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.
We have developed a generic physical modeling scheme for high resolution spectroscopy based on simple optical principles. This model predicts the position of centroids for a given set of spectral features with high accuracy. It considers off-plane grating equations and rotations of the different optical elements in order to properly account for tilts in the spectral lines and order curvature. In this way any astronomical spectrograph can be modeled and controlled without the need of commercial ray tracing software. The computations are based on direct ray tracing applying exact corrections to certain surfaces types. This allows us to compute the position on the detector of any spectral feature with high reliability. The parameters of this model, which describe the physical properties of the spectrograph, are continuously optimized to ensure the best possible fit to the observed spectral line positions. We present the physical modeling of CARMENES as a case study. We show that our results are in agreement with commercial ray tracing software. The model prediction matches the observations at a pixel size level, providing an efficient tool in the design, construction and data reduction of high resolution spectrographs.
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.
The Waltz Spectrograph is a fiber-fed high-resolution échelle spectrograph for the 72 cm Waltz Telescope at the Landessternwarte, Heidelberg. It uses a 31.6 lines/mm 63.5° blaze angle échelle grating in white-pupil configuration, providing a spectral resolving power of R ~ 65,000 covering the spectral range between 450-800nm in one CCD exposure. A prism is used for cross-dispersion of échelle orders. The spectrum is focused by a commercial apochromat onto a 2k×2k CCD detector with 13.5μm per pixel. An exposure meter will be used to obtain precise photon-weighted midpoints of observations, which will be used in the computation of the barycentric corrections of measured radial velocities. A stabilized, newly designed iodine cell is employed for measuring radial velocities with high precision. Our goal is to reach a radial velocity precision of better than 5 m/s, providing an instrument with sufficient precision and sensitivity for the discovery of giant exoplanets. Here we describe the design of the Waltz spectrograph and early on-sky results.
Using a photonic reformatter to eliminate the effects of conventional modal noise could greatly improve the stability of a high resolution spectrograph. However the regimes where this advantage becomes clear are not yet defined. Here we will look at where modal noise becomes a problem in conventional high resolution spectroscopy and what impact photonic spectrographs could have. We will theoretically derive achievable radial velocity measurements to compare photonic instruments and conventional ones. We will discuss the theoretical and experimental investigations that will need to be undertaken to optimize and prove the photonic reformatting concept.
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.
This paper gives an overview of the CARMENES instrument and of the survey that will be carried out with it
during the first years of operation. CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths
with Near-infrared and optical Echelle Spectrographs) is a next-generation radial-velocity instrument
under construction for the 3.5m telescope at the Calar Alto Observatory by a consortium of eleven Spanish
and German institutions. The scientific goal of the project is conducting a 600-night exoplanet survey targeting
~ 300 M dwarfs with the completed instrument.
The CARMENES instrument consists of two separate echelle spectrographs covering the wavelength range
from 0.55 to 1.7 μm at a spectral resolution of R = 82,000, fed by fibers from the Cassegrain focus of the telescope.
The spectrographs are housed in vacuum tanks providing the temperature-stabilized environments necessary to
enable a 1 m/s radial velocity precision employing a simultaneous calibration with an emission-line lamp or with
a Fabry-Perot etalon. For mid-M to late-M spectral types, the wavelength range around 1.0 μm (Y band) is the
most important wavelength region for radial velocity work. Therefore, the efficiency of CARMENES has been
optimized in this range.
The CARMENES instrument consists of two spectrographs, one equipped with a 4k x 4k pixel CCD for
the range 0.55 - 1.05 μm, and one with two 2k x 2k pixel HgCdTe detectors for the range from 0.95 - 1.7μm.
Each spectrograph will be coupled to the 3.5m telescope with two optical fibers, one for the target, and one
for calibration light. The front end contains a dichroic beam splitter and an atmospheric dispersion corrector,
to feed the light into the fibers leading to the spectrographs. Guiding is performed with a separate camera;
on-axis as well as off-axis guiding modes are implemented. Fibers with octagonal cross-section are employed to
ensure good stability of the output in the presence of residual guiding errors. The fibers are continually actuated
to reduce modal noise. The spectrographs are mounted on benches inside vacuum tanks located in the coud´e
laboratory of the 3.5m dome. Each vacuum tank is equipped with a temperature stabilization system capable
of keeping the temperature constant to within ±0.01°C over 24 hours. The visible-light spectrograph will be
operated near room temperature, while the near-IR spectrograph will be cooled to ~ 140 K.
