SDO Launch Live!
On Tuesday 9th February, NASA will launch its latest mission: the
Solar Dynamics Observatory (SDO). The Jeremiah Horrocks Institute invites
everyone to come and watch the launch live and find out about the amazing
science that will be carried out by SDO, as well as UCLan’s involvement in
this mission.
The event will take place in Harris Building Room H307, starting at 3:00 pm*.
Dr Robert Walsh will describe the science to be carried out
with this groundbreaking solar satellite and the role of UCLan researchers.
Then watch the rocket launch live from Kennedy Space Center at 3:30pm* on
the big screen. More information and updates can be found on Twitter at
http://twitter.com/UCLanSDO
and on the web at http://www.sdo.uclan.ac.uk
*Launch times can be subject to change, please
check for latest updates. Contact Mike Marsh (mmarsh {at} uclan.ac.uk)
for
further information.
Turbulent Reconnection in Braided Magnetic Fields
Dr. Gunnar Hornig
Magnetic braiding of coronal loops due to the motion of their photospheric footpoints has long been discussed as a possible mechanism for the heating of the solar corona. This motivated a series of numerical experiments (Wilmot-Smith et al. 2009, 2010) on the turbulent relaxation of braided magnetic fields. These experiments have produced relaxed states which differ drastically from the predictions of the Taylor hypothesis. We discuss possible reasons for this and present a new topological measure, a type of generalised flux function, which allows us to analyse the reconnection processes and which shows that there are further constraints on the relaxation beyond the conservation of the total helicity, which prevent the system from reaching a Taylor state.
Formation of Star Clusters
Dr. Bruce Elmegreen
Star clusters form in the densest part of a hierarchy of structures in the interstellar medium. Unbound stars continue the hierarchy to larger scales in OB associations and star complexes, while the clusters themselves contain smaller sub-clusters when they are very young, before the bound stars mix up. The conditions for cluster formation are present in the gas even before the stars form, including the high mass fraction of dense cores that is necessary for cluster boundedness when the less-dense gas eventually leaves. The initial stellar mass function and the cluster mass function seem to have similar origins, both coming from cloud structure. This talk will review the processes of star formation, cluster formation, and the IMF that are observed to operate over a wide range of scales.
Carbon-Enhanced Metal-Poor (CEMP) Stars in the Galactic Halo and their Link to High-Redshift Damped Lyman Alpha Systems
Prof. Tim Beers
It has been recognized for some time that the halo system of the Galaxy
exhibits a large fraction of metal-poor stars ([Fe/H]<-1.5) with significant over-abundances of carbon, [C/Fe] > +0.7. These are known collectively as
Carbon-Enhanced Metal-Poor (CEMP) stars. The great majority of these stars,
roughly 80%, exhibit heavy element abundance patterns typically associated with
the s-process (CEMP-s), and hence are thought to be produced by mass transfer
from the envelope of a binary companion that has passed through the AGB stage.
However, roughly 20% of the so-called stars show no enhancements of
neutron-capture elements. The CEMP-no stars are also primarily found at lower
metallicity, and dominate samples of halo CEMP stars with [Fe/H] < -2.5.
After summarizing the nature of the CEMP stars, I present an argument that the
inner halo of our Galaxy is dominated by the CEMP-s variety of such stars,
while
the outer halo is dominated by the CEMP-no stars. This inference may provide
insight into the origin of the two populations, and the nucleosynthetic
production of carbon and other light elements in the earliest generations of
stars, thus completing the link
between local metal-poor stars and high-redshift
Damped Lyman Alpha (DLA) systems.
Constraining the Milky Way Halo with Cold Streams
Dr. Hanni Lux
Constraining the shape of dark matter halos directly tests predictions of LCDM. The
Milky Way halo shape is the only one we can hope to measure without degeneracies from
projection effects. So far its best constraints are derived from the orbit of the
Sagittarius stream. However, these results have been inconclusive so far (Helmi 2004,
Johnston et al. 2005, Fellhauer et al. 2006, Law & Majewski 2010). We investigate what
constraints on the Milky Way halo shape can be placed by cold streams. As these are
much simpler to model they can potentially probe a larger parameter space. In
particular, the globular cluster stream NGC 5466 shows great potential for
distinguishing spherical from non-spherical halos.
Noble Gases in Solar System Samples
Prof. Jamie Gilmour
Noble gases were not incorporated very efficiently into the
solid phase during the formation of the solar system. This low
background means that large isotopic effects can be observed
due to radioactive decay, nuclear reactions and the presence of
inherited presolar material from specific nucleosynthetic sites.
This seminar will describe some of the analytical techniques
involved, and illustrate some of the applications of noble gas
isotopic analysis to understanding the prehistory, formation and
evolution of the solar system.
Recent sunquakes: new implications for energy transport in solar flares
Sergei Zharkov
It is well established that solar flares are initiated by magnetic reconnection
in the solar atmosphere/chromoshpere and extend to solar corona with unconnected
magnetic helical field and the material that it contains sometimes violently
expanding outwards forming a coronal mass ejection. However, the flare energy
transport to the underlying photosphere is less understood.
Sunquakes are tsunami-like acoustic waves induced in the solar interior by solar
flares. The theoretical prediction that flares can excite acoustic waves in the
underlying photosphere was made in Wolff 1972, with first observations of the
phenomena reported in Kosovichev & Zharkova, 1998. Yet only a limited number of
M and X-class flares are known to have produced seismic signatures in the form
of ripples or egression sources, with many of the most powerful flares being
acoustically quiet. Furthermore, some of the most powerful signatures were
recorded from an M-class flares. This raises important questions about how the
flare energy and momentum are transported to the solar surface and interior in
order to produce sun-quakes.
Observations of ripples associated with the first few sun-quakes suggested that
hydrodynamic shocks arising from a hydrodynamic response of the ambient plasma
to precipitation of energetic particles (electrons or protons) are plausible
sources of the seismic emission. Later, noting that sun-quakes are often
co-spatial with hard X-ray and white light, another source of seismic emission
was proposed related to back-warming of the photosphere by the enhanced
chromospheric and coronal radiation caused by physical processes in flares. A
third mechanism proposed to account for sun-quakes is related to possible
Lorentz force transients that occur as a result of the coronal restructuring of
the magnetic field in flares.
