The design and construction of CARMENES has been presented at previous SPIE conferences. It is a next-generation radial-velocity instrument at the 3.5m telescope of the Calar Alto Observatory, which was built by a consortium of eleven Spanish and German institutions. CARMENES consists of two separate échelle spectrographs covering the wavelength range from 0.52 to 1.71μm at a spec-tral resolution of R < 80,000, fed by fibers from the Cassegrain focus of the telescope. CARMENES saw “First Light” on Nov 9, 2015.
During the commissioning and initial operation phases, we established basic performance data such as throughput and spectral resolution. We found that our hollow-cathode lamps are suitable for precise wavelength calibration, but their spectra contain a number of lines of neon or argon that are so bright that the lamps cannot be used in simultaneous exposures with stars. We have therefore adopted a calibration procedure that uses simultaneous star / Fabry Pérot etalon exposures in combination with a cross-calibration between the etalons and hollow-cathode lamps during daytime. With this strategy it has been possible to achieve 1-2 m/s precision in the visible and 5-10 m/s precision in the near-IR; further improvements are expected from ongoing work on temperature control, calibration procedures and data reduction. Comparing the RV precision achieved in different wavelength bands, we find a “sweet spot” between 0.7 and 0.8μm, where deep TiO bands provide rich RV information in mid-M dwarfs. This is in contrast to our pre-survey models, which predicted comparatively better performance in the near-IR around 1μm, and explains in part why our near-IR RVs do not reach the same precision level as those taken with the visible spectrograph.
We are now conducting a large survey of 340 nearby M dwarfs (with an average distance of only 12pc), with the goal of finding terrestrial planets in their habitable zones. We have detected the signatures of several previously known or suspected planets and also discovered several new planets. We find that the radial velocity periodograms of many M dwarfs show several significant peaks. The development of robust methods to distinguish planet signatures from activity-induced radial velocity jitter is therefore among our priorities.
Due to its large wavelength coverage, the CARMENES survey is generating a unique data set for studies of M star atmospheres, rotation, and activity. The spectra cover important diagnostic lines for activity (H alpha, Na I D1 and D2, and the Ca II infrared triplet), as well as FeH lines, from which the magnetic field can be inferred. Correlating the time series of these features with each other, and with wavelength-dependent radial velocities, provides excellent handles for the discrimination between planetary companions and stellar radial velocity jitter. These data are also generating new insight into the physical properties of M dwarf atmospheres, and the impact of activity and flares on the habitability of M star planets.
The CARMENES instrument is a pair of high-resolution (R⪆80,000) spectrographs covering the wavelength range from 0.52 to 1.71 μm, optimized for precise radial velocity measurements. It was installed and commissioned at the 3.5m telescope of the Calar Alto observatory in Southern Spain in 2015. The first large science program of CARMENES is a survey of ~ 300 M dwarfs, which started on Jan 1, 2016. We present an overview of all subsystems of CARMENES (front end, fiber system, visible-light spectrograph, near-infrared spectrograph, calibration units, etalons, facility control, interlock system, instrument control system, data reduction pipeline, data flow, and archive), and give an overview of the assembly, integration, verification, and commissioning phases of the project. We show initial results and discuss further plans for the scientific use of CARMENES.
In the summer of 2011, the first on-sky astrometric commissioning of PRIMA-Astrometry delivered a performance of 3 m″ for a 10 ″ separation on bright objects, orders of magnitude away from its exoplanet requirement of 50 μ″ ~ 20 μ″ on objects as faint as 11 mag ~ 13 mag in K band. This contribution focuses on upgrades and characterizations carried out since then. The astrometric metrology was extended from the Coudé focus of the Auxillary Telescopes to their secondary mirror, in order to reduce the baseline instabilities and improve the astrometric performance. While carrying out this extension, it was realized that the polarization retardance of the star separator derotator had a major impact on both the astrometric metrology and the fringe sensors. A local compensation of this retardance and the operation on a symmetric baseline allowed a new astrometric commissioning. In October 2013, an improved astrometric performance of 160 μ″ was demonstrated, still short of the requirements. Instabilities in the astrometric baseline still appear to be the dominating factor. In preparation to a review held in January 2014, a plan was developed to further improve the astrometric and faint target performance of PRIMA Astrometry. On the astrometric aspect, it involved the extension of the internal longitudinal metrology to primary space, the design and implementation of an external baseline metrology, and the development of an astrometric internal fringes mode. On the faint target aspect, investigations of the performance of the fringe sensor units and the development of an AO system (NAOMI) were in the plan. Following this review, ESO decided to take a proposal to the April 2014 STC that PRIMA be cancelled, and that ESO resources be concentrated on ensuring that Gravity and Matisse are a success. This proposal was recommended by the STC in May 2014, and endorsed by ESO.
