Three-dimensional structure of the Upper Scorpius association with the Gaia first data release

Using new proper motion data from recently published catalogs, we revisit the membership of previously identified members of the Upper Scorpius association. We confirmed 750 of them as cluster members based on the convergent point method, compute their kinematic parallaxes and combined them with Gaia parallaxes to investigate the 3D structure and geometry of the association using a robust covariance method. We find a mean distance of $146\pm 3\pm 6$~pc and show that the morphology of the association defined by the brightest (and most massive) stars yields a prolate ellipsoid with dimensions of $74\times38\times32$~pc$^{3}$, while the faintest cluster members define a more elongated structure with dimensions of $98\times24\times18$~pc$^{3}$. We suggest that the different properties of both populations is an imprint of the star formation history in this region.Comment: 5 pages, 1 figure, MNRAS letters (in press

Imagerie Doppler des étoiles T Tauri

Dans ce travail de thèse, nous analysons pour la première fois à l'aide de la technique d'imagerie doppler, les raies photosphériques de deux étoiles T Ttauri à faibles raies d'émission, pour cartographier leur brillance de surface et localiser ainsi les inhomogenéités en température, qui signent la présence de forts champs magnétiques. Pour ce faire, nous avons développé une méthode numerique fondée sur la paramétrisation de taches, dont les caractéristiques sont déterminées lors de la minimisation, de type moindres carrés, des différences entre les modèles de raie calculés et l'ensemble des raies (issues de divers éléments chimiques) observées à plusieurs phases rotationnelles. Nous étudions le type et l'amplitude de déformations engendrées par la présence de taches froides, ce qui nous permet d'en déduire les conditions optimales d'application de l'imagerie doppler. Nous etudions par ailleurs les limitations intrinséques de cette technique déterminées par la qualité des données (résolution instrumentale et rapport signal sur bruit). L'application à des étoiles T Tauri, jeunes étoiles en fin de formation, similaires au soleil dans sa jeunesse, nous permet de mettre en évidence la présence de larges taches froides, préférentiellement localisées aux latitudes élevées. La position de ces taches suggère une géometrie de type dipolaire pour le champ magnétique. Seule une étude exhaustive pourra déterminer si cette géometrie est commune à toute cette classe d'étoiles, ou si elle est liée à des caractéristiques particulières (fort taux de rotation 70km/s ; 80 km/s). cette réponse est cruciale pour déterminer l'origine du champ magnétique : fossile, engendré par un mecanisme particulier de type dynamo, peut-etre les deux à la fois. L'application future de cette technique aux etoiles T Tauri classiques, supposées etre entourées d'un disque d'accrétion, sera determinante pour comprendre l'interaction entre l'environnement circumstellaire et l'objet central.pas de résum

Multiplicity and clustering in Taurus star-forming region: I. Unexpected ultra-wide pairs of high-order multiplicity in Taurus

International audienceAims. This work analyses the spatial distribution of stars in Taurus with a specific focus on multiple stars and wide pairs in order to derive new constraints on star formation and early dynamical evolution scenarios. Methods. We collected the multiplicity data of stars in Taurus to build an up-to-date stellar/multiplicity catalog. We first present a general study of nearest-neighbor statistics on spatial random distribution, comparing its analytical distribution and moments to those obtained from Monte Carlo samplings. We introduce the one-point correlation Ψ function to complement the pair correlation function and define the spatial regimes departing from randomness in Taurus. We then perform a set of statistical studies to characterize the binary regime that prevails in Taurus. Results. The Ψ function in Taurus has a scale-free trend with a similar exponent as the correlation function at small scale. It extends almost 3 decades up to ~60 kAU showing a potential extended wide binary regime. This was hidden in the correlation function due to the clustering pattern blending. Distinguishing two stellar populations, single stars versus multiple systems (separation ≤1 kAU), within Class II/III stars observed at high angular resolution, we highlight a major spatial neighborhood difference between the two populations using nearest-neighbor statistics. The multiple systems are three times more likely to have a distant companion within 10 kAU when compared to single stars. We show that this is due to the presence of most probable physical ultra-wide pairs (UWPs, defined as such from their mutual nearest neighbor property), that are themselves generally composed of multiple systems containing up to five stars altogether. More generally, our work highlights; 1) a new large population of candidate UWPs in Taurus within the range 1–60 kAU in Taurus and 2) the major local structural role they play up to 60 kAU. There are three different types of UWPs; either composed of two tight and comparatively massive stars (MM), by one single and one multiple (SM), or by two distant low-mass singles (SS) stars. These UWPs are biased towards high multiplicity and higher-stellar-mass components at shorter separations. The multiplicity fraction per ultra-wide pair with separation less than 10 kAU may be as high as 83.5 ± 19.6%. Conclusions. We suggest that these young pre-main sequence UWPs may be pristine imprints of their spatial configuration at birth resulting from a cascade fragmentation scenario of the natal molecular core. They could be the older counterparts, at least for those separated by less than 10 kAU, to the ≤0.5 Myr prestellar cores/Class 0 multiple objects observed at radio/millimeter wavelengths

