Dr Clare Dobbs (Exeter University) - ARC seminar Wednesday 23RD May 2018 3pm
I will present results from both recent simulations and observations of molecular clouds in spiral galaxies. I will focus on the importance of stellar feedback and galaxtic structure. I will discuss the role of feedback in controlling molecular cloud evolution and the overall star formation rate in galaxies. I will also show results on molecular cloud lifetimes, and what determines cloud lifetimes. The relevance of galactic spiral structure to molecular cloud properties has long been unclear. Both simulations and observations indicate that cloud properties vary between arm and inter-arm regions. The exact nature of spiral arms does not have a huge effect on molecular clouds and star formation, although tidally induced galaxies tend to exhibit more massive GMCs which has a disproportionate effect on the star formation rate.
Dr Farzana Meru (Warwick university) - ARC Seminar Wed 18th April 2018 3pm
We have recently entered an era of high resolution, spatially resolved observations of protoplanetary discs, which are revealing exciting disc structures. Such structures give us clues on the protoplanetary disc and planet formation processes. I will discuss some of the causes of spirals, rings, gaps and asymmetries in protoplanetary discs. I will also discuss the possible processes that are causing the spirals in the Elias 2-27 disc, and will show how we might observationally determine if a planet is migrating.
Prof Melvyn B.Davies (Lund Observatory) - ARC Seminar on Wed., 2018 Feb 21st/ 15h
Stellar clusters are common. Globular clusters contain some of the oldest stars, whilst the youngest stars are found in OB associations or in other clusters associated with recent star formation. Such crowded places are hostile environments: a large fraction of stars will collide or undergo close encounters. I will explain how stellar clusters are factories for producing exotic objects, including back hole binaries which spiral together and merge as they emit gravitational waves. I will consider how supermassive black holes may form and grow within the nuclear stellar clusters located at the very centres of galaxies. I will also discuss how planetary systems similar to our own solar system are vulnerable within stellar clusters due to interactions with other stars. Thus by studying stellar clusters we will learn more about the rarity of planetary systems similar to our own solar system.
Dr Stephen Wilkins (Sussex University) - Arc Seminar on Wed., 2018 Feb 7th/ 15h
Understanding the early phase of galaxy formation and evolution is one of the key goals of modern extragalactic astronomy and one key drivers of upcoming observational facilities. This critical phase of the Universe's history began with the formation of the first stars and super-massive black holes (SMBHs) some few hundred million years after the recombination, bringing an end to the cosmological dark ages. Over the subsequent billion years (the epoch of reionisation, EoR) the intense radiation produced by these galaxies likely drove the reionisation of the Universe. The first generations of stars to form in these galaxies enriched their surroundings with heavy elements, resulting in the transition from (metal-free) population III to population II star formation and laying the foundations for subsequent chemical evolution of the Universe.
Thanks to the Hubble Space Telescope, ALMA, and other facilities along with advances in numerical simulations significant progress in understanding this period of the Universe’s history has been made in the last few years. In this talk I’ll outline some of this recent progress and discuss prospects for the future, and in particular what we expect to learn from JWST.
Professor Andrea Ferarra (Uni. of Pisa) - ARC Seminar on Wed., 2017 Dec. 6th/ 15h
In the last decade we have explored the cosmic depths and found a statistically significant number of galaxies well into the Epoch of Reionization. However, our physical knowledge of these pristine objects remains very scant. Investigating the internal structure, interstellar medium and evolution of early galaxies is the next challenge to understand key processes as the cosmic history of baryons, feedback, reionization and metal enrichment of the intergalactic medium, This ambitious plan can be tackled by combining a new generation of physically-rich, high resolution, zoom simulations with data in the sub-mm bands provided by ALMA. This approach will be soon strengthened by the forthcoming JWST power. I will review the present status and the open questions in the field.
Dr. Jason Sanders (IoA) - ARC Seminar on Wed., 2017 Nov. 15th/ 15h
Cosmological simulations predict that massive dark-matter haloes are home to a spectrum of smaller, less massive haloes. Gaining access to these low mass haloes will give important clues to the fundamental nature of dark matter but is only possible through observations of baryonic tracers. I will discuss two different tracers that will shed some light on the properties of the Local Group’s subhalo population. First, tidal streams are sensitive to close encounters with dark matter subhaloes. I will discuss recent progress in the modelling of tidal streams, how gaps in streams caused by subhaloes can be efficiently modelled and the current constraints from data. Secondly, many of the larger subhaloes are expected to be the hosts of the dwarf spheroidal (dSph) galaxies in the Local Group. I will discuss recent results on the shapes and alignments of the Local Group dSph population.
Stephanie Merritt (QUB) - ARC Seminar on Wed., 2017 Oct 25th/ 15h
In recent years, the atmospheres of so-called “hot Jupiter” exoplanets have astounded us with their variety. Various detection methods have unearthed a trove of atomic and molecular species in their atmospheres, along with the discovery of cloud decks and hazes. However, one component thought to exist in the atmospheres of hot Jupiters has, until recently, eluded us: the temperature inversion. In the most irradiated of these planets, metal hydrides such as TiO and VO are thought to exist in gaseous form, and these remarkably efficient optical absorbers cause the temperature to heat up in upper layers of the atmosphere. Recent work has only just begun to uncover evidence of these inversions. Using a technique called Doppler spectroscopy, which takes advantage of the planet's much greater radial velocity (and thus Doppler shift) to disentangle planetary spectral lines from those of the parent star, this work hopes to find an unambiguous detection of TiO in the atmosphere of WASP-121b, the first such detection of its kind.
Dr. Stefano Antonellini (QUB) - ARC Seminar on Wed., 2017 Oct. 4/15h
Protoplanetary disks are the places in which planets form around young stars. These environments consist of dust and gas mainly in forms of molecules. Water is an abundant molecule with a rich spectroscopy in the entire IR spectral regime. It can be used to probe local gas physical conditions from the inner through the outer disk. Observations of water show often non-detections for still unclear reasons. With this thesis we suggest an explanation based on the physical properties of individual protoplanetary disks, their central star and mid-IR dust spectral features. Finally we investigate the hidden reservoirs of water and other species frozen in the coldest regions of the disk. We conclude that opacity due to the dust is one of the main causes for the suppression of IR water lines in disks, then disks around more luminous stars should have stronger mid-IR water lines. We also found possible traces of planet formation going on in several disks with strong mid-IR water line fluxes. Finally, we present additional work in progress related to CO, another volatile abundant in disks, and with a great diagnostic power.
Ondřej Procházka (QUB) - ARC Seminar on Wed., 2017 May. 17 / 15h
White-light flares are a class of flares with an optical counterpart. Such events are known since 1859, but there are only few spectral observations in visible and near-UV range where we can observe higher order Balmer lines and Balmer jump. In order to observe WL flares, we developed a post-focal instrument that treats an issue with a low contrast and providing a very high temporal resolution. In June 2014 we observed three X-class flares with very distinctive spectral features. All events were produced in the same active region in only 24 hours. As supporting observations from X-ray satellites didn’t provide an answer on what the beam parameters were, we had to employ radiative hydrodynamic models. Modelling work suggests that for extraordinarily high value of low energy cut-off, a layer of unaffected atmosphere is formed in upper chromosphere, which forbids us to see commonly observed lines emission.
Dr. Pier-Emmanuel Tremblay (Warwick) - ARC Seminar on Wed., 2017 May. 10 / 15h
The vast majority of stars will become white dwarfs at the end of the stellar life cycle. These remnants are precise cosmic clocks owing to their well constrained cooling rates. The Gaia Data Release 2 in April 2018 is expected to discover up to 300,000 new white dwarfs, which will then be observed spectroscopically with WEAVE and 4MOST. By employing spectroscopically derived atmospheric parameters combined with Gaia parallaxes, white dwarfs can constrain the stellar formation history in the early developing phases of the Milky Way, the initial mass function in the 1.5 to 8 solar mass range, and the mass loss during the post main-sequence evolution. Furthermore, at least 30% of white dwarfs are hosts to evolved planetary systems, and the Gaia sample will provide much better statistics on the frequency and composition of rocky planets as a function of Galactic age.
Prof. Geoff Clayton (LSU) - ARC Seminar on Wed., 2017 Apr. 12 / 15h
RCB stars form a class of cool, carbon-rich supergiants that have almost no hydrogen. They undergo extreme, irregular declines in brightness of up to 8 magnitudes due to the formation of thick clouds of carbon dust. Two scenarios have been proposed for the origin of an RCB star: the merger of a CO/He WD binary and a final helium-shell flash. RCB stars show periodic or semi-periodic light and radial velocity fluctuations due to both radial and non-radial pulsations. A number of RCB stars are now being studied with K2. A correlation between pulsation phase and the timing of dust formation has been found in several RCB stars. This relationship shows that the dust forms near the surface of the RCB star due to density and temperature perturbations caused by the stellar pulsations. The distribution on the sky and radial velocities of the RCB stars tend toward those of the bulge population but a much larger sample of stars is needed to determine the true population. In order discover more RCB stars, we have used a series of WISE IR colorcolor cuts, to produce a sample of several thousand candidates that may yield over 200 new RCB star identifications. Solving the mystery of how the RCB stars evolve will lead to a better understanding of other important types of stellar merger events such as Type Ia SNe.
Prof. Alan Harris (DLR-Berlin) - ARC Seminar on Wed., 2017 Mar. 22 / 15h
Most asteroids and comets are thought to be remnant collisional fragments of planetesimals, the building blocks from which planets in our solar system formed around 4.5 billion years ago. Asteroids and comets from diverse regions of the planetary disk probably enriched the early Earth and other planets in minerals, water, and organic materials. In later epochs, impacts of asteroids and comets on the Earth may have abruptly altered the course of evolution and paved the way for mankind. However, mankind should now be aware that this natural process has not ceased. In particular, the current population of so-called near-Earth asteroids contains many objects that are considered potentially hazardous. On the positive side, near-Earth asteroids may prove to be valuable sources of raw materials (metals, water, rocket propellant, etc.) for future generations. I will illustrate the significance of asteroids for life on Earth and describe recent results of astronomical research into relevant physical properties of these bodies. This research may help us to better understand how harmless asteroids become hazardous and how we can prevent a catastrophic impact on our planet.
Dr. Emily Petroff (Astron) - ARC Seminar on Wed., 2017 Mar. 15 / 15h
Fast radio bursts (FRBs) are quickly becoming a subject of intense interest in time-domain astronomy. FRBs have the exciting potential to be used as cosmological probes of both matter and fundamental parameters, but such studies require large populations. Advances in FRB detection using current and next-generation radio telescopes will enable the growth of the population in the next few years. Real-time discovery of FRBs is now possible with 6 sources detected in real-time within the past 2 years at the Parkes telescope. I will discuss the developing strategies for maximising real-time science with FRBs including polarisation capture and multi-wavelength follow-up. Particularly, I will focus on the real-time detections of four new sources that provide a test bed for fast radio burst science. I will also discuss how our response to these events can inform next generation surveys and pave the way for the enormous number of FRB discoveries expected in the SKA era.
Dr. Elizabeth Stanway (Warwick) - ARC Seminar on Wed., 2017 Mar. 08 / 15h
Observations of star-forming galaxies in the distant Universe (z > 2) are starting to confirm the importance of massive stars in shaping galaxy emission and evolution. The intense starbursts common at high redshift, and rare but identifable in local analogue populations, boast a very high specific star formation rate and are physically compact, leading to a similarly high star formation volume density. Understanding these populations, and their evolution with age and metallicity is likely to be key to interpreting processes such as supernova and gamma-ray burst rates, cosmic reionization and the chemical enrichment of the Universe through galaxy-scale winds. One avenue of exploring these populations is through the study of local galaxies which share the star formation properties of the distant Universe. A second, overlapping, approach is through modelling. Inevitably, distant stellar populations are unresolved, and the limited data available must be interpreted in the context of stellar population synthesis models. With the imminent launch of JWST and the prospect of spectral observations of galaxies within a gigayear of the Big Bang, the uncertainties in modelling of massive stars are becoming increasingly important to our interpretation of the high redshift Universe. In turn, these observations of distant stellar populations will provide ever stronger tests against which to gauge the success of, and flaws in, current massive star models.
