Table of Contents

ARC Seminar Abstracts

Revealing the Evolution of Comet Nuclei with Ground Photometric Observations

Dr Rosita Kokotanekova (ESO)- ARC Seminar Wednesday 12 December 2018 3 pm

The complex nature of comets has earned them a spot among the most interesting objects in the Solar System. Comets are believed to still preserve information about the physical conditions in the protoplanetary disk. At the same time, they also bear signatures of the epoch of planetary migration ~4 billion years ago, of the time spent in the outer solar system, as well as of their recent activity. In the past three decades, a great progress in untangling the intricate history of comets has come from the in-situ studies during a series of space missions which culminated with the Rosetta mission between 2014 and 2016. However, with no plans for space missions to further comets in the next couple of decades, we have to rely more heavily on telescope observations to reveal new clues on the unanswered questions in cometary science. In this talk, I will present results from our effort to study Jupiter-family comet nuclei and their source populations in the Centaur region and the Kuiper Belt from the ground. This work has demonstrated that photometric observations of the rotation and surface properties of comet nuclei can be key for understanding their evolution.

Internal Gravity Waves in Massive Stars

Dr Tamara Rogers (Newcastle University)- ARC Seminar Wednesday 05 December 2018 1 pm

Internal Gravity Waves (IGW) can lead to angular momentum transport and chemical mixing in stellar interiors. In this talk I will present numerical simulations of these waves in massive stars and discuss how they might contribute to the understanding of a variety of observational mysteries.

Unveiling extreme dusty star-formation in the distant Universe

Dr Julie Wardlow (Lancaster University)- ARC Seminar Wednesday 28 November 2018 3.30 pm

In recent years the high-redshift Universe has been increasingly opened to scrutiny at far-infrared wavelengths, where cool dust emission from star-formation dominates. The dusty star-forming galaxies (DSFGs), selected at these wavelengths likely represent an important, but short-lived phase in the growth of massive galaxies. These DSFGs often have star-formation rates in excess of ~1000 solar masses per year and are confirmed beyond z~6, although their redshifts and high dust contents make them faint and difficult to study at other wavelengths. I will present results probing their nature and the triggering mechanisms of their immense star-formation rates, using data from ALMA and other leading facilities.

Transverse Wave Induced Kelvin-Helmholtz Rolls in Spicules

Dr Patrick Antolin (University of St. Andrews)- ARC Seminar Wednesday 21 November 2018 3pm

In addition to their jet-like dynamic behavior, spicules usually exhibit strong transverse speeds, multi-stranded structure, and heating from chromospheric to transition region temperatures. In this work we first analyze Hinode and IRIS observations of spicules and find different behaviors in terms of their Doppler velocity evolution and collective motion of their sub-structure. Some have a Doppler shift sign change that is rather fixed along the spicule axis, and lack coherence in the oscillatory motion of strand-like structure, matching rotation models, or long- wavelength torsional Alfvén waves. Others exhibit a Doppler shift sign change at maximum displacement and coherent motion of their strands, suggesting a collective magnetohydrodynamic (MHD) wave. By comparing with an idealized 3D MHD simulation combined with radiative transfer modeling, we analyze the role of transverse MHD waves and associated instabilities in spicule-like features. We find that transverse wave induced Kelvin– Helmholtz (TWIKH) rolls lead to coherence of strand-like structure in imaging and spectral maps, as seen in some observations. The rapid transverse dynamics and the density and temperature gradients at the spicule boundary lead to ring-shaped Mg II k and Ca II H source functions in the transverse cross-section, potentially allowing IRIS to capture the Kelvin–Helmholtz instability dynamics. Twists and currents propagate along the spicule at Alfvénic speeds, and the temperature variations within TWIKH rolls, produce the sudden appearance/disappearance of strands seen in Doppler velocity and in Ca II H intensity. However, only a mild intensity increase in higher-temperature lines is obtained, suggesting there is an additional heating mechanism at work in spicules.

The origin of the highest energy particles in the universe: A "Whodunnit"

Dr James Matthews (Oxford)- ARC Seminar Wednesday 7 November 2018 1pm

The origin of ultra-high energy cosmic rays (UHECRs) - protons and nuclei striking our atmosphere with energies extending beyond 1e20 eV - has been an open question for decades. In this talk I will review what we know about UHECRs from an observational and theoretical perspective, focusing particularly on diffusive shock acceleration. I will discuss the physical requirements for acceleration, before exploring whether radio galaxies might meet these requirements. Aided by hydrodynamic simulations, I will show that shocks can be formed in backflows in the radio lobe and that these shocks are better accelerators to ultra-high energies than the relativistic termination shock. I will then discuss a model in which giant-lobed radio galaxies such as Centaurus A and Fornax A act as slowly-leaking UHECR reservoirs, with the UHECRs being accelerated during a more powerful past episode. These radio galaxies may also explain the observed hotspots in the UHECR data, but deflections in Galactic and extragalactic magnetic fields make robust associations difficult.

