Coravel— A new tool for radial velocity measurements

Dual-beam cross-correlation spectrometer for radial velocity measurements

Measuring the radial velocity of an object can be achieved by quantifying the Doppler shift of Fraunhofer lines. Measurements are typically made using high-resolution conventional spectroscopy, in which the Doppler shift is calculated numerically on a computer. An alternative technique includes cross-correlation spectroscopy, which performs an optical correlation of the incident spectrum against a reference spectrum embedded in the instrument. Many existing correlation spectrometers leverage a chrome mask and obtain a single beam measurement, making the sensors more sensitive to atmospheric turbulence without moving parts. In this paper, we present a static dual-beam polarization-based technique for acquiring cross-correlation spectra that is insensitive to atmospheric turbulence and contains no moving parts. The instrument is based on acquiring light both inside and outside of the solar Fraunhofer lines using a twisted nematic liquid-crystal spatial light modulator. Correlation spectra can be calculated as a ratio of these two components. A model of the dual-beam cross-correlation spectrometer is presented and subsequently validated with experimental observations of Venus. Radial velocity accuracies, as calculated against reference ephemerides, yielded an absolute error less than 0.24%.

CORAVEL Surveys to Study Binaries of Different Masses and Ages

Preliminary results are given for a systematic survey of K-dwarf stars in the solar vicinity. Nine companions to the G and K dwarfs have very low M2 sin i, less than 0.08 M⊙. These detections from a sample of 540 G and K primary stars support the reality of the existence of companions with mass below 0.08 M⊙: brown dwarfs exist.

A comparison of the relative mass function distribution f(m)/M1 between low-mass (M1 < 1.3 M⊙) and intermediate-mass (2 < M1 < 5 M⊙) binaries suggests a dependence of the mass-ratio distribution on the mass of the primary: f(q, M1).

By combining the photometric information with orbital elements constraints, we have derived the mass-ratio distribution for intermediate-mass stars. As is the case for low-mass stars, this distribution does not have any maximum close to M2/M1 = 1.

From Brown Dwarfs to Planets

The burst of discoveries of planets and brown dwarfs during the past year has revealed an unexpected diversity of planetary systems. 51 Pegasi, the first extrasolar planet detected in orbit around a solar-type star appears to be the prototype of a new family of Jovian planets, the «Hot Jupiters». Though the physical mechanisms underlying the orbital decay of protoplanets are already understood, we are far from having a general view of planetary formation and of the diversity of planetary systems. If the orbital decay of protoplanets is sometimes so efficient, what is the frequency of planetary systems like ours, what is the frequency of telluric planets, what is the limit between planets and brown dwarfs?