Dr. Philip Lucas (Herts.) - ARC Seminar on Wed., 2017 Mar. 01 / 15h
I describe the results of searches for high amplitude infrared variable stars in the VISTA Variables in the Via Lactea (VVV) survey and the UKIDSS Galactic Plane Survey (UGPS). Almost 1500 sources with Delta K > 1 mag have been found in the two surveys. We find that YSOs dominate the high amplitude infrared sky, making up more than half of the sample. Amongst the YSOs, the amplitude of variability increases towards younger evolutionary classes (class I and flat-spectrum sources) except on short time-scales (<25 d) where this trend is reversed. The sample of known eruptive YSOs driven by episodic accretion is increased by at least a factor of 5 by the VVV results alone. Most of these are members of an optically hidden eruptive variable YSO population very rarely seen until now, which has some significance for our basic picture of star formation as a steady, or unsteady, process of accretion. Unlike VVV, the new UGPS variable catalogue is based on just 2 widely separated epochs but it includes more optically visible YSOs in nearby, well studied star forming regions owing to the larger area surveyed. We encourage the community to follow up this diverse sample, which is likely to include many unusual, rarely observed types of astronomical object. I also briefly describe the new VVVX survey, which is extending the VVV survey across the southern plane.
Dan Gay (QUB) - ARC Seminar on Wed., 2017 Feb. 22 / 15h
The objective of this research is to produce light curves and spectra for core collapse supernovae from hydrodynamic and radiative transfer modelling. We use the code PROMETHEUS to evolve supernova explosion models from 1 second to shock breakout and beyond. Once homologous expansion is reached, the output from PROMETHEUS can be mapped onto CMFGEN, which is a radiative transfer code, to produce the spectra and light curves. Using PROMETHEUS has required the addition of a co-moving grid, a new equation of state regime and the inclusion of an artificial atmosphere. So far 1D and 2D simulations have been performed and work continues towards implementing them in 3D The model currently being investigated is a 9.6M⊙, zero metallicity, red supergiant progenitor for which a self-consistent explosion model of the first ∼1 second is available. Future models will include peculiar supernova, such as electron capture and ultra-stripped supernovae. The results from these types of models should give clues on what to expect in observed spectra and help to test multidimensional supernova explosion models against observation.
Tom Seccull (QUB) - ARC Seminar on Wed., 2017 Feb. 15 / 15h
Study of the surfaces of Trans-Neptunian Objects (TNOs) using reflectance spectroscopy reveals much about the composition of these distant icy bodies and hence the formation and evolution of the Solar System. Our team has observed the spectra of 7 small TNOs using the X-Shooter spectrograph on VLT. While 5 exhibit the linear near-UV behaviour that is typical of TNO spectra, 2 exhibit a strikingly drastic drop in reflectance at wavelengths shorter than ~450 nm. Such behaviour has never been observed before in the spectrum of a TNO. The same 2 spectra also show relatively increased absorption bands in the NIR which are likely indicative of water ice. Laboratory spectra of polycyclic aromatic hydrocarbons exhibit significant drops in near-UV reflectance, often exhibit red optical slopes and NIR absorption features, all of which are broadly consistent with our TNO spectra. I will summarise what is currently known about the surface compositions of TNOs and present the new spectral behaviour we have discovered, along with analysis of the potential surface material we may have revealed.
Dr. Meghan Gray (Nottingham) - ARC Seminar on Wed., 2017 Feb. 08 / 15h
The question of whether or not galaxies are affected by their external environment is well known to be much more nuanced than a simple “nature vs nurture” argument. In this talk I will describe the STAGES survey (www.nottingham.ac.uk/astronomy/stages): a detailed multiwavelength examination of a single piece of large-scale structure. We examine the complex interplay between galaxy environment and galaxy properties, including morphology, size, and star formation. I will also outline how large hydrodynamical simulations can help us understand not only the effect of the instantaneous environment of a galaxy, but also the integrated effect of its environmental history. In this way we aim to understand both cluster assembly as well as the importance of 'preprocessing' of cluster galaxies as they are accreted along filaments and in groups. Finally, I will describe prospects for upcoming surveys that will allow us to observationally map the key infall regions of clusters well beyond the virial radius.
Dr. Karen Masters (Portsmouth) - ARC Seminar on Wed., 2017 Feb. 01 / 15h
We live in a universe filled with galaxies with an amazing variety of sizes and shapes. One of the biggest challenges for astronomers working in this field is to understand how all these types relate to each other in the background of an expanding universe. The morphology of a galaxy provides a frozen snapshot of the orbits of stars within it. As such, important clues to the formation history of galaxies is revealed by their morphologies. Modern astronomical surveys (like the Sloan Digital Sky Survey, www.sdss.org) revolutionized astronomy, by providing vast numbers of galaxies to study, however the sheer size of the these databases made traditional visual classification of the types galaxies impossible. In 2007 this problem inspired the Galaxy Zoo project (www.galaxyzoo.org), which asks members of the public to help classify images galaxies from modern surveys by type and shape. The morphological information collected by Galaxy Zoo has since shown itself to be a powerful database for studying galaxy evolution. I will review results which combine visual morphologies from the Galaxy Zoo project with other information about the galaxies to investigate the physical processes which transform the “zoo” of galaxies in our Universe. I will conclude by introducing, the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA, part of SDSS-IV), a new survey which aims to obtain spatially resolved spectral maps for 10,000 nearby galaxies (all of which have Galaxy Zoo morphologies). MaNGA began observations on the Sloan 2.5m Telescope in July 2014 and is now the largest sample of resolved spectroscopy in the world, with over 3000 galaxies observed.
Dr. Michael Marsset (QUB) - ARC Seminar on Wed., 2017 Jan. 25 / 15h
Asteroids in our solar system are metallic, rocky and/or icy objects, ranging in size from a few meters to a few hundreds of kilometers. Their physical nature, distribution, formation, and evolution are fundamental in understanding how the solar system formed and evolved. In the present day solar system, they are - along comets and trans-Neptunian objects - the most direct remnants of the original building blocks that formed the terrestrial planets and the solid cores of the giant planets. As such, they contain a relatively pristine record of the initial conditions that existed in our solar nebula some 4.6 Gyrs ago. The asteroids that have survived since that epoch, however, have experienced numerous collisional, dynamical and thermal events that have shaped their present-day physical and orbital properties. Interpreting this record via observations, laboratory studies, and theoretical/numerical modelling can tell us much about the primordial state of these bodies and how they have evolved thereafter. Here, I will review our current knowledge of the composition of asteroids by focusing (1) on the links that exist between these objects and our current collections of meteorites and (2) on the methods we use to infer their internal structure (ice/rock ratio, porosity), arguably one of the most fundamental and yet poorly known properties of these objects.
Dr. Thomas Ertl (MPA) - ARC Seminar on Wed., 2017 Jan. 18 / 15h
We perform hydrodynamic supernova simulations in spherical symmetry for several hundred progenitor models across the stellar mass range (~10 to 120 M_sun) and for different metallicities to explore the progenitor-explosion and progenitor-remnant connections for the neutrino-driven mechanism. We use an approximate, grey neutrino transport solver and replace the neutron star (NS) interior by an analytic proto-NS core-cooling model, whose free parameters are chosen to reproduce the observables of SN 1987A and the Crab SN for theoretical models of their progenitor stars. Judging the fate of a massive star, either a NS or a black hole, solely by its structure prior to collapse has been ambiguous. Our work and previous attempts find a non-monotonic variation of successful and failed supernovae with zero-age main-sequence mass. We identify two parameters of the pre-collapse structure based on the “critical luminosity” concept for neutrino-driven explosions, which in combination allows for a clear separation of exploding and non-exploding cases. Continuing our simulations beyond shock break-out, we are able to determine nucleosynthesis, light curves, explosion energies, and remnant masses. These can be compared to the observed population of SNe.
Dr. Sibasish Laha (QUB) - ARC Seminar on Wed., 2016 Dec. 07 / 16h
The evolution of the quasar luminosity function with redshift has been a hot topic of research since last few decades. The precise question we would like to ask is “why are there more luminous and more numerous quasars/AGN at high redshift (z~1-2) compared to the local universe (z~0)”. Popular belief is that the quasar phase of high redshift galaxies were triggered by galaxy mergers which subsequently subsided due to the ‘feedback’ due to the Active galactic nuclei (AGN), which stops the supply of matter from being accreted to the super-massive black hole. Here we present some interesting results from our sample study of local AGN in X-rays where we investigated the effects of ionised outflows on host galaxies (WAX sample). We will also present results on two other samples of Low luminosity AGN and Quasars with molecular outflows, and try to find out how exactly the AGN and its outflows impact the host galaxy. We have used the X-ray observations from XMM-Newton, Chandra and Suzaku for our sample studies.
Dr. Donnacha Kirk (UCL) - ARC Seminar on Wed., 2016 Nov. 30 / 16h
Precision cosmology has mainly relied on two-point correlations functions which ignore the complex morphological structure of the cosmic web. I will describe how new experiments, like Dark Energy Survey (DES), are turning their attention to studying the distribution and evolution of clusters, voids, filaments and sheets over cosmic scales. This is of vital importance for the study of galaxy formation and evolution but it can also shed light on fundamental questions like the mass of the neutrino and the nature of gravity.
Dr. Jeronimo Bernard-Salas (OU) - ARC Seminar on Wed., 2016 Nov. 23 / 16h
The end’s life of a star is one of the most critical phases of stellar evolution. By the ejection of the outer layers, evolved stars enrich the interstellar medium with dust and gas. The detection of dust at high-redshift has raised many questions about its origin (Asymptotic Giant Branch stars AGBs vs super novae, other) and its composition across all redshifts. At least half of all ISM dust in the Local Universe is produced by Asymptotic Giant Branch stars, where more than 60 molecular species have been detected in their outflows. These stars are the source of the main organic species we see in space today including PAHs, which are ubiquitous in the Universe, and fullerenes, the largest molecules identified in space and recently firmly established as the carrier of two Diffuse Interstellar Bands. The past decades have witnessed the detection of a rich and complex molecular inventory produced by these stars, and the production of the first extragalactic census of dust production from evolved stars (including AGBs, RSGs, and super nova). With its capabilities, JWST is ideally placed to revolutionise our understanding of this last phases of stellar evolution. It will allow us to, for the first time, spatially resolve and locate the emission of many molecular species providing key insights into their formation and evolution as a function o the local physical conditions, including the elusive phase where PAHs form. With its sensitivity JWST will push the detection limit of these stars to the Local Group, covering a wide range of environments, and providing a comprehensive survey of dust production in the Universe. In this presentation I will review our current knowledge of carbonaceous dust evolution in circumstellar media (in particular PAHs and fullerenes), the current challenges, and describe the opportunities that JWST will provide in this field.
Matthew Hooton (QUB) - ARC Seminar on Wed., 2016 Nov. 16 / 16h
Whilst detecting and confirming the existence of Earth-like extrasolar planets is an ultimate goal of the exoplanet researcher, it is currently an elusive one. With telescopes, instrumentation and relevant techniques constantly improving and our understanding gradually increasing, this will eventually be achieved. At present, big exoplanets with small separations to their host stars, so-called `hot Jupiters’, are the hosts of the easiest atmospheres to observe and classify, especially using ground-based facilities. Many planets in our own solar system host thermal inversions, in which the temperature rises with increasing altitude in certain layers of their atmospheres. When an exoplanet is occulted by its star, the component of the system’s flux associated with the thermal emission from the exoplanet is no longer visible. By observing the size of this drop in flux at different wavelengths, brightness temperatures can be assigned to different altitudes in the exoplanet’s atmosphere, from which the presence of a thermal inversion can be inferred. However, reported detections of such thermal inversions, along with their causes, remain contentious. I will summarise the most significant discoveries using secondary eclipse observations, the most widely studied models to explain the existence of thermal inversions in hot Jupiters, as well as my own research of WASP-103b and HAT-P-1b.
Dr. Andrew Casey (IoA) - ARC Seminar on Wed., 2016 Nov. 02 / 16h
Stars could defensively be considered boring when we thought they were well-understood: the models were simple, and noisy data meant that those simple models were reasonable representations. Increasing data volume and quality (resolution, S/N ratio) have shown that existing stellar models produce systematically biased results, and more worryingly, that experts fitting the same model to the same spectrum will consistently report significantly different results. When the field is awash with these unquantified systematics, they limit scientific inferences on exoplanet host stars, stellar populations, clusters, as well as unresolved stellar populations. In this talk I will review results from the Gaia-ESO Survey that highlight current challenges in stellar astrophysics, before presenting new results derived from data-driven modelling (“Bayesian machine learning”) for stellar astrophysics.
