2018 Abstracts

2018 Abstracts

Dr Jeffrey Simpson

Title: The GALAH survey: Co-orbiting stars and chemical tagging

Abstract: This is a study using the second data release of the GALAH survey of stellar parameters and elemental abundances of 15 pairs of stars identified as potentially co-moving pairs using proper motions and parallaxes from Gaia DR1. We find that nine very wide (>1.7 pc) pairs of stars do in fact have similar Galactic orbits, while a further six claimed co-moving pairs are not truly co-orbiting. Six of the nine co-orbiting pairs have reliable stellar parameters and abundances, and we find that three of them are quite similar in their abundance patterns, while three have significant [Fe/H] differences.

Prof Geoffrey Clayton

Title: Is the Earth Flat?

Abstract: You may ask why I am asking a question with such an obvious answer, but a few minutes on Google will demonstrate that the Flat Earth Society is still going strong. Rappers, professional athletes, and lots of youtube videos argue that the Earth is indeed Flat. This is the ultimate Conspiracy Theory, and in the post-truth era the Flat Earth is doing very well. It is very important for us as scientists, during classes and outreach activities, to meet this conspiracy theory head-on and be able to give clear explanations showing that, yes, the Earth is round. Come to this talk with your favourite proof that the Earth is Round. I will give a few examples of my own.

Ms Anke Arentsen

Title: Extremely metal-poor (carbon-enhanced) stars as probes of the Early Universe

Abstract: Our Milky Way still hosts remnants from the era of first star formation in the form of extremely metal-poor stars, which we can study in detail. The chemical compositions of these stars give indirect insight into the properties of the very first generation of stars. In the first part of my talk I will discuss recent results of the Pristine survey, which is a photometric survey aiming to significantly extend the number of known extremely metal-poor stars in our Galaxy. In this talk I will focus mainly on the Galactic Bulge program within the Pristine survey. In the second part of my talk I will focus on a sub-class of extremely metal-poor stars, the carbon-enhanced metal-poor (CEMP) stars. The fraction of stars enhanced in carbon increases dramatically at the lowest metallicities, and these CEMP stars can place additional constraints on the properties of the first generation of stars. I will discuss recent findings from our radial velocity monitoring program of CEMP-no stars, where we have found an interesting relation between the binarity of these stars and their absolute carbon abundance.

Dr Chris Gordon

Title: "Is the Galactic Bulge Shining in Gamma Rays?"

Abstract: "Data from the Fermi Large Area Telescope indicates that there is an extended source of GeV gamma-ray photons coming from the Galactic Centre. Initially, it was thought that this could be due to self-annihilating dark matter. However, recent work shows that the spatial morphology better matches the shape of the Galactic bulge rather than a spherically symmetric shape that would be expected from a dark matter signal. I will discuss this result and also give details on the evidence that the source of the excess is due to an unresolved population of millisecond pulsars."

Dr. Farhad Yusef-Zadeh

Title: The Interaction of Cosmic Rays with Molecular Clouds in the Galactic Center

Abstract: The ISM in the inner few hundred pc of the Galactic center differs from elsewhere in the Galaxy. This region is centered on a 4 million supermassive black hole and is occupied by a large concentration of molecular gas with high column density, high velocity dispersion and high gas temperature. Recent IR and X-ray observations indicate that the cosmic ray ionization rate is higher than elsewhere in the Galaxy by one to two orders of magnitudes.

The interaction of an enhanced cosmic-ray flux with molecular clouds in this region explains a number of observations: i) the ubiquitous warm molecular gas observed throughout the Galactic center, ii) the power law spectrum of GeV emission, iii) FeI Kalpha emission at 6.4 keV and iv) the unusual chemistry of molecular gas, as probed by a number of molecular tracers. In this picture, relativistic bremsstrahlung radiation explains the origin of diffuse gamma-ray and 6.4 keV line emission from the Galactic center region.

Dr Andrew Lehmann

Title: High velocity shock waves in extragalactic turbulent cold gas

Abstract: The formation and evolution of galaxies is determined by the processes regulating the conversion of cold molecular gas into stars. In this talk I summarise the MIST project (Molecules, magnetic fields and Intermittence in coSmic Turbulence) , a european effort to study these processes inspired by surprising ALMA observations of CH+ emission and absorption in a sample of high-z starburst galaxies. I will also outline my place in the project which includes extending the Paris-Durham public code, a state-of-the-art magnetised shock model, to higher velocities (>30 km/s). This will allow us to more accurately predict the molecular emission from the distribution of shocks expected to be present in turbulent reservoirs  of cold gas.

