We present preliminary results of a radial-velocity search for companions to a volume limited sample of M dwarfs. Typical accuracy range between 10m/s for the brighter stars and 70m/s at our limiting ...magnitude. We complement the radial velocity monitoring with adaptive optics imaging to identify close visual companions in a larger volume-limited sample. For stellar companions the two techniques together cover the full separation range, to beyond the limiting distance of the sample. We will therefore eventually obtain a statistically meaningful inventory of the stellar multiplicity of nearby M-dwarf systems. We also have useful sensitivity to giant planets, as illustrated by our recent detection of a planetary companion to Gl 876. After 2.5 years, we have discovered 12 previously unknown components in this 127 stars sample. 7 of these are actually beyond our 9 pc limit, and were included on the basis of photometric parallaxes which were biased-down by the unrecognized companion. The remaining 5 are true additions to the 9 pc inventory. More are certainly forthcoming, given our present selection bias towards short periods and relatively massive companions. We have derived orbital elements for 7 of the new systems, and for some previously known binaries. One system is a Post-Common-Envelope WD+M binary. Some of the new binaries have excellent prospects for an accurate mass determination over the next few years. Preliminary masses have accuracies of 2% at 0.4-0.6 \Msol and 10% at 0.1 \Msol.
We present the discovery of a tight M8V binary, with a separation of only 1.2 astronomical units, obtained with the PUEO and NACO adaptive optics systems, respectively at the CFHT and VLT telescopes. ...The estimated period of LP 349-25 is approximately 5 years, and this makes it an excellent candidate for a precise mass measurement.
We report the first astrometrically determined mass of an extrasolar planet, a companion previously detected by Doppler spectroscopy. Radial velocities first provided an ephemeris with which to ...schedule a significant fraction of the {\it HST} observations near companion peri- and apastron. The astrometry residuals at these orbital phases exhibit a systematic deviation consistent with a perturbation due to a planetary mass companion. Combining {\it HST} astrometry with radial velocities, we solve for the proper motion, parallax, perturbation size, inclination, and position angle of the line of nodes, while constraining period, velocity amplitude, longitude of periastron, and eccentricity to values determined from radial velocities. We find a perturbation semi-major axis and inclination, \(\alpha\) = 0.25 \(\pm\) 0.06 mas, \(i\) = 84\arcdeg \(\pm\)6\arcdeg, and Gl 876 absolute parallax, \(\pi_{abs}= 214.6 \pm\) 0.2 mas. Assuming that the mass of the primary star is \(M_* = 0.32M_{\sun}\), we find the mass of the planet, Gl 876b, \(M_b = 1.89\pm0.34M_{Jup}\).
Les recherches qui ont été effectuées sur le myrtillier (Vaccinium corymbosum) ont pour but d'étudier les incidences d'un stress hydrique plus ou moins sévère sur la production fruitière (rendement ...et qualité). Les effets de périodes de sécheresse d'une durée de 2 semaines, imposées à différents stades phénologiques (grossissement des fruits, maturation des fruits et récolte) montrent que la période la plus sensible se situe pendant le grossissement des fruits. L'application d'un stress entre fin mai et mi-juin a de graves conséquences sur la production des fruits, leur taille étant fortement réduite. Parallèlement, une étude complète a été effectuée sur l'état physiologique du myrtillier au cours d'une période de sécheresse : des mesures de potentiel hydrique, d'embolie, de transpiration, de photosynthèse foliaire et de micro-variations du diamètre des tiges ont été réalisées. On a ainsi mis en évidence (1) que le myrtillier présente une nette sensibilité au manque d'eau qui se traduit notamment par une rapide fermeture stomatique et parallèlement par une forte diminution de la photosynthèse, (2) que cette fermeture stomatique rapide lui permet de limiter ses pertes en eau et d'éviter en grande partie l'embolie des vaisseaux, et (3) que le myrtillier présente une bonne capacité de récupération après réhydratation
