Reinhard W. Hanuschik

A flux-calibrated, high-resolution atlas of optical sky emission from UVES

This paper presents a flux-calibrated, high-resolution, high-SNR atlas of optical and near-IR sky emission. It provides a complete template of the high-resolution night-sky emission spectrum with the deepest exposures ever obtained from the ground. The data have been acquired by UVES, ESOs echelle spectrograph at the 8.2-m UT2 telescope of the Very Large Telescope (VLT). Raw data stacks with up to 16 hours of integration time have been combined. The spectrum covers the range 3140-10 430 A at a resolving power of about 45 000. A total of 2810 sky emission lines have been measured. This high-resolution spectrum is intended to be used for the identification of previously unknown faint sky lines, for simulations of ground based observations where the sky background is important, as a template for checks on the accuracy and stability of the wavelength scale, and as a reference for the reduction of spectra of faint objects.

The outer regions of the giant Virgo galaxy M 87 Kinematic separation of stellar halo and intracluster light

We present a spectroscopic study of 287 Planetary Nebulas (PNs) in a total area of ~0.4 deg^2 around the BCG M87 in Virgo A. With these data we can distinguish the stellar halo from the co-spatial intracluster light (ICL). PNs were identified from their narrow and symmetric redshifted lambda 5007\4959 Angstrom [OIII] emission lines, and the absence of significant continuum. We implement a robust technique to measure the halo velocity dispersion from the projected phase-space to identify PNs associated with the M87 halo and ICL. The velocity distribution of the spectroscopically confirmed PNs is bimodal, containing a narrow component centred on the systemic velocity of the BCG and an off-centred broader component, that we identify as halo and ICL, respectively. Halo and ICPN have different spatial distributions: the halo PNs follow the galaxys light, whereas the ICPNs are characterised by a shallower power-law profile. The composite PN number density profile shows the superposition of different PN populations associated with the M87 halo and the ICL, characterised by different PN alpha-parameters, the ICL contributing ~3 times more PNs per unit light. Down to m_5007=28.8, the M87 halo PN luminosity function (PNLF) has a steeper slope towards faint magnitudes than the IC PNLF, and both are steeper than the standard PNLF for the M31 bulge. Moreover, the IC PNLF has a dip at ~1-1.5 mag fainter than the bright cutoff, reminiscent of the PNLFs of systems with extended star formation history. The M87 halo and the Virgo ICL are dynamically distinct components with different density profiles and velocity distribution. The different alpha values and PNLF shapes of the halo and ICL indicate distinct parent stellar populations, consistent with the existence of a gradient towards bluer colours at large radii. These results reflect the hierarchical build-up of the Virgo cluster.

Data reduction pipelines for the Very Large Telescope

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.

Support for site testing of the European Extremely Large Telescope: precipitable water vapor over Paranal

In support of characterization of potential sites for the European Extremely Large Telescope (E-ELT) the European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the astrometeorology group of the Universidad Valparaiso have jointly established an improved understanding of atmospheric precipitable water vapour (PWV) above ESOs La Silla Paranal Observatory. In a first step, 8 years worth of high resolution near-IR spectra taken with VLT-UVES have been statistically analysed to reconstruct the PWV history above Paranal. To this end a radiative transfer model of Earths atmosphere (BTRAM) developed by ISIS has been used. A median PWV of 2.1 mm is found for Paranal based on UVES data covering the period 2001-2008. Furthermore we conclude that Paranal can serve as a reference site for Northern Chile due to the stable atmospheric conditions in the region. The median offset between Paranal and Armazones is derived to be 0.3 mm, but local arbitrary variations of a few tenths of a mm between the sites have been found by measurement. In order to better understand the systematics involved two dedicated campaigns were conducted in August and November 2009. Several methods for determining the water column were employed, including radiosonde launches, continuous measurements by infrared radiometer, and VLT instruments operating at various wavelengths: CRIRES, UVES, VISIR and X-shooter. In a first for astronomical instruments all methods have been evaluated with respect to the radiosondes, the established standard in atmospheric research. Agreement between the radiosondes and the IR radiometer (IRMA) is excellent while all other astronomical methods covering a wavelength range from 700 - 20000 nm have also been successfully validated in a quantitative manner. All available observations were compared to satellite estimates of water vapour above the observatory in an attempt to ground-truth the satellite data. GOES can successfully be used for site evaluation in a purely statistical approach since agreement with the radiosondes is very good on average. For use as an operational tool at an observatory GOES data are much less suited because of significant deviations depending on atmospheric conditions. We propose to routinely monitor PWV at the VLT and to use it as an operational constraint to guide scheduling of IR observations at Paranal. For the E-ELT we find that a stand-alone high time resolution PWV monitor will be essential for optimizing the scientific output.

