The Dynamics of Star Cluster Formation

How do star clusters form? We care, since these are the birth sites of most stars, perhaps including our own Sun. There are a great variety of different theoretical models of cluster formation and our main goal in this thesis is to examine the implications of these for the dynamical evolution of a cluster\u27s stellar population, including the ejected stars. In contrast to the majority of previous cluster formation studies, the focus of this work is on detailed modeling, using the Nbody6 code, of stellar dynamics, including binaries, with the structure, kinematics and star formation of the natal gas cloud explored with simple analytic prescriptions. In particular, we adopt the Turbulent Clump Model of pressure-truncated singular polytropic spheres, which sets global and local initial conditions of the newly formed stars. In a first paper, exploring a fiducial 3,000 solar mass clump, we investigated the effects of overall clump density, global star formation efficiency, degree of primordial mass segregation, degree of primordial binarity and binary population properties on the dynamical evolution of the cluster. Here, like most previous works, we assumed stars are formed very quickly, i.e., approximated as instantaneously, compared to the free-fall time of the clump. In our next work, after implementing a major code development to Nbody6 that allows modeling of gradual formation of stars, we investigated how the timescale of cluster formation, parameterized via the star formation efficiency per free-fall time, affects its early dynamical evolution. This is the first time that such a study, including a realistic binary population, has been carried out. We showed that star clusters that form rapidly expand more quickly after they emerge from the gas, while slowly-formed clusters evolve into a much more stable configuration during the gas rich phase. We also showed how the stellar population is affected by the timescale of formation, including the frequency of runaway/walkaway stars, stellar age gradients and primordial binary processing. We have then carried out preliminary explorations of a broad range of star-forming clump parameters, i.e., with masses from 300 to 30,000 solar masses and background cloud mass surface densities from 0.1 to 1 g cm\ub2. For the largest clusters simulated, we make use of a GPU-enabled version of the code. Further improvements to the modeling that have been implemented include global elongation of the clump so that nonspherical, including very filamentary, initial conditions can be studied. Models with internal spatial and kinematic substructure for the birth locations of the stars, based on hydrodynamic simulations of supersonic turbulence, have also been studied. In parallel, we have also carried out two projects that focus on observed systems related to dynamical ejections within the Orion Nebula Cluster (ONC). First, we examined a particular set of runaway stars associated with the Orion KL massive star forming region and carried out a systematic exploration of N-body simulations to understand the properties of the dynamical ejection that produced them. Second, we have performed a census of runaway stars from the ONC using Gaia data, estimating the total unbound population from the cluster. We have compared these results with our cluster formation simulations leading to new constraints on the star formation rate and dynamical age of the system

Could Segue 1 be a destroyed star cluster? - a dynamical perspective

We attempt to find a progenitor for the ultra-faint object Segue 1 under the assumption that it formed as a dark matter free star cluster in the past. We look for orbits, using the elongation of Segue 1 on the sky as a tracer of its path. Those orbits are followed backwards in time to find the starting points of our N-body simulations. The successful orbit, with which we can reproduce Segue 1 has a proper motion of mu_alpha = -0.19 mas/yr and mu_delta = -1.9 mas/yr, placing Segue 1 near its apo-galacticon today. Our best fitting model has an initial mass of 6224 Msun and an initial scale-length of 5.75 pc.Comment: 9 pages, 5 figures, 3 tables, accepted by MNRA

Quem está no controle? O entre-lugar do Grupo DACTA nos serviços de navegação aérea civis brasileiros

Trabalho de Conclusão de Curso (Graduação)Este trabalho tem como objetivo trazer à superfície a história dos DACTAs, grupo de Controladores de Tráfego Aéreo Civis, criado durante a Ditadura civil-militar para operar, em conjunto com os militares da Aeronáutica, seu novo sistema de radares – o SISDACTA. A partir da pesquisa histórica sobre esse grupo de controladores buscou-se 1) compreender as reivindicações deste grupo surgidas durante o Caos Aéreo numa perspectiva histórica, entendidas como uma reedição daquelas levadas à cabo pelos DACTAs já na década de 1970; 2) revisitar a história do controle de tráfego aéreo brasileiro, numa tentativa pioneira de reunir fontes documentais para a escrita de uma história do aéreo no Brasil; 3) propor um estrutura historiográfica que abarque a aviação, considerando-se os efeitos nocivos do patrimonialismo e do autoritarismo sobra a escrita da história dos DACTA e, portanto, sobre o ofício do historiador

