High-velocity runaway stars from three-body encounters

We performed numerical simulations of dynamical encounters between hard massive binaries and a very massive star (VMS; formed through runaway mergers of ordinary stars in the dense core of a young massive star cluster), in order to explore the hypothesis that this dynamical process could be responsible for the origin of high-velocity (\geq 200-400 km/s) early or late B-type stars. We estimated the typical velocities produced in encounters between very tight massive binaries and VMSs (of mass of \geq 200 Msun) and found that about 3-4 per cent of all encounters produce velocities of \geq 400 km/s, while in about 2 per cent of encounters the escapers attain velocities exceeding the Milky Ways's escape velocity. We therefore argue that the origin of high-velocity (\geq 200-400 km/s) runaway stars and at least some so-called hypervelocity stars could be associated with dynamical encounters between the tightest massive binaries and VMSs formed in the cores of star clusters. We also simulated dynamical encounters between tight massive binaries and single ordinary 50-100 Msun stars. We found that from 1 to \simeq 4 per cent of these encounters can produce runaway stars with velocities of \geq 300-400 km/s (typical of the bound population of high-velocity halo B-type stars) and occasionally (in less than 1 per cent of encounters) produce hypervelocity (\geq 700 km/s) late B-type escapers.Comment: 4 pages, 2 figure, to appear in Star Clusters -- Basic Galactic Building Blocks throughout Time and Space, Proceed. of the IAU Symp. 266, eds. R. de Grijs and J. Lepin

The Becklin-Neugebauer Object as a Runaway B Star, Ejected 4000 years ago from the theta^1C system

We attempt to explain the properties of the Becklin-Neugebauer (BN) object as a runaway B star, as originally proposed by Plambeck et al. (1995). This is one of the best-studied bright infrared sources, located in the Orion Nebula Cluster -- an important testing ground for massive star formation theories. From radio observations of BN's proper motion, we trace its trajectory back to Trapezium star theta^1C, the most massive (45 Msun) in the cluster and a relatively tight (17 AU) visual binary with a B star secondary. This origin would be the most recent known runaway B star ejection event, occurring only \~4000 yr ago and providing a unique test of models of ejection from multiple systems of massive stars. Although highly obscured, we can constrain BN's mass (~7 Msun) from both its bolometric luminosity and the recoil of theta^1C. Interaction of a runaway B star with dense ambient gas should produce a compact wind bow shock. We suggest that X-ray emission from this shocked gas may have been seen by Chandra: the offset from the radio position is ~300 AU in the direction of BN's motion. Given this model, we constrain the ambient density, wind mass-loss rate and wind velocity. BN made closest approach to the massive protostar, source ``I'', 500 yr ago. This may have triggered enhanced accretion and thus outflow, consistent with previous interpretations of the outflow being a recent (~10^3 yr) "explosive" event.Comment: 6 pages, accepted to ApJ Letter

Hypervelocity Stars. I. The Spectroscopic Survey

We discuss our targeted search for hypervelocity stars (HVSs), stars traveling with velocities so extreme that dynamical ejection from a massive black hole is their only suggested origin. Our survey, now half complete, has successfully identified a total of four probable HVSs plus a number of other unusual objects. Here we report the most recently discovered two HVSs: SDSS J110557.45+093439.5 and possibly SDSS J113312.12+010824, traveling with Galactic rest-frame velocities at least +508+-12 and +418+-10 km/s, respectively. The other late B-type objects in our survey are consistent with a population of post main-sequence stars or blue stragglers in the Galactic halo, with mean metallicity [Fe/H]=-1.3 and velocity dispersion 108+-5 km/s. Interestingly, the velocity distribution shows a tail of objects with large positive velocities that may be a mix of low-velocity HVSs and high-velocity runaway stars. Our survey also includes a number of DA white dwarfs with unusually red colors, possibly extremely low mass objects. Two of our objects are B supergiants in the Leo A dwarf, providing the first spectroscopic evidence for star formation in this dwarf galaxy within the last ~30 Myr.Comment: 10 pages, uses emulateapj, accepted by Ap

Marine sponge as a source of antiangiogenic compounds. The case of aeroplysinin-1

The vast majority of the natural compounds that have been previously described as inhibitors of angiogenesis have been isolated from plants and terrestrial microorganisms, mainly due to their higher availability and because their therapeutic effects had been previously known in folk traditional medicines. However, increasing attention is being paid to the development of marine-derived antiangiogenic agents, probably fuelled by the increase in the number of marine-derived anticancer drugs which are being successfully used for cancer therapy. Marine organisms, adapted to survive in extreme environments by developing chemical means of defence, produce interesting and singular pharmacological lead compounds, derived from the large diversity of marine habitats and environmental conditions. Among the many different types of marine organisms used as a source for drug discovery, sponges represent one of the most promising sources of leads in the research of new cancer drugs. Some angiogenesis inhibitors isolated from marine sponges have been described by us and others. Aeroplysinin-1, a brominated metabolite extracted from the marine sponge Aplysina aerophoba, has been characterized by our group as a potent antiangiogenic compound in vitro and in vivo. Aeroplysinin-1 induces apoptosis in endothelial cells by a mechanism which involves activation of the BH3-only pro-apoptotic protein Bad, cytochrome c release and activation of caspases 2, 3, 8 and 9, what indicates a relevant role of the mitochondria in the apoptogenic activity of this compound. Recent results suggest that aeroplysinin-1 could also be a novel potential anti-inflammatory compound. These results open new ways to the potential pharmacological action of aeroplysinin-1 not only on angiogenesis and cancer, but also on atherosclerosis and inflammation-dependent diseases.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Pedagogical Practice – Index of Readiness of Future Physics Teacher to Professional Activity

