Space based microlensing planet searches

The discovery of extra-solar planets is arguably the most exciting development in astrophysics during the past 15 years, rivalled only by the detection of dark energy. Two projects unite the communities of exoplanet scientists and cosmologists: the proposed ESA M class mission EUCLID and the large space mission WFIRST, top ranked by the Astronomy 2010 Decadal Survey report. The later states that: "Space-based microlensing is the optimal approach to providing a true statistical census of planetary systems in the Galaxy, over a range of likely semi-major axes". They also add: "This census, combined with that made by the Kepler mission, will determine how common Earth-like planets are over a wide range of orbital parameters". We will present a status report of the results obtained by microlensing on exoplanets and the new objectives of the next generation of ground based wide field imager networks. We will finally discuss the fantastic prospect offered by space based microlensing at the horizon 2020-2025.Comment: 8 pages, Proceedings to the ROPACS meeting "Hot Planets and Cool Stars" (Nov. 2012, Garching), invited contributio

Beyond Gravitoelectromagnetism: Critical Speed in Gravitational Motion

A null ray approaching a distant astronomical source appears to slow down, while a massive particle speeds up in accordance with Newtonian gravitation. The integration of these apparently incompatible aspects of motion in general relativity is due to the existence of a critical speed. Dynamics of particles moving faster than the critical speed could then be contrary to Newtonian expectations. Working within the framework of gravitoelectromagnetism, the implications of the existence of a critical speed are explored. The results are expected to be significant for high energy astrophysics.Comment: 13 pages, to appear in the Special December 2005 Issue of Int. J. Mod. Phys.

Adaptation de la mesure potentiométrique à l'estimation en continu de la teneur en cuivre de solutions aqueuses présentant de fortes variations physico-chimiques

La mesure en continu, sans prélèvement et sous conditions physico-chimiques variables, de la teneur en cuivre d'une solution aqueuse, constitue le cadre de ce travail. La méthode d'estimation proposée est basée sur la potentiométrie sélective à l'aide d'une électrode spécifique au cuivre. Le comportement de l'électrode est modélisé par une loi non linéaire s'inspirant de la relation de Nernst généralisée. Le modèle intègre les paramètres température, conductivité et pH de la solution. Il rend possible une estimation de la concentration totale de cuivre même en présence de complexations hydroxyles. La phase de modélisation est présentée en détail. Les performances de l'estimateur sont évaluées puis discutées.Ion Selective electrodes (ISEs) offer an attractive solution for continuously evaluating the content of certain ionic species in aqueous media. Manufacturers propose a wide range of electrodes specific to heavy metals (Cu2+, Pb2+ …). Because they eliminate the need for sampling, are of reasonable size and have few electronic parts, ISEs seem highly appropriate for continuous monitoring in urban purification systems. Measurements obtained by these sensors in controlled media in the laboratory are usually precise, reliable and reproducible. However, it is not so with complex and uncontrolled media. This work falls within the general scope of the continuous measurement of heavy metals in wastewater. More particularly, it is devoted to the description of the behaviour of a copper-selective electrode (ISECu) in a medium presenting wide physicochemical variations.Experimental set-upIn order to study ISE behaviour, we developed an experimental platform that allowed us to reproduce in a reactor the physicochemical variations observed in wastewater, particularly with regards to salinity and acidity. The reactor was fitted with a measuring set consisting of five electrodes that measured the following parameters: pH (ref. integrated Ag/Agcl), redox (red), ISECu (ECu), temperature (T) and conductivity (s). A computer system carried out the acquisition of the five signals with a 10-second sampling period. The species concentration in the reactor was determined by calculating the weight of the solutions extracted from or injected into the reactor. Controlling the temperature of the system was undertaken using a cryostat. Sequential tests allowed the pH, redox potential and conductivity of the medium to be varied and were carried out by successive injections of different chemical products. The response times of the conductivity probe and of the pH and redox electrodes are shown here; the short response time of the sensors (20 to 30 s) and the strong correlation between the measured pH and redox are noted. ISE modellingThe model used to explain the ISE response is based on a generalization of Nernst's Law that takes into account the temperature and the activity of the free ions (Cu2+). Taking into consideration chemical equilibria and mass equations allowed us to link the activity of the free copper ions to the total injected copper concentration |Cu2+|tot and to the pH. Redox, strongly correlated to pH, was ignored in the mathematical model. Since hydroxyl complexation is the major complexation reaction (compared to other copper-binding ligands), the potential measured with the ISE took the following form:ECu=b0+b1T.log[(ϒ2|Cu2+|tot) / (1+b2ϒ210pH+b3ϒ2102pH) + b4]The activity coefficient ϒ2 of the Cu2+ ions was calculated from the ionic strength (I) of the solution, using the Debye-Hückel approximation. Ionic strength was derived from conductivity corrected to 25 °C. In wastewater, the ranges of the physicochemical parameters were as follows: T from 5 to 35°C; pH from 4 to 9; Omega from 500 to 2000 mS/cm; redox from 400 to -400 mV/ENH; and copper concentrations 10-3 mol/dm3.In order to identify the bi coefficients of the model, we established an experimental plan comprising 108 measurement points that covered, with a minimal number of experiments, the ranges of variations of the parameters of influence. A dispersion diagram of measured and modelled values gave a linear adjustment coefficient close to 0.99 and a standard deviation of 8.8 mV, which corresponds to a 0.34 decadal standard error in the concentration estimate. With a temperature of 25 °C, the model has a sensitivity of -26.4 mV/decade, very close to the theoretical slope of an electrode sensitive to divalent ions.ISE measurement of the copper concentration with large pH variations pH is the parameter which exerts the greatest influence on ISE response, which is why tests simulating copper pollution with large variations of pH were carried out. These tests enabled us to evaluate the performances of the model in terms of the estimation of copper content. Four solutions of total copper concentration equal to 10-6, 10-5, 10-4, 10-3 mol/dm3 respectively, were used. Their temperature was 25 °C and their conductivity was fixed at approximately 500 mS/cm. We varied the pH of each solution between 4 and 10. For the four tests, we show the estimate of the copper concentration obtained with our model starting from the potential measured by the ISE.In the case of strong copper pollution (10-3 mol/dm3), the model yields an overestimated concentration below pH 7 with a decadal error of less than 0.5. Above pH 7, the concentration is underestimated while maintaining a decadal error of less than 0.5. At pH 7, a 0.04-decade minimal error is found. For pollution equal to or less than 10-4 mol/dm3, the model gives good results in an acid or neutral medium with a decadal error usually less than 0.3. In an alkaline medium, concentration is overestimated. In this case the error increases in a roughly linear manner with the pH and the co-logarithm of copper concentration. From the results of these tests, we defined a valid domain of ISE copper concentration measurement using our model. In conclusion, the suggested method, although not very accurate, could be used as an indicator of the copper concentration level in wastewater. The ISE-response correction model is currently being tested under operational conditions at a water treatment plant in Nancy-Maxéville (France)

