A new method for an objective, χ2\chi^2-based spectroscopic analysis of early-type stars

A precise quantitative spectral analysis - encompassing atmospheric parameter and chemical elemental abundance determination - is time consuming due to its iterative nature and the multi-parameter space to be explored, especially when done "by eye". A robust automated fitting technique that is as trustworthy as traditional methods would allow for large samples of stars to be analyzed in a consistent manner in reasonable time. We present a semi-automated quantitative spectral analysis technique for early-type stars based on the concept of $\chi^2$ minimization. The method's main features are: far less subjective than typical "by eye" methods, correction for inaccurate continuum normalization, consideration of the whole useful spectral range, simultaneous sampling of the entire multi-parameter space (effective temperature, surface gravity, microturbulence, macroturbulence, projected rotational velocity, radial velocity, elemental abundances) to find the global best solution, applicable also to composite spectra. The method is fast, robust and reliable as seen from formal tests and from a comparison with previous analyses. Consistent quantitative spectral analyses of large samples of early-type stars can be performed quickly with very high accuracy.Comment: 32 pages, 4 figures, Astronomy and Astrophysics, accepte

Irradiation of an Accretion Disc by a Jet: General Properties and Implications for Spin Measurements of Black Holes

X-ray irradiation of the accretion disc leads to strong reflection features, which are then broadened and distorted by relativistic effects. We present a detailed, general relativistic approach to model this irradiation for different geometries of the primary X-ray source. These geometries include the standard point source on the rotational axis as well as more jet-like sources, which are radially elongated and accelerating. Incorporating this code in the relline model for relativistic line emission, the line shape for any configuration can be predicted. We study how different irradiation geometries affect the determination of the spin of the black hole. Broad emission lines are produced only for compact irradiating sources situated close to the black hole. This is the only case where the black hole spin can be unambiguously determined. In all other cases the line shape is narrower, which could either be explained by a low spin or an elongated source. We conclude that for all those cases and independent of the quality of the data, no unique solution for the spin exists and therefore only a lower limit of the spin value can be given.Comment: accepted by MNRAS for publication; now proof corrected Versio

