Disruption of a Red Giant Star by a Supermassive Black Hole and the Case of PS1-10jh

The development of a new generation of theoretical models for tidal disruptions is timely, as increasingly diverse events are being captured in surveys of the transient sky. Recently, Gezari et al. reported a discovery of a new class of tidal disruption events: the disruption of a helium-rich stellar core, thought to be a remnant of a red giant (RG) star. Motivated by this discovery and in anticipation of others, we consider tidal interaction of an RG star with a supermassive black hole (SMBH) which leads to the stripping of the stellar envelope and subsequent inspiral of the compact core toward the black hole. Once the stellar envelope is removed the inspiral of the core is driven by tidal heating as well as the emission of gravitational radiation until the core either falls into the SMBH or is tidally disrupted. In the case of tidal disruption candidate PS1-10jh we find that there is a set of orbital solutions at high eccentricities in which the tidally stripped hydrogen envelope is accreted by the SMBH before the helium core is disrupted. This places the RG core in a portion of parameter space where strong tidal heating can lift the degeneracy of the compact remnant and disrupt it before it reaches the tidal radius. We consider how this sequence of events explains the puzzling absence of the hydrogen emission lines from the spectrum of PS1-10jh and gives rise to its other observational features.Comment: Revised version accepted for publication in ApJ, 788, 99 (12 pages, 2 figures

Shaping a high-mass star-forming cluster through stellar feedback. The case of the NGC 7538 IRS 1-3 complex

Context: NGC 7538 IRS 1-3 is a high-mass star-forming cluster with several detected dust cores, infrared sources, (ultra)compact H$_{\rm II}$ regions, molecular outflows, and masers. In such a complex environment, important interactions and feedback among the embedded objects are expected to play a major role in the evolution of the region. Aims: We study the dust, kinematic, and polarimetric properties of the NGC 7538 IRS 1-3 region to investigate the role of the different forces interplaying in the formation and evolution of high-mass star-forming clusters. Methods: We perform SMA high angular resolution observations at 880 $\mu$m with the compact configuration. We develop the RATPACKS code to generate synthetic velocity cubes from models of choice to be compared to the observational data. We develop the "mass balance" analysis to quantify the stability against gravitational collapse accounting for all the energetics at core scales. Results: We detect 14 dust cores from 3.5 $M_{\odot}$ to 37 $M_{\odot}$ arranged in two larger scale structures: a central bar and a filamentary spiral arm. The spiral arm presents large scale velocity gradients in H$^{13}$CO$^+$ 4-3 and C$^{17}$O 3-2, and magnetic field segments well aligned to the dust main axis. The velocity gradient is well reproduced by a spiral arm expanding at 9 km s$^{-1}$ with respect to the central core MM1, which is known to power a large precessing outflow. The energy of the outflow is comparable with the spiral arm kinetic energy, which is dominant over gravitational and magnetic energies. In addition, the dynamical ages of the outflow and spiral arm are comparable. ... (Full abstract in the pdf version)Comment: 15 pages, 9 figures, 4 tables. Accepted for publication in A&

An efficient method to include equality constraints in branch current distribution system state estimation

Distribution system state estimation is a fundamental tool for the management and control functions envisaged for future distribution grids. The design of accurate and efficient algorithms is essential to provide estimates compliant with the needed accuracy requirements and to allow the real-time operation of the different applications. To achieve such requirements, peculiarities of the distribution systems have to be duly taken into account. Branch current-based estimators are an efficient solution for performing state estimation in radial or weakly meshed networks. In this paper, a simple technique, which exploits the particular formulation of the branch current estimators, is proposed to deal with zero injection and mesh constraints. Tests performed on an unbalanced IEEE 123-bus network show the capability of the proposed method to further improve efficiency performance of branch current estimators

Els arxius familiars i patrimonials aranesos: documents per a l'estudi de la Societat de la Val d'Aran

The Archiu Generau d'Aran holds forty-six family and heritage archives from the Vall D'Aran towns of Bausen, Canejan, Les, Bossòst, Arres de Sus, Arres de Jos, Vilamòs, Arró, Es Bòrdes, Benós, Arròs, Vilac, Vielha, Betren, Garòs, Arties, Salardú, Unha, Tredòs and Bagergue. To a lesser or greater extent, all these archives contain a series of documents that provide a view of the tangible and intangible assets of these families. The family archives contain documents related to members from same family and their legal affairs, especially marriage contracts, wills and dowries. Heritage archives have documents related to private property, which changed hands using a range of instruments. The Arxiu de çò de Joanchiquet (1509-1971) contains family, heritage and personal documentation for the Aunòs family in Vilamòs. This includes documents on their family alliances, inheritances, businesses and lists of family members in government offices in the Val d'Aran. A library with over four hundred volumes completes this archive, one of the most important conserved at the Archiu Generau d'Aran.A l'Archiu Generau d'Aran es troben dipositats quaranta-sis arxius familiars i patrimonials dels pobles aranesos de Bausen, Canejan, Les, Bossòst, Arres de Sus, Arres de Jos, Vilamòs, Arró, Es Bòrdes, Benós, Arròs, Vilac, Vielha, Betren, Garòs, Arties, Salardú, Unha, Tredòs i Bagergue. En tots aquests arxius es troben, en major o menor quantitat, una sèrie de documents que donen una visió de quin és el patrimoni material i immaterial d'aquestes famílies. La documentació familiar va lligada a la mateixa família i als seus negocis jurídics, dels quals destaquen el capítol matrimonial, el testament i el dot. La documentació patrimonial va relacionada amb la propietat particular, que canvia de mans a través de diversos instruments. L'arxiu de çò de Joanchiquet (1509-1971) recull la documentació familiar, patrimonial i personal de la família Aunòs de Vilamòs. En ell es conserven documents sobre les seves aliances familiars, el seu patrimoni, els seus negocis i les relacions dels seus membres en els oficis que regeixen l'administració de la Val d'Aran. Una biblioteca amb més de quatre-cents volums completa aquest arxiu, un dels més importants que es conserven a l'Archiu Generau d'Aran