Professor Marten van Kerkwijk (Uni. of Toronto) - ARC Seminar on Wed., 2016 October 26 / 16h
The interstellar medium scatters pulsar radiation, which results in multiple images in which radiation arrives at slightly offset angles and with small time delays. As a result, shorter radio pulses are scatter broadened and longer ones scintillate. I will briefly describe how we hope to use scintillation to do nano-arcsecond astrometry, in particular of pulsar binaries. Next, I'll describe concrete results obtained so far, from using giant pulses, both of the black widow pulsar, PSR B1957+20, and the Crab pulsar, to measure the screen's impulse response function. For PSR B1957+20, we find that giant pulses that occur close in time share the same scattering function and that, as expected, they decorrelate on the scintillation timescale. From close pairs of giant pulses, we infer that the intrinsic duration is very short, at most 200 ns. For the Crab pulsar, however, we find that even giant pulses that occur in the same rotation are not correlated. This suggests that the pulses arise in regions sufficiently far apart that they are resolved by the scattering screen. This is very difficult to understand for any model in which the emission arises inside the light cylinder radius.
Rachel Booth (QUB) - ARC Seminar on Wed., 2016 October 19 / 16h
Ages of stars are important in astrophysics, particularly in the exoplanet field. As more research is dedicated to finding bio-markers in the atmosphere of an earth-like exoplanet, it will be important to determine the age of the host star as this will give insight into the exoplanet’s evolution. We can measure many properties of stars, but one of the most difficult parameters to measure is age particularly for field stars that are isolated and do not change very much throughout their main sequence lifetimes. Age relationships aim to use the change in a stellar property over time to infer an age. However, these relationships require calibrator stars whose ages have been determined via another method. Typically clusters were used as calibrators as their ages are well known, but they are generally younger than a gigayear therefore it was unknown if the relationship was valid for older ages. Now that asteroseismology has been successful in determining the ages of field stars, we can now use these stars as calibrators for the age relationships. I will present the results from my work which has used stars from asteroseismology studies as calibrators to investigate the magnetic activity – age relationship beyond a gigayear.
Dr. Thomas Greve (UCL) - ARC Seminar on Wed., 2016 Oct. 12 / 16h
The [CII] 158micron fine structure line has become the ALMA work-horse line with which to study the gaseous formation of the first galaxies at redshifts > 6. In the nearby universe, space-borne [CII] observations have calibrated it as a star formation rate (SFR) tracer - albeit, with a significant dependency on metallicity. Further complicating the picture is the fact that [CII] can arise from the ionised, atomic and molecular interstellar medium. Modelling of the [CII] line is traditionally done within the realm of classical photo-dominated region models, in which an UV-field impinging on a gas cloud results in stratified layers with the [CII] emission emanating from a thin 'skin'-layer of the cloud. Galaxy-wide simulations of [CII], which incorporates all phases of the ISM, has so far been lacking. In this talk I will present SIGAME (SImulator of Galaxy Millimetre/submillimetre Emission) a code capable of simulating the [CII] and CO line emission from cosmological SPH simulations of galaxies. I will present results from SIGAME [CII] simulations of z=2 and z=6 main sequence galaxies. Our simulations are able to reproduce the [CII]-SFR relation observed and, crucially, we are able to quantify the contribution from the overall [CII] emission from the ionised, atomic and molecular gas phases. I will also briefly touch upon using SIGAME to make predictions for upcoming [CII] intensity mapping experiments.
Dr. Michele Bannister (QUB) - ARC Seminar on Wed., 2016 October 5 / 16h
Discovered just two decades ago, the Kuiper belt contains a reservoir of debris left from the formation of the giant planets of the Solar System. This population of small icy worlds has distinct orbital groupings: some, such as the low-inclination, low-eccentricity cold classical Kuiper belt objects, may still be orbiting at the location of their condensation from the nebula. Others, on dynamically excited orbits, are a signature of emplacement by giant planet migration. I will show how the more than 800 new discoveries from the Outer Solar System Origins Survey on CFHT are revealing new features in the intricate dynamical structure of this region. The dynamical and physical properties of the OSSOS sample will constrain the migratory history of the Solar System.
Dr. Ondřej Pejcha (Princeton University) - ARC Seminar on Wed., 2016 Sept. 28 / 16h
The collapse of the core and the associated supernova explosion mark the end of life of most massive stars, but the mechanism of explosion is poorly understood and perhaps even unknown. By parameterizing the systematic uncertainty in the explosion mechanism, we study how the explosion threshold maps onto observables - fraction of successful explosions, remnant neutron star and black hole mass functions, explosion energies, nickel yields - and their mutual correlations. Successful explosions are intertwined with failures in a complex but well-defined pattern that is not well described by the progenitor initial mass and is tied to the pre-collapse structure of the progenitor star. We present a new method to extract the supernova parameters from light curves and expansion velocities, and illustrate how can these observables constrain the explosion mechanism in the future.
Dr. Mike Kelley (University of Maryland) - ARC Seminar on Wed., 2016 June 19 / 16h
Solar system formation is an engine that can either preserve or transform interstellar medium (ISM) dust. Any dust that reached the hot inner zones of our proto solar system would be annealed or even destroyed and reformed as new minerals. These processed grains and condensates were then mixed into the outer disk with nominally preserved ISM grains. Comet nuclei formed from this mixture of dust. Their interiors have remained cold and the dust mineralogically stable for the past 4.5 Gyr. Thus, the study of comets may allow us to simultaneously investigate our Solar System's inputs and outputs. We are surveying the dust properties of comets through mid-infrared spectroscopy with an aim to understand the diversity of dust in comets and the comet formation zone. In this talk, I review the known properties of comet dust, the current status of our survey, and examine the properties of the Stardust mission's ISM collection.
Dr. Nikolay Nikolov (University of Exeter) - ARC Seminar on Wed., 2016 June 15 / 16h
Over the past decade, observations of transits have revolutionized our understanding of exoplanet atmospheres thanks in large part to spectroscopy with the Hubble and Spitzer Space Telescopes. I will review some of the most recent results from transmission spectroscopy of exoplanets, that have contributed to enhance our understanding of these distant worlds. I will discuss how the combination of multi-wavelength data sets from different instruments enable us to better understand the atmospheres of gas-giant planets and will present new results from two surveys.
Dr. Aline Vidotto (Trinity College Dublin) - ARC Seminar on Wed., 2016 May 18 / 16h
In this talk I will overview the recent works on magnetism of cool, main-sequence stars, their winds and impact on surrounding exoplanets. The winds of these stars are very tenuous and persist during their lifetime. Although carrying just a small fraction of the stellar mass, these winds regulate the rotation of the star and can affect surrounding planets. Because they are incredibly tenuous, their detection has been a very challenging task. Numerical models are therefore an important tool to grasp a better understanding of cool stars’ winds. Our numerical simulations include observationally-derived surface magnetic field maps, which are necessary given the key effects of magnetic fields on stellar winds. Since cool stars are generally surrounded by planets, understanding their stellar winds is a key step towards characterisation of exoplanetary environments. Although these environments may be potentially dangerous for a planet's atmosphere, the interaction between planets and the host star winds can provide other avenues for planet detection and maybe even assess planetary properties (eg, planet's magnetic field), which would otherwise remain unknown.
Prof. Jürgen Schmitt (Hamburg University) - ARC Seminar on Wed., 2016 May 04 / 16h
The physics of solar magnetic activity is not well understood despite enormous research efforts over many decades. The study of magnetic activity in stars other than the Sun allows to study magnetic activity phenomena in very different environments and with the advent of extrasolar planets as an own research theme there has been a substantial rejuvenation of studies of magnetic activity in late-type stars: Almost all known planet hosts are of late-type, thus magnetically active and influence their planets and our observations of them in various ways. I will provide an overview of the activities in cool star research at Hamburg, with a focus on recent studies of long-term activity variations in various wavebands.
Meabh Hyland (QUB) - ARC Seminar on Wed., 2016 Apr. 27 / 16h
Since the discovery of the first Kuiper Belt object in 1992 more than 1500 bodies have been discovered in the region of space beyond Neptune. These trans-Neptunian objects (TNOs) are known to have a wide variety of surface colours ranging from neutral to very red; however, the reason for this colour diversity remains unexplained. By making accurate measurements of the colours and phase coefficients of TNOs we can begin to constrain their surface compositions and understand how they are affected by processes such as irradiation. In this seminar I will present the results of a photometric study of several TNOs using data collected by the Pan-STARRS 1 survey.
Dr. Marc Sarzi (Herts.) - ARC Seminar on Wed., 2016 Apr. 13 / 16h
I will present MUSE data for the Virgo central galaxy NGC~4486 (M87). I will show how the initial stellar mass function of stars changes within the optical regions of this galaxy, and discuss the consequences of this changes for mass modelling. I will also show how the brightest planetary nebulae are notably absent in these same regions, and how this result connects to the mass-loss history of stars in a metal-rich environment such as those of massive galaxies.
Dr. Alexandra Kozyreva (Keele) - ARC Seminar on Wed., 2016 Apr. 06 / 16h
With an increasing number of superluminous supernovae (SLSNe) the mystery of their origin remains and causes heated debates in the supernova community. Currently, there are three proposed mechanisms for SLSNe: (1) pair-instability supernovae (PISN), (2) magnetar-driven supernovae, and (3) models in which the supernova ejecta interacts with a circumstellar material ejected before the explosion (a shell or wind). The PISN origin of SLSNe is disflavoured for a number of reasons. Many PISN models provide overly broad light curves and too reddened spectra, because of massive ejecta and a high amount of nickel. In the current study we re-examine PISN progenitor models computed with the GENEC code. We produce our supernova evolution with the radiation hydrodynamics code STELLA. We found that high-mass models (200 M⊙ and 250 M⊙) at relatively high metallicity (Z = 0.001) produce sufficiently fast evolving PISNe and are suitable for the explanation of some SLSNe. We simulate an additional set of PISNe and compare light curves computed with the following radiation codes: STELLA, SEDONA, CMFGEN, RADA, RAGE-SPECTRUM, SuperNu, PHOENIX, V1D. The results of STELLA are generally in good agreement with output of other codes, although STELLA light curves rise to maximum faster than light curves computed with other codes. Two reasons for this are (1) different treatment of opacity in different codes, and (2) nickel- bubble effect.
Dr. Manda Banerji (IoA) - ARC Seminar on Wed., 2016 Mar. 25 / 16h
Among the major outstanding questions in galaxy formation research is understanding how galaxies regulate their overall star formation rate over cosmic time to yield the complex diversity of structures seen today. Supermassive black holes (SMBHs), a ubiquitous central component of massive galaxies, have emerged as promising candidates for moderating star formation and quenching the growth of massive galaxies. Yet the connection between supermassive black holes and their host galaxies still remains poorly understood. I will discuss how wide-field galaxy surveys are now offering new insights into the formation of massive galaxies and the growth of their central black holes by discovering previously unstudied populations of distant quasars.
Dr. David Kuridze (QUB) - ARC Seminar on Wed., 2016 Mar. 16 / 16h
The chromosphere is a highly inhomogeneous layer of the solar atmosphere, populated by a wide range of dynamic jet-like features such as spicules, fibrils, mottles, and Rapid Redshifted/Blueshifted Excursions (REs). These small-scale plasma structures are observed ubiquitously near the network boundaries in strong chromospheric spectral lines such as Hα, Ca II H & K, and the Ca II IR triplet. Some of these structures are characterised by very fast upflow velocities and rapid fading which is currently unexplained. Theoretical considerations suggest that the small-scale chromospheric jets could become unstable due to the Kelvin-Helmholtz instability (KHI). The instability growth time of chromospheric jets could be very short (few seconds) at the observed high upflow speeds. Furthermore, analysis of the energy equation in the partially ionized chromospheric plasma shows that the ion-neutral collisions may lead to the fast heating of the KH vortices and consequently the structure itself over timescales comparable to the lifetime of REs.
Dr. Matthew Knight (University of Maryland) - ARC Seminar on Wed., 2016 Mar. 9 / 16h
Solar and Heliospheric Observatory (SOHO) recently completed its 20th year of observing. During that time it has become the most prolific comet hunting platform of all time, with more than 3000 comets discovered in its images. SOHO has revealed that the inner solar system is far more populous that previously believed, with a steady stream of small comets reaching perihelion at “sungrazing” and “sunskirting” distances every few days. The majority of these comets are dynamically related to each other as members of the well known Kreutz group, but many belong to previously unknown groups, and some may even be asteroidal in origin. In addition, SOHO has occasionally obtained spectacular observations of bright comets that passed close to the Sun, such as C/2012 S1 ISON. I will review SOHO’s various comet observations and discuss how they aid our understanding of solar system evolution, act as probes of the solar environment, reveal unique information about properties of dust, and may even yield insight into exo-planetary systems.