The Extrasolar Planet Search with PRIMA project (ESPRI) aims at characterising and detecting extrasolar planets by measuring the host star's reflex motion using the narrow-angle astrometry capability of the PRIMA facility at the Very Large Telescope Interferometer. A first functional demonstration of the astrometric mode was achieved in early 2011. This marked the start of the astrometric commissioning phase with the purpose of characterising the instrument's performance, which ultimately has to be sufficient for exoplanet detection. We show results obtained from the observation of bright visual binary stars, which serve as test objects to determine the instrument's astrometric precision, its accuracy, and the plate scale. Finally, we report on the current status of the ESPRI project, in view of starting its scientific programme.
PRIMA (Phase-Referenced Imaging and Microarcsecond Astrometry) is an ESO/VLTI instrument designed for
phase-referenced imaging and narrow-angle astrometry, dedicated to exoplanet detection. The astrometric datareduction
software (ADRS) is a key component of the system, calculating very precise (~ 10 μas) differential
angular separations projected on the sky. For an interferometer with a baseline of 100 m, this separation
corresponds to measuring the (differential) optical path difference with a precision of 5 - 15 nanometers. This
precision can only be achieved with careful calibration of the instrument, including effects that are irrelevant for
almost any other scientific application. PRIMA is currently being commissioned on Paranal, and we expect to obtain the first astrometric data in September 2010. These data will provide a new insight into the operation and calibration of the instrument.
The NULLTIMATE project developed and realized three concepts of achromatic phase shifters for nulling interferometry.
One of the concepts is based on dispersive plates made of three materials which where fully
characterized regarding their refractive index and thermo-optic behavior between 100K and 330 K. The other
two concepts are based on mirror optics, one of which uses the phase shift of π when crossing a focus, the
other the reversal of electric fields at reflection. An optical bench has been set up to test and characterize these
phase shifters at wavelengths 2 − 2.4 μm with the option of changing to the 10 μm domain. We summarize the
development of the achromatic phase shifters and report on the current status of the test bench.
PRIMA/PACMAN is scheduled for commissioning on Paranal in late 2008 as part of the VLTI. In this paper, we
discuss the important aspects of its astrometric data-reduction software. For example, the top-level requirements,
interfaces to existing ESO software, data types, data levels, and data flow among the recipes dictate the overall
design of any software package. In addition, the complexity of the PACMAN instrument, the long-term nature
of astrometric observations, and the need to improve algorithms as the understanding of the hardware improves,
impose additional requirements on the astrometric data-reduction software.
PRIMA, the instrument for Phase-Referenced Imaging and Micro-arcsecond Astrometry at the VLTI, is currently being
developed at ESO. PRIMA will implement the dual-feed capability, at first for two UTs or ATs, to enable simultaneous
interferometric observations of two objects that are separated by up to 1 arcmin. PRIMA is designed to perform narrow-angle
astrometry in K-band with two ATs as well as phase-referenced aperture synthesis imaging with instruments like
Amber and Midi. In order to speed up the full implementation of the 10 microarcsec astrometric capability of the VLTI
and to carry out a large astrometric planet search program, a consortium lead by the Observatoire de Genève, Max
Planck Institute for Astronomy, and Landessternwarte Heidelberg, has built Differential Delay Lines for PRIMA and is
developing the astrometric observation preparation and data reduction software. When the facility becomes fully
operational in 2009, we will use PRIMA to carry out a systematic astrometric Exoplanet Search program, called ESPRI.
In this paper, we describe the narrow-angle astrometry measurement principle, give an overview of the ongoing hardand
software developments, and outline our anticipated astrometric exoplanet search program.
