Time-dependent, long-term hydrodynamic simulations of the inner protoplanetary disk II: The importance of stellar rotation

The spin evolution of young protostars, surrounded by an accretion disk, still poses problems for observations and theoretical models. In recent studies, the importance of the magnetic star-disk interaction for stellar spin evolution has been elaborated. The accretion disk in these studies, however, is only represented by a simplified model and important features are not considered. We combined the implicit hydrodynamic TAPIR disk code with a stellar spin evolution model. The influence of stellar magnetic fields on the disk dynamics, the radial position of the inner disk radius, as well as the influence of stellar rotation on the disk were calculated self-consistently. Within a defined parameter space, we can reproduce the majority of fast and slow rotating stars observed in young stellar clusters. Additionally, the back reaction of different stellar spin evolutionary tracks on the disk can be analyzed. Disks around fast rotating stars are located closer to the star. Consequently, the disk midplane temperature in the innermost disk region increases significantly compared to slow rotating stars. We can show the effects of stellar rotation on episodic accretion outbursts. The higher temperatures of disks around fast rotating stars result in more outbursts and a longer outbursting period over the disk lifetime. The combination of a long-term hydrodynamic disk and a stellar spin evolution model allows the inclusion of previously unconsidered effects such as the back-reaction of stellar rotation on the long-term disk evolution and the occurrence of accretion outbursts. However, a wider parameter range has to be studied to further investigate these effects. Additionally, a possible interaction between our model and a more realistic stellar evolution code (e.g., the MESA code) can improve our understanding of the stellar spin evolution and its effects on the pre-main sequence star.Comment: 12 pages, 7 figures, accepted by Astronomy & Astrophysic

Effects of the disk’s gravitational potential on the structure and long-term evolution of protoplanetary disks

Protoplanetare Scheiben gelten als mögliche Lösung des Drehimpulsproblems und werden meist mittels expliziter, numerischer Verfahren simuliert. Für diese expliziten Verfahren gelten jedoch spezielle Einschränkungen. Daher verspricht die implizite Berechnung protoplanetarer Scheiben auf einem adaptiven Gitter, neue Erkenntnisse in der Struktur und Evolution der Scheiben zu liefern. Der TAPIR-code löst die Gleichungen der Radiation-Hydrodynamic (RHD), unter der Annahme einer vernachlässigbaren Scheibenmasse. Daher hat das gravitative Potential der Scheibe keinen Einfluss auf ihre Struktur und ihre zeitliche Entwicklung. Ziel dieser Arbeit ist es, den Einfluss der Scheibenmasse zu dem bestehenden Model hinzuzufügen, indem das gravitative Eigenpotenzial einer dünnen Scheibe für eine beliebige Dichteverteilung in des bestehende Model implementiert wird. In weiterer Folge soll die Auswirkung des Eigenpotenzials auf die Scheibe untersucht werden. Ausgehend von der allgemeinen Lösung der Poisson-Gleichung, wird das Potenzial in radialer Richtung unter der Annahme einer dünnen, symmetrischen Scheibe mittels kompletter elliptischer Integrale beschrieben. Dank der Finiten Volumens Methode lässt sich das Potenzial sowie dessen Gradient in eine Summe umschreiben, die numerisch leicht zu berechnen ist. In vertikaler Richtung wird der Einfluss des Potenzials auf die Skalenhöhe beschrieben. Ein Vergleich der gravitativen Beschleunigung des Sterns und der Scheibe liefert schließlich ein Kriterium $Q_{\rm SG}$, das veranschaulichen soll, ab wann der Einfluss der Eigengravitation der Scheibe zu berücksichtigen ist. Das resultierende Potenzial kann sowohl durch die Berechnung der Gravitationsenergie, überprüfen der Massenerhaltung sowie weitere Tests verifiziert werden. Anschließend werden für verschiedene Werte von $Q_{\rm SG}$ die Scheibenstruktur und die zeitliche Entwicklung, mit und ohne Eigenpotenzial, verglichen. Die Ergebnisse legen nahe, dass für schwerer werdende Scheiben die Scheibengravitation eine immer größere Rolle spielt. Erhöht sich die Masse einer Scheibe bis zu dem Punkt, an dem der Wert von $Q_{\rm SG}$ in einem Bereich der Scheibe unter $1$ liegt, lassen sich erhebliche Unterschiede in der Struktur und der zeitlichen Entwicklung der Scheibe feststellen. Für eine geringe Scheibenmasse und somit einem hohen $Q_{\rm SG}$, kann die Scheibengravitation vernachlässigt werden

The Rise of Fund Managers in Foreign Exchange

This Paper analyses the behaviour and motivation of fund managers in foreign exchange markets reflected in questionnaire evidence. We find that fund managers and FX dealers differ significantly. Fund managers rely more on fundamentals, basically due to their longer forecasting horizons, and reject non-fundamental influences on exchange rates more than FX dealers. Neither can fund managers be considered as pure fundamentalists, however. Non-fundamentalist positions markedly influence short-term decision-making. They inspire ambivalent views about market imperfections and these views seem to become stronger over time. This latter change counterbalances the strengthening fundamental influences resulting from the rise of fund managers.foreign exchange; fund management; fundamentals; market microstructure

The Use of Flow Analysis in Foreign Exchange: Explanatory Analysis

This Paper provides questionnaire evidence on the role of flow analysis for professional traders and fund managers. This evidence suggests that besides fundamental information and technical analysis, the analysis of flows provides an independent third type of information for professionals. The proposition that flows can be used to learn about fundamentals is not consistent with the data. Instead, evidence indicates that flows more likely provide insight into semi-fundamental private information, suggesting support for the efficient market hypothesis only in a weak form.flow trading; foreign exchange markets; market microstructure

The use of flow analysis in foreign exchange: exploratory evidence

This paper provides questionnaire evidence on the role of flow analysis for professional traders and fund managers. This evidence suggests that besides fundamental information and technical analysis, the analysis of flows provides an independent third type of information for professionals. The view that flows can be used to learn about fundamentals is not consistent with the data. Instead, evidence indicates that flows more likely provide insight into semi-fundamental private information.foreign exchange markets, flow trading, market microstructure

Technical Analysis in Foreign Exchange - The Workhorse Gains Further Ground

This work extends earlier survey studies on the use of technical analysis by considering flow analysis as a third form of information production. Moreover the survey covers FX dealers and also the rising fund managers. Technical analysis has gained importance over time and is now the most equally spread kind of analysis. It has by far the greatest importance in FX dealing and is second in fund management. Charts are used for shorter-term forecasting horizons while flows dominate at the shortest-term and fundamentals at longer horizons. Preferred users of each kind of analysis exhibit different views about market frictions.foreign exchange markets, technical analysis, flow analysis, fundamentals, fund managers

The Rise of Fund Managers in Foreign Exchange: Will Fundamentals Ultimately Dominate?

This paper analyzes the behaviour and motivation of fund managers in foreign exchange markets reflected in questionnaire evidence. We find that fund managers and FX dealers differ significantly. Fund managers rely more on fundamentals, basically due to their longer forecasting horizons, and reject non-fundamental influences on exchange rates more than FX dealers. However, neither can fund managers be considered as pure fundamentalists. Non-fundamentalist positions markedly influence short-term decision-making. They inspire ambivalent views about market imperfections and these views seem to become stronger over time. This latter change counterbalances the strengthening fundamental influences resulting from the rise of fund managers.foreign exchange, market microstructure, fund management, fundamentals