes under the required, usually very well defined, conditions. Since then new instruments have become operational and 1 st generation ones replaced, filling the 12 VLT foci and feeding the VLT Interferometer and its four Auxiliary Telescopes. Operating efficiently such a broad range of instruments installed and available every night of the year on four 8-metre telescopes offers many challenges. Although it may appear that little has changed since 1999, the underlying VLT operational model has evolved in order to accommodate different requirements from the user community and features of new instruments. Did it fulfil its original goal and, if so, how well? How did it evolve? What are the lessons learned after more than 15 years of operations? A careful analysis and monitoring of statistics and trends in Phase 1 and Phase 2 has been deployed under the DOME (Dashboard for Operational Metrics at ESO) project. The main goal of DOME is to provide robust metrics that can be followed with time in a user-friendly manner. Here, we summarize the main findings on the handling of service mode observations and present the most recent developments.

The Rapid-Response Mode (RRM) at ESO's Very Large Telescope (VLT) allows for rapid automatic observations of any highly variable target such as Gamma-Ray Burst (GRB) afterglows. This mode has been available for various instruments at the VLT since April 2004, and can be easily implemented for any new instumentation. Apart from discussing the operational side of this mode, we also present VLT/UVES GRB afterglow spectra observed using the RRM, which show clear variability of absorption lines at the redshift the GRB host galaxy. Without the RRM this variability would not have been observed. Using photo-excitation and -ionization modelling, we show that this varibility is due to the afterglow flux exciting and ionizing a gas cloud at distances varying from tens of parsecs to kiloparsecs away from the GRB.

The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and the four 1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The two VLTI instruments, MIDI and AMBER deliver regular scientific results. In parallel to the operation, the instruments developments are pursued, and new modes are studied and commissioned to offer a wider range of scientific possibilities to the community. New configurations of the ATs array are discussed with the science users of the VLTI and implemented to optimize the scientific return. The monitoring and improvement of the different systems of the VLTI is a continuous work. The PRIMA instrument, bringing astrometry capability to the VLTI and phase referencing to the instruments has been successfully installed and the commissioning is ongoing. The possibility for visiting instruments has been opened to the VLTI facility.

In 2007 ESO Council endorsed a concept to maintain the La Silla Site within the context of a streamlined operational and support scenario. La Silla remains part of the La Silla Paranal Observatory Division, and supports science projects of the ESO community using the 2.2m, NTT and 3.6m telescope. Infrastructure to host externally funded projects at national telescopes is provided. A detailed Site Operations Plan for La Silla 2010+ had been developed, and is been implemented since October 2009. We describe its implications on staffing, infrastructure, and science operations. We report our first experience gathered under this new operations paradigm.

APEX, the Atacama Pathfinder EXperiment, is being operated successfully, now for five years, on Llano de Chajnantor at 5107m altitude in the Chilean High Andes. This location is considered one of the worlds outstanding sites for submillimeter astronomy, which the results described in this contribution are underlining. The primary reflector with 12 m diameter is cautiously being maintained at about 15 μm by means of holography. This allows to access all atmospheric submillimeter windows accessible from the ground, up to 200 μm. Telescope and instrument performance, operational experiences and a selection of scientific results are given in this publication.

The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8 m Unit Telescopes (UT) and the four 1.8 m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The fourth AT has been delivered to operation in December 2006, increasing the flexibility and simultaneous baselines access of the VLTI. Regular science operations are now carried on with the two VLTI instruments, AMBER and MIDI. The FINITO fringe tracker is now used for both visitor and service observations with ATs and will be offered on UTs in October 2008, bringing thus the fringe tracking facility to VLTI instruments. In parallel to science observations, technical periods are also dedicated to the characterization of the VLTI environment, upgrades of the existing systems, and development of new facilities. We will describe the current status of the VLTI and prospects on future evolution.

The European Southern Observatory has recently merged the operations of its three Chilean sites, La Silla, Paranal/VLT, and Chajnantor APEX, into one observatory, the La Silla Paranal Observatory. Recent developments, latest achievements and future challenges at the different sites are presented in this paper.

The European Southern Observatory (ESO) operates its Very Large Telescope (VLT) on Cerro Paranal (Chile) with to date 11 scientific instruments including two interferometric instruments and their numerous auxiliary systems at 4 Unit Telescopes (UTs) and 3 Auxiliary Telescopes (ATs). The rigorous application of preventive and corrective maintenance procedures and a close monitoring of the instruments' engineering data streams are the key ingredient towards the minimization of the technical downtime of the instruments. The extensive use of standardized hardware and software components and their strict configuration control is considered crucial to efficiently manage the large number of systems with the limited human and technical resources available. A close collaboration between the instrument engineers, the instrument scientists in instrument operation teams (IOTs) turns out to be vital to maintain and to the performance of the instrumentation suite. In this paper, the necessary tools, workflows, and organizational structures to achieve these objectives are presented.

