Observational calibration of the projection factor of Cepheids. II. Application to nine Cepheids with HST/FGS parallax measurements

The distance to pulsating stars is classically estimated using the parallax-of-pulsation (PoP) method, which combines spectroscopic radial velocity measurements and angular diameter estimates to derive the distance of the star. An important application of this method is the determination of Cepheid distances, in view of the calibration of their distance scale. However, the conversion of radial to pulsational velocities in the PoP method relies on a poorly calibrated parameter, the projection factor (p-factor). We aim to measure empirically the value of the p-factors of a homogeneous sample of nine Galactic Cepheids for which trigonometric parallaxes were measured with the Hubble Space Telescope Fine Guidance Sensor. We use the SPIPS algorithm, a robust implementation of the PoP method that combines photometry, interferometry, and radial velocity measurements in a global modeling of the pulsation. We obtained new interferometric angular diameters using the PIONIER instrument at the Very Large Telescope Interferometer, completed by data from the literature. Using the known distance as an input, we derive the value of the p-factor and study its dependence with the pulsation period. We find the following p-factors: 1.20 $\pm$ 0.12 for RT Aur, 1.48 $\pm$ 0.18 for T Vul, 1.14 $\pm$ 0.10 for FF Aql, 1.31 $\pm$ 0.19 for Y Sgr, 1.39 $\pm$ 0.09 for X Sgr, 1.35 $\pm$ 0.13 for W Sgr, 1.36 $\pm$ 0.08 for $\beta$ Dor, 1.41 $\pm$ 0.10 for $\zeta$ Gem, and 1.23 $\pm$ 0.12 for $\ell$ Car. These values are consistently close to p = 1.324 $\pm$ 0.024. We observe some dispersion around this average value, but the observed distribution is statistically consistent with a constant value of the p-factor as a function of the pulsation period. The error budget of our determination of the p-factor values is presently dominated by the uncertainty on the parallax, a limitation that will soon be waived by Gaia.Comment: 18 pages, 13 figure

Observational calibration of the projection factor of Cepheids I. The Type II Cepheid kappa Pavonis

The distances of pulsating stars, in particular Cepheids, are commonly measured using the parallax of pulsation technique. The different versions of this technique combine measurements of the linear diameter variation (from spectroscopy) and the angular diameter variation (from photometry or interferometry) amplitudes, to retrieve the distance in a quasi-geometrical way. However, the linear diameter amplitude is directly proportional to the projection factor (hereafter p-factor), which is used to convert spectroscopic radial velocities (i.e., disk integrated) into pulsating (i.e., photospheric) velocities. The value of the p-factor and its possible dependence on the pulsation period are still widely debated. Our goal is to measure an observational value of the p-factor of the type-II Cepheid kappa Pavonis, whose parallax was measured with an accuracy of 5% using HST/FGS. We used this parallax as a starting point to derive the p-factor of kappa Pav, using the SPIPS technique, which is a robust version of the parallax-of-pulsation method that employs radial velocity, interferometric and photometric data. We applied this technique to a combination of new VLTI/PIONIER optical interferometric angular diameters, new CORALIE and HARPS radial velocities, as well as multi-colour photometry and radial velocities from the literature. We obtain a value of p = 1.26 +/- 0.07 for the p-factor of kappa Pav. This result agrees with several of the recently derived Period-p-factor relationships from the literature, as well as previous observational determinations for Cepheids. Individual estimates of the p-factor are fundamental to calibrating the parallax of pulsation distances of Cepheids. Together with previous observational estimates, the projection factor we obtain points to a weak dependence of the p-factor on period.Comment: 8 pages, 6 figures, accepted in A&

Kernel machines : une nouvelle méthode pour l'optimisation de l'alignement des noyaux et l'amélioration des performances

