2018 Abstracts

2018 Abstracts

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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