The ESO Very Large Telescope (VLT) started operations on Cerro Paranal (Chile) in April 1999 with one Unit Telescope and two science instruments. Seven years later it is still a growing facility consisting of four 8.2-m telescopes, three auxiliary telescopes for interferometry, and 11 science instruments. In addition two dedicated survey telescopes with wide-field cameras, VST and VISTA, a fourth auxiliary telescope, and several new instruments will become available in the coming months. Since the very beginning, VLT operations were planned to contain a substantial component of Service Mode observing, amounting to approximately 50% of the available time. The success of the full-scale implementation of Service Mode operations is reflected nowadays by the steady increase in its demand by the community, both in absolute terms and also relative to the demand in Visitor Mode, by the highly positive feedback received from the users, and also by the increasing flow of scientific results produced by programs that have exploited the unique advantages of flexible short-term scheduling. It is also fulfilling the requirement of creating a science archive and populating it with a data stream having through a quality control process. Here we review the current status of Service Mode observing at the VLT and the VLT Interferometer (VLTI), the challenges posed by its implementation on a wide variety of instrument modes, and its strong requirement of an integrated, end-to-end approach to operations planning with adequate tools and carefully defined policies and procedures. The experience of these seven years of VLT operations have led to a thorough exploration of operations paradigms that will be essential to the scientific success of ALMA and the extremely large optical telescopes in the coming decades.

With the completion of the first generation instrumentation set on the Very Large Telescope, a total of eleven instruments are now provided at the VLT/VLTI for science operations. For each of them, ESO provides automatic data reduction facilities in the form of instrument pipelines developed in collaboration with the instrument consortia. The pipelines are deployed in different environments, at the observatory and at the ESO headquarters, for on-line assessment of observations, instruments and detector monitoring, as well as data quality control and products generation. A number of VLT pipelines are also distributed to the user community together with front-end applications for batch and interactive usage. The main application of the pipeline is to support the Quality Control process. However, ESO also aims to deliver pipelines that can generate science ready products for a major fraction of the scientific needs of the users. This paper provides an overview of the current developments for the VLT/VLTI next generation of instruments and of the prototyping studies of new tools for science users.

The purpose of the recent installation of eight interference filters in UVES is to isolate certain echelle orders to allow the use of a maximal slit length of 30". The typical decker height of the spectrograph slit for science operations is usually of the order of 10-12". The central wavelength of each filter was chosen to permit observations of the most important emission lines in extended objects. We discuss the performance of these filters and show the first science images obtained with the test run.

This work presents the use of system modeling with the aim of maintaining and improving instrument performances. The complexity and cryogenic nature of infrared systems prevent continuous hardware upgrades, so that the advantages of modeling are of high value. Two applications of modeling and basic control theory are shown. The first example concerns the performance monitoring of the ISAAC cryogenic system. The measured and simulated cold structure temperatures are compared in real time, allowing for anticipation of possible failures of the cooling system and therefore for reduction of operational downtime. The second case is about the position control of the duo-echelle grating of the VISIR spectrometer. The controlled system was identified and simulated to select controller parameters that improve the image stability. Preliminary results show the possibility to get better compensation of the disturbances induced by the telescope movements, leading to an enhancement of the data quality.

The ESO Very Large Telescope Interferometer (VLTI) is the first general-user interferometer that offers near- and mid-infrared long-baseline interferometric observations in service and visitor mode to the whole astronomical community. Over the last two years, the VLTI has moved into its regular science operation mode with the two science instruments, MIDI and AMBER, both on all four 8m Unit Telescopes and the first three 1.8m Auxiliary Telescopes. We are currently devoting up to half of the available time for science, the rest is used for characterization and improvement of the existing system, plus additional installations. Since the first fringes with the VLTI on a star were obtained on March 17, 2001, there have been five years of scientific observations, with the different instruments, different telescopes and baselines. These observations have led so far to more than 40 refereed publications. We describe the current status of the VLTI and give an outlook for its near future.