Recent work comparing samples of white-light flares with and without sun-quakes,
and new observations with GONG, Hinode and SDO of seismic emission associated
with the X-class flares of 14 December 2006 and 15 February 2011 demonstrate
inconsistencies with some existing models. In this work these inconsistencies
are explored and possible alternative scenarios are discussed.
REFERENCE: Zharkov et al. 2011, ApJ, 741, L35,
ADS link
Young stars and their protoplanetary discs
Alex Brown
I describe results from extensive recent observations by space-based
(HST, Chandra) and ground-based telescopes that reveal unprecedented
detail about protoplanetary system evolution. Our studies of
FUV molecular hydrogen and carbon monoxide emission are
providing unique insights into the properties of the
circumstellar disks of young low mass stars, how these disks
and their central stars interact, and how disks evolve
from strongly accreting structures to protoplanetary systems.
Young stars strongly influence the complex environment that surrounds
them. Their high energy (FUV/EUV/X-ray) radiation controls the
physical and chemical processes in their circumstellar disks out to
hundreds of AU from the star. The high energy emission, both as
radiation and particles, resulting from magnetic activity on the
central star controls the thermal structure of disks, the formation
process of planetesimals, and the photoexcitation and photoionization
of protoplanets and young planetary atmospheres. Modeling of the
dust and gas evolution requires an accurate understanding of the
local radiation field throughout the UV and X-ray spectral regions,
even those parts of the spectrum that are impossible to observe
from Earth.
Cosmic Ray Transport in the Heliosphere and its
Connection to Their Interstellar Propagation
Horst Fichtner
In recent years one could witness tremendous progress regarding the physics of
the transport of cosmic rays in the heliosphere. This progress derives from both
theoretical advances and new measurements from the outer boundary region of the
heliosphere. At the same time theory and observations have implications for the
(local) interstellar cosmic ray spectra and propagation. The talk will address
the new data, ideas and corresponding developments.
REFERENCE: Scherer, Fichtner et al. 2011, ApJ, 735, 128
ADS link
Near-Field Cosmology with CLUES
(Constrained Local UniversE Simulations)
Stefan Gottloeber
During the last decade our understanding of the formation of structure
in the universe grew substantially. Due to the non-linear nature of
the gravitational dynamics and the complicated gas-astrophysical
processes numerical simulations have been the driving force behind
much of this theoretical progress.
Cosmological simulations must cover a large dynamical and mass range.
A representative volume of the universe should be large, but this
comes at the expense of the resolution. To overcome this problem we
have developed a new approach which consists of using observations of
the nearby universe as constraints imposed on the initial conditions
of the simulations. The resulting constrained simulations successfully
reproduce the observed structure within a few tens of megaparsecs
around the Milky Way.
I will discuss the formation of the Local Group and the Local Volume
based on a series of simulations performed within the CLUES project –
Constrained Local UniversE Simulations
(http://www.clues-project.org/).
A Non-Linear Force-Free Field Model for the Solar Magnetic Carpet
Karen Meyer
A new two-component model for the dynamic evolution of the Sun’s magnetic carpet
is presented. The first component is a 2D model for the photospheric evolution
of the small-scale solar magnetic field, that reproduces many observed
parameters. The basic evolution of magnetic elements within the model is
governed by a supergranular flow profile. In addition, magnetic elements may
evolve through the processes of emergence, cancellation, coalescence and
fragmentation. The synthetic magnetograms produced by the 2D model are then
applied as photospheric boundary data to drive the continuous evolution of a 3D
non-linear force-free coronal field.
Reference:
Solar Magnetic
Carpet I. Simulation of Synthetic Magnetograms 2011, K. Meyer et al., Solar
Physics
Unbending the light
Massimo Viola
Weak gravitational lensing has become in the last decades a very competitive cosmological tool to study the distribution of matter in the universe and to understand the properties of dark matter halos.
Measuring lens-induced distortions in noisy galaxy images is however a very challenging task, even more so for the stringent requirements of the upcoming cosmic shear surveys (DES, KIDS, EUCLID): the goal is to measure a 1% variation in galaxy ellipticity with a multiplicative error in the permille range. I will discuss why reaching this precision is extremely difficult and I will present some new methods to tackle this problem.
In the second part of the talk I will discuss about gravitational flexion. It is caused by the derivatives of the gravitational tidal field and it is potentially important for the analysis of the dark matter distribution in gravitational lenses, such as galaxy clusters or the dark matter haloes of galaxies. However the measurement of this signal and its interpretation are not trivial. I will critically discuss those aspects and I will present possible solutions.
A Non-Linear Force-Free Field Model for the Solar Magnetic Carpet
Karen Meyer
A new two-component model for the dynamic evolution of the Sun’s magnetic carpet
is presented. The first component is a 2D model for the photospheric evolution
of the small-scale solar magnetic field, that reproduces many observed
parameters. The basic evolution of magnetic elements within the model is
governed by a supergranular flow profile. In addition, magnetic elements may
evolve through the processes of emergence, cancellation, coalescence and
fragmentation. The synthetic magnetograms produced by the 2D model are then
applied as photospheric boundary data to drive the continuous evolution of a 3D
non-linear force-free coronal field.
Reference:
Solar Magnetic
Carpet I. Simulation of Synthetic Magnetograms 2011, K. Meyer et al., Solar
Physics
EIT waves: observations and modelings
Peng-Fei Chen
Coronal EIT waves appear as EUV bright fronts propagating across a
significant part of the solar disk. The large-scale phenomenon provoked
continuing debates on their nature and their relation with coronal mass
ejections (CMEs). In this talk, we first summarize all the observational
features of EIT waves, which should be accounted for by any successful model.
The theoretical models constructed during the past 10 years are then reviewed.
Finally, the implication of EIT waves on the CME models is discussed.
Water on the Moon
Vincent Eke
I will provide a review of studies pertaining to the existence of lunar
water, before describing in more detail relevant results from the recent
flurry of lunar missions. These include Chandrayaan-1, the Lunar
Reconnaisance Orbiter and LCROSS. Along the way, I’ll explain why this
cosmologist is talking about the Moon.
