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- 26.04., Mark Kennedy (U Cork): Invisible Monsters and Spider Webs
Abstract: Where is the missing Galactic population of black holes? How do we obtain precise and accurate masses for black holes and neutron stars in our galaxy? These are two of the most pressing questions in astrophysics, and ones which the enormous databases produced by telescopes such as GAIA, the Zwicky Transient Factory (ZTF), and the upcoming Vera Rubin Observatory can help us answer. During this talk, I will discuss where I believe an answer to the missing black hole population may be found. This involves combining data taken by GAIA and ZTF and applying machine learning techniques to find light curves which challenge our understanding of binary classification. I will also highlight the many challenges, pitfalls, and rabbit holes that can be encountered when dealing with these large data sets. I will also give a summary of how the masses of invisible companions can be estimated in these types of binaries, with a focus on some interesting recent results and advances in how the companions in these systems are being modelled.
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- 03.05. Jordan Simpson (IFY, NTNU): Cataclysmic variables with HiPERCAM
Abstract: Cataclysmic variables (CVs) are close interacting binary systems consisting of a white dwarf star (primary) accreting matter from a low-mass companion (secondary). As the end-state of many main sequence binaries, and potential progenitors to Type Ia supernovae, CVs form a crucial stage in the evolution of a wide variety of systems. The classical theory of CV evolution has persisted for over 40 years, despite its continuing failures to explain observations. Recently, a new empirical model has emerged that potentially explains many issues in CV evolution - however, a physical basis for this model is still needed. Using the ultra-fast quintuple-band imager HiPERCAM, along with advanced modelling techniques, the team at Sheffield (and collaborators) measures CVs with unprecedented precision to test this new model and ultimately resolve the long-standing problems in CV evolution once and for all.
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- 14.6., Kari Koljonen (IFY, NTNU): The origin of optical emission lines in the soft state of X-ray binary outbursts
Abstract: The optical emission line spectra of X-ray binaries are thought to be produced in an irradiated atmosphere, potentially the base of a wind, positioned above the outer accretion disc. However, the physical nature and conditions of the region that forms these lines are not well understood. In this presentation, I will discuss our study of X-ray binary MAXI J1820+070 in the soft state associated with its 2018 outburst. We modeled a line-rich, soft state, broadband spectrum using the X-Shooter instrument at the Very Large Telescope, with a Monte Carlo radiative transfer code that employed a simple biconical disc wind model. This model was inspired by radiation-hydrodynamic simulations of irradiation-driven outflows from X-ray binary discs. I will demonstrate that such a model can qualitatively replicate the observed features and that almost all of the optical emission in the model arises from the transonic "transition region" between the disc atmosphere and a thermally-driven wind. Our research shows that this transition region can be the source of the abundant optical lines seen in the soft state spectra of X-ray binaries during outburst events. These "wind bases" can also have a significant effect on the infrared-to-ultraviolet continua, and can even dominate the emission in the red part of the spectrum. Overall, the strong irradiation of the outer disc by the inner accretion flow can naturally create both the optical line-forming layer and an overlying outflow/atmosphere that generates X-ray absorption lines that are typically observed during the bright soft states of X-ray binary outbursts.
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- summer break
- 28.08.. Vittoria Vecchiotti (IFY, NTNU): H....
Abstract: C....
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