Refined masses and distance of the young binary Haro 1-14 C

We aim to refine the dynamical masses of the individual component of the low-mass pre-main sequence binary Haro 1-14 C. We combine the data of the preliminary orbit presented previously with new interferometric observations obtained with the four 8m telescopes of the Very Large Telescope Interferometer. The derived masses are M_a=0.905\pm0.043\,\Msun and M_b=0.308\pm0.011\,\Msun for the primary and secondary components, respectively. This is about five times better than the uncertainties of the preliminary orbit. Moreover, the possibility of larger masses is now securely discarded. The new dynamical distance, $d=96\pm\,9\,$pc, is smaller than the distance to the Ophiuchus core with a significance of $2.6\,\sigma$. Fitting the spectral energy distribution yields apparent diameters of \phi_a=0.13\pm0.01\mas and \phi_b=0.10\pm0.01\mas (corresponding to \Ra=1.50\,\Rsun and \Rb=1.13\,\Rsun) and a visual extinction of $A_v\approx1.75$. Although the revised orbit has a nearly edge-on geometry, the system is unlikely to be a long-period eclipsing binary. The secondary in Haro~1-14C is one of the few low-mass, pre-main sequence stars with an accurately determined dynamical mass and distance

A PIONIER View on Mass-Transferring Red Giants

Symbiotic stars display absorption lines of a cool red giant together with emission lines of a nebula ionized by a hotter star, indicative of an active binary star system in which mass transfer is occurring. PIONIER at the VLT has been used to combine the light of four telescopes at a time to study in unprecedented detail how mass is transferred in symbiotic stars. The results of a mini-survey of symbiotic stars with PIONIER are summarised and some tentative general results about the role of Roche lobe overflow are presented.Comment: Report for the ESO Messenger June issu

Afficher les documents scientifiques sur le Web

Every day CERN handles a large number of research documents, mostly marked up in \LaTeX{} and coming from many Internet servers. Our aim is to make them easily locatable on the Web with the help of the CERN Library's \emph{Preprint Catalogue} in several formats (\PS, \PDF, \GIF). We review the conversion procedures and give some details on some massive production trial runs to directly genera te \HTML{} from the \TeX{} sources. We conclude with a discussion of recent developments in the framework of the \XML{} (and \MML) efforts which should ease the support of mathematics formulae in W eb browsers

Entanglement of four qubit systems: a geometric atlas with polynomial compass I (the finite world)

We investigate the geometry of the four qubit systems by means of algebraic geometry and invariant theory, which allows us to interpret certain entangled states as algebraic varieties. More precisely we describe the nullcone, i.e., the set of states annihilated by all invariant polynomials, and also the so called third secant variety, which can be interpreted as the generalization of GHZ-states for more than three qubits. All our geometric descriptions go along with algorithms which allow us to identify any given state in the nullcone or in the third secant variety as a point of one of the 47 varieties described in the paper. These 47 varieties correspond to 47 non-equivalent entanglement patterns, which reduce to 15 different classes if we allow permutations of the qubits.Comment: 48 pages, 7 tables, 13 figures, references and remarks added (v2

Seasonality in coastal macrobenthic biomass and its implications for estimating secondary production using empirical models

Macrobenthic secondary production is widely used to assess the trophic capacity, health, and functioning of marine and freshwater ecosystems. Annual production estimates are often calculated using empirical models and based on data collected during a single period of the year. Yet, many ecosystems show seasonal variations. Although ignoring seasonality may lead to biased and inaccurate estimates of annual secondary production, it has never been tested at the community level. Using time series of macrobenthic data collected seasonally at three temperate marine coastal soft-bottom sites, we assessed seasonal variations in biomass of macrobenthic invertebrates at both population and community levels. We then investigated how these seasonal variations affect the accuracy of annual benthic production when assessed using an empirical model and data from a single sampling event. Significant and consistent seasonal variations in biomass at the three study sites were highlighted. Macrobenthic biomass was significantly lower in late winter and higher in summer/early fall for 18 of the 30 populations analyzed and for all three communities studied. Seasonality led to inaccurate and often biased estimates of annual secondary production at the community level when based on data from a single sampling event. Bias varied by site and sampling period, but reached similar to 50% if biomass was sampled at its annual minimum or maximum. Since monthly sampling is rarely possible, we suggest that ecologists account for uncertainty in annual production estimates caused by seasonality.Agência financiadora EDF French Ministry of Higher Education, Research and Innovation French Ministry for the Ecological and Inclusive Transition through the Marine Strategy Framework Directive Agreement French Biodiversity Agency (Agence francaise pour la biodiversite) as part of the CAPANOUR projectinfo:eu-repo/semantics/publishedVersio

Thermodynamics and Phase Structure of the Two-Flavor Nambu--Jona-Lasinio Model Beyond Large-N_c

The optimized perturbation theory (OPT) method is applied to the $SU(2)$ version of the Nambu--Jona-Lasinio (NJL) model both at zero and at finite temperature and/or density. At the first nontrivial order the OPT exhibits a class of 1/N_c corrections which produce nonperturbative results that go beyond the standard large-N_c, or mean-field approximation. The consistency of the OPT method with the Goldstone theorem at this order is established, and appropriate OPT values of the basic NJL (vacuum) parameters are obtained by matching the pion mass and decay constant consistently. Deviations from standard large-N_c relations induced by OPT at this order are derived, for example, for the Gell--Mann-Oakes-Renner relation. Next, the results for the critical quantities and the phase diagram of the model, as well as a number of other thermodynamical quantities of interest, are obtained with OPT and then contrasted with the corresponding results at large N_c.Comment: 29 pages, 20 figures, revtex. Minor corrections. In press Phys. Rev.

The C(3P) + NH3 reaction in interstellar chemistry: II. Low temperature rate constants and modeling of NH, NH2 and NH3 abundances in dense interstellar clouds

A continuous supersonic flow reactor has been used to measure rate constants for the C + NH3 reaction over the temperature range 50 to 296 K. C atoms were created by the pulsed laser photolysis of CBr4. The kinetics of the title reaction were followed directly by vacuum ultra-violet laser induced fluorescence (VUV LIF) of C loss and through H formation. The experiments show unambiguously that the reaction is rapid at 296 K, becoming faster at lower temperatures, reaching a value of 1.8 10-10 cm3 molecule-1 s-1 at 50 K. As this reaction is not currently included in astrochemical networks, its influence on interstellar nitrogen hydride abundances is tested through a dense cloud model including gas-grain interactions. In particular, the effect of the ortho-to-para ratio of H2 which plays a crucial role in interstellar NH3 synthesis is examined