A Nanoflare Explanation for Periodic Variations in Flare Stars -- A Solar Physicist's Adventure in Single Pixel Land

Christopher Dillon (QUB)- ARC Seminar Wednesday 31 October 2018 3pm

Several studies have documented periodic and quasi-periodic signals from the time series of dMe flare stars and other stellar sources. Such periodic signals, observed within quiescent phases (i.e., devoid of larger-scale microflare or flare activity), range in period from 1-1000 seconds and hence have been tentatively linked to ubiquitous p-mode oscillations generated in the convective layers of the star. As such, most interpretations for the observed periodicities have been framed in terms of magneto-hydrodynamic wave behavior. However, we propose that a series of continuous nanoflares, based upon a power-law distribution, can provide a similar periodic signal in the associated synthetic time series. Monte Carlo simulations, embodying the nanoflare signals and modelled noise profiles, produces a time series consistent with previous observations of dMe flare star lightcurves. Through an examination of nanoflare decay timescales and differing power-law indices, we provide evidence that periodic signals found in stellar time series can be explained by low-energy nanoflares embedded within the noise envelope of a stellar lightcurve. Phenomena traditionally considered a consequence of wave behaviour may be described by a number of high frequency but discrete nanoflare energy events.

ATLAS Shrugged: The search for gravitational wave counterparts with an asteroid survey

Owen McBrien (QUB)- ARC Seminar Wednesday 24 October 2018 3pm

The Laser Interferometer Gravitational-wave Observatory (LIGO) has completed two observing runs between 12th September 2015 and 25th August 2017 and found a host of gravitational wave (GW) signals owing to compact binary coalescences of massive bodies and atypical bursts of unknown origin. In the wake of any of these GW triggers however, large portions of the sky must be combed with optical instruments in the hope of identifying a visible counterpart to the GW source. This is realisable with high-cadence, full time surveys such as ATLAS, the Asteroid Terrestrial-impact Last Alert System. I will present this ATLAS search for optical counterparts to several LIGO burst triggers as well as the ATLAS search for kilonovae following the discovery of AT2017gfo last August and discuss how this will inform our follow-up campaign to triggers announced during the third LIGO observing run next year.

Concerning type Ibc supernovae

Dr Simon Prentice (QUB)- ARC Seminar Wednesday 17 October 2018 3pm

Type Ibc supernovae (aka stripped-envelope supernovae) are the final act of massive stars that have been stripped of their He and/or H envelopes. These explosions are amongst the most energetic in the Universe, and can even power gamma-ray bursts. However, despite many well observed examples, their origins are not well understood. Stellar evolution predicts they arise from very massive stars, but this is inconsistent with the observations. I will present analysis of the largest data set of SE-SNe light curves to date, and physical parameters derived from these. I will show that these objects are diverse in their properties and that the results favour “low” high mass stars, stripped through binary interaction, as the progenitors for these events.

High resolution ALMA imaging of SMGs

Dr Bitten Gullberg (Durham University)- ARC Seminar Wednesday 3 October 2018 1pm

I will present high resolution (0.03“) rest-frame 160micron continuum maps of four z~4.5 sub-mm galaxies (SMGs) selected from the ALMA-LESS and ALMA-UDS surveys. These cycle 3 observations resolve the gas and dust within the ISM of these galaxies on 0.2-1kpc scales. The data reveal an apparent range of morphologies. Though the continuum morphologies appear to be: smooth and compact or extended and ‘clumpy’, comparison with simulations reveal that all four sources are consistent with exponential discs. From the morphologies and dynamics of the gas and dust, I will show that these SMGs are most likely to contain dust discs which are smooth on scales of ~200pc. These four SMGs are also bright [CII] emitters and by considering the L([CII])/L(FIR) ratio as a function of the star-formation rate surface density I will revisit the [CII] deficit, which these measurement suggest, is consistent with local processes. I will present some of the physical drivers that may be responsible for this trend and can give rise to the properties found in the densest regions of SMGs.