Talk title
Vincent Eke
I will provide a review of studies pertaining to the existence of lunar
water, before describing in more detail relevant results from the recent
flurry of lunar missions. These include Chandrayaan-1, the Lunar
Reconnaisance Orbiter and LCROSS. Along the way, I’ll explain why this
cosmologist is talking about the Moon.
Propagation of Alfvén Waves from the Corona to Chromosphere
Alexander Russell
The corona and chromosphere are a coupled system, but how significant is
this coupling? I will present results that quantify wave transmission
from the corona to the chromosphere for different solar features
(sunspot umbra, penumbra, facula, bright facula and plage) using a 1D
multi-fluid model. Chromospheric heating due to ion-neutral friction and
enhanced electron resistivity are also measured. Wave periods of one
second allow energy transmission greater than 20%, with half of this
energy converted to heat in the middle chromosphere by ion-neutral
friction. This suggests that coronal waves could penetrate and heat the
chromosphere if generated during solar flares. Transmission is
substantially reduced for longer wave periods (30 seconds or more) and
we confirm that losses are too low to account for observed decay of
standing coronal loop oscillations.
The spectral energy distribution of dusty galaxies at low and high redshift
Kate Rowlands
Our understanding of dust evolution over cosmic time is paramount in order to further our knowledge of galaxy evolution, because of the direct link between dust and star-formation. Studies of cold dust in galaxies have until recently been biased towards high redshifts and were hampered by small sample sizes due to the difficulties of observing at submillimetre wavelengths. A definitive analysis of cold dust is now possible thanks to the wealth of multiwavelength data from the Herschel-ATLAS and GAMA surveys. The Herschel-ATLAS is the largest area survey undertaken by the Herschel Space Observatory, and provides for the first time an unbiased view of dust in the local Universe using observations at submillimetre wavelengths. I will present results which combine the low redshift H-ATLAS sample (z<0.5) with galaxies selected at high redshift (z~2) in deep survey fields in order to compare the properties of a large number of ~250μm rest-frame selected galaxies. The differences between the populations present the opportunity to study how the dust and gas content of galaxies change over time, which has important implications for future star-formation.
Propagation of Alfvén Waves from the Corona to Chromosphere
Alexander Russell
The corona and chromosphere are a coupled system, but how significant is
this coupling? I will present results that quantify wave transmission
from the corona to the chromosphere for different solar features
(sunspot umbra, penumbra, facula, bright facula and plage) using a 1D
multi-fluid model. Chromospheric heating due to ion-neutral friction and
enhanced electron resistivity are also measured. Wave periods of one
second allow energy transmission greater than 20%, with half of this
energy converted to heat in the middle chromosphere by ion-neutral
friction. This suggests that coronal waves could penetrate and heat the
chromosphere if generated during solar flares. Transmission is
substantially reduced for longer wave periods (30 seconds or more) and
we confirm that losses are too low to account for observed decay of
standing coronal loop oscillations.
The formation of SO galaxies
Alfonso Aragón-Salamanca
Evidence is mounting indicating that S0s were once spiral galaxies that
ceased forming stars and subsequently changed their morphology. Studying the
timing, location and physical mechanism(s) involved in this transformation
is not only interesting in itself, but it can also provide very useful clues
on how galaxies evolve and the possible role of the environment. During the
last few years we have been following several lines of research to test
whether this transformation is indeed taking place, find out where it
happens, and look for the physics driving it. At low redshift we have
studied in detail the final products of the transformation – the S0s
themselves – while at intermediate redshifts (z~0.5) we have concentrated on
the putative progenitors – spiral galaxies – and the galaxies caught in the
act of transforming. In this talk I present some of our more interesting
results. Although there are still some loose ends, a coherent picture may be
emerging.
Kate Rowlands
Our understanding of dust evolution over cosmic time is paramount in order to further our knowledge of galaxy evolution, because of the direct link between dust and star-formation. Studies of cold dust in galaxies have until recently been biased towards high redshifts and were hampered by small sample sizes due to the difficulties of observing at submillimetre wavelengths. A definitive analysis of cold dust is now possible thanks to the wealth of multiwavelength data from the Herschel-ATLAS and GAMA surveys. The Herschel-ATLAS is the largest area survey undertaken by the Herschel Space Observatory, and provides for the first time an unbiased view of dust in the local Universe using observations at submillimetre wavelengths. I will present results which combine the low redshift H-ATLAS sample (z<0.5) with galaxies selected at high redshift (z~2) in deep survey fields in order to compare the properties of a large number of ~250μm rest-frame selected galaxies. The differences between the populations present the opportunity to study how the dust and gas content of galaxies change over time, which has important implications for future star-formation.
Plasmoids and flow-driven instabilities in the eruptive corona
Claire Foullon
The ever-increasing number and quality of observations of the hot corona (e.g.
from RHESSI and SDO) and heliosphere (e.g. with STEREO) are ideally suited to
investigate the role of waves and instabilities into the dynamics of rarefied
magnetised plasmas and key flux rope phenomena of our Sun-Earth system.
Small-scale transients originating and being released from the base of the
Heliospheric Current Sheet (HCS) or further out in the inner heliosphere have
now been shown, in part due to new observations from STEREO, to give a layered
structure appearance to the HCS and to correspond to flux-rope and
magnetic-island type plasmoids in the associated Heliospheric Plasma Sheet. We
have now come to a greater appreciation of the importance of looking at the slow
solar wind around the HCS as a boundary layer, where aspects of differential
rotation-driven and continuous release of plasmoids could constitute some of the
main differences in the comparison with the magnetospheric plasma sheet. New
observations in the corona relate to the formation of those plasmoids and
highlight the relevance of waves and instabilities in energetic events, such as
flares and coronal mass ejections. SDO/AIA is now giving us the first
observations of the temporally and spatially resolved evolution of the magnetic
Kelvin-Helmholtz instability, which is seen developing at the surface of fast
coronal mass ejecta. The non-linear effects, multi-scale and microphysical
interactions inherent to the flow-driven instabilities can play a major role not
only in the transient kinematics by enhancing the drag in localised regions, but
also in the plasma entry across discontinuities.
