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

Spectra of weighted rooted graphs having prescribed subgraphs at some levels

Let B be a weighted generalized Bethe tree of k levels (k > 1) in which nj is the number of vertices at the level k-j+1 (1 ≤ j ≤ k). Let Δ \subset {1, 2,., k-1} and F={Gj:j \in Δ}, where Gj is a prescribed weighted graph on each set of children of B at the level k-j+1. In this paper, the eigenvalues of a block symmetric tridiagonal matrix of order n1+n2 +...+nk are characterized as the eigenvalues of symmetric tridiagonal matrices of order j, 1≤j≤k, easily constructed from the degrees of the vertices, the weights of the edges, and the eigenvalues of the matrices associated to the family of graphs F. These results are applied to characterize the eigenvalues of the Laplacian matrix, including their multiplicities, of the graph β(F) obtained from β and all the graphs in F={Gj:j \in Δ}; and also of the signless Laplacian and adjacency matrices whenever the graphs of the family F are regular.CIDMAFCTFEDER/POCI 2010PTDC/MAT/112276/2009Fondecyt - IC Project 11090211Fondecyt Regular 110007

In-Plane Magnetodrag between Dilute Two-Dimensional Systems

We performed in-plane magnetodrag measurements on dilute double layer two-dimensional hole systems, at in-plane magnetic fields that suppress the apparent metallic behavior, and to fields well above those required to fully spin polarize the system. When compared to the single layer magnetoresistance, the magnetodrag exhibits exactly the same qualitative behavior. In addition, we have found that the enhancement to the drag from the in-plane field exhibits a strong maximum when both layer densities are matched.Comment: 4 pages, 3 figures; minor corrections. Accepted in Phys. Rev. Let

Tunneling edges at strong disorder

Scattering between edge states that bound one-dimensional domains of opposite potential or flux is studied, in the presence of strong potential or flux disorder. A mobility edge is found as a function of disorder and energy, and we have characterized the extended phase. "paper_FINAL.tex" 439 lines, 20366 characters In the presence of flux and/or potential disorder, the localization length scales exponentially with the width of the barrier. We discuss implications for the random-flux problem.Comment: RevTeX, 4 page

Progress on neural parton distributions

We give a status report on the determination of a set of parton distributions based on neural networks. In particular, we summarize the determination of the nonsinglet quark distribution up to NNLO, we compare it with results obtained using other approaches, and we discuss its use for a determination of $\alpha_s$.Comment: 4 pages, 2 figs, uses dis2007.cls, to appear in the DIS 2007 workshop proceeding

Recent progress on NNPDF for LHC

We present recent results of the NNPDF collaboration on a full DIS analysis of Parton Distribution Functions (PDFs). Our method is based on the idea of combining a Monte Carlo sampling of the probability measure in the space of PDFs with the use of neural networks as unbiased universal interpolating functions. The general structure of the project and the features of the fit are described and compared to those of the traditional approaches.Comment: 4 pages, 6 figures, contribution for the proceedings of the conference "Rencontres de Moriond, QCD and High Energy Interactions

The impact of heavy quark mass effects in the NNPDF global analysis

We discuss the implementation of the FONLL general-mass scheme for heavy quarks in deep-inelastic scattering in the FastKernel framework, used in the NNPDF series of global PDF analysis. We present the general features of FONLL and benchmark the accuracy of its implementation in FastKernel comparing with the Les Houches heavy quark benchmark tables. We then show preliminary results of the NNPDF2.1 analysis, in which heavy quark mass effects are included following the FONLL-A GM scheme.Comment: 5 pages, 3 figures; to appear in the proceedings of DIS 2010, Firenz

Red Optical Planet Survey : A radial velocity search for low mass M dwarf planets

This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly citedWe present radial velocity results from our Red Optical Planet Survey (ROPS), aimed at detecting low-mass planets orbiting mid-late M dwarfs. The similar to 10 ms(-1) precision achieved over 2 consecutive nights with the MIKE spectrograph at Magellan Clay is also found on week long timescales with UVES at VLT. Since we find that UVES is expected to attain photon limited precision of order 2 ms-1 using our novel deconvolution technique, we are limited only by the