Bruno Chazelas

The Next Generation Transit Survey (NGTS)

The Next Generation Transit Survey (NGTS) is a new ground-based sky survey designed to find transiting Neptunes and super-Earths. By covering at least sixteen times the sky area of Kepler , we will find small planets around stars that are sufficiently bright for radial velocity confirmation, mass determination and atmospheric characterisation. The NGTS instrument will consist of an array of twelve independently pointed 20 cm telescopes fitted with red-sensitive CCD cameras. It will be constructed at the ESO Paranal Observatory, thereby benefiting from the very best photometric conditions as well as follow up synergy with the VLT and E-ELT. Our design has been verified through the operation of two prototype instruments, demonstrating white noise characteristics to sub-mmag photometric precision. Detailed simulations show that about thirty bright super-Earths and up to two hundred Neptunes could be discovered. Our science operations are due to begin in 2014.

The CORALIE survey for southern extrasolar planets XVII. New and updated long period and massive planets

Context. Since 1998, a planet-search program around main sequence stars within 50 pc in the southern hemisphere has been carried out with the CORALIE echelle spectrograph at La Silla Observatory. Aims. With an observing time span of more than 14 years, the CORALIE survey is now able to unveil Jovian planets on Jupiter’s period domain. This growing period-interval coverage is important for building formation and migration models since observational constraints are still weak for periods beyond the ice line. Methods. Long-term precise Doppler measurements with the CORALIE echelle spectrograph, together with a few additional observations made with the HARPS spectrograph on the ESO 3.6 m telescope, reveal radial velocity signatures of massive planetary companions on long-period orbits. Results. In this paper we present seven new planets orbiting HD 27631, HD 98649, HD 106515A, HD 166724, HD 196067, HD 219077, and HD 220689, together with the CORALIE orbital parameters for three already known planets around HD 10647, HD 30562, and HD 86226. The period range of the new planetary companions goes from 2200 to 5500 days and covers a mass domain between 1 and 10.5 MJup. Surprisingly, five of them present very high eccentricities above e > 0:57. A pumping scenario by Kozai mechanism may be invoked for HD 106515Ab and HD 196067b, which are both orbiting stars in multiple systems. Since the presence of a third massive body cannot be inferred from the data of HD 98649b, HD 166724b, and HD 219077b, the origin of the eccentricity of these systems remains unknown. Except for HD 10647b, no constraint on the upper mass of the planets is provided by Hipparcos astrometric data. Finally, the hosts of these long period planets show no metallicity excess.

New scramblers for precision radial velocity: square and octagonal fibers

One of the remaining limitation of the precise radial velocity instruments is the imperfect scrambling produced by the circular fibers. We present here experimental studies on new optical fibers aiming at an improvement of the scrambling they provide. New fibers shapes were tested: square and octagonal. Measurements have been performed of the scrambling performances of these fibers in the near field as well FRD measurements. These fibers show extremely promising performances in the near field scrambling: an improvement of a factor 5 to 10 compared to the circular fiber. They however show some strange behavior in the far field that need to be understood.

Instrumental stability requirements for exoplanet detection with a nulling interferometer: variability noise as a central issue

We revisit the nulling interferometer performances that are needed for direct detection and the spectroscopic analysis of exoplanets, e.g., with the DARWIN [European Space Agency-SCI 12 (2000)] or TPF-I [JPL Publ. 05-5, (2005)] missions. Two types of requirement are found, one concerning the mean value of the instrumental nulling function (nl(lambda)) and another regarding its stability. The stress is usually put on the former. It is stringent at short wavelengths but somewhat relaxed at longer wavelengths. The latter, which we call the variability noise condition, does not usually receive enough attention. It is required regardless of telescope size and stellar distance. The results from three nulling experiments performed in laboratories around the world are reported and compared with the requirements. All three exhibit 1/f noise that is incompatible with the performances required by the mission. As pointed out by Lay [Appl. Opt. 43, 6100-6123 (2004)], this stability problem is not fully solved by modulation techniques. Adequate solutions must be found that are likely to include servo systems using the stellar signal itself as a reference and internal metrology with high stability.

A Fabry-Perot calibrator of the HARPS radial velocity spectrograph: performance report

The radial velocity (RV) technique has pushed the planet detection limits down to super-earths. To reach the precision required to detect earth-like planets it is necessary to reach a precision around 1cm.s-1. Part of the error budget is due to noise in the wavelength calibration of the spectrograph. The Observatory of Geneva has designed, built and tested in collaboration with ESO a calibrator system based on a Fabry-Perot interferometer to explore its potential to improve the wavelength calibration of RV spectrographs. We have obtained exciting results with the calibrator system demonstrated 10 cm s-1 stability over one night. By further improving the injection system we are aiming at a 1 m s-1 repeatability over the long term.

