Stripping a debris disk by close stellar encounters in an open stellar cluster

A debris disk is a constituent of any planetary system surrounding a main sequence star. We study whether close stellar encounters can disrupt and strip a debris disk of its planetesimals in the expanding open cluster of its birth with a decreasing star number density over 100 Myrs. Such stripping would affect the dust production and hence detectability of the disk. We tabulated the fractions of planetesimals stripped off during stellar flybys of miss distances between 100 and 1000 AU and for several mass ratios of the central to passing stars. We then estimated the numbers of close stellar encounters over the lifetime of several expanding open clusters characterized by their initial star densities. We found that a standard disk, with inner and outer radii of 40 and 100 AU, suffers no loss of planetesimals over 100 Myrs around a star born in a common embedded cluster with star density <1000 pc^-3. In contrast, we found that such a disk is severely depleted of its planetesimals over this timescale around a star born in an Orion-type cluster where the star density is >20 000 pc^-3. In this environment, a disk loses >97% of its planetesimals around an M-dwarf, >63% around a solar-type star, and >42% around an A-dwarf, over 100 Myrs. We roughly estimate that two-thirds of the stars may be born in such high star density clusters. This might explain in part why fewer debris disks are observed around lower mass stars.Comment: 7 pages, 4 figures, accepted for publication in Astronomy and Astrophysics ; v2 abstract complemente

MicroRNA Profiling of BRCA1/2 Mutation-Carrying and Non-Mutation-Carrying High-Grade Serous Carcinomas of Ovary

BACKGROUND:MicroRNAs (miRNA) are 20 approximately 25 nucleotide non-coding RNAs that inhibit the translation of targeted mRNA, and they have been implicated in the development of human malignancies. High grade serous ovarian carcinomas, the most common and lethal subtype of ovarian cancer, can occur sporadically or in the setting of BRCA1/2 syndromes. Little is known regarding the miRNA expression profiles of high grade serous carcinoma in relation to BRCA1/2 status, and compared to normal tubal epithelium, the putative tissue of origin for high grade serous carcinomas. METHODOLOGY/PRINCIPAL FINDINGS:Global miRNA expression profiling was performed on a series of 33 high grade serous carcinomas, characterized with respect to BRCA1/2 status (mutation, epigenetic silencing with loss of expression or normal), and with clinical follow-up, together with 2 low grade serous carcinomas, 2 serous borderline tumors, and 3 normal fallopian tube samples, using miRNA microarrays (328 human miRNA). Unsupervised hierarchical clustering based on miRNA expression profiles showed no clear separation between the groups of carcinomas with different BRCA1/2 status. There were relatively few miRNAs that were differentially expressed between the genotypic subgroups. Comparison of 33 high grade serous carcinomas to 3 normal fallopian tube samples identified several dysregulated miRNAs (false discovery rate <5%), including miR-422b and miR-34c. Quantitative RT-PCR analysis performed on selected miRNAs confirmed the pattern of differential expression shown by microarray analysis. Prognostically, lower level miR-422b and miR-34c in high grade serous carcinomas were both associated with decreased disease-specific survival by Kaplan-Meier analysis (p<0.05). CONCLUSIONS/SIGNIFICANCE:High grade serous ovarian carcinomas with and without BRCA1/2 abnormalities demonstrate very similar miRNA expression profiles. High grade serous carcinomas as a group exhibit significant miRNA dysregulation in comparison to tubal epithelium and the levels of miR-34c and miR-422b appear to be prognostically important

Purge, excitation dynamique et structuration des disques de débris soumis à l'interaction gravitationnelle de planètes et d'étoiles voisines

A debris disk around a main sequence star is made of planetesimals, which are the remnant of the planet formation process according to the core-accretion theory. In the Solar system, the main asteroid belt and the Kuiper belt are examples of debris disks. Around other stars, debris disks are observable if they are massive enough for collisions between planetesimals to produce continuously enough dust to be detected, by their thermal emission in the far infrared, or by scattered light in the visible spectrum. In this work, we have studied the stripping, the dynamical excitation and the structuring of debris disksundergoing the gravitational interaction with a planet inside a system, a stellar companion in a binary system, and a passing star in the dense environment of an open cluster during the first 100 millions years after the birth of the star. We have addressed these problems by the numerical simulation of the dynamics of a disk of planetesimals in these various conditions. We have finally carried out a study to determine the characteristics of the debris disk population around stars of different types, with the standard collisional evolution model, our results about dynamical excitation of disks and the data of the Spitzer surveys. We show that the lack of debris disks detected around low mass M type stars can be explained by planetesimals 10 times smaller than around solar type or more massive stars.Un disque de débris autour d'une étoile de la séquence principale est composé de planétésimaux, reste de la formation des planètes selon la théorie core-accretion. Dans le Système solaire, il s'agit de la ceinture d'astéroïdes et de la ceinture de Kuiper. Autour des autres étoiles, les disques de débris sont observables s'ils sont assez massifs pour que les collisions entre planétésimaux produisent continûment assez de poussière détectable en émission thermique dans l'infrarouge lointain ou en lumière diffusée dans le visible. Dans cette thèse, nous étudions la purge (stripping), l'excitation dynamique, et la structuration d'un disque soumis à une interaction gravitationnelle avec une planète à l'intérieur du système, un compagnon stellaire dans un système binaire, et une étoile de passage dans l'environnement dense d'un amas ouvert pendant 100 millions d'années après la naissance de l'étoile. Nous avons abordé ces problèmes par la simulation de la dynamique d'un disque de planétésimaux dans ces différentes conditions. Enfin, nous avons mené une étude pour déterminer les caractéristiques de la population de disques de débris autour des étoiles de différents types stellaires à l'aide du modèle d'évolution collisionnelle standard, de nos résultats sur l'excitation dynamique des disques et des données des relevés Spitzer. Ainsi, nous montrons que la quasi-absence des disques de débris observée autour des étoiles de faibles masses de type stellaire M peut être expliquée par des planétésimaux au moins 10 fois plus petits en taille que ceux autour des étoiles de type solaire ou plus massives