Multiplicity and clustering in Taurus star forming region: II. From ultra-wide pairs to dense NESTs

International audienceContext. Multiplicity and clustering of young pre-main sequence stars appear as critical clues to understand and constrain the star formation process. Taurus is the archetypical example of the most quiescent star forming regions that may still retain primeval signatures of star formation.Aims. This work identifies local overdense stellar structures as a critical scale between wide pairs and loose groups in Taurus.Methods. Using the density-based spatial clustering of applications with noise (dbscan) algorithm, and setting its free parameters based on the one-point correlation function and the k-nearest neighbor statistics, we have extracted reliably overdense structures from the sky-projected spatial distribution of stars.Results. Nearly half of the entire stellar population in Taurus is found to be concentrated in 20 very dense, tiny and prolate regions called NESTs (for Nested Elementary STructures). They are regularly spaced (≈2 pc) and mainly oriented along the principal gas filaments axes. Each NEST contains between four and 23 stars. Inside NESTs, the surface density of stars may be as high as 2500 pc−2 and the mean value is 340 pc−2. Nearly half (11) of these NESTs contain about 75% of the class 0 and I objects. The balance between Class I, II, and, III fraction within the NESTs suggests that they may be ordered as an evolutionary temporal scheme, some of them getting infertile with time, while other still giving birth to young stars. We have inferred that only 20% of stars in Taurus do not belong to any kind of stellar groups (either multiple system, ultra wide pairs or NESTs). The mass-size relation for stellar NESTs is very close to the Bonnor–Ebert expectation. The range in mass is about the same as that of dense molecular cores. The distribution in size is bimodal peaking at 12.5 and 50 kAU and the distribution of the number of YSOs in NESTs as a function of size exhibits two regimes.Conclusions. We propose that the NESTs in their two size regimes represent the spatial imprints of stellar distribution at birth as they may have emerged within few millions years from their natal cloud either from a single core or from a chain of cores. We have identified them as the preferred sites of star formation in Taurus. These NESTs are the regions of highest stellar density and intermediate spatial scale structures between ultra-wide pairs and loose groups

Ultra-wide pairs (UWPs) in Taurus and origin of multiplicity

Multiplicity is a key feature in low-mass star-formation. However, its origin is not yet fully understood, even in Taurus that is one of the nearest (145 pc) and best-studied regions. We will present the discovery in Taurus of a new population of ultra-wide pairs (5kAU to 50kAU, hereafter UWPs), (Joncour et al 2017). These UWPs are biased towards higher multiplicity at shorter separation. We suggest that they could be the descendants of the multiple prestellar cores/Class 0 objects and that they may be resulting from a runaway cascade fragmentation of the natal molecular core

Antiphospholipid antibodies and thrombotic events in COVID-19 patients hospitalized in medicine ward

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The spatial evolution of young massive clusters

International audienceContext. Better understanding of star formation in clusters with high-mass stars requires rigorous dynamical and spatial analyses of star-forming regions.Aims. We seek to demonstrate that “INDICATE” is a powerful spatial analysis tool which when combined with kinematic data from Gaia DR2 can be used to probe star formation history in a robust way.Methods. We compared the dynamic and spatial distributions of young stellar objects (YSOs) at various evolutionary stages in NGC 2264 using Gaia DR2 proper motion data and INDICATE.Results. The dynamic and spatial behaviours of YSOs at different evolutionary stages are distinct. Dynamically, Class II YSOs predominately have non-random trajectories that are consistent with known substructures, whereas Class III YSOs have random trajectories with no clear expansion or contraction patterns. Spatially, there is a correlation between the evolutionary stage and source concentration: 69.4% of Class 0/I, 27.9% of Class II, and 7.7% of Class III objects are found to be clustered. The proportion of YSOs clustered with objects of the same class also follows this trend. Class 0/I objects are both found to be more tightly clustered with the general populous/objects of the same class than Class IIs and IIIs by a factor of 1.2/4.1 and 1.9/6.6, respectively. An exception to these findings is within 0.05° of S Mon where Class III objects mimic the behaviours of Class II sources across the wider cluster region. Our results suggest (i) current YSOs distributions are a result of dynamical evolution, (ii) prolonged star formation has been occurring sequentially, and (iii) stellar feedback from S Mon is causing YSOs to appear as more evolved sources.Conclusions. Designed to provide a quantitative measure of clustering behaviours, INDICATE is a powerful tool with which to perform rigorous spatial analyses. Our findings are consistent with what is known about NGC 2264, effectively demonstrating that when combined with kinematic data from Gaia DR2 INDICATE can be used to study the star formation history of a cluster in a robust way

Several Anaplasma phagocytophilum epidemiological cycles in France revealed by sequencing

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Les caractéristiques d'un paysage agricole influencent-elles la relation rongeur-tique ?

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