A passive cost-effective solution for the high accuracy wavelength calibration of radial velocity spectrographs

Today, the RV technique has pushed the planet detection limits down to super-earths but the reach the precision required to detect earth-like planets it is necessary to reach a precision around 1cm s-1. While a significant part of the error budget is the incompressible photon noise, another part is the noise in the wavelength calibration of the spectrograph. In the past 3 years the Observatory of Geneva has designed, built and tested an commissioned 2 wavelength calibrator systems based on a Fabry-Perot (FP) interferometer with great success. The calibrator system demonstrated 10 cm s-1 stability over one night and 1 m s-1 over 60 days. By improving the system injecting the calibration light into the calibration fiber of the spectrograph we are aiming at 1 m s-1 repeatability over the long term. This technique is now being extended to cover the near infrared to the K band in the frame of the SPIROU project.

Consequences of spectrograph illumination for the accuracy of radial-velocimetry

For fiber-fed spectrographs with a stable external waveleng th source, scrambling properties of opti- cal fibers and, homogeneity and stability of the instrument i llumination are important for the accuracy of radial- velocimetry. Optical cylindric fibers are known to have good azimuthal scrambling. In contrast, the radial one is not perfect. In order to improve the scrambling ability of the fiber and to stabilize the illumination, optical double scrambler are usually coupled to the fibers. Despite t hat, our experience on SOPHIE and HARPS has lead to identified remaining radial-velocity limitations due to the non-uniform illumination of the spectrograph. We conducted tests on SOPHIE with telescope vignetting, seeing variation and centering errors on the fiber entrance. We simulated the light path through the instrument in order to explain the radial velocity variation obtained with our tests. We then identified the illumination stabilit y and uniformity has a critical point for the extremely high-precision radial velocity instruments (ESPRESSO@VLT, CODEX@E-ELT). Tests on square and octagonal section fibers are now under development and SOPHIE will be us ed as a bench test to validate these new feed optics.

The performance of the new Fabry-Perot calibration system of the radial velocity spectrograph HARPS

The Observatory of Geneva has designed, built and tested in collaboration with ESO a calibrator system based on a Fabry-Perot (FP) interferometer to explore its potential in the calibration of radial velocity (RV) spectrographs. Today, the RV technique has pushed the planet detection limits down to super-earths but the reach the precision required to detect earth-like planets it is necessary to reach a precision around 1cm s-1. While a significant part of the error budget is the incompressible photon noise, another part is the noise in the wavelength calibration of the spectrograph. It is to address this problem that we have developed this new device. We have obtained exciting results with the calibrator system demonstrated 10 cm s-1 stability over one night and 1 m s-1 over 60 days. By further improving the injection system we are aiming at a 1 m s-1 repeatability over the long term.

The ESPRI project: astrometric exoplanet search with PRIMA

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.

The ESPRI project: astrometric exoplanet search with PRIMA I. Instrument description and performance of first light observations

Context. The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for discovering and studying planetary systems. Our survey consists of obtaining high-precision astrometry for a large sample of stars over several years to detect their barycentric motions due to orbiting planets. We present the operations principle, the instruments implementation, and the results of a first series of test observations. Aims. We give a comprehensive overview of the instrument infrastructure and present the observation strategy for dual-field relative astrometry in the infrared K-band. We describe the differential delay lines, a key component of the PRIMA facility that was delivered by the ESPRI consortium, and discuss their performance within the facility. This paper serves as reference for future ESPRI publications and for the users of the PRIMA facility. Methods. Observations of bright visual binaries were used to test the observation procedures and to establish the instruments astrometric precision and accuracy. The data reduction strategy for the astrometry and the necessary corrections to the raw data are presented. Adaptive optics observations with NACO were used as an independent verification of PRIMA astrometric observations. Results. The PRIMA facility was used to carry out tests of astrometric observations. The astrometric performance in terms of precision is limited by the atmospheric turbulence at a level close to the theoretical expectations and a precision of 30 mu as was achieved. In contrast, the astrometric accuracy is insufficient for the goals of the ESPRI project and is currently limited by systematic errors that originate in the part of the interferometer beamtrain that is not monitored by the internal metrology system. Conclusions. Our observations led to defining corrective actions required to make the facility ready for carrying out the ESPRI search for extrasolar planets.