Smooth X-ray variability from ρ\rho Ophiuchi A+B. A strongly magnetized primary B2 star?

X-rays from massive stars are ubiquitous yet not clearly understood. In an XMM-Newton observation devoted to observe the first site of star formation in the $\rho$ Ophiuchi dark cloud, we detect smoothly variable X-ray emission from the B2IV+B2V system of $\rho$ Ophiuchi. Tentatively we assign the emission to the primary component. The light curve of the pn camera shows a first phase of low, almost steady rate, then a rise phase of duration of 10 ks, followed by a high rate phase. The variability is seen primarily in the band 1.0-8.0 keV while little variability is detected below 1 keV. The spectral analysis of the three phases reveals the presence of a hot component at 3.0 keV that adds up to two relatively cold components at 0.9 keV and 2.2 keV. We explain the smooth variability with the emergence of an extended active region on the surface of the primary star due to its fast rotation (v $sin~i \sim315$ km/s). We estimate that the region has diameter in the range $0.5-0.6$ R$_*$. The hard X-ray emission and its variability hint a magnetic origin, as suggested for few other late-O$-$early-B type stars. We also discuss an alternative explanation based on the emergence from occultation of a young (5-10 Myr) low mass companion bright and hot in X-rays.Comment: 4 pages, 3 figures, 2 tables. Accepted for publication as a letter in A&

No X-rays from WASP-18. Implications for its age, activity, and the influence of its massive hot Jupiter

About 20% out of the $>1000$ known exoplanets are Jupiter analogs orbiting very close to their parent stars. It is still under debate to what detectable level such hot Jupiters possibly affect the activity of the host stars through tidal or magnetic star-planet interaction. In this paper we report on an 87 ks Chandra observation of the hot Jupiter hosting star WASP-18. This system is composed of an F6 type star and a hot Jupiter of mass $10.4 M_{Jup}$ orbiting in less than 20 hr around the parent star. On the basis of an isochrone fitting, WASP-18 is thought to be 600 Myr old and within the range of uncertainty of 0.5-2 Gyr. The star is not detected in X-rays down to a luminosity limit of $4\times10^{26}$ erg/s, more than two orders of magnitude lower than expected for a star of this age and mass. This value proves an unusual lack of activity for a star with estimated age around 600 Myr. We argue that the massive planet can play a crucial role in disrupting the stellar magnetic dynamo created within its thin convective layers. Another additional 212 X-ray sources are detected in the Chandra image. We list them and briefly discuss their nature.Comment: 8 pages, 7 figures, 5 tables. Accepted for publication in A&

Mélanges et compaction d'assemblages granulaires

Un empilement de grains soumis à une vibration ou à une série de secousses voit sa compacité augmenter. Ce phénomène, appelé compaction, peut être utilisé pour densifier les matériaux granulaires ou comme une méthode de mesure pour caractériser les propriétés d'écoulement d'une poudre. Cette méthode est d'ailleurs populaire dans l'industrie pharmaceutique en raison de sa facilité d'utilisation. Bien que le phénomène de compaction soit étudié depuis un certain temps, il reste actuellement mal compris et les modèles disponibles pour décrire sa dynamique sont, pour la plupart, empiriques. Ce travail se concentre sur le phénomène de compaction et la manière dont certains paramètres, comme les conditions de vibration et la granulométrie du milieu granulaire, peuvent impacter la dynamique de ce processus. Cette thèse se présente sous la forme d'une collection d'articles, liés entre eux par la recherche de paramètres de contrôle et de l'optimisation du processus.A granular pile submitted to a vibration or a series of shakes increases its packing fraction. This phenomenon, called compaction, can be used to densify granular materials or as a measurement method to characterize the flow properties of a powder. This method is also popular in the pharmaceutical industry because of its ease of use. Although the phenomenon of compaction has been studied for a long time, it remains poorly understood and most of models describing its dynamics are empirical. This work focuses on compaction and the impact of parameters like the conditions of vibration and the granulometry of the granular medium on the dynamics of this phenomenon. This thesis is presented as a collection of articles, linked together by the search for control parameters and the process optimization.PowderRe