Dr Gayandhi De Silva

Title: Galactic Archaeology with HERMES: open clusters and stellar streams.

Abstract: The GALAH survey is a pioneering survey that is exploring the motions and detailed chemical compositions of 1 million stars in the Milky Way. Closely related to this is the HERMES Open cluster program, collecting uniform high resolution, high signal to noise data for open clusters spanning a large range in age, metallicity and distance. In this presentation I will give an overview of the developments in Galactic Archaeology, the current status and results with a snap shot of science from these surveys.

Dr Valentina Baccetti

Title: Information loss paradox and the effects of black hole radiation.

Abstract: Event horizons are the defining feature of classical black holes. They are the key ingredient of the information loss paradox which, as paradoxes in quantum foundations, is built on a combination of predictions of quantum theory and counterfactual classical features. Within the semi-classical theory we investigate the possibility that black hole radiation still does not allow for a finite time crossing of the Schwarzschild radius of collapsing matter as seen by distant observers. The exact form of the pre-Hawking radiation is not yet settled, and we make only minimal assumptions about its nature

Dr Yang Huang

Title: The LAMOST Galactic Spectroscopic Surveys

Abstract: One of the fundamental tasks of modern astrophysics is to understand how galaxies form and evolve. Generally, the quest can be pursed in two ways: statistical analyses of large samples of distant galaxies (deep-field cosmology) and detailed studies of large samples of member stars in the Local Group of galaxies including our own, the Milky Way (near-field cosmology). Initiated and aimed to make a major contribution to this latter, ‘near-field cosmology’ quest for understanding the galaxy formation and evolution, the LAMOST Galactic Spectroscopic Surveys have hitherto collected quality spectra of over 7M Galactic stars, and this number is still increasing at a rate of 1M per annum. Combining with data from other available photometric, astrometric and spectroscopic surveys (e.g. Gaia, APOGEE, GALAH), the Surveys have yielded a unique dataset to help us draw an exquisite picture of unprecedented detail of our Galaxy, in particular of the Galactic disk. In this talk, I will present the scope and motivation, data reduction and release, as well as scientific results of the surveys.

Dr Simon Murphy

Title: An exciting haul of planetary, binary and triple systems from pulsation timing
Abstract: The orbital parameters of binary stars at intermediate periods (100-1000 d) are difficult to measure with conventional methods and are very incomplete. For the past couple of years I’ve been developing a method that uses stellar pulsations to determine the orbital parameters of binary stars, which is particularly suited to intermediate periods and can detect objects down to planetary masses. It has tripled the number of intermediate-mass stars with fully solved binary orbits. The detected companions include planets, brown dwarfs, and main sequence stars with masses between 0.1 and 2.5 Msun; over 20% are white dwarfs in blue straggler systems, and a few companions could be neutron stars or black holes. Some systems are clear triples, and many will become Type Ia supernovae and related phenomena. Statistically robust mass-ratio and eccentricity distributions will be presented, and I will explain what they tell us about binary star formation.

Dr Adriano Poci

Title: The Chemical and Dynamical Composition of NGC 3115
Abstract: The formation history of a galaxy is the integration of all dynamical and chemical processes over its lifetime. Typically, models of galactic dynamics and stellar populations are considered independently from one another, while in reality they are intimately connected facets of galaxy formation.
We exploit remarkable new spatially-resolved data from the MUSE integral-field unit to conduct a combined dynamics/stellar-populations analysis of the nearby S0 galaxy NGC3115, in order to infer its true formation history. I will present the detailed models that go into this analysis - namely the fully general, triaxial Schwarzschild orbit-based dynamical models, and full-spectral-fitting star-formation histories, as well as how we combine these two concepts to uncover the assembly history of this galaxy.

Dr Christopher Usher

Title: Using Globular Cluster Stellar Populations to Understand Galaxy Formation
Abstract: Globular clusters are important tools to help us understand how galaxies form and evolve. Globular cluster formation tells us about the conditions of extreme star formation while their survival from high redshift tell us about the processes of galaxy assembly. Being much brighter than red giant stars, globular clusters allow the stellar populations of galaxies to be studied at much greater distances. Thus a wider range of galaxy masses, environments and morphologies to be studied than can be with resolved stars. Using data from the WAGGS survey of massive star clusters in the Milky Way and its satellite galaxies and the SLUGGS survey of the globular cluster systems of massive early-type galaixes, I will talk about how we can measure the metallicities of globular clusters using the strength of the calcium triplet in integrated light. Using globular cluster metallicity distributions and the relationships between globular cluster colour and metallicity, I will present evidence that different galaxies with similar masses experienced different formation histories. I will compare these observations with the predictions of the E-MOSAICS cosmological simulations of the formation of globular cluster systems. I will also talk about how the E-MOSAICS simulations have allowed to us to understand how globular cluster colour distributions vary with globular cluster luminosity (the 'blue tilt').