The VLTI now has performed three years of science operations using the VINCI instrument since the first fringes on a star were obtained on March 17, 2001. Since December 5th, 2001, shared risk science observations have been performed with VINCI. In April 2004 (period 73) we have started science operations with the MIDI instrument. Subsequently both the AMBER instrument and the Auxiliary Telescopes (ATs) will be also running under the science Operations at Paranal and offered to the astronomical community. We will present how the VLTI Science operations currently are performed and integrated into the general Paranal Science Operations scheme, using the extensive experience of Service Mode operations performed by the Paranal Science operations group. We focus on the execution of the Service mode operations, how they are planned, performed, evaluated, and processed and the data finally sent to ESO Garching. The near future developments are also presented and how the new instruments and telescopes will be integrated into the Paranal Science Operations.

The ESO Very Large Telescope Interferometer (VLTI) is the first general-user interferometer that offers near- and mid-infrared long-baseline interferometric observations in service mode as well as visitor mode to the whole astronomical community. Regular VLTI observations with the first scientific instrument, the mid-infrared instrument MIDI, have started in ESO observing period P73, for observations between April and September 2004. The efficient use of the VLTI as a general-user facility implies the need for a well-defined operations scheme. The VLTI follows the established general operations scheme of the other VLT instruments. Here, we present from a users' point of view the VLTI specific aspects of this scheme beginning from the preparation of the proposal until the delivery of the data.

OzPoz is the multi-fiber positioner feeding the spectrographs GIRAFFE and UVES from a Nasmyth focus of VLT Unit Telescope 2. Together with GIRAFFE and UVES, it forms the FLAMES facility. FLAMES has been available for observing since successful completion of its science verification in Jan/Feb 2003. An aim of paramount importance in the design and construction of OzPoz was achievement of high reliability with minimal maintenance in the demanding Cerro Paranal VLT environment. Judged by its first 13 months of operation, it has been very successful in this respect, with an average of only 1% of observing time lost to problems; in the last 5 months of this period, the average was less than 0.1%. Of about 360 fibers and fiber bundles fed from deployable buttons on the two field plates, only one has become unusable (through breakage). The time taken to re-configure the fibers on one plate is always less than the exposure time (a minimum of 20 minutes) on the other (observing) plate, so no observing time is lost on that account and the time to interchange the two plates and acquire the new field is only about 5 minutes. The faintness of objects for which useful spectra can be obtained depends on the accuracy with which the sky background can be subtracted and this, in turn, depends on how well the relative spectral transmissions of fibers allocated to sky and to objects can be calibrated. An accuracy of 0.3% rms has been achieved.

Four years after its announcement at SPIE, FLAMES, the VLT fibre facility, has been completed, integrated into the VLT observatory and commissioned. It has been in operation since February 2003. More than 250000 scientific (single) spectra have been obtained, which have enabled the on-sky performance of the instrument to be compared to the predictions. We show that in several relevant aspects the real instrument significantly outperforms the specified astronomical performance. Some of the early scientific results are finally presented.

UVES-fiber is part of the FLAMES instrument mounted on the 8.2m Kueyen Telescope (UT2) of the ESO VLT. Up to eight single object fibers can be linked from the FLAMES focus to the red arm of the echelle spectrograph UVES. Science and calibration data are pipeline-processed by the Data Flow Operations group of ESO. Parameters to monitor the performance of the instrument are routinely extracted from calibration frames, stored into a database, and monitored over time. In addition to the Quality Control parameters already present for UVES in slit mode, several specific procedures had to be added in order to monitor the performance in the multi-object case. Particular attention is required for the positioning of the fibers on the detector and the transmission of the fibers. In this paper, we present details of the Quality Control process for UVES-fiber and results from the first year of operations.

FLAMES is the VLT Fibre Facility, installed and being commissioned at the Nasmyth A of UT2 (Kueyen Telescope). FLAMES has been built and assembled at the VLT telescope in about 4 years through an international collaboration between 10 institutes in 6 countries and 3 continents. It had first light with the fibre link to the red arm of UVES on April 1, and with the GIRAFFE spectrograph on July 3. We have not yet enough data to compare the observed vs. expected astronomical performances, although these first data are encouraging in many respects. We aim at proceeding soon with the remaining tests

UVES is the UV-Visual high-resolution echelle spectrograph mounted at the 8.2m Kueyen (UT2) telescope of the ESO Very Large Telescope. Its data products are pipeline-processed and quality checked by the Data Flow Operations Group (often known as QC Garching). Calibration data are processed to create calibration products and to extract Quality Control (QC) parameters. These parameters provide instrument health checks and monitor instrument performance. Typical UVES QC parameters are: bias level, read-out-noise, dark current of the three CCD detectors used in the instrument, rms of dispersion, resolving power, CCD pixel-to-pixel gain structure, instrument efficiency. The measured data are fed into a database, compared to earlier data, trended over time and published on the web (http://www.eso.org/qc/index_uves.html). The QC system has evolved with time and proven to be extremely useful. Some examples are given which highlight the impact of careful QC on instrument performance.