Hot Jupiters accreting onto their parent stars: effects on the stellar activity

Hot Jupiters (HJs) are massive gaseous planets orbiting close to their host stars. Due to their physical characteristics and proximity to the central star, HJs are the natural laboratories to study the process of star-planet interaction (SPI). Phenomena related to SPI may include the inflation and the evaporation of planetary atmospheres, the formation of cometary tails and bow shocks and magnetospheric interaction between the magnetic field of the planet and that of the star. Several works suggest that some systems show enhanced stellar activity in phase with the planetary rotation period. In this work, we use a 3D magneto-hydrodynamic model that describes a system composed of a star and an HJ and that includes the corresponding planetary and stellar winds. The aim is to investigate whether the material evaporating from the planet interacts with the stellar extended corona, and generates observable features. Our simulation shows that, in some conditions, the planetary wind expands and propagates mainly along the planetary orbit. Moreover, part of the planetary wind collides with the stellar wind and a fraction of the planet's outflow is funnelled by the stellar magnetic field and hits the stellar surface. In both events, the material is heated up to temperatures of a few MK by a shock. These phenomena could manifest in the form of enhanced stellar activity at some orbital phases of the planet.Comment: Accepted for publication in Astronomische Nachrichten - Astronomical Note

Day care cataract surgery in Central and Southern Italy: a multicentric survey

surgical techniques and costs are generally lower than those involved in ordinary hospitalization. Cataract surgery serves as a proxy indicator of the trend towards day surgery hospitalization in Italy and, therefore, of regional variability in health-care delivery and cost. The aim of this study was to update the diffusion of cataract day surgery through various surgical ophthalmological centers in central and southern Italy during 2005. Methods: A two-stage stratified cluster sampling method was used to draw a sample of Cataract Surgery Unit from Ophthalmic Units of central and southern Italy. A questionnaire was sent to 25 cataract surgery centers in nine health districts that represented the range of establishments (public, private, accredited or otherwise) in which cataract surgery is performed. Data were collected on numbers of procedures performed in 2005, hospital admission type, time from the onset of cataract day surgery, surgical procedure, and presence of other surgical centers. Results: The response rate was 42% (10 surveys), resulting in at least one completed questionnaire for each of these 9 districts. There is a positive trend towards day surgery hospitalization in all surgical centers. The percentage of patients treated as outpatients during 2005 varied from 50–60% (Avellino, Naples, Campobasso), to 80–90% (Rome, Bari), up to 90–100% (Catania, Palermo, Siracusa and Trapani), with an increasing trend in all the centers studied. Few differences were found in surgical procedures, and these were statistically insignificant. Conclusion: Our results confirm a positive trend towards day surgery in place of hospital inpatient admission for cataract surgery. This trend is expected to close the existing regional gap in Italy. Increased efficiency is an overriding need for the National Health Service in order to improve the rationalization of resources

How size ratio and segregation affect the packing of binary granular mixtures

For reaching high packing fractions, grains of various sizes are often mixed together allowing the small grains to fill the voids created by the large ones. However, in most cases, granular segregation occurs leading to lower packing fractions. We performed a wide set of experiments with different binary granular systems, proving that two main parameters are respectively the volume fraction f of small beads and the grain size ratio a. In addition, we show how granular segregation affects the global packing fraction. We propose a model with a strong dependency on a that takes into account possible granular segregation. Our model is in good agreement with both earlier experimental and simulation data.Peer reviewe