Ultra--cold gases and the detection of the Earth's rotation: Bogoliubov space and gravitomagnetism

The present work analyzes the consequences of the gravitomagnetic effect of the Earth upon a bosonic gas in which the corresponding atoms have a non--vanishing orbital angular momentum. Concerning the ground state of the Bogoliubov space of this system we deduce the consequences, on the pressure and on the speed of sound, of the gravitomagnetic effect. We prove that the effect on a single atom is very small, but we also show that for some thermodynamical properties the consequences scale as a non--trivial function of the number of particles.Comment: 4 page

Predictions of selected flavour observables within the Standard Model

This letter gathers a selection of Standard Model predictions issued from the metrology of the CKM parameters performed by the CKMfitter group. The selection includes purely leptonic decays of neutral and charged B, D and K mesons. In the light of the expected measurements from the LHCb experiment, a special attention is given to the radiative decay modes of B mesons as well as to the B-meson mixing observables, in particular the semileptonic charge asymmetries a^d,s_SL which have been recently investigated by the D0 experiment at Tevatron. Constraints arising from rare kaon decays are addressed, in light of both current results and expected performances of future rare kaon experiments. All results have been obtained with the CKMfitter analysis package, featuring the frequentist statistical approach and using Rfit to handle theoretical uncertainties.Comment: 8 pages, 1 figure, 2 tables. Typos corrected and discussion of agreement between SM and data update

Preliminary results for RR Lyrae stars and Classical Cepheids from the Vista Magellanic Cloud (VMC) Survey

The Vista Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting $K_S$-band time series photometry of the system formed by the two Magellanic Clouds (MC) and the "bridge" that connects them. These data are used to build $K_S$-band light curves of the MC RR Lyrae stars and Classical Cepheids and determine absolute distances and the 3D geometry of the whole system using the $K$-band period luminosity ($PLK_S$), the period - luminosity - color ($PLC$) and the Wesenhiet relations applicable to these types of variables. As an example of the survey potential we present results from the VMC observations of two fields centered respectively on the South Ecliptic Pole and the 30 Doradus star forming region of the Large Magellanic Cloud. The VMC $K_S$-band light curves of the RR Lyrae stars in these two regions have very good photometric quality with typical errors for the individual data points in the range of $\sim$ 0.02 to 0.05 mag. The Cepheids have excellent light curves (typical errors of $\sim$ 0.01 mag). The average $K_S$ magnitudes derived for both types of variables were used to derive $PLK_S$ relations that are in general good agreement within the errors with the literature data, and show a smaller scatter than previous studies.Comment: 7 pages, 6 figure. Accepted for publication in Astrophysics and Space Science. Following a presentation at the conference "The Fundamental Cosmic Distance Scale: State of the Art and the Gaia Perspective", Naples, May 201

Angular Symmetry Breaking Induced by Electromagnetic Field

It is well known that velocities does not commute in presence of an electromagnetic field. This property implies that angular algebra symmetries, such as the sO(3) and Lorentz algebra symmetries, are broken. To restore these angular symmetries we show the necessity of adding the Poincare momentum M to the simple angular momentum L. These restorations performed succesively in a flat space and in a curved space lead in each cases to the generation of a Dirac magnetic monopole. In the particular case of the Lorentz algebra we consider an application of our theory to the gravitoelectromagnetism. In this last case we establish a qualitative relation giving the mass spectrum for dyons.Comment: 19 page

On the Reported Death of the MACHO Era

We present radial velocity measurements of four wide halo binary candidates from the sample in Chaname & Gould (2004; CG04) which, to date, is the only sample containing a large number of such candidates. The four candidates that we have observed have projected separations >0.1 pc, and include the two widest binaries from the sample, with separations of 0.45 and 1.1 pc. We confirm that three of the four CG04 candidates are genuine, including the one with the largest separation. The fourth candidate, however, is spurious at the 5-sigma level. In the light of these measurements we re-examine the implications for MACHO models of the Galactic halo. Our analysis casts doubt on what MACHO constraints can be drawn from the existing sample of wide halo binaries.Comment: 6 Pages, 4 Figures, Accepted for MNRAS Letter