The constant magnetic field of xi 1 CMa: geometry or slow rotation?

We report recent observations of the sharp-lined magnetic beta Cep pulsator xi 1 CMa (= HD 46328). The longitudinal magnetic field of this star is detected consistently, but it is not observed to vary strongly, during nearly 5 years of observation. In this poster we evaluate whether the nearly constant longitudinal field is due to intrinsically slow rotation, or rather if the stellar or magnetic geometry is responsible

A multisite photometric study of two unusual Beta Cep stars: the magnetic V2052 Oph and the massive rapid rotator V986 Oph

We report a multisite photometric campaign for the Beta Cep stars V2052 Oph and V986 Oph. 670 hours of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry were obtained with eight telescopes on five continents during 182 nights. Frequency analyses of the V2052 Oph data enabled the detection of three pulsation frequencies, the first harmonic of the strongest signal, and the rotation frequency with its first harmonic. Pulsational mode identification from analysing the colour amplitude ratios confirms the dominant mode as being radial, whereas the other two oscillations are most likely l=4. Combining seismic constraints on the inclination of the rotation axis with published magnetic field analyses we conclude that the radial mode must be the fundamental. The rotational light modulation is in phase with published spectroscopic variability, and consistent with an oblique rotator for which both magnetic poles pass through the line of sight. The inclination of the rotation axis is 54o <i< 58o and the magnetic obliquity 58o <beta< 66o. The possibility that V2052 Oph has a magnetically confined wind is discussed. The photometric amplitudes of the single oscillation of V986 Oph are most consistent with an l=3 mode, but this identification is uncertain. Additional intrinsic, apparently temporally incoherent, light variations of V986 Oph are reported. Different interpretations thereof cannot be distinguished at this point, but this kind of variability appears to be present in many OB stars. The prospects of obtaining asteroseismic information for more rapidly rotating Beta Cep stars, which appear to prefer modes of higher l, are briefly discussed.Comment: 12 pages, 8 figures, MNRAS, in pres

Etude des structures du disque mince Galactique

Our Galaxy is to be a barred spiral. Nevertheless, its detailed structure is still unknown and there is ongoing debate on the number and shape of its spiral arms and bar orientation. One of the main tools that has been developped to study our Galaxy is photometry which is the study of stellar light. However, this light is affected by the instellar medium through which it passes between the emission point and the observation point. This effect is called interstellar extinction, and how it affects the light depends on the properties of the environment through which it passes. That is why it is important to have detailed maps of interstellar extinction. Few 3D (position - non cumulative values) extinction maps exist today, and most of them rely on Galactic stellar population models. The goal of my PhD research was to establish new techniques to map the extinction in 3D, independantly of any model. Initialy, I developed an algorithm to find the interstellar extinction in a line of sight, by taking advantage of the properties of Red Clump Stars. I used stars taken from near-infrared observations. In the presence of extinction, Red Clump stars form a tail in colour-magnitude diagrams. If one can detect the position of the tail, one can deduce the distance-extinction relation for this field. By generalising this process to all our data, we build up a 3D map of the insterstellar extinction in the first quadrant. Because of the limitation of the above method, I subsequently used Bayesien deconvolution to develop a method to determine interstellar extinction. The principal benefit of this method is that it is versatile enough that one can also recover the stellar density.Notre Galaxie est de type spirale barrée. Cependant, sa structure reste très mal connue à ce jour et le nombre et la forme de ses bras ainsi que la longueur et l'orientation de la barre sont encore l'objet de vifs débats. Une des techniques à notre disposition pour étudier notre Galaxie est la photométrie. Mais elle est altérée par le milieu interstellaire traversé entre le point d'émission et le point d'observation : c'est l'extinction interstellaire. Elle varie en fonction des propriétés du milieu traversé, c'est pourquoi il est essentiel de disposer de cartographies détaillées de l'extinction interstellaire. Peu de cartographies 3D (position / valeur non-cumulative) existent à ce jour et elles reposent pour la plupart sur un modèle de population stellaire Galactique. Le but de ma thèse a été d'établir de nouvelles techniques de cartographie 3D de l'extinction, indépendantes de toute modélisation de la Galaxie. Pour cela, j'ai développé un algorithme permettant de retrouver l'extinction interstellaire dans une direction d'observation en exploitant les propriétés des étoiles du Red Clump. En présence d'extinction, ces étoiles forment une traînée dans les CMD. En arrivant à détecter la position de cette traînée, on peut déduire la relation distance-extinction dans le champ étudié. En appliquant massivement ce procédé, j'ai établi une carte 3D de l'extinction dans le premier quadrant. Dans un deuxième temps, j'ai utilisé une déconvolution bayésienne pour mettre en place une méthode permettant d'établir une cartographie de l'extinction interstellaire qui sera par la suite adaptable pour obtenir une cartographie 3D de la densité d'étoiles

FEDReD: I. 3D extinction and stellar maps by Bayesian deconvolution

International audienceContext. While Gaia enables us to probe the extended local neighbourhood in great detail, the thin disc structure at larger distances remains sparsely explored.Aims. We aim here to build a non-parametric 3D model of the thin disc structures handling both the extinction and the stellar density simultaneously.Methods. We developed a Bayesian deconvolution method in two dimensions: extinction and distance. It uses a reference catalogue whose completeness information defines the selection function. It is designed so that any complementary information from other catalogues can be added. It has also been designed to be robust to outliers, which are frequent in crowded fields, and differential extinction. The prior information is designed to be minimal: only a reference H-R diagram. We derived for this an empirical H-R diagram of the thin disc using Gaia DR2 data, but synthetic isochrone-based H-R diagrams can also be used.Results. We validated the method on simulations and real fields using 2MASS and UKIDSS data complemented by Gaia DR2 photometry and parallaxes. We detail the results of two test fields: a 2MASS field centred around the NGC 4815 open cluster, which shows an over-density of both extinction and stellar density at the cluster distance, and a UKIDSS field at l = 10° where we recover the position of the Galactic bar