Stripping, dynamical excitation and structuring of debris disks undergoing gravitational interactions from neighbouring planets of stars

A debris disk around a main sequence star is made of planetesimals, which are the remnant of the planet formation process according to the core-accretion theory. In the Solar system, the main asteroid belt and the Kuiper belt are examples of debris disks. Around other stars, debris disks are observable if they are massive enough for collisions between planetesimals to produce continuously enough dust to be detected, by their thermal emission in the far infrared, or by scattered light in the visible spectrum. In this work, we have studied the stripping, the dynamical excitation and the structuring of debris disksundergoing the gravitational interaction with a planet inside a system, a stellar companion in a binary system, and a passing star in the dense environment of an open cluster during the first 100 millions years after the birth of the star. We have addressed these problems by the numerical simulation of the dynamics of a disk of planetesimals in these various conditions. We have finally carried out a study to determine the characteristics of the debris disk population around stars of different types, with the standard collisional evolution model, our results about dynamical excitation of disks and the data of the Spitzer surveys. We show that the lack of debris disks detected around low mass M type stars can be explained by planetesimals 10 times smaller than around solar type or more massive stars.Un disque de débris autour d'une étoile de la séquence principale est composé de planétésimaux, reste de la formation des planètes selon la théorie core-accretion. Dans le Système solaire, il s'agit de la ceinture d'astéroïdes et de la ceinture de Kuiper. Autour des autres étoiles, les disques de débris sont observables s'ils sont assez massifs pour que les collisions entre planétésimaux produisent continûment assez de poussière détectable en émission thermique dans l'infrarouge lointain ou en lumière diffusée dans le visible. Dans cette thèse, nous étudions la purge (stripping), l'excitation dynamique, et la structuration d'un disque soumis à une interaction gravitationnelle avec une planète à l'intérieur du système, un compagnon stellaire dans un système binaire, et une étoile de passage dans l'environnement dense d'un amas ouvert pendant 100 millions d'années après la naissance de l'étoile. Nous avons abordé ces problèmes par la simulation de la dynamique d'un disque de planétésimaux dans ces différentes conditions. Enfin, nous avons mené une étude pour déterminer les caractéristiques de la population de disques de débris autour des étoiles de différents types stellaires à l'aide du modèle d'évolution collisionnelle standard, de nos résultats sur l'excitation dynamique des disques et des données des relevés Spitzer. Ainsi, nous montrons que la quasi-absence des disques de débris observée autour des étoiles de faibles masses de type stellaire M peut être expliquée par des planétésimaux au moins 10 fois plus petits en taille que ceux autour des étoiles de type solaire ou plus massives.PARIS-Observatoire (751142302) / SudocSudocFranceF

On the steady state collisional evolution of debris disks around M dwarfs

International audienc

The creation of MOx surface species on pure silica MCM-48, using gas- and liquid phase modification with M-acetylacetonate complexes

Pure silica MCM-48 is prepared by a novel synthesis method, using the [C18H37N+(CH3)(2) - (CH2)(12) - N+(CH3)(2)C18H37].2Br(-) surfactant, abbreviated as GEMINI 18-12-18. The MCM-48, obtained after careful calcination, is a highly crystalline, mesoporous material, with the characteristics of the Ia3d cubic phase, a surface area exceeding 1000 m(2)/g and a narrow mesoporous pore size distribution (r = 1.4 nm; FWHH < 0.2 nm). This MCM support is grafted with VOx species, using a designed dispersion of VO(acac)(2) in a gas deposition reactor. In a first step, the complex is anchored to the support, in a subsequent step the adsorbed complex is thermolyzed to yield chemically bonded VOx surface species. The final material contains 1.7 mmol V/g (8.7 w% V), still has narrow pore size distribution and a surface area of 800 m(2)/g. It is observed that all silanols are consumed during the adsorption of the VO(acac)(2) complex to the MCM support. Therefore, the maximum achievable number of surface V-species is limited by the silanol number, and not by the geometrical surface, which has a higher capacity. After calcination of the adsorbed complex, the supported VOx species are present in a strictly tetrahedral configuration, but mainly as chains of linked tetrahedra and not as isolated species