Mr. Aaron Reid (QUB/Armagh) - ARC Seminar on Wed., 2016 Feb. 25 / 16h
Ellerman bombs are small scale explosive events in the lower solar atmosphere. Using high resolution ground and space based telescopes, we are able to observe and study chromospheric jet connections with these photospheric explosions. It is also possible to show magnetic flux cancellation at Ellerman Bomb sites, using spectro-polarimetry of magnetically sensitive line profiles. A statistical study of Ellerman Bombs is also shown with comparisons of energy estimates obtained from different observational setups, along with state of the art inversions of the observations to give physical parameters of Ellerman Bombs.
Dr. Stephan Geier (Warwick) - ARC Seminar on Wed., 2016 Feb. 17 / 16h
Hot subdwarfs are compact helium stars formed by stripping a red giant from its hydrogen envelope by close binary interactions. Hot subdwarfs in close binaries with massive white dwarf companions are candidates for the progenitors of thermonuclear supernovae. As soon as the white dwarf explodes, the surviving hot subdwarf might the ejected from the binary and accelerated to velocities high enough to leave our Galaxy. Such hypervelocity hot subdwarfs might therefore become important tools to study thermonuclear supernovae. I will report on an ongoing project to find and study such supernova progenitors and ejected companions.
Stephen Durkan (QUB) - ARC Seminar on Wed., 2016 Feb. 10 / 16h
In this seminar I report the results of a re-analysis of archival Spitzer IRAC direct imaging surveys encompassing a variety of nearby stars. For Spitzer, and similar space telescopes, imaging capability has been severely limited by the large PSF associated with the small (0.85m) telescope diameter, leading to a strong preference in conducting imaging surveys with AO corrected instruments on 8m class ground based telescopes. The resolution and achievable contrast afforded by such instruments has allowed numerous imaging studies to place robust constraints on the frequency of 0.5 - 13 MJ planets over separations on the order of 10 − 100 AU. However limitations have confined sensitivity to this separation range, leaving the wide giant planet population beyond that poorly constrained. Here we apply sophisticated high-contrast techniques to our sample in order to remove the stellar PSF and open up sensitivity to planetary mass companions down to 5′′ separations. This enables sensitivity to 0.5 - 13 MJ planets at physical separations on the order of 100 − 1000 AU , allowing us to probe a parameter space which has not previously been systematically explored to any similar degree of sensitivity. Based on a colour and proper motion analysis we do not record any planetary detections. Exploiting this enhanced survey sensitivity, employing Monte Carlo simulations with a Bayesian approach, and assuming a mass distribution of dn/dm ∝ m^−1.31, we constrain (at 95% confidence) a population of 0.5 - 13 MJ planets at separations of 100 - 1000 AU with an upper frequency limit of 9%.
Dr. Matthew Kenworthy (Sterrewacht Leiden) - ARC Seminar on Wed., 2016 Jan. 27 / 16:30h
All the giant planets in our Solar system have rings and moons in orbit around them, and act as a fossil record of their formation. Despite the large numbers of detected extrasolar planets, though, no Saturn-like rings have yet been observed. In May 2007, a young star (called J1407) underwent a complex series of fluctuations in brightness lasting over two months. At one point, the star dimmed by over 95% over a few hours. We have modelled this light curve as a giant, highly structured ring system that is hundreds of times larger than Saturn's rings orbiting around an unseen substellar secondary companion, J1407b. This is the first detection of exorings around an astronomical object outside our Solar system, and the structure of these rings suggests the formation of moons around J1407b. I will talk about our model and the potential for seeing more of these eclipses in the future.
S. Krishna Prasad (QUB) - ARC Seminar on Wed., 2015 Dec. 09 / 16h
Sunspots on the surface of the Sun are the observational signatures of tightly packed magnetic field lines, with near-vertical field strengths exceeding 6,000 G in extreme cases. The magnetic field strength drops rapidly away from the solar surface, making high-cadence coronal measurements through traditional Zeeman and Hanle effects difficult. Magnetohydrodynamic (MHD) techniques have previously been applied to coronal structures, with single and spatially isolated magnetic field strengths estimated as 9–55 G. In our recent work, we demonstrated a new, powerful technique that harnesses the omnipresent nature of sunspot oscillations to provide, for the first time, spatially resolved coronal magnetic fields with high precision.
Mark Magee (QUB) - ARC Seminar on Wed., 2015 Dec. 02 / 16h
Despite the importance of Type Ia supernovae in our study of the cosmos, fundamental questions on their nature remain unanswered. The discovery of many peculiar SNe Ia has resulted in a diverse set of explosion scenarios being proposed to explain these equally diverse objects. Potentially the most numerous class of peculiar SNe Ia are the Type Iax supernovae. In this talk I will discuss our current understanding of this class of object and how they differ from normal SNe Ia. I will present new observations of a recent member of the class and show how its features are consistent with theoretical models.
Dr. Caroline d'Angelo (Sterrewacht Leiden) - ARC Seminar on Wed., 2015 Nov. 23 / 16h
Accreting neutron stars present themselves as a surprisingly large diversity of astronomical objects, depending on their magnetic field strength and accretion rate. At the very highest accretion rates, neutron stars have been identified as ultraluminous X-ray sources, which accrete well above the Eddington limit, while high-field, fast-spinning newly-born neutron stars have been suggested to partly power core-collapse supernovae explosions. At much lower accretion rates, weak field accreting pulsars and non-pulsating accreting neutron stars are precursors to the large population of radio pulsar, and show accretion at much lower luminosities. However, the underlying physics of magnetospheric accretion remains constant across the wide range luminosity and magnetic field strength, so that studying one class can yield insights applicable to all accreting sources. In my talk I will present recent studies of several low-field, low-luminosity accreting neutron stars, and show how some surprising results of these investigations are relevant for understanding the much more extreme physics of high field neutron stars.
Dr. Paul M. Woods (QUB) - ARC Seminar on Wed., 2015 Nov. 18 / 16h
In this seminar I will describe an innovative interdisciplinary project to learn more about a small family of isomeric organic molecules that have been detected in space: glycolaldehyde (CH2OHCHO), acetic acid (CH3COOH) and methyl formate (HCOOCH3). Our primary focus was glycolaldehyde, a prebiotic sugar-like molecule, that was detected fairly recently in both high-mass and low-mass star-forming regions on very compact scales. We drew together a team of theoretical and observational astrochemists; laboratory astrochemists and chemical physicists in order to increase our knowledge on all four fronts. I will give an overview of the results of chemical modelling, that helped us to identify the primary formation mechanism for glycolaldehyde at low temperatures, and which was subsequently confirmed experimentally. I will show results from the lab which will help us to identify these molecules in astrophysical ice spectra, and understand the distribution of these molecules in star-forming regions. Our observational programme resulted in new detections of glycolaldehyde in a variety of high-mass star-forming regions, and a tentative detection of acetic acid for the first time in a hot core. Finally, I will give an outline of where this project is heading: understanding this system of CHO-bearing organics more fully and incorporating the formation of the amino acid glycine, which is chemically linked to acetic acid.
Andrew Thompson (QUB) - ARC Seminar on Wed., 2015 Nov. 11 / 16h
One of the goals of exoplanet research is to find smaller more Earth-like planets. Although a number of Super-Earth and Neptune sized planets have been discovered by photometry, their nature makes spectroscopic follow-up very difficult. To this end, new wide field surveys such as NGTS (Next Generation Transit Survey) aims to find viable follow-up targets by looking for transiting planets around brighter, smaller (late K and early M type) stars. Follow-up work on these object, although more viable, is not without its problems. Stellar noise from starspot and plages can mimic the effects - both photometrically and spectroscopically - that a planet would have on its host star while other stellar noise sources such as granulation add a level of noise that can mask a planet signal. Understanding and removal of this noise is then a vital part of the search for more Earth-like planets. Gaussian Processes (GP) are a form or machine learning that is being utilised in order to model the stellar noise seen in radial velocity measurements by modeling variation that is seen in simultaneous photometric measurements. We look at developing out own GP code for modeling the RV variation with the hope of generalising it for use with NGTS targets. Initial results of lightcurve modeling for the planetary system CoRoT-7 will be presented. Other work we are doing looks at prioritisation of NGTS targets based on lightcurve variation being linked to stellar noise to give an estimate of the expected RV jitter that a target may have.
Dr. Daisuke Kawata (MSSL) - ARC Seminar on Wed., 2015 Nov. 04 / 16h
Recently numerical simulation studies are provocatively suggesting that the long-lived spiral arms suggested by the density wave theory of Lin & Shu (1964, ApJ, 140, 646) are difficult to be reproduced by self-consistent numerical simulations. Using N-body simulations of Milky Way-sized barred spiral galaxies, we demonstrate that the simulated galaxy shows short-lived and recurrent spiral arms which co-rotate with the same speed as the circular speed. We find that the such transient co-rotating spiral arms induce a systematic motion of stars that migrate toward the outer (inner) radii on the trailing (leading) side of the spiral arm at all the radii, which causes the significant radial migration. We discuss the observability of the systematic stellar motion around the spiral arm in the upcoming Gaia data, taking into account stellar population, the dust extinction and the expected Gaia observational errors.
Dr. Luke Shingles (QUB) - ARC Seminar on Wed., 2015 Oct. 21 / 16h
Stars with initial masses between about 0.8 Msun and 8 Msun (AGB stars) play an important role as the main site of the slow neutron capture (s-)process, which produces roughly half of the elements heavier than iron. In this talk, I will present results from my PhD thesis, which explores several topics related to AGB stars and the s-process. The focus is on comparing theoretical models with observations in the literature on planetary nebulae, post-AGB stars, and globular cluster stars. From this work, we gain a better understanding of AGB nucleosynthesis, the chemical evolution of globular clusters, and the properties of helium-rich stars.
Prof. Justin Read (Uni. of Surrey) - ARC Seminar on Wed., 2015 Oct. 14 / 16h
The LCDM cosmological model has been tremendously successful at explaining a host of observational data on scales larger than ~1Mpc. However, on smaller scales there have been two long standing puzzles: the cusp/core and missing satellites problems. While many solutions have been suggested for both, it remains unclear whether the full solution lies purely in “baryonic physics” or whether we must modify the cosmological model on small scales. In this talk, I present new simulations of dwarf galaxies that resolve the impact from individual supernovae explosions. I show how this leads to bursty star formation that collisionlessly heats the central dark matter, transforming an initial cusp into a core. Such cored dwarfs are very susceptible to tidal disruption on infall to the Milky Way, leading to a dramatic scouring of the dark matter halo mass function. Our simulated dwarfs give a remarkable match to the stellar light profile; star formation history; metallicity distribution function; and star/gas kinematics of isolated dwarf irregular galaxies, without any fine-tuning of the model parameters. This suggests that both the cusp-core and missing satellites problems likely owe to baryonic physics. We conclude that LCDM gives a remarkable description of structure formation, even at the extremities of galaxy formation.
Lisa Esteves (Uni. of Toronto) - ARC Seminar on Wed., 2015 Oct. 07 / 16h
The Kepler mission's long-term monitoring of stars through high-precision photometry has not only revealed a plethora of exoplanet transits but also provided valuable data for characterizing a subset of these planets. Using over four years of Kepler observations, we have derived phase curves for over a dozen planets, and use these measurements to constrain their mass, brightness/temperature and energy redistribution between the day and the night sides. In our paper, we also investigate possible offsets of the peak brightness of the phase curve, which could be indicative of inhomogeneous clouds and/or substantial winds in the planet's atmosphere. We find significant offsets for over a half-dozen planets. With this growing sample of measured phase curves, we are able to better examine the trends of hot Jupiter energy budgets and albedos, and for the first time relate these properties to the presence of clouds or winds on a planet.
Dr. Takashi Moriya (Bonn) - ARC Seminar on Wed., 2015 Sept. 09 / 16h
Superluminous supernovae (SLSNe) are a recently recognized class of extremely bright supernovae. Especially, the luminosity source of Type Ic SLSNe which do not show signatures of hydrogen at the early time is unclear. A leading scenario is to power them by the magnetar spin-down. However, we often observe Type Ic SLSN light curves decaying with the timescale of the 56Co decay, which leads to the suggestion that 56Ni powers some Type Ic SLSNe. If magnetars actually power Type Ic SLSNe, the fact that we often observe 56Co-like decay indicates that magnetars should be able to “mimic” 56Ni-powered supernovae rather easily. I will discuss how well magnetars can mimic 56Ni.