Beobachtungen aktiver galaktischer Kerne von Radiowellen bis zu Gammastrahlen

In this work, Active Galactic Nuclei (AGN) - the brightest persistent objects in the universe - are discussed. According to current knowledge they consist out of several components. The central object of such systems is a supermassive black hole located in the center of a galaxy. Estimated masses of such black holes range from millions to billions of solar masses. The enormous gravitational field of the black hole affects material in its surrounding. Matter, such as gas, dust particles or stellar wind virtually provides the fuel for the AGN. The accretion process is highly efficient and partly explains the extreme luminosities of Active Galactic Nuclei. The thermal emission of the accretion disk is, however, insufficient for explaining the total emission of AGN. Observations show that some of these objects are visible throughout the complete electromagnetic spectrum. The emission in the radio regime as well as, most likely, high-energy emission seem to originate from jets. Unlike material accreted by the black hole, jets are collimated outflows with velocities near the speed of light. AGN are not completely understood. There are numerous open questions remaining, such as the exact accretion geometry, the formation and composition of the relativistic jets, the interaction between different components of these systems, as well as the place of origin and the underlying physical processes of the emission in different energy ranges. In order to address these questions a multiwavelength analysis of AGN has been performed in this work. The different energy regimes and observational techniques allow for insights into different processes and properties of such objects. A study of the connection between the accretion disk and properties of the jet has been done based on the object NGC 1052 using radio and X-ray observations. This object is a galaxy with an active nucleus. In the radio regime a double-sided jet with a projected length of several kpc is visible. In addition, the center of NGC 1052 hosts a clear X-ray source. The massive data set consists of numerous observations with different instruments allowing for detailed analyses. In the X-ray regime deep observations with sensitive telescopes are available, with which the distribution of X-ray emission within the host galaxy can be studied with high angular resolution. Furthermore the spectral properties can be analyzed in detail. Ths analysis allows one to draw conclusions on the environment of the supermassive black hole. Interferometric radio observations with long baselines yield angular resolutions higher than milliarcseconds. In this way it is possible to resolve structures in jets on scales of a tenth of a parsec. Within the scope of this work the available radio observations with this technique, which were performed between 1995 and 2012, were analyzed. With it, the temporal evolution of structures in the jet can be tracked and velocities can be determined. In addition, the typical intensity evolution of features in the jet could be determined. For a better understanding of AGN, studies of AGN samples complement analyses of individual sources. In this work the TANAMI and MOJAVE programs are described, as well as the thereby enabled studies. In both programs AGN samples are monitored with very-long-baseline-interferometry (VLBI). In these long-term studies it is possible to determine jet properties, such as the jet speed, and to compare them with observations in other energy regimes. Contributions to the TANAMI program have been done within the scope of this work, e.g., visualization methods for radio images have been developed. In the last section of this work, the gamma-ray properties of the AGN in the TANAMI and MOJAVE samples are discussed. Initially an overview on gamma-ray astronomy and the Fermi mission, which has been in operation since 2008, is given. Based on data obtained with Fermi-LAT, the properties of the objects in the sample in the energy range of 100 MeV to 100 GeV are analyzed. A comparison of radio and gamma-ray properties of the AGN confirms the assumption that gamma-rays in AGN originate from relativistic jets.In dieser Arbeit werden aktive galaktische Kerne - die hellsten Objekte mit dauerhafter Emission im Universum - behandelt. Nach aktuellem Wissensstand bestehen sie aus mehreren Komponenten. Das zentrale Objekt solcher Systeme ist ein supermassives schwarzes Loch, das sich im Zentrum einer Galaxie befindet. Abschätzungen der Masse von schwarzen Löchern dieser Art liegen im Bereich von Millionen bis zu mehreren Milliarden von Sonnenmassen. Das enorme Gravitationsfeld eines schwarzen Lochs wirkt auf Material in seiner Nähe, das gewissermaßen den Treibstoff des aktiven galaktischen Kerns darstellt. Der Akkretionsprozess, bei dem sich Material dem schwarzen Loch nähert und Energie abstrahlt, ist äußerst effizient und erklärt teilweise die extremen Leuchtkräfte aktiver galaktischer Kerne. Die erwartete thermische Emission einer Akkretionsscheibe reicht jedoch nicht aus, um die komplette Strahlung aktiver galaktischer Kerne zu erklären. Beobachtungen zeigen, dass manche dieser Objekte im kompletten elektromagnetischen Spektrum sichtbar sind. Der Ursprung der Emission im Radio- sowie vermutlich auch im Hochenergiebereich scheinen Jets zu sein. Es handelt sich dabei um gebündelte Teilchenstrahlen, die sich vom schwarzen Loch mit nahezu Lichtgeschwindigkeit entfernen. Aktive galaktische Kerne sind noch nicht komplett verstanden. Es gibt noch zahlreiche offene Fragen, wie zum Beispiel die exakte Akkretionsgeometrie, die Entstehung und Zusammensetzung der relativistischen Jets, die Wechselwirkungen zwischen den Bestandteilen dieser Systeme, sowie die genauen Ursprungsorte und die zugrundeliegenden physikalischen Prozesse der Emission in verschiedenen Energiebereichen. Um diese Fragen zu adressieren wird in dieser Arbeit eine Multiwellenlängenanalyse aktiver galaktischer Kerne durchgeführt. Die unterschiedlichen Energiebereiche und Beobachtungesmethoden erlauben Einblicke in verschiedene Prozesse und Eigenschaften dieser Objekte. Eine Studie des Zusammenhangs zwischen Akkretion und Eigenschaften des Jets erfolgt anhand der aktiven Galaxie NGC 1052 unter Verwendung von Radio- und Röntgenbeobachtungen. Im Radiobereich zeigt sich ein doppelseitiger Jet mit einer projizierten Länge von mehreren kpc. Zusätzlich befindet sich im Zentrum von NGC 1052 eine deutliche Röntgenquelle. Zahlreiche Beobachtungen dieser Quelle mit verschiedenen Instrumenten und erlauben detaillierte Analysen. Im Röntgenbereich sind dabei lange Beobachtungen mit empfindlichen Teleskopen verfügbar, mit welchen einerseits die Verteilung der Röntgenstrahlung innerhalb der Galaxie mit hoher Winkelauflösung und andererseits spektrale Details untersucht werden können. Diese Analyse erlaubt Rückschlüsse auf die Umgebung des supermassiven schwarzen Lochs. Interferometrische Radiobeobachtungen mit großen Entfernungen zwischen Teleskopen ermöglichen Winkelauflösungen, die feiner als Millibogensekunden sind. Damit ist es möglich, Strukturen im Jet auf Größenordnungen eines Zehntel Parsecs zu untersuchen. Im Rahmen dieser Arbeit wurden die verfügbaren Radiobeobachtungen dieser Art untersucht, die im Zeitraum von 1995 bis 2012 durchgeführt wurden. Es lässt sich damit die zeitliche Entwicklung der Strukturen im Jet verfolgen und deren Bewegungsgeschwindigkeit bestimmen. Zusätzlich konnte die typische Intensitätsentwicklung dieser Jetkomponenten auf ihrer Bewegung entlang der Jetachse bestimmt werden. Für ein besseres Verständnis aktiver galaktischer Kerne ergänzen Studien größerer Samples die Analysen individueller Quellen. In dieser Arbeit werden das TANAMI und das MOJAVE Programm erläutert, sowie die dadurch ermöglichten Studien. In beiden Programmen werden Auswahlen aktiver galaktischer Kerne mit Jets mit einer radiointerferometrischen Beobachtungskampagne untersucht. Mit diesen Langzeitstudien ist es möglich, Eigenschaften, wie etwa die Jetgeschwindigkeit, zu bestimmen und mit Beobachtungen in anderen Energiebereichen zu vergleichen. Diese Arbeit stellt einen wichtigen Beitrag zum TANAMI-Programm dar. Es wurden beispielsweise Visualisierungsmethoden für Radiobilder entwickelt. Im letzten Abschnitt der Arbeit werden die Gammastrahlungseigenschaften der aktiven galaktischen Kerne der TANAMI- und MOJAVE-Samples behandelt. Hierfür wird zunächst ein überblick über die Gammastrahlenastronomie und die Fermi-Mission, die seit 2008 in Betrieb ist, gegeben. Basierend auf Daten, die mit Fermi-LAT gemessen wurden, werden die Eigenschaften der Objekte in den Samples im Energiebereich von 100 MeV bis 100 GeV analysiert. Ein Vergleich der Radio- und Gammastrahlungseigenschaften der AGN unterstützt die Vermutung, dass die Gammastrahlung in AGN ihren Ursprung in relativisitischen Jets hat