Dr Chris Tout

Title: Highly Magnetic White Dwarfs and other Stars
Abstract: White dwarfs with surface magnetic fields in excess of 1MG are found as isolated single stars and relatively more often in magnetic cataclysmic variables.  Some 1,253 white dwarfs with a detached low-mass main-sequence companion are identified in the Sloan Digital Sky Survey but none of these is observed to show evidence for Zeeman splitting of hydrogen lines associated with a magnetic field in excess of 1MG.  If such high magnetic fields on white dwarfs result from the isolated evolution of a single star then there should be the same fraction of high field white dwarfs among this SDSS binary sample as among single stars.  Thus we deduce that the origin of such high magnetic fields must be intimately tied to the formation of cataclysmic variables.  The formation of a CV must involve orbital shrinkage from giant star to main-sequence star dimensions.  It is believed that this shrinkage occurs as the low-mass companion and the white dwarf spiral together inside a common envelope.  CVs emerge as very close but detached binary stars that are then brought together by magnetic braking or gravitational radiation.  We propose that the smaller the orbital separation at the end of the common envelope phase, the stronger the magnetic field and investigate simple dynamo models for which this is a natural outcome.

Jielai Zhang

Title: Exploring the low surface brightness Universe with the Dragonfly Telephoto Array
Abstract: The low surface brightness Universe is largely unexplored. The limiting factors for low surface brightness observations are not photon statistics or image resolution, instead they are systematic factors such as a telescope s internal reflections, sky subtraction, flat fielding and the wide-angle point-spread-function. The Dragonfly Telephoto Array addresses these factors by a combination of hardware and software. The telescope consists of 48 commercial Canon telephoto lenses, and is able to see low surface brightness structures about 10 times fainter than previously possible with its 2.4 x 3.2 degree wide field of view. I will describe the technology behind Dragonfly, and how I and my team have used it to discover enormous stellar disks, properties of interstellar dust and ultra-diffuse-galaxies .

Dr Stuart Ryder

Title: Binary companions to stripped-envelope supernovae
Abstract: The classes of Type, Ib, and Ic core-collapse supernovae appear to represent progressively greater stripping of the progenitor star's outer envelope prior to explosion, but it is unclear how much of this stripping is due to stellar winds and mass-loss, or to interaction with a massive binary companion. We have used the Hubble Space Telescope to search for surviving binary companions to nearby stripped-envelope supernovae in the ultraviolet. I will describe our results for the broad-lined Type Ic SN 2002ap, and for the Type IIb SN 2001ig.

Dr Rubina Kotak

Title: Faint and fast, bright and long-lived transient: what are they telling us?
Abstract: One of the main challenges of current supernova research is to identify the nature of stars that explode, and to link this knowledge to observed supernova properties. Nowhere is this problem more urgent than the most massive stars in the local and the distant Universe. Recent exciting results have challenged currently accepted paradigms of stellar evolution, and for these supernovae, ever more exotic scenarios are being proposed. I will discuss a few special cases with the currently-accepted framework that highlight gaps in our knowledge.

Dr Themiya Nanayakkara

Title: Hunting for the first star I: Attempts to demystify He II with MUSE
Abstract: In the request for identifying pop-III stars, the most sought-after emission line is He II, however, stellar population models are unable to accurately predict the He II features while being consistent with other emission line diagnostics. To produce He II ionizing photons, stellar populations require sources of heard ionizing radiation with energies >= 54.4 eV and sources as AGN, shocks, X-Ray binaries, stellar rotation and /or binary stellar evolution, and post-AGB stars have been suggested as possible contributors.  To accurately identify relative contributions from these with wide variety of sources, high signal-to-noise spectra with rest-frame UV/optical coverage and advanced stellar population/photoionization models are required.

The VLT/MUSE GTO program has obtained deep 10-30h exposures of Hubble legacy fields yielding rest-UV spectra of galaxies at z≈2-6. In this talk I will represent recent results of the MUSE program and compare the z≈2-4 He II emitters with expectations from photoionization modelling to explore their stellar population and ISM conditions. I will address the necessity to obtain high signal-to-noise spectra of individual galaxies to model rest UV emission and absorption systems along with auxiliary rest-NIR lines to constrain stellar population properties of galaxies at high-z, which will be aided by combined studies by MUSE and JWST in future. I will further briefly discuss the prospects of observing population IIII systems in the early universe.

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