Sainte-Foy-lès-Lyon, France
Sainte-Foy-lès-Lyon, France

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Sordo R.,National institute for astrophysics | Vallenari A.,National institute for astrophysics | Tantalo R.,University of Padua | Liu C.,MPIA | And 20 more authors.
Journal of Physics: Conference Series | Year: 2011

Gaia will observe up to a billion stellar sources. Automated algorithms are under development to derive the atmospheric parameters of all observed spectra, from low resolution optical spectra alone or in synergy with high resolution spectra in the near-IR Ca II triplet region. To do so, a large database of state-of-the-art stellar libraries has been produced for the Gaia community, computed using different codes optimized for specific purposes. The choice to use different spectral codes in different regions of the H-R diagram raises the problem of the coherence of the different spectra, specifically in the transition zones. We present a comparison between the libraries from the point of view of spectra simulations for training the Gaia algorithms. We also present the implementation of these libraries into a Simple Stellar Population code.

Biller B.A.,University of Edinburgh | Biller B.A.,Max Planck Institute for Astronomy | Vos J.,University of Edinburgh | Bonavita M.,University of Edinburgh | And 17 more authors.
Astrophysical Journal Letters | Year: 2015

As part of our ongoing NTT SoFI survey for variability in young free-floating planets and low-mass brown dwarfs, we detect significant variability in the young, free-floating planetary-mass object PSO J318.5-22, likely due to rotational modulation of inhomogeneous cloud cover. A member of the 23 ± 3 Myr β Pic moving group, PSO J318.5-22 has Teff = K and a mass estimate of 8.3 ± 0.5 MJup for a 23 ± 3 Myr age. PSO J318.5-22 is intermediate in mass between 51 Eri b and β Pic b, the two known exoplanet companions in the β Pic moving group. With variability amplitudes from 7% to 10% in JS at two separate epochs over 3-5 hr observations, we constrain the rotational period of this object to >5 hr. In KS, we marginally detect a variability trend of up to 3% over a 3 hr observation. This is the first detection of weather on an extrasolar planetary-mass object. Among L dwarfs surveyed at high photometric precision (<3%), this is the highest amplitude variability detection. Given the low surface gravity of this object, the high amplitude preliminarily suggests that such objects may be more variable than their high-mass counterparts, although observations of a larger sample are necessary to confirm this. Measuring similar variability for directly imaged planetary companions is possible with instruments such as SPHERE and GPI and will provide important constraints on formation. Measuring variability at multiple wavelengths can help constrain cloud structure. © 2015. The American Astronomical Society. All rights reserved.

Bonnefoy M.,Laboratoire dAstrophysique | Chauvin G.,Laboratoire dAstrophysique | Rojo P.,University of Chile | Allard F.,CRAL ENS | And 4 more authors.
Astronomy and Astrophysics | Year: 2010

Context.We have already imaged a co-moving companion at a projected separation of ∼260 AU from the young star AB Pic A. Evolutionary model predictions based on JHK photometry of AB Pic b suggest a mass of ∼13-14 MJup, placing the object at the deuterium-burning boundary. Aims.We aim to determine the spectral type, the surface gravity, and the effective temperature of AB Pic b. From the comparison of our absolute photometry to surface fluxes generated by atmospheric models, we also aim at deriving mass and radius estimates that are independent of evolutionary model predictions to test and refine them. Methods.We used the adaptive-optics-fed integral field spectrograph SINFONI to obtain high-quality, medium-resolution spectra of AB Pic b (Rλ = 1500-2000) over the 1.1-2.5 μ m range. Our analysis relie on comparing our spectra to young standard templates and to the latest libraries of synthetic spectra developed by the Lyon group. Results. AB Pic b is confirmed as a young early-L dwarf companion. We derive a spectral type L0-L1 and find several features indicative of an intermediate gravity atmosphere. A comparison to synthetic spectra yields Teff = 2000+100-300 K and log(g) = 4±0.5 dex. Determination of the derived atmospheric parameters of AB Pic b is limited by an imperfect match of current atmosphere spectra with our near-infrared observations of AB Pic b. The current treatment of dust settling and the missing molecular opacity lines in the atmosphere models could be responsible. By combining the observed photometry, the surface fluxes from atmosphere models and the known distance of the system, we derive new mass, luminosity, and radius estimates of AB Pic b. They independently confirm the evolutionary model predictions. We finally review the current methods used for characterizing planetary mass companions and discuss them in the perspective of future planet deep-imaging surveys that will be faced with the same limitations. © 2010 ESO.