On August 8, 2001, Melipal became the fourth Unit Telescope of ESO's VLT to start regular scientific operations. Accordingly, the Paranal Science Operations team is now providing support for execution of observation programmes of the astronomical community on all four individual 8 m telescopes of the VLT. The operational model developed and applied by this team is based on the concept that optimal exploitation of the unique potential of the VLT and of its instrumentation requires support by dedicated qualified and experienced astronomers. This applies to observing both in visitor mode and in service (queue) mode, between which VLT operations are shared approximately in a 50/50 proportion. The Paranal Science Operations team has been staffed to implement the above-mentioned operational concept in collaboration with a mountain-based engineering team for technical support, and with groups based at ESO's headquarters in Germany for front- and back-end contacts with the astronomical community. Together with these teams, and based on the experience acquired since the start of operations of the first UT in April 1999, operational procedures have been refined and new operational tools have been implemented. In this process, the aspects that are particularly revelant for on-site operations include the short-term scheduling of service mode operations, and the reporting and tracking of the service mode programme execution status.

We describe the design and construction of the ESO UV-visual echelle spectrograph and the performance that was measured during its commissioning 1999. UVES is a dual-beam, grating crossdispersed echelle spectrograph. The resolution for a 1 arcsecond slit is 40,000. With narrower slits, resolutions of up to 80,000 and 115,000 are achieved with adequate sampling. UVES provides order separations of minimum 10 arcseconds at any wavelength between 320 and 1050 nm. The wavelength coverage is 100 nm in the blue arm and 200 or 400 nm in the red arm, with possibility to use a dichroic. Some concepts pioneered in UVES are now increasingly being used in other echelle spectrograph for large telescopes: a white pupil design, very steep replicated mosaic echelles, and large refractive cameras with external focus. Regular observations are starting in April 2000 at the Nasmyth focus of Kueyen, Unit Telescope 2 of the VLT array.

FLAMES is a fiber facility to be installed on the A platform of the VLT Kueyen telescope, which can feed up to three spectrographs with fibers positioned over a corrected 25 arcminutes field of view. The initial configuration will include connections to the GIRAFFE and to the red arm of the UVES spectrographs, the latter, located on the Nasmyth B platform of the same telescope, is already in operation as a long slit stand alone instrument. The 8 fibers to UVES will give R approximately 45000 and a large spectral coverage, while GIRAFFE will be fed by 132 single fibers, or by 15 deployable integral field units or by one central large integral unit. GIRAFFE will be equipped with two gratings, giving R equals 5000-9000 and R equals 15000-25000 respectively. It will be possible to obtain GIRAFFE and UVES observations simultaneously. Special attention is paid to optimizing night operations and to providing appropriate data reduction. The instrument is rather complex and it is now in the construction phase; in addition to ESO, its realization has required the collaboration of several institutes grouped in 4 consortia.

FEROS is a new fiber-fed bench-mounted prism crossdispersed echelle spectrograph for the ESO 1.52-m telescope at the European Southern Observatory (ESO) in La Silla, Chile. It works with a 79 lines/mm R2 echelle grating in quasi-Littrow mode and in white pupil configuration. With two fibers of 100 micrometer core diameter for the object and the nearby sky, the complete optical spectrum from 370 - 860 nm is recorded in one single exposure on a 2k X 4k thinned CCD with 15 micrometer pixels. Therefore, the instrument can work in a fixed configuration on the optical bench without movable parts besides the CCD shutter mechanics. For the highest-possible opto-mechanical stability. FEROS will be housed in a temperature and humidity controlled room in the former Coude room of the telescope. The resolving power of R equals 48,000 is reached by the use of a newly designed two-slice image slicer which is fed by the two fibers. Alternatively, the sky fiber can be illuminated with a calibration lamp during the whole object exposure to monitor the spectrograph's residual motions for high-precision radial-velocity work. FEROS is built for ESO by a consortium of four European astronomical institutes under the leadership of the Landessternwarte Heidelberg, Germany. Further members of the consortium are the Astronomical Observatory Copenhagen, Denmark, the Institut d'Astrophysique de Paris, and the Observatoire de Paris/Meudon, France. It is planned that FEROS will be fully operational at the ESO 1.52-m telescope in December 1998 and will be available to the community in early 1999.