Dwarf Spheroidal Galaxies: Cosmological probes on our doorstep

Dr Mark Wilkinson (Leicester University)- ARC Seminar Wednesday 6 June 2018 3pm

The Local Group dwarf spheroidal galaxies (dSphs) are widely recognised as valuable targets for the study of the processes of galaxy formation on small scales. However, there are a number of major outstanding questions (commonly referred to as the “cusp-core”, “Missing Satellites” and “Too Big To Fail” problems) whose resolution requires us to delve into the evolution of both the dark matter and baryonic components of dSphs. In this talk, I will discuss a new mass modelling technique which uses N-body simulations to estimate the masses of dSphs to much larger radii than has previously been possible. Using this approach, we have been able to constrain the mass of the Carina dSph both at the current epoch and at the time it fell into the Milky Way, finding a surprisingly low pre-infall mass. I will present the results of hydrodynamic simulations which demonstrate the difficulty of sustaining star formation in such low-mass dSph progenitors at high redshift, suggesting that stochasticity in the star formation process in low-mass galaxies may be responsible for the non-linearity of the mapping between simulated dark matter haloes and observed satellite galaxies. Finally, I will show how the technique of Gaussian Process Emulation can be applied to the dynamical modelling of dSphs, providing the opportunity to explore a much broader range of dSph evolutionary pathways than has previously been feasible.

Type-IIP Supernovae: Origins, variability and the low-luminosity group

David O'Neill (QUB)- ARC Seminar Wednesday 30th May 2018 3pm

Of all supernovae types, type-IIPs show some of the greatest variation in properties. Despite being the most common form of core collapse SNe, the effects of the progenitor on the photometric and spectroscopic properties of the SN are not fully understood. Modelling and pre-explosion progenitor detections have improved our understanding of these effects. However, progenitor detections are rare due to the large resolving power required. In this presentation I will be talking about what we know about IIP SNe, and in particular the low-luminosity IIP group, including my work on SN 2014bi, a low luminosity IIP that displays atypical properties as well as my more recent work on SN 2018aoq which has a potential progenitor candidate identified using HST photometry.

Star Formation, Molecular clouds and spiral arms

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.

Shocking Events in the Solar Atmosphere

Scott Houston (QUB) - ARC Seminar Wed 16th May 2018 3pm

Previous research has documented the ubiquitous presence of non-linear shocks that are introduced by upwardly propagating magneto-acoustic waves in sunspot umbral atmospheres. In recent years, extensive analyses have been undertaken to examine the effect of these shocks on the surrounding magnetically-dominated plasma, with previous work identifying line-of-sight modulations of the magnetic field strengths and temperature enhancements on the order of several hundred degrees Kelvin. We employ simultaneous slit-based spectro-polarimetry and spectral imaging observations of the chromospheric He I 10830Å and Ca II 8542Å lines to examine full vector fluctuations in the umbral magnetic field caused by the steepening of magneto-acoustic waves into umbral flashes. Following the application of the HAZEL inversion routine, we find evidence to support the scenario that umbral shock events cause expansion of the embedded magnetic field lines due to the increased adiabatic pressure, hence providing increased transversal magnetic field fluctuations up to ~600 Gauss. Through comparisons with non-linear force-free field extrapolations, we demonstrate how the development of umbral flashes can deflect the quiescent magnetic field geometry by up to 8 degrees in both inclination and azimuthal directions.

Characterising the atmosphere of a benchmark Hot Jupiter

Dr Tom Evans (Exeter University) - ARC Seminar Wed 9th May 2018 2pm

Only about 1% of FGK dwarfs have a hot Jupiter. Despite being relatively rare, the hot Jupiters are our key to understanding the complex physics and chemistry of tidally-locked atmospheres, for which we have no solar system analogs. This is important, for instance, because all terrestrial planets in the habitable zone of M dwarfs should be tidally-locked within 1Gyr. If we do not understand the atmospheres of hot Jupiters, we have little hope of understanding these more challenging targets, which will become an increasing priority over the next decade. In this talk I will present our latest efforts to observationally characterise the atmosphere of the benchmark hot Jupiter, WASP-121b. The dayside thermal emission implies a hot stratosphere, while the transmission spectrum reveals a rich array of features. The latter includes evidence of a strong NUV absorber, not currently accounted for by models, and which we speculate may be a product of sulfur photochemistry.

Transit Visibility Zones of the Solar System Planets

Robert Wells (QUB) - ARC Seminar Wed 2nd May 2018 3pm

The detection of thousands of extrasolar planets by the transit method naturally raises the question of whether potential extrasolar observers could detect the transits of the Solar system planets, and in particular those of the Earth. In this talk I will present an analysis of the regions in the sky from where transit events of the Solar system planets can be detected - named “transit zones”. I will discuss how probable it is to detect one or more Solar system planet, the timescales over which they are valid, plus the prospects of finding temperate extrasolar planets which could observe transits of Earth. I will also report on a habitable zone candidate situated in one of the transit zones - a super-Earth near the inner-edge of the HZ of an early M-dwarf. Lastly, I will outline the search for more systems with the ongoing Kepler-K2 mission, including the hunt for “monster” planets.