Star formation in low-density regions and influence of the environment
Edouard Bernard
Star formation is not an efficient process, and is typically extremely
low in low density regimes such as the far outer disk of spiral galaxies and
low surface brightness galaxies. On the other hand, the environment is known to have a significant influence on the physical properties of galaxies and their star formation histories, and may even trigger intense bursts of star formation in
these low density regions. I will illustrate this with two examples of
nearby
galaxies in which a recent burst may have been triggered by tidal
interaction
and ram pressure.
Plasmoids and flow-driven instabilities in the eruptive corona
Claire Foullon
The ever-increasing number and quality of observations of the hot corona (e.g.
from RHESSI and SDO) and heliosphere (e.g. with STEREO) are ideally suited to
investigate the role of waves and instabilities into the dynamics of rarefied
magnetised plasmas and key flux rope phenomena of our Sun-Earth system.
Small-scale transients originating and being released from the base of the
Heliospheric Current Sheet (HCS) or further out in the inner heliosphere have
now been shown, in part due to new observations from STEREO, to give a layered
structure appearance to the HCS and to correspond to flux-rope and
magnetic-island type plasmoids in the associated Heliospheric Plasma Sheet. We
have now come to a greater appreciation of the importance of looking at the slow
solar wind around the HCS as a boundary layer, where aspects of differential
rotation-driven and continuous release of plasmoids could constitute some of the
main differences in the comparison with the magnetospheric plasma sheet. New
observations in the corona relate to the formation of those plasmoids and
highlight the relevance of waves and instabilities in energetic events, such as
flares and coronal mass ejections. SDO/AIA is now giving us the first
observations of the temporally and spatially resolved evolution of the magnetic
Kelvin-Helmholtz instability, which is seen developing at the surface of fast
coronal mass ejecta. The non-linear effects, multi-scale and microphysical
interactions inherent to the flow-driven instabilities can play a major role not
only in the transient kinematics by enhancing the drag in localised regions, but
also in the plasma entry across discontinuities.
The abundance and clustering properties of infrared galaxies
Lingyu Wang
The Herschel Multi-Tiered Extragalactic Survey (HerMES) is the largest Guaranteed Time Key Project on Herschel. It covers most of the well-studied extragalactic multi-wavelength fields, enabling detailed studies of the physical properties of infrared galaxies out to high redshifts. Its wedding cake survey design allows us to probe a wide of luminosities and environments. In my talk, I will briefly describe the HerMES project, its science goals and current datasets. For the main part of my talk, I will focus on the statistical properties of the infrared galaxy populations we observe. In particular, I will present the number counts of infrared galaxies derived from a variety of methods, including direct source extraction, P(D) (probability of deflection) and stacking. I will also present our results on the clustering properties of infrared galaxies, including the correlation functions of bright sources and power spectrum of the background intensity fluctuations. The abundance and clustering statistics of infrared galaxies, interpreted through a halo model, provide crucial information on the connection between star formation and dark matter halos.
Star formation in low-density regions and influence of the environment
Edouard Bernard
Star formation is not an efficient process, and is typically extremely
low in low density regimes such as the far outer disk of spiral galaxies and
low surface brightness galaxies. On the other hand, the environment is known to have a significant influence on the physical properties of galaxies and their star formation histories, and may even trigger intense bursts of star formation in
these low density regions. I will illustrate this with two examples of
nearby
galaxies in which a recent burst may have been triggered by tidal
interaction
and ram pressure.
Solar cycle 24: Where are we and where are we going?
Mathew Owens
March 2012 brought the first solar and geomagnetic disturbances of any note during solar cycle 24. But perhaps what was most remarkable about these events was how unremarkable they were in magnitude compared to others during the space-age, only attracting attention because solar activity had been so quiet. Because it follows an exceptionally low and long-lived solar cycle minimum, this cycle is likely to extend a long-term decline in solar activity that started around 1985 and that could even lead to conditions similar to the Maunder minimum within 40 years from now, with implications for solar-terrestrial science and the mitigation of space weather hazards and maybe even for climate in certain regions and seasons.
Ensemble asteroseismology of solar-like oscillations
Tim White
With the advent of the Kepler mission, the number of main-sequence and
subgiant stars with detected solar-like oscillations has exploded and we
are now able to perform large-scale ensemble asteroseismology of these
stars. We look at several asteroseismic observables, including the large
and small separations, and investigate their dependence upon stellar
parameters such as mass and age. We also demonstrate how the relationship
between effective temperature and the asteroseismic observable epsilon can
be used to resolve the mode identification problem in F stars.
Related articles:
Calculating Asteroseismic Diagrams for Solar-like Oscillations
(2011, ApJ, 743, 161)
Asteroseismic Diagrams from a Survey of Solar-like Oscillations with Kepler
(2011, ApJL, 742, 3)
Anisotropic and anomalous diffusion of energetic particles in
heliospheric and galactic magnetic fields
Frederic Effenberger
The kinetic description of cosmic ray (CR) transport processes in the galaxy and
of the propagation of energetic particles in the heliosphere commonly involves a
diffusion operator connected to the turbulent magnetic fields embedded in the
background plasma. Up to now, most often only a scalar spatial diffusion
coefficient is employed to describe the galactic CR propagation. Due to the
large scale mean magnetic fields, however, anisotropic diffusion has to be taken
into account, yielding different latitudinal variations in the CR intensity
along the Sun’s galactic orbit. Similarly, refined models of anisotropic
diffusion can result in modifications to heliospheric CR modulation scenarios
and the description of solar energetic particle propagation. Finally, the
diffusion approximation can be generalized to cases of anomalous diffusion which
is based in unusual turbulence properties of the background plasma. The
numerical methods to solve the involved transport equations, namely the
Fokker-Planck and fractional Fokker-Planck equation, are discussed alongside
with the physical interpretation and prerequisites of the corresponding
transport processes.
Related articles:
A Generalized Diffusion Tensor for Fully Anisotropic Diffusion of Energetic
Particles in the Heliospheric Magnetic Field
(2012, ApJ, 750, 108)
The long-term azimuthal structure of the Galactic Cosmic Ray proton distribution
due to anisotropic diffusion
(2011, Memorie della Soc. Astronomica Italiana, 82, 867)
Generation of Quasi-periodic Waves
and Flows in the Solar Atmosphere by Oscillatory Reconnection
James McLaughlin
We investigate the long-term evolution of an initially buoyant magnetic flux
tube emerging into a gravitationally stratified coronal hole environment and
report on the resulting oscillations and outflows. We perform 2.5-dimensional
nonlinear numerical simulations, generalizing the models of McLaughlin et al.