Dr. Ralf Napiwotzki (Uni. of Herts.) - ARC Seminar on Wed., 2015 May 26 / 16h
The Magellanic Bridge is connecting the Large and Small Magellanic Bridge. It was first seen by radio observations detecting gas. Subsequent investigations found a young stellar population, consistent with in situ star formation from gas dragged into the Bridge. The Magellanic Clouds and the Bridge are target of the VMC survey carried out with the ESO Vista telescope. We have used this and other IR surveys to identify a stellar population older then the first interaction (according to models) leading to the formation of the Bridge. Spectroscopic follow up is described, which produced some quite surprising results.
Dr. Timothy Davis (Uni. of Herts.) - ARC Seminar on Wed., 2015 May 13 / 16h
Massive early-type galaxies (ETGs) are often assumed to be 'red and dead' systems, which have been passively evolving since z~2. In fact, many such systems host residual star formation and contain large cold gas reservoirs. I will show how observations of the cold and warm ISM, combined with simulations and models, can be used to shed light on the mysterious origin of this material which changes the late-time evolution of red-sequence galaxies. I will show that star formation in these objects is dynamically suppressed, leading to stars forming with a much lower efficiency than in spiral and starburst galaxies. Star formation is also suppressed in ETGs which have undergone a recent minor merger. These dynamical processes that suppress star formation are likely to be important in other galactic nuclei, and perhaps even in our own Milky Way. Finally I will show that molecular gas is an excellent kinematic tracer, providing a powerful tool for both studying the large scale mass distribution in galaxies, the initial stellar mass function, and probing dark objects lurking at the hearts of galaxies.
Prof. Ismael Martel (Uni. of Huelva) - ARC Seminar on Thurs., 2015 Mar. 26 / 15h
The development of radioactive beam facilities has recently allowed the study of reaction dynamics of exotic (or radioactive) nuclei. Nuclear reactions involving weakly bound nuclei exhibit new phenomena, like exotic cluster structures and decay modes, the formation of skins and haloes. On the other hand, stellar nucleosynthesis and supernovae follow reaction paths involving radioactive nuclei all the way up to the heaviest masses. In this seminar the experimental activity of the Nuclear Physics group at the University of Huelva will be presented and discussed.
Dr. Ernst de Mooij (QUB) - ARC Seminar on Wed., 2015 Mar. 18 / 16h
Since the discovery of the first plane outside our solar-system almost two decades ago, the field of exoplanet research has made a lot of progress. Not only has the number of known exoplanets increased to over 1500, the atmospheres of dozens of these planets have been detected. These atmospheric studies have mainly been made for transiting planets. For these planets is not only possible to study their atmosphere in emission/reflection during the secondary eclipse, but also in transmission during the transit. I will show that ground-based telescopes can be used to reach the high precision required to detect the atmospheric signatures of transiting exoplanets
Prof. Ken Ganga (Labo. Astroparticule et Cosmologie, Paris) - ARC Seminar on Wed., 2015 Mar. 11 / 16h
The Planck Satellite was launched in 2009 and studied the Cosmic Microwave Background and the rest of the millimeter and sub-millimeter sky through 2013. It has yielded a wealth of scientific results both about the birth and evolution of the Universe and about the Galaxy in which we live. I will present some of the history of the project and will try to summarize what I think are its major results, including its latest measurements of the cosmological parameters of the Universe, and implications for recent results and future measurements of Inflationary parameters.
Prof. Alan Harris (DLR) - ARC Seminar on Wed., 2015 Mar. 4 / 16h
The European-Union-funded (FP7) NEOShield project, which commenced in January 2012, is funded until May 2015. A follow-on project, NEOShield-2, has recently been granted funding until 2017. The main goals of the projects are to improve our knowledge of the mitigation-relevant physical characteristics of near-Earth objects (NEOs), and to investigate and assess feasible NEO deflection techniques.
After a brief introduction to the nature of the impact hazard and what we should do about it, I will briefly discuss the NEOShield work and present some recent scientific results. A key task is to develop some understanding of the likely physical properties of the threatening NEO that will trigger the first deflection attempt. Much still needs to be done in terms of physical characterization of NEOs, using not only astronomical facilities but also space probes for robotic exploration.
In recent years not only have the scientific and space-technology communities begun to pay more attention to impact-hazard issues, but some national space agencies and international organizations are now investing significant funding in various endeavours, motivated by increased awareness of the problem. While it seems the stage is now set for coordinated international activities in pursuit of a response to the NEO impact threat, it remains to be seen if the momentum built up over the past few years can be maintained. We are still far removed from having an international agreement on who would do what, who would pay for what, and who would take responsibility for failure, in the event of a deflection action becoming necessary.
Dr. Tomoko Kawata (QUB) - ARC Seminar on Wed., 2015 Feb. 11 / 16h
Solar white light flares, which are solar flares with visible continuum enhancements, first observed in 1859. They have been observed in energetic flares with small area of brightening (~arcsec), weak intensity enhancement (<10%), and had some different characteristics of structures and spectra at the same time. In spite of its long history, how and where they are formed are still under discussion. The main cause of white light flares is said to be accelerated electrons which are precipitated to the solar surface, and revealing the formation mechanism of white light flare may tell us some clues for one of the biggest problems in Solar Physics; “Particle acceleration in solar flare”. I will present my recent research on solar white light flares by a spectroscopic and a high cadence imaging ways, with some speculations on the formation mechanisms of the white light emissions.
Dr. Krishna Prasad (QUB) - ARC Seminar on Wed., 2015 Jan. 28 / 16h
Coronal loops, the basic building blocks of the magnetically dominant solar corona, often host oscillations propagating along them. Based on the observed properties it was believed that these propagating oscillations are signatures of slow magneto-acoustics waves. But recent high-resolution spectroscopic observations suggest that quasi-periodic upflows can also produce similar signatures causing an ambiguity. In this talk, I will discuss the origin of this problem, my contributions (as a part of my thesis), and the present status.
Dr. Juliet Datson (Turku/QUB) - ARC Seminar on Wed., 2015 Jan. 21 / 14h
In this era of large stellar surveys, like the Geneva-Copenhagen-Survey (GCS), solar twins and analogues provide a means to test the calibration of these stellar catalogues, because the Sun is the best-studied star and provides precise fundamental parameters. Solar twins should therefore be centred on the solar values in any stellar catalogue. In this talk I provide the steps and results from my PhD work, the search for solar twins, how to use the full sample of solar analogues to test catalogue calibrations and I independently derive their spectroscopic parameters for comparison to literature values, like the ones given in the GCS and test the calibration of my own values around the solar values.
Dr. Els Peeters (Uni. of Western Ontario) - ARC Seminar on Wed., 2015 Jan. 14 / 16h
The infrared (IR) spectra of objects associated with dust and gas – including evolved stars, reflection nebulae, the interstellar medium (ISM), star-forming regions, and galaxies out to redshifts of z ∼ 3 – are dominated by emission bands at 3.3, 6.2, 7.7, 8.6 and 11.2 μm, the so-called unidentified infrared (UIR) bands. They are generally attributed to the IR fluorescence of Polycyclic Aromatic Hydrocarbon molecules (PAHs) UV pumped by nearby massive stars. Hence, the UIR band strengths are used to determine the star formation rate in galaxies, one of the key indicators for understanding galaxy formation and evolution. To date, PAHs are among the largest and most complex molecules known in space and emit up to 10% of the total power output of star-forming galaxies. Space-based telescopes such as the Infrared Space Observatory (ISO) and the Spitzer Space Telescope revealed the richness of the PAH spectrum and provided extensive evidence for significant variability in the PAH spectrum from source to source and spatially within sources. In this talk, I will focus on the PAH properties in the reflection nebula NGC2023. I will present spectral maps of NGC2023 obtained with the SL and SH mode of the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. These observations clearly illustrate that the detailed characteristics of the PAH emission features vary across the reflection nebula and that different sets of PAH bands correlate spatially across the nebula. In particular, we conclude that at least 2 spatially distinct components contribute to the 7–9 μm PAH emission. We interpret these differences in spatial behavior in terms of variations in PAH characteristics such as size, charge and structure with the changing environment across the nebula.
Samuel Grant (QUB) - ARC Seminar on Wed., 2014 Dec. 03 / 16h
With the extra-ordinary heating of the upper solar atmosphere in mind, high resolution, multi-wavelength ground-based data sets are employed to study the propagation of compressible MHD waves from the photosphere through to the base of the transition region. Through Fourier and wavelet techniques, sausage-mode oscillations are detected through the identification of intensity and area fluctuations. Analysis of the phase relationships between 4 independent bandpasses confirms that these oscillations are consistent with slow mode waves, upwardly propagating, and with initial energies approaching 100,000 W per square metre. The wave energetics as a function of height are studied, and they suggest that magnetic pores are able to release vast quantities of energy into the local chromospheric plasma.
Prof. Ewine van Dishoeck (Sterrewacht Leiden / MPE Garching) - ARC Seminar on Tue., 2014 Nov. 11, 12h
Water is a key molecule in the physics and chemistry of regions in which new stars and planets are born. Thanks to recent new observational developments, especially the Herschel Space Observatory and the Spitzer Space Telescope, a comprehensive set of data on water gas and ice has been obtained toward a large sample of well-characterized protostars, covering a wide range of masses as well as evolutionary stages -from the earliest stages represented by pre-stellar cores to the late stages represented by the pre-main sequence stars surrounded only by disks. The data elucidate the physical and dynamical processes associated with forming stars and planets (outflow, infall, expansion), test basic gas-phase and gas-grain chemical processes, and reveal the chemical evolution of water and the oxygen-reservoir into planet-forming disks. New insight into the origin of the water in oceans on Earth comes from observations of deuterated water and comparison with comets, including the exciting Rosetta mission. Future prospects for the Atacama Large Millimeter Array (ALMA) are discussed as well.
Dr. Vasily Belokurov (IoA) - ARC Seminar on Wed., 2014 Oct. 15, 14h
I will talk about the physical extent of the Milky Way and shot that its mass and size might be lower than expected.
Dr. Bob O'Dell (Vanderbilt Uni.) - ARC Seminar on Wed., 2014 Oct. 01, 16h
The creation of an orbiting astronomical observatory was a natural goal of creating rockets that could place artificial satellites in orbit around the Earth. The fledgling NASA envisioned what is now called the Hubble Space Telescope (HST) in its early years and by 1971 had begun studies to see if construction was feasible. As plans for the Space Shuttle matured, it began to be possible to design a long-duration observatory, not simply a limited-duration telescope. The speaker was involved with the HST program from its beginning and will describe the many steps and battles that occurred over the 19 years that it took to build it. He’ll also describe some of the results on his favorite astronomical object, the Orion Nebula, that have been produced over the nearly 25 years of HST operation.
Prof. Carole Mundell (LJMU) - ARC Seminar on Wed., 2014 Sep. 24, 14h
I will describe recent advances in autonomous robotic observation of the instantaneously most luminous objects in the Universe - Gamma Ray Bursts (GRB). In particular, I will present new experiments using novel 'RINGO' optical polarimeters on the 2-m Liverpool Telescope to study the magnetic fields predicted to collimate and accelerate the ultra-relativistic GRB jets. I will discuss the unexpected dearth of bright optical flashes that were expected to be ubiquitous in the early optical afterglow, produced by the so-called reverse shock, and introduce an adaptation to the standard model that predicts flares at radio and mm wavelengths instead. I will finish with a look to the future of transient source studies - physics and technology - and discuss prospects for using GRBs as probes of fundamental laws of physics.
Dr. Spiro Antiochos (NASA/GSFC) - ARC Seminar on Fri., 2014 Sep. 05, 10h
Coronal mass ejections (CME) / eruptive flares are the largest and most energetic form of solar activity and are the drivers of the most destructive space weather throughout interplanetary space. Understanding the physical origin of these giant magnetic explosions and their propagation in the heliosphere is absolutely essential for any first-principles based space weather forecasting. Furthermore, these well- observed events offer the best opportunity to study the fundamental physics of magnetic field and plasma interactions; in particular, the key processes of magnetic reconnection and particle acceleration. We describe how magnetic reconnection is responsible for the energy buildup that leads to CMEs/flares, how it drives the explosive energy release, and how it controls the propagation of the event. Reconnection turns out to be especially important for understanding the escape of high-energy particles into the heliosphere. The implications of our results for interpreting observations and for space weather modeling will be described.
