Searching for outflows signatures in sdss spectra of x-ray selected, obscured agn in the cosmos field

Partendo dal campione di AGN presente nella survey di XMM-COSMOS, abbiamo cercato la sua controparte ottica nel database DR10 della Sloan Digital Sky Survey (SDSS), ed il match ha portato ad una selezione di 200 oggetti, tra cui stelle, galassie e quasar. A partire da questo campione, abbiamo selezionato tutti gli oggetti con un redshift z<0.86 per limitare l’analisi agli AGN di tipo 2, quindi siamo giunti alla selezione finale di un campione di 30 sorgenti. L’analisi spettrale è stata fatta tramite il task SPECFIT, presente in IRAF. Abbiamo creato due tipi di modelli: nel primo abbiamo considerato un’unica componente per ogni riga di emissione, nel secondo invece è stata introdotta un’ulteriore com- ponente limitando la FWHM della prima ad un valore inferiore a 500 km\s. Le righe di emissione di cui abbiamo creato un modello sono le seguenti: Hβ, [NII]λλ 6548,6581, Hα, [SII]λλ 6716,6731 e [OIII]λλ 4959,5007. Nei modelli costruiti abbiamo tenuto conto della fisica atomica per quel che riguarda i rapporti dei flussi teorici dei doppietti dell’azoto e dell’ossigeno, fissandoli a 1:3 per entrambi; nel caso del modello ad una componente abbiamo fissato le FWHM delle righe di emissione; mentre nel caso a due componenti abbiamo fissato le FWHM delle componenti strette e larghe, separatamente. Tenendo conto del chi-quadro ottenuto da ogni fit e dei residui, è stato possibile scegliere tra i due modelli per ogni sorgente. Considerato che la nostra attenzione è focalizzata sulla cinematica dell’ossigeno, abbiamo preso in considerazione solo le sorgenti i cui spettri mostravano la riga suddetta, cioè 25 oggetti. Su questa riga è stata fatta un’analisi non parametrica in modo da utilizzare il metodo proposto da Harrison et al. (2014) per caratterizzare il profilo di riga. Sono state determinate quantità utili come il 2 e il 98 percentili, corrispondenti alle velocità massime proiettate del flusso di materia, e l’ampiezza di riga contenente l’80% dell’emissione. Per indagare sull’eventuale ruolo che ha l’AGN nel guidare questi flussi di materia verso l’esterno, abbiamo calcolato la massa del gas ionizzato presente nel flusso e il tasso di energia cinetica, tenendo conto solo delle componenti larghe della riga di [OIII] λ5007. Per la caratterizzazione energetica abbiamo considerato l’approccio di Cano-Diaz et al (2012) e di Heckman (1990) in modo da poter ottenere un limite inferiore e superiore della potenza cinetica, adottando una media geometrica tra questi due come valore indicativo dell’energetica coinvolta. Confrontando la potenza del flusso di gas con la luminosità bolometrica dell’AGN, si è trovato che l’energia cinetica del flusso di gas è circa lo 0.3-30% della luminosità dell’AGN, consistente con i modelli che considerano l’AGN come principale responsabile nel guidare questi flussi di gas.

Investigating the potential magnetic origin of wind variability in OB stars

In this thesis, the origin of large-scale structures in hot star winds, believed to be responsible for the presence of discrete absorption components (DACs) in the absorption troughs of ultraviolet resonance lines, is constrained using both observations and numerical simulations. These structures are understood as arising from bright regions on the stellar surface, although their physical cause remains unknown. First, we use high quality circular spectropolarimetric observations of 13 well-studied OB stars to evaluate the potential role of dipolar magnetic fields in producing DACs. We perform longitudinal field measurements and place limits on the field strength using Bayesian inference, assuming that it is dipolar. No magnetic field was detected within this sample. The derived constraints statistically refute any significant dynamical influence from a magnetic dipole on the wind for all of these stars, ruling out such fields as a cause for DACs. Second, we perform numerical simulations using bright spots constrained by broadband optical photometric observations. We calculate hydrodynamical wind models using three sets of spot sizes and strengths. Co-rotating interaction regions are yielded in each model, and radiative transfer shows that the properties of the variations in the UV resonance lines synthesized from these models are consistent with those found in observed UV spectra, establishing the first consistent link between UV spectroscopic line profile variability and photometric variations and thus supporting the bright spot paradigm (BSP). Finally, we develop and apply a phenomenological model to quantify the measurable effects co-rotating bright spots would have on broadband optical photometry and on the profiles of photopheric lines in optical spectra. This model can be used to evaluate the existence of these spots, and, in the event of their detection, characterize them. Furthermore, a tentative spot evolution model is presented. A preliminary analysis of its output, compared to the observed photometric variations of xi Persei, suggests the possible existence of “active longitudes” on the surface of this star. Future work will expand the range of observational diagnostics that can be interpreted within the BSP, and link phenomenology (bright spots) to physical processes (magnetic spots or non-radial pulsations).