Supernovae in the Era of High Cadence Sky Surveys

Peter Clark (QUB) - ARC Seminar Wed 25th April 2018 3pm

Supernovae continue to play a key role our comprehension of the fundamental physical processes of our universe. Whether through modelling of high mass element nucleosynthesis or through Type Ia supernovae observations, supernovae are ideal tools to map the expansion history of the universe and explore the effect of dark energy at high redshift. I will discuss the fundamentals of supernova identification and classification with particular focus on the new options provided by current and upcoming high cadence surveys as well as detailing my own current work into the unusual ‘fast’ evolving transient LSQ13ddu.

Spirals, rings, gaps and asymmetries: using disc structure to infer planet formation processes

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.

The Astrophysics of Stellar Clusters

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.

Exploring the Epoch of Reionisation

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.

The Interstellar Medium of High Redshift Galaxies

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.

Dark matter subhaloes in the Local Group

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.

Doppler spectroscopy and the detection of a temperature inversion in hot Jupiters

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.

Water in Protoplanetary Disks, line flux modelling and Disk structure

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.

Emission Mechanism of White-light Solar Flares

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.

Rediscovering the Milky Way with Gaia white dwarfs

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.

Pulsations and Declines in R Coronae Borealis

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.

The Pros and Cons of Asteroids: A Thermophysical View

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.

Detection and follow-up of fast radio bursts

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.

Exploring the properties of star formation with observations and models

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.

Extreme infrared variable sources in the Galactic plane

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.

Theoretical Modelling of Supernovae Spectra and Lightcurves

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.

TNO Surface Reflectance Spectra: Evidence for the Presence of Aromatic Hydrocarbons

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.

STAGES: Galaxy evolution and environment

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.

Galaxy Evolution in a Zoo of Galaxies

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.

Surface composition and internal structure of 
Main-Belt Asteroids

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.

Modelling Neutrino-Driven Supernova Explosions Across the Stellar Mass Range

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.

Quasar evolution and outflows in X-rays

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.

Cosmic Web to Cosmology

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.

Organic Circumstellar studies with the James Webb Space Telescope

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.

Thermal Inversions in Hot Jupiters

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.

Data-driven models for stellar astrophysics

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.

Pulsar Scintillometry: using the interstellar medium to elucidate where giant pulses arise.

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.

Ages of Exoplanets and their Host Stars: Extending the Age-Activity Relationship

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.

High redshift [CII]158micron observations - it's all the rage these days but how to make sense of it?

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.

The New Shape of the Outer Solar System

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.

The Rugged Landscape of the Core-Collapse Supernova Explosions

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.

Comet Dust and the Interstellar Medium Connection

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.

Atmospheric characterization of hot-Jupiter exoplanets

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.

Stellar magnetic activity and their effects on planetary environments

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.

Magnetic Activity of Cool Stars

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.

A photometric study of trans-Neptunian objects using Pan-STARRS 1

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.

From the beginning till the end: some news on the Initial Stellar Mass Function and on Planetary Nebulae with MUSE

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.

Fast evolving pair-instability supernovae

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.

The hunt for quasars in wide-field surveys: Understanding the formation of supermassive black holes

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.

Are the chromospheric fine structures holding the key to solar atmospheric heating?

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.

Insights from 20 Years of SOHO Comets

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.

Ellerman Bombs in the Solar Photosphere

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.

Hot subdwarf stars and their connection to thermonuclear supernovae

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.

High Contrast Imaging with Spitzer

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%.

A Transiting Extrasolar Ring System around the Substellar Companion J1407b

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.

Spatially resolved coronal magnetic fields obtained from omnipresent sunspot waves

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.

Do SNe Iax result from thermonuclear deflagrations? Observations of a new member of the class

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.

Understanding magnetically-channelled accretion using faint accreting neutron stars

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.

Organic Molecules in Space and the Laboratory

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.

Can a GP Help your Spot Problem? Bayesian Inference for Stellar Activity Modeling

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.

Spiral Arm Paradigm in Disk Galaxies

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.

Neutron-Capture Nucleosynthesis and the Chemical Evolution of Globular Clusters

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.

Near-field cosmology at the edge of galaxy formation

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.

Changing Phases of Kepler Exoplanets: Evidence for Clouds and Winds

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.

Superluminous supernovae: 56Ni vs magnetars

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.

Stellar populations in the Magellanic Bridge

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.

New life in dead galaxies: star formation, the IMF, and black holes

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.

Nuclear reactions with exotic nuclei at University of Huelva

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.

Characterising the atmospheres of exoplanets

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

The Cosmic Microwave Background and Results from the Planck satellite

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.

Asteroid Impacts and Modern Civilisation - Can we prevent a catastrophe?

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.

Imaging and spectral studies of solar white light flares

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.

Periodic propagating features on the Sun: waves or flows?

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.

A spectroscopic study of solar twins and analogues

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.

PAH emission in the reflection nebula NGC2023

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.

public/seminar_abstracts.txt · Last modified: 2018/12/04 15:17 by Mark Magee

Back to Top Sitemap News