Ralf Palsa

FLAMES: a multi-object fiber facility for the VLT

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.

PRIMA for the VLTI: a status report

PRIMA, the Phase-Referenced Imaging and Micro-arcsecond Astrometry facility for the Very Large Telescope Interferometer, is now nearing the end of its manufacturing phase. An intensive test period of the various sub-systems (star separators, fringe sensor units and incremental metrology) and of their interactions in the global system will start in Garching as soon as they are delivered. The status and performances of the individual sub-systems are presented in this paper as well as the proposed observation and calibration strategy to reach the challenging goal of high-accuracy differential astrometry at 10 μas level.

Lithium abundance in the metal-poor open cluster NGC 2243

Context. Lithium is a fundamental element for studying the mixing mechanisms acting in the stellar interiors, for understanding the chemical evolution of the Galaxy and the Big Bang nucleosynthesis. The study of Li in stars of open clusters (OC) allows a detailed comparison with stellar evolutionary models and permits us to trace its galactic evolution. The OC NGC 2243 is particularly interesting because of its low metallicity ([Fe/H] = −0.54 ± 0.10 dex). Aims. We measure the iron and lithium abundance in stars of the metal-poor OC NGC 2243. The first aim is to determine whether the Li dip extends to such low metallicities, the second is to compare the results of our Li analysis in this OC with those present in 47 Tuc, a globular cluster of similar metallicity. Methods. We performed a detailed analysis of high-resolution spectra obtained with the multi-object facility FLAMES at the ESO VLT 8.2 m telescope. Lithium abundance was derived through line equivalent widths and the OSMARCS atmosphere models. Iron abundances from Fe i and Fe ii lines have also been measured and used to check the atmospheric model parameters. Results. The Li line is detected in 27 stars confirmed as likely cluster members by repeated radial velocity measurements. We determine a Li dip center of 1.06 M� , which is much smaller than that observed in solar metallicity and metal-rich clusters. This finding confirms and strengthens the conclusion that the mass of the stars in the Li dip strongly depends on stellar metallicity. The mean Li abundance of the cluster is log n(Li) = 2.70 dex, which is substantially higher than that observed in 47 Tuc. We estimated an iron abundance of [Fe/H] = −0.54 ± 0.10 dex for NGC 2243, which is similar (within the errors) to previous findings. The [α/Fe] content ranges from 0.00 ± 0.14 for Ca to 0.20 ± 0.22 for Ti, which is low when compared to thick disk stars and to Pop II stars, but compatible with thin disk objects. We found a mean radial velocity of 61.9 ± 0. 8k m s −1 for the cluster. Conclusions. We confirm a correlation between the Li dip cool-side position in mass as a function of the cluster’s [Fe/H]. The Li abundance found in the metal-poor OC NGC 2243 agrees well with results obtained for the interstellar medium in the Small Magellanic Cloud having similar low metallicity. This value of Li is comparable to the primordial Li abundance deduced from WMAP measurements, therefore putting strong constraints on the models of Li enrichment during the early history of our Galaxy.

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.

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.

The common pipeline library: standardizing pipeline processing

The European Southern Observatory (ESO) develops and maintains a large number of instrument-specific data processing pipelines. These pipelines must produce standard-format output and meet the need for data archiving and the computation and logging of quality assurance parameters. As the number, complexity and data-output-rate of instrument increases, so does the challenge to develop and maintain the associated processing software. ESO has developed the Common Pipeline Library (CPL) in order to unify the pipeline production effort and to minimise code duplication. The CPL is a self-contained ISO-C library, designed for use in a C/C++ environment. It is designed to work with FITS data, extensions and meta-data, and provides a template for standard algorithms, thus unifying the look-and-feel of pipelines. It has been written in such a way to make it extremely robust, fast and generic, in order to cope with the operation-critical online data reduction requirements of modern observatories. The CPL has now been successfully incorporated into several new and existing instrument systems. In order to achieve such success, it is essential to go beyond simply making the code publicly available, but also engage in training, support and promotion. There must be a commitment to maintenance, development, standards-compliance, optimisation, consistency and testing. This paper describes in detail the experiences of the CPL in all these areas. It covers the general principles applicable to any such software project and the specific challenges and solutions, that make the CPL unique.

Toward accurate radial velocities with the fiber-fed GIRAFFE multi-object VLT spectrograph

We describe briefly the Data-Reduction of the VLT fiber-fed multi-object GIRAFFE spectrograph - part of the VLT FLAMES facility. We focus on specific features of GIRAFFE - the simultaneous wavelength calibration - and their impact on the data-reduction strategy. We describe the implementation of the global physical model and we compare the results obtained with the simulated, laboratory and preliminary data. We discuss the influence of critical parameters, the overall accuracy of the wavelength solution, and the stability and the robustness of the global model approach. We address the accuracy of radial velocity measurements illustrated by solar spectra obtained during the Preliminary Acceptance in Europe.

Quality control of VLT FLAMES/GIRAFFE data

GIRAFFE is a medium to high resolution spectrograph forming part of the complex multi-element fibre spectrograph FLAMES on the 8.2m VLT-UT2 telescope which also has a fibre link to the high-resolution spectrograph UVES. It has been operational since March 2003. GIRAFFE has been designed to be very stable and efficient. Here, first results concerning the Quality Control process are presented.

Perspective of imaging in the mid-infrared at the Very Large Telescope Interferometer

MATISSE is a mid-infrared spectro-interferometer combining the beams of up to four Unit Telescopes or Auxiliary Telescopes of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory. MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. New characteristics present in MATISSE will give access to the mapping and the distribution of the material, the gas and essentially the dust, in the circumstellar environments by using the mid-infrared band coverage extended to L, M and N spectral bands. The four beam combination of MATISSE provides an efficient uv-coverage: 6 visibility points are measured in one set and 4 closure phase relations which can provide aperture synthesis images in the mid-infrared spectral regime. We give an overview of the instrument including the expected performances and a view of the Science Case. We present how the instrument would be operated. The project involves the collaborations of several agencies and institutes: the Observatoire de la Côte d’Azur of Nice and the INSU-CNRS in Paris, the Max Planck Institut für Astronomie of Heidelberg; the University of Leiden and the NOVA-ASTRON Institute of Dwingeloo, the Max Planck Institut für Radioastronomie of Bonn, the Institut für Theoretische Physik und Astrophysik of Kiel, the Vienna University and the Konkoly Observatory.

Quality control of VLT-VIMOS data

VIMOS is the Visible Multi-Object Spectrograph mounted at the Nasmyth focus of the 8.2m Melipal (UT3) telescope of the ESO Very Large Telescope. VIMOS operates with four channels in three observing modes: imaging, multi-object spectroscopy (MOS), and integral field spectroscopy. VIMOS data are pipeline-processed and quality-checked by the Data Flow Operation group in Garching. The quality check is performed in two steps. The first one is a visual check of each pipeline product that allows the identification of any potential major data problem, such as, for example, a failure in the MOS mask insertion or an over/under exposure. The second step is performed in terms of Quality Control (QC) parameters, which are derived from both raw and processed data to monitor the instrument performance. The evolution in time of the QC parameters is recorded in a publically available database (http://www.eso.org/qc/). The VIMOS QC parameters include, for each of the four VIMOS channels, the bias level, read-out-noise, dark current, gain factor, flat-field and arc-lamps efficiencies, resolution and rms of dispersion, sky flat-field structure, image quality and photometric zeropoints. We describe here some examples of quality checks of VIMOS data.