Telluric correction in the near-infrared: Standard star or synthetic transmission?

Context. The atmospheric absorption of the Earth is an important limiting factor for ground-based spectroscopic observations and the near-infrared and infrared regions are the most affected. Several software packages that produce a synthetic atmospheric transmission spectrum have been developed to correct for the telluric absorption; these are Molecfit, TelFit, and TAPAS. Aims. Our goal is to compare the correction achieved using these three telluric correction packages and the division by a telluric standard star. We want to evaluate the best method to correct near-infrared high-resolution spectra as well as the limitations of each software package and methodology. Methods. We applied the telluric correction methods to CRIRES archival data taken in the J and K bands. We explored how the achieved correction level varies depending on the atmospheric T-P profile used in the modelling, the depth of the atmospheric lines, and the molecules creating the absorption. Results. We found that the Molecfit and TelFit corrections lead to smaller residuals for the water lines. The standard star method corrects best the oxygen lines. The Molecfit package and the standard star method corrections result in global offsets always below 0.5% for all lines; the offset is similar with TelFit and TAPAS for the H2O lines and around 1% for the O2 lines. All methods and software packages result in a scatter between 3% and 7% inside the telluric lines. The use of a tailored atmospheric profile for the observatory leads to a scatter two times smaller, and the correction level improves with lower values of precipitable water vapour. Conclusions. The synthetic transmission methods lead to an improved correction compared to the standard star method for the water lines in the J band with no loss of telescope time, but the oxygen lines were better corrected by the standard star method.Comment: 18 pages, 13 figures, Accepted to A&

A library of near-infrared integral field spectra of young M-L dwarfs

We present a library of near-infrared (1.1-2.45 microns) medium-resolution (R~1500-2000) integral field spectra of 15 young M6-L0 dwarfs, composed of companions with known ages and of isolated objects. We use it to (re)derive the NIR spectral types, luminosities and physical parameters of the targets, and to test (BT-SETTL, DRIFT-PHOENIX) atmospheric models. We derive infrared spectral types L0+-1, L0+-1, M9.5+-0.5, M9.5+-0.5, M9.25+-0.25, M8+0.5-0.75, and M8.5+-0.5 for AB Pic b, Cha J110913-773444, USco CTIO 108B, GSC 08047-00232 B, DH Tau B, CT Cha b, and HR7329B, respectively. BT-SETTL and DRIFT-PHOENIX models yield close Teff and log g estimates for each sources. The models seem to evidence a 600-300+600 K drop of the effective temperature at the M-L transition. Assuming the former temperatures are correct, we derive new mass estimates which confirm that DH Tau B, USco CTIO 108B, AB Pic b, KPNO Tau 4, OTS 44, and Cha1109 lay inside or at the boundary of the planetary mass range. We combine the empirical luminosities of the M9.5-L0 sources to the Teff to derive semi-empirical radii estimates that do not match "hot-start" evolutionary models predictions at 1-3 Myr. We use complementary data to demonstrate that atmospheric models are able to reproduce the combined optical and infrared spectral energy distribution, together with the near-infrared spectra of these sources simultaneously. But the models still fail to represent the dominant features in the optical. This issue casts doubts on the ability of these models to predict correct effective temperatures from near-infrared spectra alone. We advocate the use of photometric and spectroscopic data covering a broad range of wavelengths to study the properties of very low mass young companions to be detected with the planet imagers (Subaru/SCExAO, LBT/LMIRCam, Gemini/GPI, VLT/SPHERE).Comment: 27 pages, 14 tables, 19 figures, accepted for publication in Astronomy & Astrophysic

High resolution imaging of young M-type stars of the solar neighborhood: Probing the existence of companions down to the mass of Jupiter

Context. High contrast imaging is a powerful technique to search for gas giant planets and brown dwarfs orbiting at separation larger than several AU. Around solar-type stars, giant planets are expected to form by core accretion or by gravitational instability, but since core accretion is increasingly difficult as the primary star becomes lighter, gravitational instability would be the a probable formation scenario for yet-to-be-found distant giant planets around a low-mass star. A systematic survey for such planets around M dwarfs would therefore provide a direct test of the efficiency of gravitational instability. Aims. We search for gas giant planets orbiting around late-type stars and brown dwarfs of the solar neighborhood. Methods. We obtained deep high resolution images of 16 targets with the adaptive optic system of VLT-NACO in the Lp band, using direct imaging and angular differential imaging. This is currently the largest and deepest survey for Jupiter-mass planets around Mdwarfs. We developed and used an integrated reduction and analysis pipeline to reduce the images and derive our 2D detection limits for each target. The typical contrast achieved is about 9 magnitudes at 0.5" and 11 magnitudes beyond 1". For each target we also determine the probability of detecting a planet of a given mass at a given separation in our images. Results. We derived accurate detection probabilities for planetary companions, taking into account orbital projection effects, with in average more than 50% probability to detect a 3MJup companion at 10AU and a 1.5MJup companion at 20AU, bringing strong constraints on the existence of Jupiter-mass planets around this sample of young M-dwarfs.Comment: Accepted for publication in A&

A Fully Spectral 3D Time-Domain Model for Second-Order Simulation of Wavetank Experiments. Part B: Validation; Calibration versus experiments and Sample Applications