(2009) and Murray et al. (2009). We find that the physical mechanism of
oscillatory reconnection naturally generates quasi-periodic vertical outflows,
with a transverse/swaying aspect. The vertical outflows consist of both a
periodic aspect and evidence of a positively directed flow. The speed of the
vertical outflow (20-60 km/s) is comparable to those reported in the
observational literature. We also perform a parametric study varying the
magnetic strength of the buoyant flux tube and find a range of associated
periodicities: 1.75 – 3.5 minutes. Thus, the mechanism of oscillatory
reconnection may provide a physical explanation to some of the high-speed,
quasi-periodic, transverse outflows/jets recently reported by a multitude of
authors and instruments.
Related articles:
Generation of Quasi-periodic Waves and Flows in the Solar Atmosphere by
Oscillatory Reconnection
(2012, ApJ, 749, 30)
Mykola Gordovskyy
Particle acceleration in
reconnecting twisted coronal loops
Twisted magnetic fields should be ubiquitous in the corona. At the same time,
twisted fields can store substantial amount of energy that can be released
during flares. Based on the combination of MHD and test-particle methods we
develop a numerical model of magnetic reconnection and particle kinetics in
twisted coronal loops (Gordovskyy et al. 2012). In contrast with the standart
solar flare scenario, particle acceleration in our model is not localized in the
corona, but is distributed within the loop. Furthermore, magnetic field
convergence near loop footpoints results in re-acceleration of supratermal
particles in the lower atmosphere. I will discuss observational implications of
our model focusing on the spatial distribution of high-energy particles and
shapes of hard X-ray sources observed in flares.
Related articles:
Magnetic Relaxation and Particle Acceleration in a Flaring Twisted Coronal Loop
(2012, Solar Physics, 277, 299)
David MacTaggart
Theoretical Flux Emergence: Context and Connections
In this talk I shall review some of the theoretical work on magnetic flux
emergence. I will show how these models link in with other models for
large-scale (CME-type) eruptions.
Related articles:
Flux emergence within mature solar active regions
(2011, A&A, 531)
On Signatures of Twisted Magnetic Flux Tube Emergence
(2012, Solar Phys., 278, 33)
Stefano Pasetto
Thin and thick disk kinematics with RAVE and the solar motion
We present a kinematic analysis of the Galactic thin and thick disk based on RAdial Velocity Experiment (RAVE). Thin and thick disk components are considered as two distinct galactic populations and disentangled from their mixture with a method based on decomposition of matrices. The prospects and limitations of this method are explored with the use of photometric distances and proper motions and compared with the galactic Padua star-count model.
We deduced the components of the solar motion relative to the local standard of rest in the radial and vertical direction, the velocity lag of the thick disk and the components of the velocity dispersion tensor for the thin and thick disk in the meridional plane.
Pierre Maxted
Discovering the progenitors of very low mass white dwarfs
White dwarfs less massive than about half a solar mass are the remnants of red
giant stars that have been stripped of their outer layers by mass transfer onto
a companion star, or a stellar collision, or tidal stripping by a supermassive
black hole. The evolution of very low mass white dwarfs differs from normal,
more massive, white dwarfs because they have thick hydrogen layers on their
surface that can support p-p chain shell-burning for several gigayears. There
are very few observed examples of the remnants in the phase during which they
evolve to hotter effective temperatures at constant luminosity, during which
time they may undergo unstable flashes of CNO shell-burning. I will describe how
several such stars have been discovered in eclipsing binary systems using the
WASP archive and the excellent prospects for using these systems to better
understand the formation of very low mass white dwarfs and the various extreme
environments in which they are found.
Paul Beck
Asteroseismology of red giant stars in an eccentric binary system
Before the Kepler space telescope became operational, only a handful of red
giants were known to oscillate with pressure modes, propagating in the outer
layers of the stars. The unprecedented quality of photometry from Kepler
provided answers to many open questions in red giant asteroseismology. An
important new tool to probe the deep interior of the stars comes from mixed
modes, which were recently identified in red giants.
Asteroseismology of the red giants is very powerful as it enables us to
constrain many parameters of the star. The recent detection of a red giant in an
eccentric binary, system showing the heart beat phenomenon is therefore an
interesting case to test our theories on binary stars, as we can determine the
parameters of the main component and therefore put strong constraints on the
binary system.
Related articles:
Fast core rotation in red-giant stars as revealed by gravity-dominated mixed
modes
(2012, Nature, 481)
Probing the core structure and evolution of red giants using gravity-dominated
mixed modes observed with Kepler
(2012, A&A, 540, 143)
Andrej Prsa
Kepler Mission Harvest of Close Binaries and Circumbinary Planets
The primary goal of NASA’s Kepler mission is to detect extrasolar planets by the
transit method and estimate the frequency of Earth-like planets that orbit
Sun-like stars in the habitable zone. There are currently over 2300 planet
candidates, dozens Earth-sized and smaller, and quite a few in the habitable
zone. At the same time, the yield of the mission in stellar astrophysics and
asteroseismology is just as impressive. There are over 2700 eclipsing binaries
discovered and characterized. I will review the detection and analysis methods
and present statistical properties of the data-set and individual gems that keep
us scratching our heads. Recently, three planets have been found revolving
around binary stars in circumbinary orbits: Kepler-16, Kepler-34 and Kepler-35.
The latest cherry is a multiple circumbinary system Kepler-47. I will present
the prime results of Kepler in the field of close binary stars, highlight the
discoveries of circumbinary planets and estimate their occurrence rate
throughout the Galaxy.
Marco Pignatari
Evolution and nucleosynthesis in low-mass and intermediate-mass stars
Low and intermediate mass stars have a fundamental impact for the production of elements in the Universe.
The complete understanding of the nucleosynthesis processes in these objects present several challenges,
despite less extreme thermodynamic conditions and a less complex evolution compared to more massive stars.
In this presentation I will overview evolution and nucleosynthesis in low and intermediate mass stars.