ESPRI is a project which aims at searching for and characterizing extra-solar planets by dual-beam astrometry with
PRIMA@VLTI. Differential Delay Lines (DDL) are fundamental for achieving the micro-arcseconds accuracy required
by the scientific objective. Our Consortium, consisting of the Geneva Observatory, the Max-Planck Institut for
Astronomy Heidelberg, and the Landessternwarte Heidelberg, in collaboration with ESO, has built and tested these
DDLs successfully and will install them in summer 2008 at the VLTI. These DDLs consist of high quality cat's eyes
displaced on a parallel beam-mechanics and by means of a two-stage actuation with a precision of 5 nm over a stroke
length of 70 mm. Over the full range, a bandwidth of about 400 Hz is achieved. The DDLs are operated in vacuum. We
shall present, in this paper, their design and their exceptional performances.
Direct detections of Earth-like extrasolar planets are extremely challenging and require to overcome the huge brightness
contrast between two sources that have a very small angular separation. One possible solution to this problem is nulling
interferometry at mid-infrared wavelengths where the flux ratio between host star and planet is more favorable than in
the visible. The beams of an array of telescopes are combined so that the light from the on-axis direction (the star) is
canceled by destructive interference, while the light from an off-axis direction (the planet) is kept. The global
performance of such a system depends strongly on the accuracy and stability of the achromatic phase shift and the beam
combination. To assess the technological feasibility of this technique, the European Space Agency (ESA) and IAS Paris
have initiated a study of different physical concepts and technical realizations of achromatic phase shifters (APS) that
fulfill the following requirements: allowing a >10<sup>-6</sup> rejection rate or better over a wavelength range 6-20μm and
providing a transmission better than 95%. MPIA, in collaboration with the Kayser-Threde GmbH in Munich and the IOF
Fraunhofer institute for applied optics in Jena has breadboarded and studied a phase shifter that is based on the geometric
reversal of the electric field vectors (pupil flip) at two successive antisymmetric 90 degree reflections. In this paper we
describe the bread-boarded phase-shifter device and the results of our characterization measurements in the Lab.
The achromatic phase shifter (APS) is a component of the Bracewell nulling interferometer studied in preparation
for future space missions (viz. <i>Darwin</i>/TPF-I) focusing on spectroscopic study of Earth-like exo-planets. Several
possible designs of such an optical subsystem exist. Four approaches were selected for further study. Thales
Alenia Space developed a dielectric prism APS. A focus crossing APS prototype was developed by the OCA,
Nice, France. A field reversal APS prototype was prepared by the MPIA in Heidelberg, Germany. Centre Spatial
de Liege develops a concept based on Fresnel's rhombs. This paper presents a progress report on the current
work aiming at evaluating these prototypes on the Synapse test bench at the Institut d'Astrophysique Spatiale
in Orsay, France.
The last step in designing and building instruments are the verification and acceptance tests of the assembled units and of
the final instrument. For instruments, which are engineered to work at the limit of feasibility, these tests must be accurate
and stable at a level much better than the expected performance of the instrument. Particularly for interferometric
instruments, this requires special care for the test planning and implementation in order to achieve the necessary
performance. This paper describes the verification and acceptance tests of the PRIMA DDL optics in terms of wavefront
error and tilt requirements as well as the assembling and aligning accuracy. We demonstrate the conformity of the optics
and point out the limitations of the test methods.
ESO's PRIMA (Phase-Referenced Imaging and Micro-arcsecond Astrometry) facility at the VLT Interferometer
on Cerro Paranal in Chile is expected to be fully operational in only a couple of years from now. With
PRIMA/VLTI, it will then be possible to perform relative astrometry with an accuracy of the order of 10 μas
over angles of about 10".
The main science driver for this astrometric capability is the detection and characterization of extrasolar
planets, including (1) the observation of known radial velocity planets and planetary systems to fully constrain
their orbital geometry and accurately determine the mass of the planet(s), (2) a search for extrasolar planets
around stars which are less suitable for the radial velocity method (for example young and active stars as well as
early type stars), and (3) a systematic search around the most nearby stars to detect low mass planets (Uranus
or Neptune masses).
Preparatory observations of possible target stars, with the aim of identifying nearby suitable astrometric
reference stars, have already started with SOFI at the NTT and are described. Furthermore, we compare the
goals and prospects of the PRIMA Astrometric Planet Search to other projects aiming at detecting planets
astrometrically, mostly from space.