Protracted Thermal Evolution of a Migmatitic Terrane as Revealed by Multiple Geochronometers From the Retro-Arc of the Early Paleozoic Famatinian Orogen in NW Argentina

U-Pb dates of zircon, monazite, and titanite combined with trace element composition, allows characterization of the thermal evolution of the migmatitic Agua del Sapo complex. This complex comprises Al-rich and Ca-rich metasedimentary rocks with a detrital zircon maximum depositional age of 550 Ma. The rocks record two consecutive early Paleozoic orogenies. During subduction associated with the 550–510 Ma Pampean orogeny, the complex was in the fore-arc region and was intruded by 550–520 Ma granites indicative of anomalous heating possibly related to ridge subduction. During the subsequent 500–440 Ma Famatinian orogeny, the arc migrated trenchwards and the region became part of a retro-arc that underwent melting at upper-amphibolite facies. This event was recorded differently by each of the accessory phases. Detrital zircon cores were overgrown by rare Famatinian rims that range from 500 to 420 Ma, while monazite records only Famatinian dates with a growth peak at ∼457 Ma that extends to 410 Ma, possibly due to coupled dissolution-precipitation. Published titanite dates define a 120 Myr thermal history, starting at ∼500 Ma with temperatures of ∼750°C ± 25°C, ending at 380 Ma and ∼700°C ± 25°C. Cooling was accompanied by a decrease in titanite light rare earth element contents in response to increased abundance of allanite/epidote. Thus, the complementary time-compositional record of the accessory phases reveals continued high heat flow, associated with deformation, to 380 Ma. This prolonged event blurs the boundary between the Famatinian and the subsequent Achalian/Chanic orogenies and extends the Silurian Rinconada tectonic phase of the Famatinian orogeny to the east into the Eastern Sierras Pampeanas

U-Pb dating of Ordovician felsic volcanism in the Schistose Domain of the Galicia-Trás-os-Montes Zone near Cabo Ortegal (NW Spain)

The northern termination of the Schistose Domain of the Galicia-Trás-os-Montes Zone is a tectonic slice named the Rio Baio Thrust Sheet, which is sandwiched between the Cabo Ortegal Complex and the Ollo de Sapo Domain of the Central-Iberian Zone. The Rio Baio Thrust Sheet is formed by two volcanosedimentary series, the Loiba and the Queiroga Series. The Loiba Series contains calc-alkaline dacite and rhyolite, while the overlying Queiroga Series has alkaline rhyolite. These series were considered to be in stratigraphically upwards continuity and believed to be Silurian in age. U-Pb dating of an alkaline rhyolite in the Queiroga Series provides an Arenig age of 475 ± 2 Ma. This age makes the Queiroga Series the oldest known stratigraphic unit in the Schistose Domain of the Galicia-Trás-os-Montes Zone, impeding correlation between the lithostratigraphic sequences of Ortegal and Central Galicia. As well as providing evidence of an unforeseen structural complexity within the Rio Baio Sheet, the new data supports the notion that the Schistose Domain is not parautochtonous, but a separate lithotectonic unit in thrust contact with the underlying Central-Iberian Zone

Are hierarchically formed embedded star clusters surviving gas expulsion depending on their initial conditions?

We investigate the dissolution process of young embedded star clusters with different primordial mass segregation levels using fractal distributions by means of N-body simulations. We combine several star clusters in virial and subvirial global states with Plummer and uniform density profiles to mimic the gas. The star clusters have masses of M-stars = 500 M-circle dot that follow an initial mass function where the stars have maximum distance from the centre of r = 1.5 pc. The clusters are placed in clouds that at the same radius have masses of M-cloud = 2000 M-circle dot, resulting in star formation efficiency of 0.2. We remove the background potential instantaneously at a very early phase, mimicking the most destructive scenario of gas expulsion. The evolution of the fraction of bound stellar mass is followed for a total of 16 Myr for simulations with stellar evolution and without. We compare our results with previous works using equal-mass particles where an analytical physical model was used to estimate the bound mass fraction after gas expulsion. We find that independent of the initial condition, the fraction of bound stellar mass can be well predicted just right after the gas expulsion but tends to be lower at later stages, as these systems evolve due to the stronger two-body interactions resulting from the inclusion of a realistic initial mass function. This discrepancy is independent of the primordial mass segregation level