Inflation Targeting in the Context of IMF-Supported Adjustment Programs

This paper argues that the IMF's traditional monetary conditionality--a ceiling on net domestic assets of the central bank and a floor on its net international reserves--should be adapted in IMF-supported adjustment programs with countries that have a framework of explicit inflation targets for the implementation of monetary policy. This adaptation should aim at enhancing correspondence and consistency between the monetary objectives of the central bank and the targets established under the IMF-supported adjustment program, as well as between the different instruments used to achieve the policy objectives and targets. The paper reviews various general options in this regard, and, using the case of Brazil as an example, demonstrates how these options may be implemented in practice. . Copyright 2002, International Monetary Fund

Inflation Targeting in the Context of IMF-Supported Adjustment Programs

This paper analyzes how an inflation targeting regimes relate with the conditioning established in the IMF assistance programs, and, in particular, with its inclusion within the performance criteria associated with that conditioning. The paper analyzes the Brazil's case, the first country in an IMF program to adopt an inflation target, and the lessons that can be derived from this experience. In its last section, we evaluate the idea of using Taylor rules to assess the inflationary performance. Simulations generated by the rule produces are not very similar to the effective policy rates, although differences diminish when expected inflation replaces current inflation within the rule.

Progetto e realizzazione di un setup per l’analisi del rolling contact: risultati preliminari

Presso il Dipartimento di Ingegneria Meccanica dell’Università di Cagliari (DIMECA) è attiva, da alcuni anni, una linea di ricerca orientata alla valutazione dei principali parametri di contatto (forma e dimensioni dell’area nominale di contatto, area reale di contatto, distribuzione delle pressioni di contatto) in interfacce metalliche, mediante una tecnica sperimentale basata sull’impiego di onde ultrasoniche. L’applicazione di questo metodo ha consentito di ottenere informazioni su contatti a geometria semplice quali, ad esempio, quelli sfera-piano [1-2] su casi più complessi di rilevante impatto ingegneristico come quello relativo all’interazione tra ruota e rotaia ferroviaria [3-4]. Il principale punto di forza dell’indagine ultrasonica risiede nella sua capacità di fornire informazioni sullo stato del contatto a partire da misure del coefficiente di riflessione all’interfaccia, garantendo in tal modo sia la più completa non-invasività (nessun mezzo viene ad interporsi tra i corpi a contatto) e sia la possibilità di investigare “in process”. In particolare quest’ultima peculiarità permette di monitorare le variazioni del parametri di contatto in tempo reale (ad esempio a seguito di variazioni nel carico applicato o nella configurazione geometrica dell’accoppiamento) senza che sia necessario rimuovere i corpi per esaminare gli effetti che tali modifiche hanno generato. Appare importante sottolineare che, a tutt’oggi, la letteratura riporta esempi di impiego de metodo ultrasonico a problemi di contatto quasi esclusivamente nell’analisi di situazioni statiche. Tuttavia, è facilmente intuibile che la possibilità di estendere il campo di applicazione della tecnica a situazioni dinamiche, aumenterebbe in misura considerevole il range di casi di interesse ingegneristico potenzialmente testabili. In considerazione di ciò, il presente studio si pone come obiettivo principale quello di verificare la validità ed affidabilità del metodo ultrasonico per lo studio di situazioni dinamiche, con particolare riferimento a problemi di “rolling contact”

Sowing the seeds of massive black holes in small galaxies: Young clusters as the building blocks of Ultra-Compact-Dwarf Galaxies

Interacting galaxies often have complexes of hundreds of young stellar clusters of individual masses $\sim 10^{4-6}~M_\odot$ in regions that are a few hundred parsecs across. These cluster complexes interact dynamically, and their coalescence is a candidate for the origin of some ultracompact dwarf galaxies (UCDs). Individual clusters with short relaxation times are candidates for the production of intermediate-mass black holes of a few hundred solar masses, via runaway stellar collisions prior to the first supernovae in a cluster. It is therefore possible that a cluster complex hosts multiple intermediate-mass black holes that may be ejected from their individual clusters due to mergers or binary processes, but bound to the complex as a whole. Here we explore the dynamical interaction between initially free-flying massive black holes and clusters in an evolving cluster complex. We find that, after hitting some clusters, it is plausible that the massive black hole will be captured in an ultracompact dwarf forming near the center of the complex. In the process, the hole typically triggers electromagnetic flares via stellar disruptions, and is also likely to be a prominent source of gravitational radiation for the advanced ground-based detectors LIGO and VIRGO. We also discuss other implications of this scenario, notably that the central black hole could be considerably larger than expected in other formation scenarios for ultracompact dwarfs.Comment: 15 pages, published in ApJ; for movies, please visit http://members.aei.mpg.de/amaro-seoane/ultra-compact-dwarf-galaxie