ESO's PRIMA (Phase-Referenced Imaging and Micro-arcsecond Astrometry)
facility at the VLT Interferometer on Cerro Paranal in Chile is expected to be fully operational in only a few years from now.
With PRIMA/VLTI, it will then be possible to perform relative astrometry with an accuracy of the order of 10 microarcseconds over angles of about 10 arcseconds. The main science driver for this astrometric capability is a systematic search for extrasolar planets around nearby stars.
Target stars as well as reference stars for this astrometric planet search have to be very carefully chosen in order to make the measurements robust and effective. Most importantly, reference stars have to be astrometrically stable to only a few microarcseconds in order to provide a suitable reference for the astrometric measurements. Target stars should be located at small distances so that a possible planet would cause a detectable astrometric signal.
Moreover, a suitable target star and a suitable reference star have to be found within about 10 arcseconds of each other to ensure the highest accuracy and effectiveness, which obviously requires some trade-off in the final target list. Possible strategies and preparatory observations for the assembly of a suitable target list for the astrometric planet search with PRIMA/VLTI will be discussed.
A search for extrasolar planets using the ESO VLTI PRIMA facility
will become feasible in 2007. An astrometric accuracy of 10 micro-arcseconds will allow us to detect sub-Uranus mass planets around the
most nearby stars, as well as to conduct a planet search around stars of different ages. Most of the PRIMA hardware subsystems are currently being developed by industry. At the same time a scientific Consortium has formed that will deliver the differential delay lines and astrometric software for PRIMA to ESO.
In this paper we describe the planned efforts by the Consortium
related to the "PRIMA astrometry operations and software". These
activities include an overall "PRIMA astrometry error budget", a
"PRIMA astrometry calibration and observation strategy", the "PRIMA astrometry observation preparation tools" and the "PRIMA astrometry data reduction tools". We describe how all these components fit together in an overall approach to the flow of knowledge within the project. First by quantifying the fundamental limits of the VLTI infrastructure and the astronomical sources under study. Followed by elimination or suppression of the errors through either a hardware change to the system, software control of the system, or a proper calibration and observation strategy.
The ultimate goal is being able to calibrate all PRIMA astrometric data acquired over the full lifetime of PRIMA (5 to 10 years) to a uniform accuracy of 10 micro-arcseconds. This will allow identification of long-term trends in the astrometric parameters due to planetary companions around nearby stars and to determine the distances and proper motions for the selected sources.
The PRIMA facility will implement dual-star astrometry at the VLTI. We have formed a consortium that will build the PRIMA differential delay lines, develop an astrometric operation and calibration plan, and deliver astrometric data reduction software. This will enable astrometric planet surveys with a target precision of 10μas. Our scientific goals include determining orbital inclinations and masses for planets already known from radial-velocity surveys, searches for planets around stars that are not amenable to high-precision radial-velocity observations, and a search for large rocky planets around
nearby low-mass stars.
The Darwin/TPF mission aims at detecting directly extra solar
planets. It is based on the nulling interferometry, concept proposed
by Bracewell in 1978, and developed since 1995 in several European and
American laboratories. One of the key optical devices for this
technique is the achromatic phase shifter (APS). This optical
component is designed to produce a π phase shift over the whole
Darwin spectral range (i.e. 6-18 μm), and will be experimentally
tested on the NULLTIMATE consortium nulling test bench (Labèque et
al). Three different concepts of APS are being simulated: dispersive plates focus crossing and field reversal. In this paper, we show how thermal, mechanical and optical models are merged into a single robust model, allowing a global numerical simulation of the optical component performances. We show how these simulations help us to optimizing the design and present results of the numerical model.
We present high-resolution polarization maps, obtained with near-infrared instruments such as ISAAC at the VLT, SOFI at the NTT, and SCUBA at the JCMT. While we use the near-infrared polarization maps to determine the structure of the optical reflection nebula Cederblad 110 IRS 4 and to investigate the alignment of circumstellar disks around T Tauri binary stars, submillimeter polarization maps are used to derive the magnetic field structure and strength in Bok globules. Furthermore we show that near-infrared polarimetry represents a powerful tool to distinguish between different
polarization models developed for active galactic nuclei.