Prof. Martin Ward (Durham) - ARC Seminar on Wed., 2014 Sep. 03, 16h
The broad-energy SEDs of quasars and active galaxies have been studied for many decades. The basic components that make up the optical/ultraviolet and X-ray continuum, are well known. I will described recent results from fitting a new SED model over this energy range, which conserves energy, and which is consistent with the black hole mass derived from the Balmer emission line profiles. Our results show that there is considerable diversity in these SEDs, which has implications for estimates of bolometric luminosity based on proxy indicators such as the [OIII] emission line luminosity, and infrared continuum luminosity. I will also how SEDs of some AGN can be used to constrain their black hole spin.
Rebecca Hewitt - ARC Seminar on Wed., 2014 Jun. 11, 16h
Abstract: Magnetic Bright Points (MBPs) are manifestations of small-scale highly magnetic fields on the quiet solar surface. Their ubiquitous nature makes their potential to affect the global solar properties hard to ignore. Using 3D magneto-hydrodynamical simulations and and radiative diagnostics of solar granulation, the evolution of plasma properties and Stokes parameters in MBPs have been investigated. Through degradation of the simulated data to match the spatial resolution of SOT, we show that high spatial resolution is crucial for the detection of changing spectro-polarimetric signatures throughout a MBP’s lifetime. I will also discuss a comparison of the simulated results with IBIS observations.
Elisabeth Gall - ARC Seminar on Wed., 2014 Jun. 04, 16h
The expanding photosphere method (EPM, Kirshner & Kwan 1974) is a technique that compares photospheric angular size of an expanding SN photosphere at different points of time to the ratio of observed and theoretical flux to estimate the distance of the SN. This method is usually applied to Type II-P SNe for which a spherical photosphere (i.e. a spherically symmetric explosion) is a good approximation. However SNe II-P are intrinsically faint and hard to observe. As a consequence this method has only rarely been applied for SNe with redshifts higher than 0.05. Over the past 1.5 years of my PhD I have acquired data for a sample of 10 objects with redshifts between about 0.04 and 0.33. This gives us the unprecedented possibility to perform high-redshift EPM and thereby test the Type Ia SN cosmology. However, with higher redshifts relativistic effects have to be taken into account, that are not relevant for the low-redshift samples used so far. The main problem is that the comparison between the flux and the angular size of an object – on which the idea of EPM is based – breaks down at high redshifts where “angular distance” and “luminosity distance” differ by a factor of $(1+z)^2$. In order to understand the exact implications of this problem I have re-derived the basic equation of the EPM taking into account relativistic effects and exploring its effects on the application and results of this method. This will be demonstrated in my talk.
Dr. Yvonne Unruh - ARC Seminar on Wed., 2014 May. 28, 16h
Until well into the space age, total solar irradiance was considered to be constant and it required radiometers in space to detect its variability. The variations in the solar irradiance are strongly wavelength-dependent: over the solar cycle, variability in the UV can reach several percent, while it usually remains below 0.1% in the visible. The extent of the variablity on time scales longer than the solar cycle is still poorly known, and it is still not clear how strongly these changes affect the Earth's climate. The advent of high-precision stellar variability measurements, typically as an byproduct of exoplanet transit searches, has rekindled interest in placing the Sun in the context of stellar observations. After a short overview of historical as well as recent variability observations on the Sun and Sun-like stars, I will discuss solar irradiance models and how these may be adapted to other stars.
Darryl Wright - ARC Seminar on Wed., 2014 May. 20, 16h
The problem of reliable transient detection in large data streams that contain many artefacts as a result of difference imaging is common to modern synoptic sky surveys such as Pan-STARRS1. Currently the process of selecting the real objects from the artefacts is left to human scanners. We attempt to construct a machine learned classification system that is scalable to the next generation of all-sky surveys that will allow us to select only images of real transients providing a reliable stream of sources for scientific follow-up.
Paul Woods - ARC Seminar on Wed., 2014 May. 07, 16h
SAGE-Spec is a spectroscopic survey of the Large Magellanic Cloud with the Spitzer Space Telescope, which has the grand aim to understand the cycle of matter in a galaxy. As part of this project, over 1,000 spectra were obtained of point-source-like objects in the LMC, one of our nearest neighbouring galaxies. I will explain the process behind the classification of these mid-IR spectra into groups according to object type: young stellar objects, AGB stars, red supergiants, etc. and then what we can understand about the stellar populations of the LMC from such a classification. The data from SAGE-Spec has a large range of applications, not least the testing of previous, photometric classifications; the identification of new sub-classes of object; and improved understanding of the dust budget of galaxies.
Ryan Brothwell - ARC Seminar on Wed., 2014 Apr. 09, 16h
The study of gas giants orbiting close to their host stars allows an insight into the formation and evolution of exoplanets. For example, combined transit photometry and radial velocity (RV) measurements enables the planetary density to be found, providing constraints on planetary composition. Whilst this provides clues to the formation processes at work, the Rossiter-McLaughlin (RM) effect is thought to be a complementary probe of exoplanet dynamical histories. The RM effect is measured using in-transit spectroscopic observations, revealing a deviation from the Keplerian orbital motion as the star orbits the barycentre of the star-planet system. The RM waveform allows the sky projected spin-orbit alignment angle, the angle between the rotation axis of the host star and the normal to the planetary orbital plane to be determined. Hot-Jupiters are known to migrate in to their short period orbits either via dynamically gentle planet-disk interactions or more dynamically violent gravitational interactions (e.g. Kozai-Lidov mechanism). Thus, measuring the alignment of exoplanets around a range of host stars is thought to give an insight into how hot-Jupiters migrate and dynamically evolve. I will present Rossiter-McLaughlin observations of WASP-13b, WASP-32b and WASP-37b observed with the SOPHIE spectrograph mounted on the 1.93m telescope at the Observatoire Haute Provence (OHP). I’ll discuss modelling the RM profile for all systems and what this might tell us about how these planets migrated. For the WASP-32 system, star-spot modulations in SuperWASP light-curves allowed us to measure the stellar rotation period and the stellar inclination. This allowed us to measure the true 3D alignment angle of the system, indicating WASP-32b is unambiguously aligned. Finally, I’ll discuss the alignment of exoplanets orbiting `cool' host stars. Our analysis lends further evidence that tidal interactions play an important role in aligning the stellar rotation axis with the normal to the planetary orbital plane.
Dr Louise Harra - ARC Seminar on Wed., 2014 Apr. 2, 16h
I will discuss observations of different levels of solar activity made by Hinode, SDO and IRIS.The two main science goals are 'what causes the slow solar wind?' and 'what triggers solar flares?'. Observations from Hinode have revealed persistent upflow at the edges of active regions - I will discuss how we can determine whether this upflow can form part of the solar wind or not. The triggering of solar flares can start at a very small spatial scale on the Sun - and can be related to large-scale global events related to coronal mass ejections. I'll discuss both the small-scale triggering and global response. Finally I'll describe the future Solar Orbiter and Solar-C missions.
Colin Hill - ARC Seminar on Wed., 2014 Mar. 5, 16h
Differential rotation of a solar-like star is thought to be a key component in stellar dynamo theory, and comparisons between systems of varying fundamental parameters is crucial for our understanding of the underlying dynamo mechanism. To this end, a measure of the differential rotation rate on cataclysmic variables would allow a test of dynamo theory in a parameter space with both rapid rotation and tidal distortion. Magnetic activity plays a critical role in the evolution and behaviour of CVs, and since differential rotation is a key component of such activity, a study of the secondary star in CVs allows a test of stellar dynamo theory and further insight into this class of system. Using the indirect imaging technique of Roche tomography, we have unambiguously imaged starspots on two Roche tomograms of the secondary star in the cataclysmic variable AE Aqr. In this talk I will discuss the techniques used to create these tomograms. I will show the number, size and distribution of starspots imaged, and using them as a tracer, I will present measurements of the differential rotation rate, showing that the secondary star is not fully tidally locked, as was previously assumed for CVs.
Michael Kennedy - ARC Seminar on Wed., 2014 Feb. 26, 16h
Solar flares are highly energetic events that occur on the Sun due to the process of magnetic reconnection in the solar corona. During the early stage of a flare, energy is deposited in the lower layers of the atmosphere by non-thermal electrons which lose their energy through electron-electron Coulomb collisions. In this talk I present results from extreme-ultraviolet and X-ray observations of a large solar flare that occurred on 9th March 2011. Analysis of hard X-ray spectra was performed to determine the evolution of the non-thermal electron beam parameters that describe how energy is deposited in the atmosphere. The response of the solar atmosphere to electron beam heating was then modelled using a 1D radiative transfer and hydrodynamics code to investigate the temperature and density structure, and energy transfer through the lower atmosphere during flares.
Dr. Richard Stancliffe (Bonn) - ARC Seminar on Wed., 2014 Jan. 29, 16h
A surprisingly large fraction of metal-poor stars are found to be carbon-rich. In addition, many of these display enhancements of neutron capture elements which give clues to their origin. I will discuss what we think we know about these so-called carbon-enhanced metal-poor (CEMP) stars, with a focus on those that display barium enrichments. These CEMP stars are thought to be formed in binary star systems that formerly contained an asymptotic giant branch (AGB) star, which polluted its companion through mass transfer. I will review our picture of AGB nucleosynthesis at low metallicity, how we think mass transfer happens and what happens to material once it is accreted by the secondary. This will highlight the problems we have when we try to confront observed CEMP star abundances with predictions from increasingly detailed stellar models.
Dr. Dimitri Veras - ARC Seminar on Fri, 2014 Jan. 24, 16h. Venue: Bell LT
One of the great challenges of planetary science is to identify the mechanisms which lead to abundant metal pollution in the atmospheres of over one quarter of hydrogen-rich white dwarfs and one third of helium-rich white dwarfs. Compounding the difficulty is the complete absence of confirmed exoplanets orbiting white dwarfs, even though the pollution must be generated from circumstellar material and not the interstellar medium. In this talk, I outline the wide-ranging topics which must be considered to tackle this problem, and show how advances in long-term stability analyses, tidal theory, stellar evolution, disk evolution, collisional fragmentation and mass loss-induced orbital dynamics have made progress towards finding a solution.
Prof. Katherine Blundell (Uni. of Oxford) Wed. 2014 Jan. 22 Venue: Bell LT
Black holes in our Galaxy, such as those in the microquasars SS433 and Cygnus X-3, demonstrate dynamic behaviour in accretion and dramatic mass outflows. We observe winds and relativistic plasma jets to emerge from these objects which resemble the modes of mass-loss in the supermassive black holes of powerful quasars in the distant universe. Time-resolved observations of the accretion and subsequent mass-loss from microquasars offers great rewards in terms of information about the nature of these remarkable phenomena in the Universe. I will describe how combined multi-wavelength strategies across the electromagnetic spectrum continue to yield new discoveries and discuss how time-resolved observations have led to the discovery of a further mode of mass-loss in SS433 via a circumbinary disc. I shall present the exquisitely detailed behaviour of these modes of mass-loss before, during and after a major flare event in this object, with reference to comparable behaviour seen in similar objects.
Emma Reilly (QUB) - ARC Seminar on Wed, 2013 Nov. 27, 16h. Venue: IRCEP Seminar Rm.
SN 2009ip has left the Supernovae community guessing since its first classification as a SN imposter in 2009. Its incredible eruptions in 2012 have called into question the Type IIn classification and the evolution of massive stars. Spectropolarimetry is an observing technique that allows us to determine the 3D structure of distant SN explosions, beyond the direct imaging capabilities of current optical telescopes. Here we present a sequence of spectropolarimetric observations of SN 2009ip, acquired with ESO VLT FORS in November and December 2012 catching the decline of the remarkable 2012b event. The data indicates that both the photosphere and the line forming regions are highly aspherical and dynamic. The continuum polarisation shows a major change in observations conducted before and after a dramatic drop in the optical lightcurve, also exhibiting a gradual rotation of the polarization angle of 60 degrees. The significant line polarization (~1-1.5%) observed for Halpha suggests a highly aspherical, possibly disk-like line forming region. The polarization line profiles of H alpha, H beta and Na I D indicate that they arise in a shared clumpy line forming region. These unparalleled observations indicate that not only is this event highly aspherical but that material from the latest outburst is misaligned with material from the previous eruptions of this rare transient. We propose that polarimetric observations rule out a spherically symmetric explosion event, and are instead consistent with a disk-like configuration for the CSM. These spectropolarimetric observations suggest that previous observations need to be considered in light of its peculiar, asymmetric structure.