Manjavacas E.,Max Planck Institute for Astronomy | Bonnefoy M.,Max Planck Institute for Astronomy | Bonnefoy M.,French National Center for Scientific Research | Schlieder J.E.,Max Planck Institute for Astronomy | And 8 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Gravity modifies the spectral features of young brown dwarfs (BDs). A proper characterization of these objects is crucial for the identification of the least massive and latest-type objects in star-forming regions, and to explain the origin(s) of the peculiar spectrophotometric properties of young directly imaged extrasolar planets and BD companions. Aims. We obtained medium-resolution (R ~ 1500-1700) near-infrared (1.1-2.5 μm) spectra of seven young M9.5-L3 dwarfs classified at optical wavelengths. We aim to empirically confirm the low surface gravity of the objects in the near-infrared. We also test whether self-consistent atmospheric models correctly represent the formation and the settling of dust clouds in the atmosphere of young late-M and L dwarfs. Methods. We used the Infrared Spectrometer And Array Camera (ISAAC) at the Very Large Telescope (VLT) to obtain the spectra of the targets. We compared the spectra to those of mature and young BDs, and to young late-type companions to nearby stars with known ages 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 atmospheric models. Using the best fit, we derived the atmospheric parameters of the objects and identified which spectral characteristics the models do not reproduce. Results. We confirmed that our objects are young BDs and we found near-infrared spectral types in agreement with the ones determined at optical wavelengths. The spectrum of the L2γ dwarf 2MASSJ232252.99- 615127.5 reproduces the spectrum of the planetary mass companion 1RXS J160929.1-210524b well. The BT-Settl models fit the spectra and the 1-5 μm spectral energy distribution 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 near-infrared 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. Conclusions. 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. Our spectra provide additional templates for the characterization of the numerous young L-type companions that will be detected in the coming years by planet imaging instruments such as VLT/SPHERE, Gemini/GPI, Subaru/SCexAO, and LBTI/LMIRCam. © 2014 ESO.

Sordo R.,National institute for astrophysics | Vallenari A.,National institute for astrophysics | Tantalo R.,University of Padua | Allard F.,CRAL ENS | And 17 more authors.
Astrophysics and Space Science | Year: 2010

ESA's Gaia mission will collect low resolution spectroscopy in the optical range for ~109 objects. Complete and up-to-date libraries of synthetic stellar spectra are needed to built algorithms aimed to automatically derive the classification and the parametrization of this huge amount of data. In addition, libraries of stellar spectra are one of the main ingredients of stellar population synthesis models, aiming to derive the properties of unresolved stellar populations from their integrated light. We present (a) the newly computed libraries of synthetic spectra built by the Gaia community, covering the whole optical range (300-1100 nm) at medium-high resolution of (0.3 nm) for stars spanning the most different types, from M to O, from A-peculiar to Emission lines to White Dwarfs, and (b) the implementation of those libraries in our SSP code (Tantalo in The Initial Mass Function 50 Years Later, 327:235 2005), exploring different stellar evolution models. © 2010 Springer Science+Business Media B.V.

Bonnefoy M.,Max Planck Institute for Astronomy | Chauvin G.,Max Planck Institute for Astronomy | Chauvin G.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | Lagrange A.-M.,CNRS Grenoble Institute for Particle Astrophysics and Cosmology Laboratory | And 5 more authors.
Astronomy and Astrophysics | Year: 2014

Context. At young ages, low surface gravity affects the atmospheric properties of ultracool dwarfs. The impact on medium-resolution near-infrared (NIR) spectra has only been slightly investigated at the M-L transition so far. Aims. We present a library of NIR (1.1-2.45 μm) medium-resolution (R ~ 1500-2000) integral field spectra of 15 young M6-L0 dwarfs. We aim at deriving updated NIR spectral type, luminosity, and physical parameters (Teff, log g, M, L/L⊙) for each source. This work also aims at testing the latest generation of BT-SETTL atmospheric models. Methods. We estimated spectral types using spectral indices and the spectra of young objects classified in the optical. We used the 2010 and 2012 releases of the BT-SETTL synthetic spectral grid and cross-checked the results with the DRIFT-PHOENIX models to derive the atmospheric properties of the sources. Results. We do not find significant differences between the spectra of young companions and those of young isolated brown dwarfs in the same spectral type range. 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 + 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. The BT-SETTL and DRIFT-PHOENIX models yield close T eff and log g estimates for each source. The models seem to show a 600+600 -300 60 0-300 + 600 K drop in the effective temperature at the M-L transition. Assuming the former temperatures are correct, we then derive new mass estimates that confirm that DH Tau B, USco CTIO 108B, AB Pic b, KPNO Tau 4, OTS 44, and Cha1109 lie 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 NIR spectra of these sources simultaneously. But the models still fail to represent the dominant features in the optical. This issue raises doubts on the ability of these models to predict effective temperatures from NIR spectra alone. Conclusions. The library provides templates for characterizing other young and late type objects. The study advocates the use of photometric and spectroscopic information over 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). ©2014 ESO.

Bonnefoy M.,British Petroleum | Chauvin G.,British Petroleum | Dumas C.,ESO | Lagrange A.-M.,British Petroleum | And 5 more authors.
EAS Publications Series | Year: 2010

Tight binaries discovered in young nearby associations are ideal targets to provide dynamical mass measurments through orbital monitoring. Coupled with estimated temperatures, surface gravities and luminosities, direct mass measurments provide benchmarks for evolutionary models of low-mass stars and brown dwarfs at young ages. TWA22 AB is likely to be a member of the nearby TW Hydrae association. It was resolved in a tigh binary with a projected separation of a few AU. In this paper we present preliminary results on the companion orbital monitoring and on the spectral characterisation of the system. © EAS, EDP Sciences, 2010.

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