Investigating the potential magnetic origin of wind variability in OB stars

In this thesis, the origin of large-scale structures in hot star winds, believed to be responsible for the presence of discrete absorption components (DACs) in the absorption troughs of ultraviolet resonance lines, is constrained using both observations and numerical simulations. These structures are understood as arising from bright regions on the stellar surface, although their physical cause remains unknown. First, we use high quality circular spectropolarimetric observations of 13 well-studied OB stars to evaluate the potential role of dipolar magnetic fields in producing DACs. We perform longitudinal field measurements and place limits on the field strength using Bayesian inference, assuming that it is dipolar. No magnetic field was detected within this sample. The derived constraints statistically refute any significant dynamical influence from a magnetic dipole on the wind for all of these stars, ruling out such fields as a cause for DACs. Second, we perform numerical simulations using bright spots constrained by broadband optical photometric observations. We calculate hydrodynamical wind models using three sets of spot sizes and strengths. Co-rotating interaction regions are yielded in each model, and radiative transfer shows that the properties of the variations in the UV resonance lines synthesized from these models are consistent with those found in observed UV spectra, establishing the first consistent link between UV spectroscopic line profile variability and photometric variations and thus supporting the bright spot paradigm (BSP). Finally, we develop and apply a phenomenological model to quantify the measurable effects co-rotating bright spots would have on broadband optical photometry and on the profiles of photopheric lines in optical spectra. This model can be used to evaluate the existence of these spots, and, in the event of their detection, characterize them. Furthermore, a tentative spot evolution model is presented. A preliminary analysis of its output, compared to the observed photometric variations of xi Persei, suggests the possible existence of “active longitudes” on the surface of this star. Future work will expand the range of observational diagnostics that can be interpreted within the BSP, and link phenomenology (bright spots) to physical processes (magnetic spots or non-radial pulsations).

The Rotational Evolution and Magnetospheric Emission of the Magnetic Early B-type Stars

How do the magnetic fields of massive stars evolve over time? Are their gyrochronological ages consistent with ages inferred from evolutionary tracks? Why do most stars predicted to host Centrifugal Magnetospheres (CMs) display no H$\alpha$ emission? Does plasma escape from CMs via centrifugal breakout events, or by a steady-state leakage mechanism? This thesis investigates these questions via a population study with a sample of 51 magnetic early B-type stars. The longitudinal magnetic field \bz~was measured from Least Squares Deconvolution profiles extracted from high-resolution spectropolarimetric data. New rotational periods $P_{\rm rot}$ were determined for 15 stars from \bz, leaving only 3 stars for which $P_{\rm rot}$ is unknown. Projected rotational velocities \vsini~were measured from multiple spectral lines. Effective temperatures and surface gravities were measured via ionization balances and line profile fitting of H Balmer lines. Fundamental physical parameters, \bz, \vsini, and $P_{\rm rot}$ were then used to determine radii, masses, ages, dipole oblique rotator model, stellar wind, magnetospheric, and spindown parameters using a Monte Carlo approach that self-consistently calculates all parameters while accounting for all available constraints on stellar properties. Dipole magnetic field strengths $B_{\rm d}$ follow a log-normal distribution similar to that of Ap stars, and decline over time in a fashion consistent with the expected conservation of fossil magnetic flux. $P_{\rm rot}$ increases with fractional main sequence age, mass, and $B_{\rm d}$, as expected from magnetospheric braking. However, comparison of evolutionary track ages to maximum spindown ages $t_{\rm S,max}$ shows that initial rotation fractions may be far below critical for stars with $M_*>10 M_\odot$. Computing $t_{\rm S,max}$ with different mass-loss prescriptions indicates that the mass-loss rates of B-type stars are likely much lower than expected from extrapolation from O-type stars. Stars with H$\alpha$ in emission and absorption occupy distinct regions in the updated rotation-magnetic confinement diagram: H$\alpha$-bright stars are found to be younger, more rapidly rotating, and more strongly magnetized than the general population. Emission strength is sensitive both to the volume of the CM and to the mass-loss rate, favouring leakage over centrifugal breakout.