Performance of FLAMES at the VLT: one year of operation

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.

A water vapour monitor at Paranal Observatory

We present the performance characteristics of a water vapour monitor that has been permanently deployed at ESO’s Paranal observatory as a part of the VISIR upgrade project. After a careful analysis of the requirements and an open call for tender, the Low Humidity and Temperature Profiling microwave radiometer (LHATPRO), manufactured by Radiometer Physics GmbH (RPG), has been selected. The unit measures several channels across the strong water vapour emission line at 183 GHz, necessary for resolving the low levels of precipitable water vapour (PWV) that are prevalent on Paranal (median ~2.5 mm). The unit comprises the above humidity profiler (183-191 GHz), a temperature profiler (51-58 GHz), and an infrared radiometer (~10 μm) for cloud detection. The instrument has been commissioned during a 2.5 week period in Oct/Nov 2011, by comparing its measurements of PWV and atmospheric profiles with the ones obtained by 22 radiosonde balloons. In parallel an IR radiometer (Univ. Lethbridge) has been operated, and various observations with ESO facility spectrographs have been taken. The RPG radiometer has been validated across the range 0.5 – 9 mm demonstrating an accuracy of better than 0.1 mm. The saturation limit of the radiometer is about 20 mm. Currently, the radiometer is being integrated into the Paranal infrastructure to serve as a high time-resolution monitor in support of VLT science operations. The water vapour radiometer’s ability to provide high precision, high time resolution information on this important aspect of the atmosphere will be most useful for conducting IR observations with the VLT under optimal conditions.

Scoring: a novel approach toward automated and reliable certification of pipeline products

By 2010, the Paranal Observatory will host at least 15 instruments. The continuous increase in both the complexity and quantity of detectors has required the implementation of novel methods for the quality control of the resulting stream of data. We present the new and powerful concept of scoring which is used both for the certification process and the Health Check monitor. Scoring can reliably and automatically measure and assess the quality of arbitrarily amounts of data.

Quality control of VLT-UVES data

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.

Quality Control of the ESO-VLT instruments

Currently four instruments are operational at the four 8.2m telescopes of the European Southern Observatory Very Large Telescope: FORS1, FORS2, UVES, and ISAAC. Their data products are processed by the Data Flow Operations Group (also known as QC Garching) using dedicated pipelines. Calibration data are processed in order to provide instrument health checks, monitor instrument performance, and detect problems in time. The Quality Control (QC) system has been developed during the past three years. It has the following general components: procedures (pipeline and post-pipeline) to measure QC parameters; a database for storage; a calibration archive hosting master calibration data; web pages and interfaces. This system is part of a larger control system which also has a branch on Paranal where quick-look data are immediately checked for instrument health. The VLT QC system has a critical impact on instrument performance. Some examples are given where careful quality checks have discovered instrument failures or non-optimal performance. Results and documentation of the VLT QC system are accessible under http://www.eso.org/qc/.

From Chile to Europe in minutes: handling the data stream from ESO's Paranal Observatory

The ESO telescopes in Chile are operated in a geographically distributed scheme, in which some of the essential steps in the end-to-end observing chain take place in Europe. Most notably, the health status of the instruments as derived from the data themselves is monitored in Europe and the results fed back to the observatory within the hour. The flexibility of this scheme strongly depends on the speed with which the data stream produced by the telescopes can be sent to Europe for analysis and storage. The main challenge to achieve a fast intercontinental data transfer is the data volume itself, which currently reaches an average 25 GB/night (compressed) for the four VLT Unit Telescopes. Since late 2008, this stream has been entirely transferred through the internet via a 4.56 Mbit/s bandwidth assured via a Quality of Service policy, which sufficed to transfer an average night of data within a few hours. A very recent enlargement of this capacity to 9.12 Mbit/s will soon allow the addition of the calibration data for VISTA, the new infrared survey telescope on Paranal, to the data stream transferred through the internet. Ultimately, the average data volume produced on Paranal once the visible VLT Survey Telescope (VST) and the full complement of second-generation VLT instruments becomes available is expected to exceed 200 GB/night. Transferring it over the internet will require a new fiber-based infrastructure currently under construction, as well as the use of additional high bandwidth channels. This infrastructure, provided by the European Union co-funded project EVALSO, should provide a data transfer capacity exceeding 1 Gbit/s that will allow the transfer to Europe of the entire Paranal data stream, as well as that of the nearby Observatory of Cerro Armazones and of the future European Extremely Large Telescope, with a delay of minutes at most since the data were taken.