Corporate social responsibility earnings management and corporate financial performance

This paper examines the relation of corporate social responsibility (CSR) with two types of earnings management (EM) measures, accrual based (AEM) and real earnings management (REM) of companies in Europe. Additionally, the moderating role of EM in the relationship between CSR and corporate financial performance (CFP) is investigated. I employ a European panel dataset for the period 2008 - 2019, consisting of 3,729 firm-year observations of companies in the STOXX Europe 600 Index, as well as smaller European companies. Using the so-called Environmental, Social and Governance (ESG) factors, provided by the Asset4 database of Thomson Reuters, are used to measure CSR, I find that higher ESG scores lead to significantly lower AEM and REM. Dividing the ESG score in its three pillar scores, the results show that social performance decreases both AEM and REM. Contrary corporate governance performance has a significant positive impact on REM and no effect on AEM. Moreover, I find that in this setting, AEM decreases the magnitude of the relationship between CSR and CFP in the short- and medium-term. REM decreases the positive impact of CSR and CFP in the short-term, however demonstrates the opposite in the medium-term, implying that REM increases the positive effect of CSR on CFP.Este documento examina a relação da responsabilidade social das empresas (CSR) com dois tipos de medidas de gestão de lucros (EM), a gestão baseada na acumulação (AEM) e a gestão de lucros reais (REM) das empresas na Europa. Além disso, é investigado o papel moderador da EM na relação entre a CSR e o desempenho financeiro das empresas (CFP). Utilizo um conjunto de dados de painel europeu para o período 2008 - 2019, constituído por 3.729 observações de empresas no índice STOXX Europe 600, bem como de empresas europeias mais pequenas. Utilizando os chamados factores ambientais, sociais e de governação (ESG), fornecidos pela base de dados Asset4 da Thomson Reuters, são utilizados para medir a CSR, constato que pontuações mais elevadas dos ESG levam a AEM e REM significativamente mais baixas. Dividindo a pontuação do ESG nas suas pontuações dos três pilares, os resultados mostram que o desempenho social diminui tanto o AEM como o REM. O desempenho contrário da governação empresarial tem um impacto positivo significativo sobre a REM e nenhum efeito sobre a AEM. Além disso, constato que neste contexto, a AEM diminui a magnitude da relação entre a CSR e a CFP a curto e médio prazo. A REM diminui o impacto positivo da CSR e da CFP a curto prazo, mas demonstra o contrário a médio prazo, o que implica que a REM aumenta o efeito positivo da CSR sobre a CFP

Multi-Satellite Observations of Cygnus X-1 to Study the Focused Wind and Absorption Dips

High-mass X-ray binary systems are powered by the stellar wind of their donor stars. The X-ray state of Cygnus X-1 is correlated with the properties of the wind which defines the environment of mass accretion. Chandra-HETGS observations close to orbital phase 0 allow for an analysis of the photoionzed stellar wind at high resolution, but because of the strong variability due to soft X-ray absorption dips, simultaneous multi-satellite observations are required to track and understand the continuum, too. Besides an earlier joint Chandra and RXTE observation, we present first results from a recent campaign which represents the best broad-band spectrum of Cyg X-1 ever achieved: On 2008 April 18/19 we observed this source with XMM-Newton, Chandra, Suzaku, RXTE, INTEGRAL, Swift, and AGILE in X-and γ-rays, as well as with VLA in the radio. After superior conjunction of the black hole, we detect soft X-ray absorption dips likely due to clumps in the focused wind covering ≥ 95 % of the X-ray source, with column densities likely to be of several 10 23 cm −2 , which also affect photon energies above 20 keV via Compton scattering