Rotational velocities of single and binary O-type stars in the Tarantula Nebula

Rotation is a key parameter in the evolution of massive stars, affecting their evolution, chemical yields, ionizing photon budget, and final fate. We determined the projected rotational velocity, υ e sin i, of ~330 O-type objects, i.e. ~210 spectroscopic single stars and ~110 primaries in binary systems, in the Tarantula nebula or 30 Doradus (30 Dor) region. The observations were taken using VLT/FLAMES and constitute the largest homogeneous dataset of multi-epoch spectroscopy of O-type stars currently available. The most distinctive feature of the υ e sin i distributions of the presumed-single stars and primaries in 30 Dor is a low-velocity peak at around 100 km s^-1. Stellar winds are not expected to have spun-down the bulk of the stars significantly since their arrival on the main sequence and therefore the peak in the single star sample is likely to represent the outcome of the formation process. Whereas the spin distribution of presumed-single stars shows a well developed tail of stars rotating more rapidly than 300 km s^-1, the sample of primaries does not feature such a high-velocity tail. The tail of the presumed-single star distribution is attributed for the most part - and could potentially be completely due - to spun-up binary products that appear as single stars or that have merged. This would be consistent with the lack of such post-interaction products in the binary sample, that is expected to be dominated by pre-interaction systems. The peak in this distribution is broader and is shifted toward somewhat higher spin rates compared to the distribution of presumed-single stars. Systems displaying large radial velocity variations, typical for short period systems, appear mostly responsible for these differences.

Changes in phytoplankton composition in response to tides, wind-induced mixing conditions, and freshwater outflows in an urbanised estuarine complex

Estudos recentes na baía de Santos (sudeste do Brasil), localizada em um sistema estuarino altamente urbanizado, mostraram o aumento de espécies fitoplanctônicas potencialmente nocivas. Apesar da importância da previsão das florações algais nocivas, é difícil determinar a estrutura da comunidade fitoplanctônica em ambientes extremamente dinâmicos. O presente estudo analisa florações dominadas pelo microfitoplâncton e sua relação com variáveis físicas e meteorológicas, a fim de determinar padrões associados às marés e às estações do ano. Foram comparadas oito situações e obtidos cinco cenários de dominância relacionados aos ventos, marés e pluviosidade: i) Surfers, diatomáceas associadas à zona de surfe, de alta energia; ii) Sinkers, diatomáceas de tamanho grande que ocorrem nas marés de sizígia, depois de períodos de alta pluviosidade; iii) Opportunistic mixers, diatomáceas pequenas ou alongadas, formadoras de cadeia, que ocorrem durante períodos de quadratura; iv) Local mixers, diatomáceas e dinoflagelados microplanctônicos que foram abundantes em todas as 298 estações amostradas, e v) Mixotrophic dinoflagellates, que ocorrem após intensas descargas estuarinas. Os resultados sugerem uma alteração no padrão temporal de algumas espécies formadoras de florações, enquanto outras apresentaram abundâncias superiores aos valores seguros para a saúde publica. Esta abordagem ilustra também os possíveis impactos de variações na descarga de água doce em estuários altamente eutrofizados.

Managing the winds of change

Environmental impacts caused during Australia's comparatively recent settlement by Europeans are evident. Governments (both Commonwealth and States) have been largely responsible for requiring landholders – through leasehold development conditions and taxation concessions – to conduct clearing that is now perceived as damage. Most governments are now demanding resource protection. There is a measure of bewilderment (if not resentment) among landholders because of this change. The more populous States, where most overall damage has been done (i.e. Victoria and New South Wales), provide most support for attempts to stop development in other regions where there has been less damage. Queensland, i.e. the north-eastern quarter of the continent, has been relatively slow to develop. It also holds the largest and most diverse natural environments. Tree clearing is an unavoidable element of land development, whether to access and enhance native grasses for livestock or to allow for urban developments (with exotic tree plantings). The consequences in terms of regulations are particularly complex because of the dynamic nature of vegetation. The regulatory terms used in current legislation – such as 'Endangered' and 'Of concern' – depend on legally-defined, static baselines. Regrowth and fire damage are two obvious causes of change. A less obvious aspect is succession, where ecosystems change naturally over long timeframes. In the recent past, the Queensland Government encouraged extensive tree-clearing e.g. through the State Brigalow Development Scheme (mostly 1962 to 1975) which resulted in the removal of some 97% of the wide-ranging mature forests of Acacia harpophylla. At the same time, this government controls National Parks and other reservations (occupying some 4% of the State's 1.7 million km2 area) and also holds major World Heritage Areas (such as the Great Barrier Reef and the Wet Tropics Rainforest) promulgated under Commonwealth legislation. This is a highly prescriptive approach, where the community is directed on the one hand to develop (largely through lease conditions) and on the other to avoid development (largely by unusable reserves). Another approach to development and conservation is still possible in Queensland. For this to occur, however, a more workable and equitable solution than has been employed to date is needed, especially for the remote lands of this State. This must involve resident landholders, who have the capacity (through local knowledge, infrastructure and daily presence) to undertake most costeffectively sustainable land-use management (with suitable attention to ecosystems requiring special conservation effort), that is, provided they have the necessary direction, encouragement and incentive to do so.