The CARMENES instrument passed its final design review in February 2013. The MAIV phase is currently
ongoing. First tests at the telescope are scheduled for early 2015. Completion of the full instrument is planned
for the fall of 2015. At least 600 useable nights have been allocated at the Calar Alto 3.5m Telescope for the
CARMENES survey in the time frame until 2018.
A data base of M stars (dubbed CARMENCITA) has been compiled from which the CARMENES sample can
be selected. CARMENCITA contains information on all relevant properties of the potential targets. Dedicated imaging, photometric, and spectroscopic observations are underway to provide crucial data on these stars that
are not available in the literature.
CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a next-generation instrument for the 3.5m telescope at the Calar Alto Observatory, built by a consortium of eleven Spanish and German institutions. The CARMENES instrument consists of two separate échelle spectrographs covering the wavelength range from 0.55 μm to 1.7 μm at a spectral resolution of R = 82, 000, fed by fibers from the Cassegrain focus of the telescope. Both spectrographs are housed in temperature-stabilized vacuum tanks, to enable a long-term 1 m/s radial velocity precision employing a simultaneous calibration with Th-Ne and U-Ne emission line lamps. CARMENES has been optimized for a search for terrestrial planets in the habitable zones (HZs) of low-mass stars, which may well provide our first chance to study environments capable of supporting the development of life outside the Solar System. With its unique combination of optical and near-infrared ´echelle spectrographs, CARMENES will provide better sensitivity for the detection of low-mass planets than any comparable instrument, and a powerful tool for discriminating between genuine planet detections and false positives caused by stellar activity. The CARMENES survey will target 300 M dwarfs in the 2014 to 2018 time frame.
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.
CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical
Echelle Spectrographs) is a next-generation instrument to be built for the 3.5m telescope at the Calar Alto
Observatory by a consortium of Spanish and German institutions. Conducting a five-year exoplanet survey
targeting ~ 300 M stars with the completed instrument is an integral part of the project. The CARMENES
instrument consists of two separate spectrographs covering the wavelength range from 0.52 to 1.7 μm at a spectral
resolution of R = 85, 000, fed by fibers from the Cassegrain focus of the telescope. The spectrographs are housed
in a temperature-stabilized environment in vacuum tanks, to enable a 1m/s radial velocity precision employing
a simultaneous ThAr calibration.
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.
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.
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.
One of the goals of the VLTI PRIMA (Phase Referenced Imaging and Micro-arcsecond Astrometry) facility will be to obtain high accuracy astrometry (of the order of 10 micro-arcsec) for the measurement of the reflex motion due to planets. In order to achieve this an offline astrometric Data Analysis Facility (DAF) is planned to perform a homogeneous and iterative analysis over several years of observations. This system will be part of the PRIMA Data Reduction Library (DRL), which also contains the online pipeline. The most important module of the DAF will be the Trend Analysis to identify and fit the systematic errors and feed them back into the data reduction. This requires an infrastructure which allows for comprehensive access to all raw and derived data and enough flexibility to easily introduce new algorithms in the system. We plan to realize this with a database, sophisticated middleware and Application Programmers' Interfaces (APIs) for the algorithms and user interface plug-ins. We present in this paper the requirements and preliminary design of the DAF, as well as the implementation issues concerning the integration with other modules of the DRL and ESO compliance.
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.
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.
Wide angle astrometry with the Space Interferometry Mission needs a set of several thousand grid stars distributed uniformly over the sky. The requirements for candidate grid stars are quite stringent: the photocenters of these stars have to be astrometrically stable to within a few microarcseconds, which makes binary stars unacceptable as grid stars. We search the most precise and comprehensive astrometric catalogs available today--the Hipparcos, Tycho-1 and Tycho-2 Catalogues--for possible grid stars, and discuss the properties of samples of K giants derived from these catalogs. Furthermore, we present results of a precise radial velocity study of a small proxy sample of Hipparcos K giants. We demonstrate that it is possible to find K giants with radial velocity variations smaller than a few tens of meters per second on timescales of several months. It is thus possible to detect stellar companions in samples of candidate grid stars by means of a radial velocity survey. We discuss the results of Monte Carlo simulations that address the consequences of the measurement accuracy of a radial velocity survey on the portion of undetected binary systems.