I will highlight present limitations in theoretical model predictions and discuss how to improve them,
in order to provide better stellar abundance yields for chemical evolution and to compare with stellar observations.
Stefano Pasetto
Thin and thick disk kinematics with RAVE and the solar motion
We present a kinematic analysis of the Galactic thin and thick disk based on RAdial Velocity Experiment (RAVE). Thin and thick disk components are considered as two distinct galactic populations and disentangled from their mixture with a method based on decomposition of matrices. The prospects and limitations of this method are explored with the use of photometric distances and proper motions and compared with the galactic Padua star-count model.
We deduced the components of the solar motion relative to the local standard of rest in the radial and vertical direction, the velocity lag of the thick disk and the components of the velocity dispersion tensor for the thin and thick disk in the meridional plane.
Esther Marmol-Queralto
Satellite galaxies around massive galaxies: the infalling pieces of the puzzle
Accretion of minor satellites has been postulated as the most likely mechanism
to explain the significant size evolution of the massive galaxies over cosmic
time. A direct way of probing this scenario is to measure the frequency of
satellites around massive galaxies at different redshifts. In Mármol-Querltó we have searched for satellites around 629 massive (Mstar ~ 10^11Msun) galaxies from the near-infrared Palomar/DEEP-2 survey within a projected radial distance of 100 kpc. We find that the fraction of massive galaxies with satellites remains basically constant and close to 30% for satellites with a mass ratio down to 1:100 up to z=1, and ~15% for satellites with a 1:10 mass ratio up to z=2. We find that the satellites present higher specific star formation rates than the massive galaxies. The analysis of the colors indicates that the satellites are, in average, 1 Gyr younger than the massive galaxies that host them. This rejuvenated material is likely to be placed in the outskirts of the massive objects. The challenge to find this age gradient in nearby massive galaxies is opened.
Paul Beck
Asteroseismology of red giant stars in an eccentric binary system
Before the Kepler space telescope became operational, only a handful of red
giants were known to oscillate with pressure modes, propagating in the outer
layers of the stars. The unprecedented quality of photometry from Kepler
provided answers to many open questions in red giant asteroseismology. An
important new tool to probe the deep interior of the stars comes from mixed
modes, which were recently identified in red giants.
Asteroseismology of the red giants is very powerful as it enables us to
constrain many parameters of the star. The recent detection of a red giant in an
eccentric binary, system showing the heart beat phenomenon is therefore an
interesting case to test our theories on binary stars, as we can determine the
parameters of the main component and therefore put strong constraints on the
binary system.
Related articles:
Fast core rotation in red-giant stars as revealed by gravity-dominated mixed
modes
(2012, Nature, 481)
Probing the core structure and evolution of red giants using gravity-dominated
mixed modes observed with Kepler
(2012, A&A, 540, 143)
Laurel Rachmeler
Forward modeling of coronal polarization
Coronal polarization measurements from the Coronal Multichannel Polarimeter
(CoMP) instrument provide quantitative information about the magnetic field
above the solar limb. We use a forward technique with both local and global
models to obtain comparisons between models and observations of the coronal
magnetic field. Specifically we have studied the magnetic nature of quiescent
coronal cavities. I will present results from the cavity analysis as well as
discussions on how to interpret the coronal polarization data and why it is a
useful dataset.
References:
Ring of Polarized
Light: Evidence for Twisted Coronal Magnetism in Cavities 2011, Dove et al.,
ApJ
Three-dimensional
Morphology of a Coronal Prominence Cavity 2010, Gibson et al., ApJ
Michiko Fujii
Dynamical evolution of star clusters in transient spiral arms
Star clusters born in galactic disks are disrupted due to both the tidal stripping and the internal evolution of star clusters. We performed N-body simulations of star clusters in a galactic disk. In our simulations, both star clusters and galactic disks are modeled as N-body systems and are integrated using a tree-direct hybrid code, BRIDGE. BRIDGE treats only star clusters as collisional systems using a direct code and the others as collisionless systems using a treecode. We found that star clusters migrate radially due to the interaction with spiral arms and disrupted when they migrate inward. The tidal tails spread over 1-2 kpc, but the tail stars are still close to their parent cluster in the velocity space.
Laurel Rachmeler
Forward modeling of coronal polarization
Coronal polarization measurements from the Coronal Multichannel Polarimeter
(CoMP) instrument provide quantitative information about the magnetic field
above the solar limb. We use a forward technique with both local and global
models to obtain comparisons between models and observations of the coronal
magnetic field. Specifically we have studied the magnetic nature of quiescent
coronal cavities. I will present results from the cavity analysis as well as
discussions on how to interpret the coronal polarization data and why it is a
useful dataset.
References:
Ring of Polarized
Light: Evidence for Twisted Coronal Magnetism in Cavities 2011, Dove et al.,
ApJ
Three-dimensional
Morphology of a Coronal Prominence Cavity 2010, Gibson et al., ApJ
Pierre Maxted
Discovering the progenitors of very low mass white dwarfs
White dwarfs less massive than about half a solar mass are the remnants of red
giant stars that have been stripped of their outer layers by mass transfer onto
a companion star, or a stellar collision, or tidal stripping by a supermassive
black hole. The evolution of very low mass white dwarfs differs from normal,
more massive, white dwarfs because they have thick hydrogen layers on their
surface that can support p-p chain shell-burning for several gigayears. There
are very few observed examples of the remnants in the phase during which they
evolve to hotter effective temperatures at constant luminosity, during which
time they may undergo unstable flashes of CNO shell-burning. I will describe how
several such stars have been discovered in eclipsing binary systems using the
WASP archive and the excellent prospects for using these systems to better
understand the formation of very low mass white dwarfs and the various extreme
environments in which they are found.
Richard Morton
MHD waves in the solar chromosphere
The chromosphere is a highly complex and dynamic region of the solar atmosphere
that has been largely neglected as an area of study. Advancements in solar
observational instrumentation have provided tantalising evidence that hints at
the chromosphere playing a key role in the heating and mass balance of the solar
atmosphere. The increase in temporal, spatial and spectral resolution of
instruments has also resulted in the observation and identification of
Magnetohydrodynamic (MHD) wave phenomena. MHD waves are thought to play a vital
role in transferring the magneto-convective energy from the solar surface to the
other layers of the solar atmosphere. The key to this is the solar magnetic
field, providing wave-guides that can support wide range of MHD waves.