Stars are made of glass : children as capable and creative communicators

This booklet is the third in the Research in Practice Series, designed to complement Belonging, being & becoming: The Early Years Learning Framework for Australia (DEEWR, 2009). It focuses on Learning Outcome 5 of the Early Years Learning Framework (EYLF): Children are effective communicators (DEEWR, 2009).

Winds of Change

Winds of Change is a short film that contrasts the Tragic Tale of Surachai by tracing the life of a rural Australian man who is left a quadriplegic after a near fatal motorcycle accident. The film highlights issues confronting people living with a disability and its impact on family. This film was developed to raise discussion amongst students studying social work and human services at Queensland University of Technology.

Infrared spectra of Mg-SiO smokes : comparison with analytical electron microscopy studies

An important component of current models for interstellar and circumstellar evolution is the infrared (IR)spectral data collected from stellar outflows around oxygen-rich stars and from the general interstellar medium [1]. IR spectra from these celestial bodies are usually interpreted as showing the general properties of sub-micron sized silicate grains [2]. Two major features at 10 and 20 microns are reasonably attributed to amorphous olivine or pyroxene (e.g. Mg2Si04 or MgSi03) on the basis of comparisons with natural standards and vapor condensed silicates [3-6]. In an attempt to define crystallisation rates for spectrally amorphous condensates, Nuth and Donn [5] annealed experimentally produced amorphous magnesium silicate smokes at 1000K. On analysing these smokes at various annealing times, Nuth and Donn [5] showed that changes in crystallinity measured by bulk X-ray diffraction occured at longer annealing times (days) than changes measured by IR spectra (a few hours). To better define the onset of crystallinity in these magnesium silicates, we have examined each annealed product using a JEOL 1OOCX analytical electron microscope (AEM). In addition, the development of chemical diversity with annealing has been monitored using energy dispersive spectroscopy of individual grains from areas <20nm in diameter. Furthermore, the crystallisation kinetics of these smokes under ambient, room temperature conditions have been examined using bulk and fourier transform infrared (FTIR)spectra.

Effect of overload cycles on thin steel roof claddings during cyclonic winds

During an investigation on thin steel roof claddings under simulated cyclonic wind loading, it was found that trapezoidal roof claddings behaved quite differently to corrugated (arc and tangent type) roof claddings due to the presence of overload cycles. The overload cycles caused a reduction in fatigue life for corrugated roofing whereas the reverse occurred for trapezoidal roofing. This contrasting behavior of the two crest-fixed roof claddings was investigated using small scale roofing models instead of the commonly used large scale two-span roof claddings. It was found that overload cycles formed a weaker locally dimpled mechanism around the fastener holes of corrugated roofing and thus accelerated the fatigue-caused pull-through failure. In contrast, a stronger deformed shape was formed in trapezoidal roofing which delayed the pull-through failure. Both laboratory testing and finite element analysis of small scale models were used to study the contrasting behavior of roof claddings.

Numerical simulation of downburst winds

The wind field of an intense idealised downburst wind storm has been studied using an axisymmetric, dry, non-hydrostatic numerical sub-cloud model. The downburst driving processes of evaporation and melting have been paramaterized by an imposed cooling source that triggers and sustains a downdraft. The simulated downburst exhibits many characteristics of observed full-scale downburst events, in particular the presence of a primary and counter rotating secondary ring vortex at the leading edge of the diverging front. The counter-rotating vortex is shown to significantly influence the development and structure of the outflow. Numerical forcing and environmental characteristics have been systematically varied to determine the influence on the outflow wind field. Normalised wind structure at the time of peak outflow intensity was generally shown to remain constant for all simulations. Enveloped velocity profiles considering the velocity structure throughout the entire storm event show much more scatter. Assessing the available kinetic energy within each simulated storm event, it is shown that the simulated downburst wind events had significantly less energy available for loading isolated structures when compared with atmospheric boundary layer winds. The discrepancy is shown to be particularly prevalent when wind speeds were integrated over heights representative of tall buildings. A similar analysis for available full scale measurements led to similar findings.

Idealised simulation of downburst winds

Convectively driven downburst winds pose a threat to structures and communities in many regions of Australia not subject to tropical cyclones. Extreme value analysis shows that for return periods of interest to engineering design these events produce higher gust wind speeds than synoptic scale windstorms. Despite this, comparatively little is known of the near ground wind structure of these potentially hazardous windstorms. With this in mind, a series of idealised three-dimensional numerical simulations were undertaken to investigate convective storm wind fields. A dry, non-hydrostatic, sub-cloud model with parameterisation of the microphysics was used. Simulations were run with a uniform 20 m horizontal grid resolution and a variable vertical resolution increasing from 1 m. A systematic grid resolution study showed further refinement did not alter the morphological structure of the outflow. Simulations were performed for stationary downbursts in a quiescent air field, stationary downbursts embedded within environmental boundary layer winds, and also translating downbursts embedded within environmental boundary layer winds.