On propose ici une méthode visant à optimiser, selon le critère d'alignement maximum, une combinaison linéaire de noyaux donnés. L'algorithme proposé s'inspire de la méthode SMO dédié à l'optimisation des SVMs : il segmente le problème d'optimisation initial en sous-problèmes pour lesquels on dispose d'une solution analytique, évitant ainsi par exemple le problème de Hessien mal conditionné. Son implémentation ne nécessite pas l'utilisation d'une bibliothèque d'optimisation particulière. Enfin, la solution obtenue s'avère en pratique plus parcimonieuse que celle trouvée par l'approche de type programmation quadratique, tout en offrant des performances similaires

Apprentissage de métrique appliqué à la classification de textes par méthodes à noyaux

Dans cet article, nous proposons une méthode pour l'optimisation de la métrique d'un classifieur textuel à noyaux. Contrairement aux techniques populaires existantes, notre approche ne nécessite pas la définition explicite de règles sémantiques. Etant donné un ensemble d'apprentissage, l'algorithme proposé permet d'optimiser la matrice sémantique, sans qu'il soit nécessaire d'exhiber celle-ci. Les résultats expérimentaux montrent l'efficacité et l'utilité de la méthode proposée en classification de textes par SVM (Support Vector Machines)

Apodized Lyot Coronagraph for VLT-SPHERE: Laboratory tests and performances of a first prototype in the visible

We present some of the High Dynamic Range Imaging activities developed around the coronagraphic test-bench of the Laboratoire A. H. Fizeau (Nice). They concern research and development of an Apodized Lyot Coronagraph (ALC) for the VLT-SPHERE instrument and experimental results from our testbed working in the visible domain. We determined by numerical simulations the specifications of the apodizing filter and searched the best technological process to manufacture it. We present the results of the experimental tests on the first apodizer prototype in the visible and the resulting ALC nulling performances. The tests concern particularly the apodizer characterization (average transmission radial profile, global reflectivity and transmittivity in the visible), ALC nulling performances compared with expectations, sensitivity of the ALC performances to misalignments of its components

: Rapport final

Three factors are likely to change daily mobilities in sparsely populated rural areas and diminish the attractiveness of such areas: fuels cost increase; sustainable development necessities which aim at reducing fossil energies dependence; public policies (Grenelle II) in favor of the development of areas best-served by public transport. Then, how could everyone be guaranteed rights to the mobility and the territory wherever they are? How could we develop mobilities which are more sustainable and less car dependent in areas where car is currently the main mean of transport? The laboratory CNRS-CITERES of Tours University tried to provide answers to this last question as part of the research program MOUR (MObilité et Urbanisme Rural). This program is co-funded by the Région Centre and the Regional Natural Park "Loire-Anjou-Touraine", in partnership with ADEME.Trois phénomènes risquent de modifier les conditions de mobilité quotidienne dans les espaces ruraux de faible densité, et de limiter l'attractivité de ces territoires : l'augmentation du coût des carburants ; les impératifs de développement durable qui cherchent à réduire la dépendance aux énergies fossiles ; et des politiques publiques (Grenelle II) qui favorisent le développement des seuls espaces desservis par des transports en commun. Comment alors garantir un droit à la mobilité et un droit au territoire partout et pour tous ? La question posée est celle du développement de mobilités plus durables et moins dépendantes de la voiture, dans des espaces aujourd'hui dépendants à l'automobile. C'est cette question qui a été analysée au cours du programme de recherche MOUR (MObilité et Urbanisme Rural), mené par le laboratoire CNRS-CITERES de l'université de Tours en partenariat Parc naturel régional Loire-Anjou-Touraine ; développé dans le cadre de l'Appel à Projet de Recherche d'Intérêt Régional de la Région Centre, ce projet est cofinancé par la Région Centre et l'ADEME