Smooth X-ray variability from ρ Ophiuchi A+B

X-rays from massive stars are ubiquitous yet not clearly understood. In an XMM-Newton observation devoted to observing the first site of star formation in the ρ Ophiuchi dark cloud, we detect smoothly variable X-ray emission from the B2IV+B2V system of ρ Ophiuchi. We tentatively assign the emission to the primary component. The light curve of the pn camera shows a first phase of low, almost steady rate, then a rise phase of duration of 10 ks, followed by a high rate phase. The variability is seen primarily in the band 1.0−8.0 keV while little variability is detected below 1 keV. The spectral analysis of the three phases reveals the presence of a hot component at 3.0 keV that adds up to two relatively cold components at 0.9 keV and 2.2 keV. We explain the smooth variability with the emergence of an extended active region on the surface of the primary star as being due to its fast rotation $(vsin \space i \sim 315 km  \space s^{-1}$. We estimate that the region has a diameter in the range $0.5−0.6\space R_∗$. The hard X-ray emission and its variability hint at a magnetic origin, as suggested for a few other late-O through early-B type stars. We also discuss an alternative explanation based on the emergence from occultation of a young (5−10 Myr) low mass companion that is bright and hot in X-rays.Astronom

La vita delle stelle in 3D: ambienti digitali per la ricerca e la didattica dell’astronomia

L'INAF - Osservatorio di Palermo nella seconda metà del 2019 ha attivato il progetto 3DMAP-VR, un acronimo che sta per Three-dimensional Modeling of Astrophysical Phenomena in Virtual Reality, sviluppando modelli 3D di fenomeni e ambienti astrofisici, frutto di simulazioni numeriche magneto-idrodinamiche realizzate dai ricercatori per interpretare i dati raccolti dai telescopi spaziali internazionali, indagare le proprietà fisiche e chimiche degli oggetti astronomici e ricostruire e osservare la loro evoluzione nel tempo. Utilizzando software per la modellazione 3D come Paraview, largamente utilizzato nella ricerca scientifica, sono stati realizzati degli ambienti immersivi e interattivi utilizzando la realtà virtuale (VR) e la realtà aumentata (AR). L’uso della AR e VR nella ricerca e didattica dell’astronomia è stato riconosciuto come uno strumento molto potente ed efficace, sia per ricercatori, proprio perché si presta bene alla rappresentazione dei dati astronomici non sempre facili da analizzare e comprendere, che per gli educatori e gli studenti, perché forniscono uno spazio di apprendimento immersivo e coinvolgente. I modelli 3D, resi artisticamente affascinanti, infatti, sono stati mostrati durante gli eventi per il pubblico e le scuole per presentare i risultati delle recenti ricerche astronomiche condotte dai ricercatori INAF; queste nuove tecnologie potenziano l’esperienza dell’utente consentendo scelte interattive e personali e offrendo opportunità educative uniche, aumentando la motivazione e la comprensione dei contenuti proposti. I modelli realizzati dall’INAF - già pubblicati su riviste scientifiche specializzate – sono stati diffusi attraverso Sketchfab, una delle più grandi piattaforme progettate per la diffusione di modelli 3D, per la realtà virtuale e aumentata, e ideando numerose iniziative di didattica e divulgazione. È possibile interagire con queste simulazioni 3D attraverso smartphone, tablet e PC, ma la visione ottimale avviene con l’utilizzo di visori appositi, come gli Oculus, che consentono una totale immersione negli ambienti virtuali. Inoltre, chiunque abbia accesso a una stampante 3D potrà stampare i modelli – che sono stati ottimizzati anche per essere compatibili con le più comuni stampanti 3D – e potrà così tenere tra le mani una stella che è appena esplosa oppure l’onda d’urto di una supernova. Infine, mostreremo un’attività didattica in VR sviluppata all’interno del progetto 3DMAP-VR: il prototipo di un programma sperimentale rivolto alle scuole, dove i ricercatori dell'INAF possono incontrare gli studenti per guidarli alla scoperta delle meraviglie del cosmo, attraverso modelli 3D di oggetti dell’universo integrati in un ambiente creato all’interno di uno studio verde