International audienceA 3D second-order numerical wavetank (NWT) model, SWEET, is presented. In the first part (A) of the paper [Bonnefoy F, Le Touzé D, Ferrant P. A fully-spectral 3d time-domain model for second-order simultion of wavetank experiments. Part A: Formulation, implementation and numerical properties. Appl Ocean Res 2005. doi:10.1016/j.apor.2006.05.004], the fully-spectral formulation we employ has been detailed, and the numerical properties of the model analyzed. In the present part (B), careful validation by comparison to analytical and experimental results is first reported. Thanks to the efficiency of the proposed spectral method, the shortest wavelengths in the wavetank can be accounted for with moderate computational times. The consequent possibilities are illustrated here for the following 2D and 3D complex wave-pattern simulations, with experimental comparisons: wave-packet and geometric focusing cases, directional wavefields, long-time evolutions of irregular waves. The numerical model features all the physical characteristics of a wavetank (snake wavemaker, experimentally-calibrated absorbing zone, etc.). Its usefulness to help preparing and analyzing experiments is shown in relation to some key practical requirements: e.g. quality and evolution of the usable test zone and usability of enhanced wavemaker motions

Solution aux problèmes hydriques de Cuba

Version anglaise disponible dans la Bibliothèque numérique du CRDI: Coping with water crisis in CubaVersion espagnole disponible dans la Bibliothèque numérique du CRDI: Enfrentando la crisis del agua en Cub

Coping with water crisis in Cuba

Spanish version available in IDRC Digital Library: Enfrentando la crisis del agua en CubaFrench version available in IDRC Digital Library: Solution aux problèmes hydriques de Cub

Enfrentando la crisis del agua en Cuba

Versión en inglés disponible en la Biblioteca Digital del IDRC: Coping with water crisis in CubaVersión en francés disponible en la Biblioteca Digital del IDRC: Solution aux problèmes hydriques de Cub

3-D HOS simulations of extreme waves in open seas

In the present paper we propose a method for studying extreme-wave appearance based on the Higher-Order Spectral (HOS) technique proposed by West et al. (1987) and Dommermuth and Yue (1987). The enhanced HOS model we use is presented and validated on test cases. Investigations of freak-wave events appearing within long-time evolutions of 2-D and 3-D wavefields in open seas are then realized, and the results are discussed. Such events are obtained in our periodic-domain HOS model by using different kinds of configurations: either i) we impose an initial 3-D directional spectrum with the phases adjusted so as to form a focused <i>forced</i> event after a while, or ii) we let 2-D and 3-D wavefields defined by a directional wave spectrum evolve up to the <i>natural</i> appearance of freak waves. Finally, we investigate the influence of directionality on extreme wave events with an original study of the 3-D shape of the detected freak waves

Discovery of a Low-Mass Companion to the F7V star HD 984

We report the discovery of a low-mass companion to the nearby (d = 47 pc) F7V star HD 984. The companion is detected 0.19" away from its host star in the L' band with the Apodizing Phase Plate on NaCo/VLT and was recovered by L'-band non-coronagraphic imaging data taken a few days later. We confirm the companion is co-moving with the star with SINFONI integral field spectrograph H+K data. We present the first published data obtained with SINFONI in pupil-tracking mode. HD 984 has been argued to be a kinematic member of the 30 Myr-old Columba group, and its HR diagram position is not altogether inconsistent with being a ZAMS star of this age. By consolidating different age indicators, including isochronal age, coronal X-ray emission, and stellar rotation, we independently estimate a main sequence age of 115$\pm$85 Myr (95% CL) which does not rely on this kinematic association. The mass of directly imaged companions are usually inferred from theoretical evolutionary tracks, which are highly dependent on the age of the star. Based on the age extrema, we demonstrate that with our photometric data alone, the companion's mass is highly uncertain: between 33 and 96 M$_{\rm Jup}$ (0.03-0.09 M$_{\odot}$) using the COND evolutionary models. We compare the companion's SINFONI spectrum with field dwarf spectra to break this degeneracy. Based on the slope and shape of the spectrum in the H-band, we conclude that the companion is an M$6.0\pm0.5$ dwarf. The age of the system is not further constrained by the companion, as M dwarfs are poorly fit on low-mass evolutionary tracks. This discovery emphasizes the importance of obtaining a spectrum to spectral type companions around F-stars.Comment: Accepted for publication in MNRAS, 10 pages, 5 figure

New constraints on the formation and settling of dust in the atmospheres of young M and L dwarfs

We obtained medium-resolution near-infrared spectra of seven young M9.5-L3 dwarfs classified in the optical. We aim to confirm the low surface gravity of the objects in the NIR. We also test whether atmospheric models correctly represent the formation and the settling of dust clouds in the atmosphere of young late-M and L dwarfs. We used ISAAC at VLT to obtain the spectra of the targets. We compared them to those of mature and young BD, and young late-type companions to nearby stars with known ages, in order to identify and study gravity-sensitive features. We computed spectral indices weakly sensitive to the surface gravity to derive near-infrared spectral types. Finally, we found the best fit between each spectrum and synthetic spectra from the BT-Settl 2010 and 2013 models. Using the best fit, we derived the atmospheric parameters of the objects and identify which spectral characteristics the models do not reproduce. We confirmed that our objects are young BD and we found NIR spectral types in agreement with the ones determined at optical wavelengths. The spectrum of the L2-gamma dwarf 2MASSJ2322-6151 reproduces well the spectrum of the planetary mass companion 1RXS J1609-2105b. BT-Settl models fit the spectra and the 1-5 $\mu$m SED of the L0-L3 dwarfs for temperatures between 1600-2000 K. But the models fail to reproduce the shape of the H band, and the NIR slope of some of our targets. This fact, and the best fit solutions found with super-solar metallicity are indicative of a lack of dust, in particular at high altitude, in the cloud models. The modeling of the vertical mixing and of the grain growth will be revised in the next version of the BT-Settl models. These revisions may suppress the remaining non-reproducibilities.Comment: Accepted in A&A, February 6, 201