: Rapport final

Three factors are likely to change daily mobilities in sparsely populated rural areas and diminish the attractiveness of such areas: fuels cost increase; sustainable development necessities which aim at reducing fossil energies dependence; public policies (Grenelle II) in favor of the development of areas best-served by public transport. Then, how could everyone be guaranteed rights to the mobility and the territory wherever they are? How could we develop mobilities which are more sustainable and less car dependent in areas where car is currently the main mean of transport? The laboratory CNRS-CITERES of Tours University tried to provide answers to this last question as part of the research program MOUR (MObilité et Urbanisme Rural). This program is co-funded by the Région Centre and the Regional Natural Park "Loire-Anjou-Touraine", in partnership with ADEME.Trois phénomènes risquent de modifier les conditions de mobilité quotidienne dans les espaces ruraux de faible densité, et de limiter l'attractivité de ces territoires : l'augmentation du coût des carburants ; les impératifs de développement durable qui cherchent à réduire la dépendance aux énergies fossiles ; et des politiques publiques (Grenelle II) qui favorisent le développement des seuls espaces desservis par des transports en commun. Comment alors garantir un droit à la mobilité et un droit au territoire partout et pour tous ? La question posée est celle du développement de mobilités plus durables et moins dépendantes de la voiture, dans des espaces aujourd'hui dépendants à l'automobile. C'est cette question qui a été analysée au cours du programme de recherche MOUR (MObilité et Urbanisme Rural), mené par le laboratoire CNRS-CITERES de l'université de Tours en partenariat Parc naturel régional Loire-Anjou-Touraine ; développé dans le cadre de l'Appel à Projet de Recherche d'Intérêt Régional de la Région Centre, ce projet est cofinancé par la Région Centre et l'ADEME

Assessing the independent contribution of maternal educational expectations to children's educational attainment in early adulthood: A propensity score matching analysis

Background Parental educational expectations have been associated with children’s educational attainment in a number of long-term longitudinal studies, but whether this relationship is causal has long been debated. The aims of this prospective study were twofold: 1) test whether low maternal educational expectations contributed to failure to graduate from high school; and 2) compare the results obtained using different strategies for accounting for confounding variables (i.e. multivariate regression and propensity score matching). Methodology/Principal Findings The study sample included 1,279 participants from the Quebec Longitudinal Study of Kindergarten Children. Maternal educational expectations were assessed when the participants were aged 12 years. High school graduation – measuring educational attainment – was determined through the Quebec Ministry of Education when the participants were aged 22–23 years. Findings show that when using the most common statistical approach (i.e. multivariate regressions to adjust for a restricted set of potential confounders) the contribution of low maternal educational expectations to failure to graduate from high school was statistically significant. However, when using propensity score matching, the contribution of maternal expectations was reduced and remained statistically significant only for males.Conclusions/Significance The results of this study are consistent with the possibility that the contribution of parental expectations to educational attainment is overestimated in the available literature. This may be explained by the use of a restricted range of potential confounding variables as well as the dearth of studies using appropriate statistical techniques and study designs in order to minimize confounding. Each of these techniques and designs, including propensity score matching, has its strengths and limitations: A more comprehensive understanding of the causal role of parental expectations will stem from a convergence of findings from studies using different techniques and designs

Developmental associations between conduct problems and expressive language in early childhood : a population-based study

Conduct problems have been associated with poor language development, however the direction of this association in early childhood remains unclear. This study examined the longitudinal directional associations between conduct problems and expressive language ability. Children enrolled in the UK Millennium Cohort Study (N = 14, 004; 50.3 % boys) were assessed at 3 and 5 years of age. Parent reports of conduct problems and standardised assessments of expressive language were analyzed using cross-lagged modeling. Conduct problems at 3 years was associated with poorer expressive language at 5 years and poorer expressive language at 3 years was associated with increased conduct problems by 5 years. The results support reciprocal associations, rather than a specific unidirectional path, which is commonly found with samples of older children. The emergence of problems in either domain can thus negatively impact upon the other over time, albeit the effects were modest. Studies examining the effects of intervention targeting conduct problems and language acquisition prior to school entry may be warranted in testing the efficacy of prevention programmes related to conduct problems and poor language ability early in childhood