Further to this, MHD waves can also be exploited for magneto-seismology.
Observed wave properties are used as diagnostic tools to reveal information
about the local plasma that would otherwise be hard to measure or
immeasurable.
I will give a (very) condensed overview of solar magnetism, MHD wave theory, key
observations of MHD waves and the potential role of waves in heating the solar
atmosphere. The focus will be on recent observations of chromospheric phenomenon
and their implications on wave generation, propagation and dissipation. I will
also provide examples of how the observed waves can be used for
magneto-seismology to reveal information about chromospheric plasma.
Simon Platt
Ex sole ad sole
The nature and importance of the effects of radiation on electronic systems are
described, with focus on single-event effects caused by atmospheric neutrons.
Some contributions of work undertaken at UCLan are described.
Lu Lu
Mass composition studies of ultra high energy cosmic rays
with the surface detector of the Pierre Auger Observatory
2012 is the centenary of the discovery of cosmic rays. They are charged
particles from our galaxy and the wider universe with a vast range of
energies. The highest energy cosmic ray observed so far is with energy
~1020 eV which is much larger than the energy of particles accelerated
in the Large Hadron Collider LHC. The Pierre Auger Observatory has been
designed to unravel the origin of the highest energy cosmic rays. It
covers an area of 3000 km2 in Argentina and has been in operation since
2004. The keys to the origin are the mass composition and the energy
spectrum. Mass sensitive parameters used so far and the recent results
will be shown. GZK photons are one of the signatures if cosmic rays are
dominated by protons and they are also important for astro scenario
interpretations. A new approach for ultra high energy photon search
using fluctuations in footprints of the shower (trace) will be
introduced. As this is a variable based on the surface array (100% duty
cycle), it allows investigation of the full Auger data set at the very
highest energies. The current state of work and outlook to the future
plan (multi parameter analysis) will be presented.
Gabriele Cescutti
Chemical elements in the early Universe
The incredible progress made by telescopes in the past years has
opened the door to the detailed study of the chemical abundances of
the oldest stars belonging to the Milky Way and to its closest satellites.
The observed chemical signatures coupled with
chemical evolution models, can provide new insights
on the formation and evolution of the different components of the Local Group;
moreover, they can be used to check the validity of the theoretical
predictions of stellar nucleosynthesis in the early Universe.
First, we present the case of the manganese where
the comparison among different stellar systems proves its relevance;
this iron peak element can be successfully reproduced in three stellar systems (the solar vicinity,
the dwarf spheroidal galaxy Sagittarius and the Galactic bulge) but only assuming a production
in supernovae type Ia with an unexpected dependence on the metallicity.
Then, we focus on chemical anomalies in the Galactic halo
that our group has successfully explained in the
framework of a first stellar generation formed by spinstars (metal poor fast rotating massive stars).
Adopting a stochastic chemical evolution model, we show that the
existence of the spinstars can offer a new twist in the interpretation of the abundance patterns
and scatter of CNO and neutron capture elements observed in the oldest
Galactic stars.
Simon Platt
Ex sole ad sole
The nature and importance of the effects of radiation on electronic systems are
described, with focus on single-event effects caused by atmospheric neutrons.
Some contributions of work undertaken at UCLan are described.
Giovanni Natale
Star Formation and Dust on Galactic Scales
In the first part of this talk I will introduce the topic of star formation on galactic scales from an observational point of view. In particular I will discuss the problem of measuring reliable star formation rates (SFR) and gas masses on regions of ~kpc sizes and how this is inevitably connected to the understanding of dust heating and emission in galaxies. In the second part I will speak about the analysis I have done on the FIR bright sources of the nearby spiral galaxy M83, as observed on the Herschel maps of this galaxy. I will discuss the results of this work for the star formation efficiency and the dust heating in these sources.
Witold Maciejewski
Nuclear Bars and Spirals in Disc Galaxies: their Origin and Implications
The inner kiloparsec of disc galaxies often hosts structures that seem to
be distinct from the galaxy outside it. Nuclear bars and spirals are
miniature versions of large-scale structures, yet their origin and nature
may be different. In this talk, I will review observational
characteristics of nested bars and nuclear spirals, and will discus the
rather conflicting theories of their origin. I will show that the common
presence of double bars in galaxies possibly requires a revision of
initial conditions at the time of the formation of the disc. Nuclear bars
and spirals can also play a role in angular momentum transfer and mass
redistribution in centres of galaxies. I will explain why nested bars may
be inefficient in driving gas inflow, while nuclear spirals can be sites
of strong shocks in gas that sustain inflow sufficient to trigger local
AGN.
Giovanni Natale
Star Formation and Dust on Galactic Scales
In the first part of this talk I will introduce the topic of star formation on galactic scales from an observational point of view. In particular I will discuss the problem of measuring reliable star formation rates (SFR) and gas masses on regions of ~kpc sizes and how this is inevitably connected to the understanding of dust heating and emission in galaxies. In the second part I will speak about the analysis I have done on the FIR bright sources of the nearby spiral galaxy M83, as observed on the Herschel maps of this galaxy. I will discuss the results of this work for the star formation efficiency and the dust heating in these sources.
Balazs Pinter
Interaction of the Solar Interior and Atmosphere
Global helioseismic oscillations are a window to the inner parts of the sun.
They are acoustic waves trapped in the solar interior and can give valuable
information about the directly unobservable inner layers. The information can be
properly decoded only if theoretical models explain how properties of the
observed oscillations can be influenced by their environment.
Recent observations provide evidence that helioseismic modes are affected not
only by the sub-photospheric layers but also the lower atmosphere. Realistic
numerical models and simplified analytical calculations try to discover the
complex nature of the interaction between helioseismic oscillations and the
atmosphere.
The presence of an atmospheric magnetic field makes the coupling complex.