У статті проаналізовано організаційно-методичні засади педагогічної практики у вищому навчальному закладі на даний час, розкрито її значення в системі професійного становлення майбутнього вчителя фізики. Зазначено, що ефективне проведення педпрактики залежить від належного рівня організації і управління діяльністю студентів. Обґрунтовано, що результати педагогічної практики виступають показником готовності студента до майбутньої професійної діяльності та одночасно вказують на недоліки і прогалини у знаннях студентів, на які необхідно звернути особливу увагу під час фахової підготовки. Описано основні розділи «Програми педагогічної практики» для студентів-майбутніх вчителів фізики (4-й курс), розробленої авторами статті у співавторстві з колективом досвідчених викладачів кафедри. Окреслено перспективи педагогічної практики студентів у зв’язку з реформуванням вищої освіти в Україні. Висвітлено деякі особливості організації педагогічної практики у вищих навчальних закладах різних країн світу.The article analyzes organizational-methodical bases of pedagogical practice in higher education at the present time, revealed its importance in the system of professional formation of future teachers of physics. Noted that effective implementation of the internship depends on the appropriate level of the organization and management of students. It is proved that the results of the pedagogical practices act as an indicator of students 'readiness for future professional activity and at the same time indicate shortcomings and gaps in students' knowledge that need special attention in training. Describes the main sections of "teaching practice Program" for students-future physics teachers (4th year) developed by the authors in collaboration with a team of experienced teachers of the Department. Perspectives of pedagogical practice of students in connection with the reform of higher education in Ukraine. Highlight some features of the organization of pedagogical practice in higher education institutions around the world

The origin of runaway stars

Milli-arcsecond astrometry provided by Hipparcos and by radio observations makes it possible to retrace the orbits of some of the nearest runaway stars and pulsars to determine their site of origin. The orbits of the runaways AE Aurigae and mu Columbae and of the eccentric binary iota Orionis intersect each other about 2.5 Myr ago in the nascent Trapezium cluster, confirming that these runaways were formed in a binary-binary encounter. The path of the runaway star zeta Ophiuchi intersects that of the nearby pulsar PSR J1932+1059, about 1 Myr ago, in the young stellar group Upper Scorpius. We propose that this neutron star is the remnant of a supernova that occurred in a binary system which also contained zeta Oph, and deduce that the pulsar received a kick velocity of about 350 km/s in the explosion. These two cases provide the first specific kinematic evidence that both mechanisms proposed for the production of runaway stars, the dynamical ejection scenario and the binary-supernova scenario, operate in nature.Comment: 5 pages, including 2 eps-figures and 1 table, submitted to the ApJ Letters. The manuscript was typeset using aaste

Estudio situacional de la equiparación de oportunidades para las personas con discapacidad en la Universidad de Panamá

La investigación tuvo como propósito conocer y describir las condiciones existentes para la equiparación de oportunidades de las personas con discapacidad en la Universidad de Panamá, en atención a las dimensiones que establece la legislación vigente para tal fin. Se trató de una investigación exploratoria-descriptiva, no experimental, transeccional, que incluyó estudios de caso. La muestra no probabilística, estuvo compuesta por 37 personas, 15 de ellas con discapacidad, de los estamentos administrativo, docente y estudiantil de la institución, elegidas de forma intencional. Se elaboraron cuatro instrumentos: dos cuestionarios para la identificación de las necesidades institucionales y de las personas con discapacidad, y dos listas de cotejo para el estudio de la accesibilidad física y el cumplimiento institucional de la normativa. Los datos obtenidos de las entrevistas a las personas del estamento administrativo se sistematizaron para describir la situación actual de la equiparación de oportunidades según lo que mandata la ley. En el caso de las personas con discapacidad, permitieron una descripción de sus principales necesidades, lo que a su vez constituye un indicador de la influencia de la estrategia actual que utiliza la institución. Los datos suministrados por el cuestionario de accesibilidad física se sometieron estadísticamente para describir en términos de porcentajes, la accesibilidad arquitectónica. Por otro lado, los resultados evidencian buenas prácticas en equiparación de oportunidades para las personas con discapacidad, algunas de las cuales van más allá de lo que mandata la ley en sus diferentes dimensiones de aplicación.Ello nos permite afirmar que la Universidad de Panamá se encuentra en un estadio inicial en la formalización de este proceso, y precisa la operacionalización de la normativa institucional para el diseño de procedimientos que garanticen la equidad en el acceso a los servicios

Discovery of an Unbound Hyper-Velocity Star in the Milky Way Halo

We have discovered a star, SDSS J090745.0+024507, leaving the Galaxy with a heliocentric radial velocity of +853+-12 km/s, the largest velocity ever observed in the Milky Way halo. The star is either a hot blue horizontal branch star or a B9 main sequence star with a heliocentric distance ~55 kpc. Corrected for the solar reflex motion and to the local standard of rest, the Galactic rest-frame velocity is +709 km/s. Because its radial velocity vector points 173.8 deg from the Galactic center, we suggest that this star is the first example of a hyper-velocity star ejected from the Galactic center as predicted by Hills and later discussed by Yu & Tremaine. The star has [Fe/H]~0, consistent with a Galactic center origin, and a travel time of <80 Myr from the Galactic center, consistent with its stellar lifetime. If the star is indeed traveling from the Galactic center, it should have a proper motion of 0.3 mas/yr observable with GAIA. Identifying additional hyper-velocity stars throughout the halo will constrain the production rate history of hyper-velocity stars at the Galactic center.Comment: 4 pages, submitted to ApJ Letter