Matt Nicholl(QUB) - ARC Seminar on Wed, 2013 Nov. 20, 16h. Venue: IRCEP Seminar Rm.
In the last decade, unbiased transient surveys have discovered a number of supernovae that are 10-100 times brighter than previously known supernova types; these have been classified as “super-luminous” supernovae. The mechanism which powers their extreme luminosities is still unclear. Popular theories include rotational power from a rapidly spinning magnetar, very high radioactive nickel masses from 'pair-instability supernovae', and collisions between massive shells of dense material. In this talk, we will look briefly at each of these theories, before I present some recent observations and modelling of two unusual, slowly fading super-luminous supernovae, which may be useful in discriminating between these theoretical scenarios. Finally, I will show some objects from the PESSTO survey, and look at what we are learning from this sample.
Mattia Bulla (QUB) - ARC Seminar on Wed, 2013 Nov. 06, 16h. Venue: IRCEP Seminar Rm.
Notwithstanding their importance in cosmology, Type Ia Supernovae (SNIa) represent a puzzle, in that the nature of their progenitor/s is still unclear. The discovery of circum-stellar material around some SNIa has confirmed that the symbiotic channel contributes to some fraction of the observed SNIa rate. This conclusion has received strong support by the recent study conducted by our collaboration on RS Oph, a recurrent nova system proposed as a possible channel to SNIa explosions, based on the high mass of the accreting White Dwarf. This work has demonstrated that this system is surrounded by a complex circum-stellar environment, hence establishing a direct link with what is seen in some SNIa. In my presentation I will discuss the work I carried out in the context of my Master thesis, a detailed study of RS Oph through high-resolution (R=80,000), high signal-to-noise (>100 at 6000A), multi-epoch spectroscopy. The data were obtained with VLT-UVES during the first part of an observing campaign aimed at sampling the full orbital period (about 460 days). I will illustrate the main results obtained so far, discuss the problems encountered during the study and present the prospects for a further and deeper analysis.
Dr. Cosimo Inserra (QUB) - ARC Seminar on Wed, 2013 Oct. 23, 16h. Venue: IRCEP Seminar Rm.
In the last five years, a population of super-luminous supernovae has been identified, which have absolute magnitudes in the range -21 to -23. These supernovae appear to occur exclusively in dwarf host galaxies but the cause of their extreme luminosity remains unknown. Theories include magnetar spin down, pair-instability explosions, shell collisions, and jet driven explosions. We show a sample of “nearby” SL-SNe (Ic type) able to “shed some light” on this newborn class. The sample points toward an explosion driven by a magnetar as a viable explanation for all SL-SNe Ic. Their high luminosity is also attracting considerable attention to the potential utility of these objects in cosmology and we will show the first steps in this direction, looking for a possible method to standardise them.
Dr. Vasco Henriques (QUB) - ARC Seminar on Wed, 2013 Oct. 16, 16h. Venue: IRCEP Seminar Rm.
Sunspots are dark and colder than the rest of the Sun due the inhibition of convection by large concentrations of magnetic flux. However, the temperature of a sunspot penumbra is much closer to that of the convective granulation pattern that covers most of the surface of the Sun than to that of the dark central umbra. The strong magnetic field observed in the penumbra and its structure led investigators to focus on developing models of the penumbra based on interlocking fluxtubes. Different mechanisms involving heat transport along these fluxtubes or with material trapped inside rising fluxtubes were proposed and simulated. High resolution spectro-polarimetric observations at the Swedish 1-meter Solar Telescope discovered a pattern of convective flows supporting an alternative model that includes convection as the supplier of heat and part of the structuring forces as well as a driver of the Evershed flow, a strong radial flow from the umbra to the outer edge of sunspots. We revisit some of the challenges that were faced to reach such result and techniques developed in the process. With the same instrument and techniques we at QUB recently obtained and processed high-resolution, multi-line, spectro-polarimetric data that we hope will give us understanding on rotating structures in the chromosphere that were recently claimed to contribute heat to the chromosphere and maybe even to the corona. Some of the promising high-resolution photospheric magnetograms and chromospheric Dopplergrams from such data are presented.
Dr. Vivienne Wild (St. Andrews) - ARC Seminar on Wed, 2013 Oct. 02, 16h. Venue: IRCEP Seminar Rm.
Massive bursts of star formation represent a transient, and perhaps infrequent phase in the life of massive galaxies, and recent studies are pointing towards a scenario in which the majority of stars in the Universe are formed in a more “quiescent” mode of star formation. However, starbursts triggered by gas-rich mergers at high redshift remain the leading contender for the morphological and spectral disruption required to form the bimodal Hubble sequence. I will present recent work to track the observational properties of an evolving sample of starburst galaxies for half a Gyr following the starburst, from the Sloan Digital Sky Survey at low redshift, the Vimos VLT Deep Survey at z~1, and multi wavelength CANDELS survey at z>1. I will show how black hole growth, star formation rate, gas and dust content and morphology evolves following a starburst, and show how we can use these methods to track the contribution of major gas-rich mergers to the birth and growth of elliptical galaxies.
Darryl Wright (QUB) - ARC Seminar on Wed, 2013 Jun. 19, 16h. Venue: IRCEP Seminar Rm.
The advent of time-domain astrophysics is a product of the availability of extensive data streams of transient events from digital synoptic sky surveys. While these surveys can autonomously transport, process and ingest the data into databases efficiently, the nature of digital imaging means that noise and artefacts can resemble real astrophysical sources. We are investigating machine learning approaches for artefact rejection within the PanSTARRS-1 Medium Deep Survey.
Dr. Nic Walton (IoA) - ARC Seminar on Wed, 2013 Jun. 12, 16h. Venue: IRCEP Seminar Rm.
Gaia is the next ESA large astronomy mission set to launch in September 2013. It will revolutionise our understanding of the Milky Way through its exquisite new determinations of the distances and motions of the stars in our Galaxy. The talk will present the key scientific goals of Gaia, and discuss the current mission status, along with a description of the science data which the community can expect from Gaia and the time line for the release of that data. I will also note the impact Gaia will have in observing the transient sky and in particular how it will be an important tool in supernova discovery.
Prof. Brad Gibson (UCLAN) - ARC Seminar on Wed, 2013 May. 15, 16h. Venue: IRCEP Seminar Rm.
The history of disk galaxy simulation is dotted with remarkable successes, tempered by frustrating impasses, including an inability to recover anything remotely similar to a late-type spiral. Recent advances suggest that we might have made a breakthrough by generating essentially bulgeless disks. I will examine the evidence for this new-found optimism and identify where the shortcomings suggest we should be concentrating our future efforts
Ting-wan Chen (a.k.a. Janet) - ARC Seminar on Wed, 2013 May. 15, 16h. Venue: IRCEP Seminar Rm.
Recently, the new generation wild-field survey telescopes, such as Pan-STARRS, have carried out surveys for SNe without an inherent galaxy bias; hence, a new type of SNe- “super-luminous supernovae (SLSNe)” was discovered. They are 10 to 100 times brighter than normal supernovae. However, the mechanism that causes the high luminosity is still unknown. One important clue is to study their unique host galaxy environments, which typically have low mass and low metallicity, but high specific star formation rates. In this talk, I will introduce our basic understanding of SLSNe from two precious events: SN2010gx and PS1-12arh. We found the host of SN2010gx to have a remarkably low metallicity of 12 + log (O/H) = 7.5 ± 0.1 dex (equal to 0.06 solar metallicity) as determined from the detection of the [OIII] λ4363 line; moreover, the host of PS1-12arh also shows a low metallicity of 8.0 ± 0.2 dex (~ 0.2 solar metallicity). We keep collecting more host galaxy samples, if the low metallicity is a common factor among them, it will be a major constraint on the progenitor channel of SLSNe, and it also helps to explain the low volumetric rates (∼10−4 of the core-collapse population) of the SLSNe detected so far.
Dr. Philip Best (ROE) - ARC Seminar on Wed, 2013 May. 08, 16h. Venue: IRCEP Seminar Rm.
HiZELS, the High-z Emission Line Survey, has been a successful panoramic narrow-band Campaign Survey using WFCAM on UKIRT to detect and study emission line galaxies over the history of the Universe. HiZELS employs narrow-band filters in the J, H and K-bands, with the primary aim of delivering large identically-selected samples of H-alpha emitting galaxies at redshifts of 0.84, 1.47 and 2.23. I will describe the main scientific results obtained so far: determination of the H-alpha luminosity function and measurement of the evolution of the cosmic star-formation rate density across the peak epoch of star-formation activity in the Universe, using a single star-formation indicator; determination of the morphologies, environments, metallicities and dust-content of the star-forming galaxies; a detailed investigation of the evolution of their clustering properties; and a study of the dependence of star-formation on mass and environment at high redshift.
Alan McLoughlin (QUB) - ARC Seminar on Wed, 2013 Apr. 24, 16h. Venue: IRCEP Seminar Rm.
Protoplanetary disks (PPDs) around T-Tauri stars are of interest because they represent the formative stages of our Solar System. Observational programs - such as ALMA - of these objects must be informed by and interpreted in light of both theory and modelling. The UMIST Database For Astrochemistry (UDFA) Rate12 has been integrated into an existing PPD model. The physical conditions of the disk required additions to the gas phase reactions of Rate12: Spectrum dependent rates for photoreactions (where available), grain accretion and desorption, surface chemistry, non-thermal desorption.
Dr. Ryan Milligan (QUB) - ARC Seminar on Wed, 2013 Apr. 17, 16h. Venue: IRCEP Seminar Rm.
For the past 3 years NASA's Solar Dynamics Observatory (SDO) has been providing unprecedented views of our Sun. SDO's primarily objective is to understand solar variability, on a wide range of timescales, and how this variability influences life on Earth and humanity's technological systems. It does so by a combination of high-resolution imaging and spectroscopy: the AIA (Atmospheric Imaging Assembly) instrument can image the Sun at resolutions 10 times greater than HD TV, while the EUV Variability Experiment (EVE) can quantify the most geoeffective component of the solar irradiance. However, the EVE data can also be used to determine fundamental properties of solar flares themselves; a major cause of solar variability. Accurate measurements of these properties (such as temperature, density and energy), and the time scales on which they vary, are crucial for comparing with current solar flare models to determine how these huge quantities of energy are released. Here I will present a number of recent advances made by novel analyses of EVE data, and how they relate to our understanding of solar activity over the rise of the current solar cycle.
Prof. Serena Viti (UCL) - ARC Seminar on Wed, 2013 Mar. 27, 16h. Venue: IRCEP Seminar Rm.
It is now well established that chemistry in our own galaxy as well as in external galaxies can be complex and well-developed. In particular, molecular emissions can be used to explore the physical conditions and the likely evolutionary status of near and far away galaxies. In this talk, I will review recent developments in observational as well as theoretical molecular astrophysics in the context of galactic, nearby and more distant galaxies. I will show how, even for the most distant galaxies, multi-species multi-transitions molecular emissions can be used as a tool to 'disentangle' the multiple and spatially unresolved gas components, with particular emphasis on tracing the star forming gas within a galaxy.
Ev McLoughlin (QUB) - ARC Seminar on Wed, 2013 Mar. 20, 16h. Venue: Bell LT
The Pan-STARRS 1 (PS1) telescope in Hawaii has been surveying the sky since 2010 and the quality of astrometry and photometry together with repeated coverage of the same areas of the sky enables discovery of various interesting objects and events down to magnitude 22.5. The Main Asteroid Belt is collisionally dominated with asteroids’ shapes, sizes and surface geology dominated by impacts. Two collisions observed recently have sparked interest in the phenomenon: asteroid P/2010 A2 in 2009 and asteroid (596) Scheila in 2010 . Events like the (596) Scheila collision should occur approximately every 5 years and collisions with asteroids <10m even more often. Studying these events can provide insights in asteroid structure and evolution. The brightness of impacted asteroids will temporarily increase due to material being ejected off their surface. I have made initial examination of 335 nights worth of PS1 data to compile a list of possible collision candidates. Both archive and current data were analysed to look for anomalous increases in brightness of known asteroids that might be indicative of a collision. Current results and sample data will be shown
David Kuridze (QUB) - ARC Seminar on Wed, 2013 Mar. 06, 16h. Venue: IRCEP Sem. Rm
The chromosphere is the highly dynamic region of the solar atmosphere between the photosphere and corona. It is dominated by fine-scale, jet-like structures, such as limb spicules, on-disc mottles and active region fibrils. These plasma jets are thought to play a significant role in the mass and anergy balance of the solar atmosphere. Modern high-resolution and multi-wavelength observations from space and ground-based telescopes have increased significantly our understanding of these structures and their oscillation properties. I discuss recent progress in this area on the theoretical and observational sides.
