Hans Dekker

Design, construction, and performance of UVES, the echelle spectrograph for the UT2 Kueyen Telescope at the ESO Paranal Observatory

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.

High-precision wavelength calibration of astronomical spectrographs with laser frequency combs

ABSTRACT We describe a possible new technique for precise wavelength calibration of high-resolutionastronomical spectrographs using femtosecond-pulsed mode-locked lasers controlled by sta-ble oscillators such as atomic clocks. Such ‘frequency combs’ provide a series of narrowmodes which are uniformly spaced according to the laser’s pulse repetition rate and whoseabsolute frequencies are known a priori with relative precision better than 10 −12 . Simula-tions of frequency comb spectra show that the photon-limited wavelength calibration preci-sion achievable with existing echelle spectrographs should be ∼1cms −1 when integrated overa 4000A range. Moreover, comb spectra may be used to accurately characterise distortionsof the wavelength scale introduced by the spectrograph and detector system. The simulationsshow that frequency combs with pulse repetition rates of 5–30GHz are required, given thetypical resolving power of existing and possible future echelle spectrographs. Achieving suchhigh repetition rates, together with the desire to produce all comb modes with uniform inten-sity over the entire optical range, represent the only significant challenges in the design ofa practical system. Frequency comb systems may remove wavelength calibration uncertain-ties from all practical spectroscopic experiments, even those combining data from differenttelescopes over many decades.Key words: instrumentation: spectrographs – instrumentation: detectors – methods: labora-tory – techniques: spectroscopic

Cosmic dynamics in the era of Extremely Large Telescopes

The redshifts of all cosmologically distant sources are expected to experience a small, systematic drift as a function of time due to the evolution of the Universes expansion rate. A measurement of this effect would represent a direct and entirely model-independent determination of the expansion history of the Universe over a redshift range that is inaccessible to other methods. Here we investigate the impact of the next generation of Extremely Large Telescopes on the feasibility of detecting and characterising the cosmological redshift drift. We consider the Lyman alpha forest in the redshift range 2 < z < 5 and other absorption lines in the spectra of high redshift QSOs as the most suitable targets for a redshift drift experiment. Assuming photon-noise limited observations and using extensive Monte Carlo simulations we determine the accuracy to which the redshift drift can be measured from the Ly alpha forest as a function of signal-to-noise and redshift. Based on this relation and using the brightness and redshift distributions of known QSOs we find that a 42-m telescope is capable of unambiguously detecting the redshift drift over a period of ~20 yr using 4000 h of observing time. Such an experiment would provide independent evidence for the existence of dark energy without assuming spatial flatness, using any other cosmological constraints or making any other astrophysical assumption.

ESPRESSO: the Echelle spectrograph for rocky exoplanets and stable spectroscopic observations

ESPRESSO, the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations, will combine the efficiency of modern echelle spectrograph design with extreme radial-velocity precision. It will be installed on ESOs VLT in order to achieve a gain of two magnitudes with respect to its predecessor HARPS, and the instrumental radialvelocity precision will be improved to reach cm/s level. Thanks to its characteristics and the ability of combining incoherently the light of 4 large telescopes, ESPRESSO will offer new possibilities in various fields of astronomy. The main scientific objectives will be the search and characterization of rocky exoplanets in the habitable zone of quiet, nearby G to M-dwarfs, and the analysis of the variability of fundamental physical constants. We will present the ambitious scientific objectives, the capabilities of ESPRESSO, and the technical solutions of this challenging project.

Performance of UVES, the echelle spectrograph for the ESO VLT and highlights of the first observations of stars and quasars

UVES is a dual beam echelle spectrograph installed at the Nasmyth focus of the UT2 telescope of the ESO VLT since October 1999. It can reach a resolution of 80000 and 115000 in the blue and red arm, respectively. The instrument is characterized by great stability and high efficiency. The smooth operation of both the new telescope and instrument has lead to a remarkable number of highly interesting scientific observations during commissioning. Examples of scientific work on these data are presented to illustrate the unique UV efficiency, the resolving power and high S/N capability and far red efficiency.

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.

The exoplanet hunter HARPS: performance and first results

HARPS is a new high resolution fibre-fed spectrograph dedicated to the extremely precise measurement of stellar radial velocities. After being used for about one year including the commissioning runs we report a very successful implementation of the measures taken to maximise stability, efficiency and spectral performance. Using the Simultaneous ThAr Reference Method a short term precision of 0.2 m/s during one night and a long term precision of the order of 1 m/s have been achieved. Equipped with a fully automated data reduction pipeline that produces solar system barycentric radial velocities in near real-time, HARPS promises to deliver data of unequalled quality. HARPS will primarily be used for the search for exoplanets and in the field of asteroseismology. First exciting scientific results confirm these expectations.

The second-generation VLT instrument MUSE: science drivers and instrument design

The Multi Unit spectroscopic Explorer (MUSE) is a second generation VLT panoramic integral-field spectrograph operating in the visible wavelength range. MUSE has a field of 1 x 1 arcmin2 sampled at 0.2x0.2 arcsec2 and is assisted by a ground layer adaptive optics system using four laser guide stars. The simultaneous spectral range is 0.465-0.93 μm, at a resolution of R~3000. MUSE couples the discovery potential of a large imaging device to the measuring capabilities of a high-quality spectrograph, while taking advantage of the increased spatial resolution provided by adaptive optics. This makes MUSE a unique and tremendously powerful instrument for discovering and characterizing objects that lie beyond the reach of even the deepest imaging surveys. MUSE has also a high spatial resolution mode with 7.5 x 7.5 arcse2 field of view sampled at 25 milli-arcsec. In this mode MUSE should be able to get diffraction limited data-cube in the 0.6-1 μm wavelength range. Although MUSE design has been optimized for the study of galaxy formation and evolution, it has a wide range of possible applications; e.g. monitoring of outer planets atmosphere, young stellar objects environment, supermassive black holes and active nuclei in nearby galaxies or massive spectroscopic survey of stellar fields.

CODEX: the high-resolution visual spectrograph for the E-ELT

A number of outstanding scientific problems require a high resolution, visual spectrograph at the E-ELT. Measuring the dynamics of the universe, finding earth-like planets with radial velocity techniques, determining the chemical evolution of the intergalactic medium and if physical constants varied in the past, all require a superior capability of measuring exceedingly small Doppler shifts. We have started a Phase A study for CODEX at the E-ELT. We present here the scientific cases, the requirements, the basic technical choices and trade offs, as well as a couple of design under evaluation. We aim at a super stable instrument, capable of obtaining a radial velocity precision of 2 cm/sec over several decades. It will be located at the coude focus. The design will make use of anamorphosis, pupil slicing, slanted VPH gratings and a novel calibration system based on laser frequency combs. Several CODEX-related R&D activities are running, and, in addition, a Call for Proposal for a precursor at the VLT has been issued.

ESPRESSO: A High Resolution Spectrograph for the Combined Coudé Focus of the VLT

Luca Pasquini, A. Manescau, G. Avila, B. Delabre, H. Dekker, J. Liske, S. D’Odorico, F. Pepe, M. Dessauges, C. Lovis, D. Megevand, D. Queloz, S. Udry, S. Cristiani, P. Bonifacio, P. Dimarcantonio, V. D’Odorico, P. Molaro, E. Vanzella, M. Viel, M. Haehnelt, B. Carswell, M. Murphy, R. Garcia-Lopez, J.M. Herreros, J. Perez, M.R. Zapatero, R. Rebolo, G. Israelian, E. Martin, F. Zerbi, P. Spano, S. Levshakov, N. Santos and S. Zucker