CAUP Researchers: Pedro Figueira, Carlos J. A. P. Martins, Manuel Monteiro, Sérgio A. G. Sousa
ESPRESSO: the ultimate rocky exoplanets hunter for the VLT,
ESPRESSO, the VLT rocky exoplanets hunter, will combine the efficiency of modern echelle spectrograph with extreme radial-velocity precision. It will be installed at Paranal on ESO's VLT in order to achieve a flux-colecting improvement of two magnitudes with respect to its predecessor HARPS, and the instrumental radial-velocity precision will be improved to reach 10 cm/s level. We have constituted a Consortium of astronomical research institutes to fund, design and build ESPRESSO on behalf of and in collaboration with ESO, the European Southern Observatory. The project has passed the preliminary design review in November 2011. The spectrograph will be installed at the "Combined Coudé Laboratory" of the VLT, it will be linked to the four 8.2 meters Unit Telescopes (UT) through four optical "Coudé trains" and will be operated either with a single telescope or with up to four UTs. In exchange of the major financial and human effort the building Consortium will be awarded with guaranteed observing time (GTO), which will be invested in a common scientific program. Thanks to its characteristics and the ability of combining incoherently the light of 4 large telescopes, ESPRESSO will offer new possibilities in many fields of astronomy. Our main scientific objectives are the search and characterization of rocky exoplanets in the habitable zone of quiet, near-by G to M-dwarfs, and the analysis of the variability of fundamental physical constants. In this paper, we present the ambitious scientific objectives, the capabilities of ESPRESSO, the technical solutions for the system and its subsystems, enlightening the main differences between ESPRESSO and its predecessors. The project aspects of this facility are also described, from the consortium and partnership structure to the planning phases and milestones.
Spectroscopic analysis has now become a cornerstone for modern astronomy research, taking a central role in many fields of astrophysical sciences. Among these scientific areas, the search for exoplanets and the search for variations in the fundamental constants are among those which have a major interest in accurate spectroscopic data.
This need for high quality spectroscopic data has led astronomers across the globe to pursue the development of spectrographs with higher resolution and stability, resulting in instruments like HARPS, UVES and HIRES. Following this line of instrumentation development, ESO approved the development of ESPRESSO (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic), a high-resolution, ultra stable, fiber-fed, cross-dispersed echelle spectrograph which will be installed in VLT as part of its second generation instrumentation.
Observations made with ESPRESSO will be specially suited to address the needs of the two aforementioned fields, i.e., detection of rocky exoplanets located within the habitable zone and detection of variations of the fundamental constants. However, this spectrograph will also be of uttermost importance for most other fields of astrophysical sciences, like the study of the interstellar and intergalactic medium, the chemical composition of stars, galaxy formation and cosmology, among many others.
ESPRESSO will be installed in the VLT Combined Coudé Laboratory and will be able to receive optical data from all of the four Unit Telescopes. The calibration light sources include a laser frequency comb, which is essential to ensure that the relative uncertainty is kept below 10cm/s across the entire frequency range, from 380 to 780 nm. This level of precision across a range of 400 nm in wavelength is also dependent on the splitting of the light into two optical arms, each specifically optimized for its range (Figure 1). Finally, the optical bench is shielded by a vacuum vessel (itself within two further thermal enclosure structures) which stabilizes temperature to a range of 0.001º K.
The spectrograph will be able to operate in 3 different modes: single high resolution, single ultra-high resolution and multi mid resolution. The first two modes consist of using ESPRESSO as a standard VLT instrument, fed by a 1.0’’ or 0.5’’ fiber, respectively, allowing spectral resolutions of 130,000 or 200,000. In the multi mid resolution mode, 2, 3 or 4 Unit Telescopes feed ESPRESSO simultaneously, achieving a resolution of 55,000.
As several different functions are scattered over tens of meters, the complexity of the instruments control surpasses that of any other traditional VLT instrument and, thus, a new approach is needed for this. The new control system will be integrated in the VLT Telescope Control Software and operated from the user stations in the control room.
This spectrograph and its control software is being designed for ESO by a consortium of academic and research institutions from Italy, Portugal, Spain and Switzerland, and will be built by the ESO instrumentation division. CAUP is part of the ESPRESSO Consortium, leading the Portuguese participation; the national consortium also includes partners in the Faculty of Science of the University of Lisbon. ESPRESSO will become available for use by the ESO astronomers community by 2016.
In exchange for its contribution for this project, the ESPRESSO Consortium will receive about 1900 hours of observing time, of which 1500 will be assigned to the search for low-mass exoplanets and 200 to research on fundamental constants. Some further 200 hours are reserved for other high-quality science projects, to be determined later.
Besides its role as in the leadership of this project, CAUP is also responsible for the development of the data reduction and analysis software, as well as of the Coudé Train control software. Furthermore, CAUP also participates in the global scientific planning of ESPRESSO. The Portuguese contribution to the project involves the design and construction of one of the key components of the instrument: the Coudé Train. This component will collect the light from the four 8.2-m Unit Telescopes that compose the VLT, and transform it in the equivalent of a 16-m telescope, several years ahead of the E-ELT.
For a full list of authors, please visit the CAUP webpage.