Dr John Magorrian (Oxford) - ARC Seminar on Wed, 2013 Feb. 20, 16h. Venue: IRCEP Sem. Rm.
In M31 is the nearest large galaxy for which we have a dust-free multi-wavelength picture of its central regions. It presents some puzzles. The inner few parsecs are dominated by a double nucleus, which is most naturally explained by Tremaine's model of an eccentric disc of old stars around a supermassive black hole. A more recent surprise is the discovery of a very compact cluster of young stars around the black hole. I review ongoing work on the construction of a coherent picture of this system
Peter Keys (QUB) - ARC Seminar on Wed, 2013 Feb. 13, 16h. Venue: IRCEP Sem. Rm.
In the past few years, advancements in both optical components, detector technology and reconstruction techniques has meant that we now have unprecedented images of the lower solar atmosphere. As such, small-scale magnetic transients can be observed with these high temporal, high spatial resolution observations. These features are important in transporting energy through the solar atmosphere and so in this seminar I will discuss how these features form and the properties and phenomena associated with them.
Dr. Chiaki Kobayashi (Uni. of Hertfordshire) - ARC Seminar on Wed, 2012 Nov. 28, 16h. Venue: IRCEP Sem. Rm.
From the observed initial conditions, a snapshot of the Universe at about 300, 000 years after the Big Bang, I am simulating the formation and evolution of galaxies over 13 billion years using a super computer. In the galaxies, stars are born and die, explode as supernovae, and eject heavy elements such as carbon and oxygen, from which human beings are born. Comparing with observations of nearby and distant galaxies, I will summarize what we know about the origin of elements.
Dr. Cosimo Inserra (QUB) - ARC Seminar on Wed, 2012 Nov. 21, 16h. Venue: IRCEP Sem. Rm.
Decades after the first detailed study of a SN, the nature of these events is still surprising. New classes (or subclasses) have been discovered in the past years challenging the paradigm of the physics and enriching the “zoo” of the SNe. Recent searches by unbiased, wide-field surveys have uncovered a group of extremely luminous (Mu ~ −22) optical transients associated with very faint host galaxies (typically Mg > −17). Detailed study of the “ultra-luminous type I” SN 2010gx showed an unexpected transformation of the transient into a fairly normal type Ic SN and an enormous luminosity at peak that cannot be powered by radioactive 56Ni. Then, the physical mechanism that produces the luminosity is uncertain, with suggestions ranging from spin down of a rapidly rotating young magnetar to interaction of the SN ejecta with a massive (3-5M⊙) C/O-rich circumstellar medium.
In this talk we show the evolution of new 5 ULSNe. The “late” light curves, differently from the other objects, seem powered by 56Ni, implying Ni masses close to 1M⊙. This new evidence poses intriguing and open problems in understanding the physics of the explosions and the nature of the progenitor stars.
Heather Cegla (QUB) - ARC Seminar on Wed, 2012 Nov. 07, 16h. Venue: IRCEP Sem. Rm.
Space-based, photometric surveys have moved us into a new era of exoplanet discovery. In order to confirm the masses and hence the planetary nature of exoplanet candidates from such surveys, radial velocity (RV) follow up is mandatory. To do this for low-mass planets typically requires cm/s RV precision. However, astrophysical noise sources (or stellar jitter) due to spots, plages, granulation and stellar oscillations, for example, become an issue at the m/s level. These phenomena alter the shape of the stellar absorption lines, injecting spurious or systematic RV signals that may mask or mimic planetary signals. As such, 'quiet’ stars (those with little activity) are the most likely candidates for the detection of low-mass planets, but even these stars will still exhibit some stellar jitter. I present our techniques to explore stellar jitter due to granulation through the use of sophisticated radiative three-dimensional magnetohydrodynamical solar simulations to develop a multi-component parameterisation of stellar surface magneto-convection.
Dr. Daniel Mortlock (Imperial College London) - ARC Seminar on Wed, 2012 Oct. 31, 16h. Venue: IRCEP Sem. Rm.
Quasars are powerful probes of the early Universe, although until recently it has not been practical to search for quasars beyond a redshift of z > 6.5 because they have been identified primarily in optical surveys. Using data from the UKIRT Infrared Deep Sky Survey (UKIDSS), it has been possible to search beyond this optical limit. I will describe the latest results for this survey, focussing on the search methodology and the implications for cosmological reionization out to a redshift of ~7.
Dr. Morgan Fraser (QUB) - ARC Seminar on Wed, 2012 Oct. 24, 16h. Venue: IRCEP Sem. Rm.
In the past decade, the combination of high-resolution space and ground-based imaging has allowed the direct detection of the massive stellar progenitors of core-collapse supernovae. While some supernova types have been linked to particular mass progenitors (for example, hydrogen rich Type IIP supernovae have been seen to come from ~8-16 solar mass red supergiants), other supernova subtypes have proven more elusive. I discuss recent progress in this field, the observational techniques which permit us to study single stars at extragalactic distances, and some of the prospects for the future.
Mr. John Burton (QUB) - ARC Seminar on Wed, 2012 Oct. 17, 16h. Venue: IRCEP Sem. Rm.
We present the ground-based detection of the secondary eclipse of the transiting exoplanet WASP-19b. The observations were made in the Sloan z'-band using the ULTRACAM triple-beam CCD camera mounted on the NTT. The measurement shows a 0.088±0.019% eclipse depth, matching previous predictions based on H- and K-band measurements. We discuss in detail our approach to the removal of errors arising due to systematics in the data set, in addition to fitting a model transit to our data. This fit returns an eclipse centre, T0, of 2455578.7676 HJD, consistent with a circular orbit. Our measurement of the secondary eclipse depth is also compared to model atmospheres of WASP-19b, and is found to be consistent with previous measurements at longer wavelengths for the model atmospheres we investigated.
Dr. Nicolas Labrosse (Uni. of Glasgow) - ARC Seminar on Wednesday, 12pm, 2012 Oct. 10
Theoretical calculations have shown that when solar prominences move away from the surface of the Sun, their radiative output is affected via the Doppler dimming or brightening effects. I will first explain how these calculations are carried out, what assumptions are made, and why this theoretical prediction is important. The question is then to ask whether observational signatures of the changes in the radiative output of eruptive prominences can be found in EUV (extreme ultraviolet) observations. We first look for suitable events in the SDO/AIA database. The variation of intensity of arbitrarily selected features in the He II 304 channel is studied as a function of velocity in the plane of the sky. These results are then compared with new non-LTE radiative transfer calculations of the intensity of the He II 304 resonance line. We find that observations of intensities in various parts of the four eruptive prominences studied here are sometimes consistent with the Doppler dimming effect on the He II 304 Å line. However, in some cases, one observes an increase in intensity in the 304 channel with velocity, in contradiction to what is expected from the Doppler dimming effect alone. The use of the non-LTE models allows us to explain the different behaviour of the intensity by changes in the plasma parameters inside the prominence, in particular the column mass of the plasma and its temperature. These non-LTE models are more realistic than what was used in previous calculations. They are able to reproduce qualitatively the range of observations from SDO/AIA analysed in this study. With the help of non-LTE modelling, we can infer the plasma parameters in eruptive prominences from SDO/AIA observations at 304 Å. EUI (Extreme Ultraviolet Imager) on Solar Orbiter will monitor the low atmosphere counterparts of large-scale solar eruptive events such as CMEs. As such it will ideally be suited to study prominence eruptions. I will discuss what we may learn from data returned by the High Resolution Imagers (HRI) in the Lyman α channel, and the Full=Sun Imager (FSI) working at the 304 A EUV passband.
Dr. Leslie Sage - School Seminar on Mon, 2012 Oct. 08 15h venue: Emeleus LT
Nature is one of the world's leading scientific journals, publishing many papers that receive wide attention by the general public. But, Nature is very selective– <7% of submitted papers are published. In order to maximize your chances of getting published, papers should present fundamental new physical insights, or startling observations/results. Theory papers pose additional problems, as we want only those papers that are likely to be the correct explanation, and not simply exploring parameter space. The writing should be clear, concise and directed at the level of a graduate course in the subject. I encourage authors to contact me in advance of submission of a paper, both to ascertain the appropriateness of the result for Nature, and to ensure that the writing is close to our standards. Posting to ArXiv is and always has been allowed, but authors should discuss the specifics with their institutional public affairs officers before doing so.
Dr. Kanti Aggarwal (QUB) - ARC Seminar on Wednesday, 2012 Oct. 03
In this seminar atomic data (namely energy levels, radiative rates, life-times, electron impact excitation collision strengths, and rate coefficients) will be discussed for a variety of ions, which are of particular interest to fusion plasmas. These results are theoretical from the fully relativistic GRASP (General purpose Relativistic Atomic Structure Package) and DARC (Dirac Atomic R-matrix Code) programs. The difficulties of performing large calculations, and importance of including relativistic effects and resonances in the determination of excitation rates will be highlighted. Comparisons will be shown and discrepancies with other available data from Distorted Wave codes, non-relativistic results, and with other semi-relativistic R-matrix results will be discussed. Results will specifically be presented from our recent calculations on H-, He- and Li-like ions up to Z = 36. Finally, comparisons between theory and measurements will be shown for the C IV emissions from the JET divertor.
Melvin Hoare (Leeds Uni.) - ARC Seminar on Wednesday, 2012 June 13
I will describe two different surveys of the Galactic Plane to systematically study massive star formation in our Galaxy. The first is the Red MSX Source (RMS) survey that uses a mid-IR satellite survey followed up by a large ground-based campaign to identify the largest sample of massive young stellar objects to date. Results on their luminosity function and distribution will be presented that constrain models for massive star formation. The second survey is the CORNISH survey that uses radio continuum surveys to deliver a large, well-selected sample of ultra-compact H II regions. This phase when ionization of the surrounding material has started is important for both triggering and quenching further star formation.
Lyndsay Fletcher (U. Glasgow) - ARC Seminar on Wednesday, 2012 May 23
Solar flares are short, dramatic episodes of energy release occurring in the atmosphere of the Sun. During flares, stressed magnetic fields suddenly reconfigure and relax, converting magnetic energy into the kinetic energy of large numbers of non-thermal charged particles, heating the solar atmosphere, and leading to ejections of field-bearing plasma into the heliosphere. Particle acceleration during flares is extremely efficient, converting around 50% of the stored energy, but the basic acceleration mechanism is still a puzzle. Recent imaging and spectroscopic observations are confronting some aspects of the 'standard model' of a flare; these will be reviewed, and different theoretical frameworks for flare particle acceleration will be discussed.
Cristina Popescu (UCLAN) - ARC Seminar on Thurs. 2012 April 25
Dust strongly affects the apparent luminosity and appearance of spiral galaxies in the UV and optical regimes, redistributing the absorbed starlight between the mid-IR and far-IR/submillimeter spectral ranges. In this colloquium I will describe a self consistent model for the propagation, absorption and re-emission of stellar light in spiral galaxies, incorporating a realistic, empirically constrained description of the relative geometries of dust and stars associated with the principal stellar populations. A minimal number of fundamental physical parameters controlling the form of the SED in direct and reradiated stellar light are identified. Some applications of the model are presented, both for resolved nearby galaxies and for a large statistical sample of spiral galaxies in the local universe observed in the GAMA and H-ATLAS surveys.
David Jewitt (UCLA) - ARC Seminar on Tuesday, 2012 March 20
In addition to the major planets, the solar system contains a large number of so-called small bodies in dynamically distinct reservoirs. These include the main-belt asteroids, main-belt comets, Trojans, Centaurs, irregular satellites, the comets of the Oort cloud and Kuiper belt, and others. These reservoirs are important both for the relics of solar system formation contained therein, and as sources for short-lived populations in the inner solar system. For the most part, the small body populations were discovered recently, their investigation is still firmly in the exploration phase and much of the excitement in planetary science stems directly from them.
I will use new observations of three “freak” and very surprising objects as a vehicle to discuss the small body populations, to highlight our ignorance of even basic issues in the origin and evolution of the solar system, and to indicate potentially productive paths to future research.