Characteristic properties of oscillations, such as frequency, lifetime and
penetration depth, can be derived from magnetohydrodynamic (MHD) equations,
which govern the processes. Those properties are functions of the temperature
profile of the coupled interior and atmospheric environment and the magnetic
profile of the atmosphere. The derived equations provide valuable information
about the ways oscillation modes can be affected by the different properties of
their medium. Various models take into account realistic vertical profiles of
temperature, plasma flows and magnetic field structures. In narrow layers, where
the characteristic frequency of local MHD waves are equal to the global
frequency of an acoustic wave, the latter will be resonantly coupled to the
atmospheric magnetic field. The consequences of this resonant coupling are also
studied by using dissipative MHD equations.
Boris Haeussler
MegaMorph – Measuring the physical properties of galaxy components in modern multi-wavelength surveys
Generally, astronomers only use a fraction of their data in a homogeneous and consistent manner, causing increasd measurement errors and even catastrophic outliers. Using all available data simultaneously can avoid such problems and reduce measurement errors, making new studies possible.
As an example, most galaxies are fundamentally multi-component systems, often comprising a spheroidal bulge and a thin disk with largely independent origins. Separating these components, however, is challenging using todays methods on large samples of galaxies, but would provide important information with which to constrain models of galaxy formation and evolution.
As an example of a newly developed tool that uses multi-band imaging data, I present MeGaMorph, an accurate, robust tool for measuring the key physical quantities of the individual structural components of galaxies imaged by large multi-band surveys (e.g. GAMA/SDSS, CANDELS/HST).
I will present the idea of MeGaMorph as well as testing results and brand-new scientific results from the GAMA survey that we can interpret as measuring colour gradients in 10s of thousands of galaxies in a consistent manner.
Balazs Pinter
Interaction of the Solar Interior and Atmosphere
Global helioseismic oscillations are a window to the inner parts of the sun.
They are acoustic waves trapped in the solar interior and can give valuable
information about the directly unobservable inner layers. The information can be
properly decoded only if theoretical models explain how properties of the
observed oscillations can be influenced by their environment.
Recent observations provide evidence that helioseismic modes are affected not
only by the sub-photospheric layers but also the lower atmosphere. Realistic
numerical models and simplified analytical calculations try to discover the
complex nature of the interaction between helioseismic oscillations and the
atmosphere.
The presence of an atmospheric magnetic field makes the coupling complex.
Characteristic properties of oscillations, such as frequency, lifetime and
penetration depth, can be derived from magnetohydrodynamic (MHD) equations,
which govern the processes. Those properties are functions of the temperature
profile of the coupled interior and atmospheric environment and the magnetic
profile of the atmosphere. The derived equations provide valuable information
about the ways oscillation modes can be affected by the different properties of
their medium. Various models take into account realistic vertical profiles of
temperature, plasma flows and magnetic field structures. In narrow layers, where
the characteristic frequency of local MHD waves are equal to the global
frequency of an acoustic wave, the latter will be resonantly coupled to the
atmospheric magnetic field. The consequences of this resonant coupling are also
studied by using dissipative MHD equations.
Boris Haeussler
MegaMorph – Measuring the physical properties of galaxy components in modern multi-wavelength surveys
Generally, astronomers only use a fraction of their data in a homogeneous and consistent manner, causing increasd measurement errors and even catastrophic outliers. Using all available data simultaneously can avoid such problems and reduce measurement errors, making new studies possible.
As an example, most galaxies are fundamentally multi-component systems, often comprising a spheroidal bulge and a thin disk with largely independent origins. Separating these components, however, is challenging using todays methods on large samples of galaxies, but would provide important information with which to constrain models of galaxy formation and evolution.
As an example of a newly developed tool that uses multi-band imaging data, I present MeGaMorph, an accurate, robust tool for measuring the key physical quantities of the individual structural components of galaxies imaged by large multi-band surveys (e.g. GAMA/SDSS, CANDELS/HST).
I will present the idea of MeGaMorph as well as testing results and brand-new scientific results from the GAMA survey that we can interpret as measuring colour gradients in 10s of thousands of galaxies in a consistent manner.
John Magorrian
The centre of M31
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.
Andreea Font
Milky Way gas-dynamical simulations for Gaia
Our understanding about how Milky Way has formed and evolved will be revolutionised in the next few years thanks to the advent of a new generation of space instruments such as Gaia, an European Space Agency space mission which will be launched later this year. Gaia will provide an a plethora of data about our Galaxy, including an accurate 3D map of about 1 billion stars in the disc, bulge and the halo. It is expected that these data will ultimately unravel the formation history of the Milky Way and thus achieve an important milestone not only in Galactic studies but also in the wider field of galaxy formation and evolution.
However, to fully make sense of the intricacy of this panoramic view of our Galaxy, ultimately one needs to resort to physically motivated simulations of galaxy formation. The current generation of gas-dynamical cosmological simulations is gearing up to meet the challenge of comparisons with the upcoming data. In this talk, I will present our progress in creating realistic simulations of Milky Way-like galaxies in the context of Lambda CDM cosmology and I will discuss some of the still outstanding problems in theoretical models of galaxy formation.
Denija Crnojevic
Galaxy evolution through resolved stellar populations in the nearby
CentaurusA group
The CenA/M83 group is a nearby dense complex (~4Mpc) dominated by a
giant elliptical and a giant spiral, hosting more than 60 dwarf
companions with a variety of morphological types and stellar contents.
My aim is to constrain galaxy evolution processes through the study of
resolved stellar populations of galaxies in this group. Firstly, for
dwarf members I characterize the recent star formation histories and
metallicity content (by using optical and near-infrared data from
ACS/HST and ISAAC/VLT), and compare them to what is known for Local
Group dwarfs, underlining similarities and differences. My results
probe the fundamental interplay between nature (mass) and nurture
(environmental effects) in shaping the evolution of dwarfs in groups
of galaxies. I furthermore present results from the first deep survey
of resolved stellar populations in the remote outer halo of our
nearest giant elliptical, CenA (VIMOS/VLT optical data). Tracing its
halo structure (radial profile, extent and metallicity) out to a
remarkable ~14 Reff and comparing the halo stellar populations to
those of CenA’s dwarf companions enables me for the first time to
constrain the mechanisms that contributed to the build-up of CenA in
the context of cosmological galaxy formation models.
Denija Crnojevic
Galaxy evolution through resolved stellar populations in the nearby
CentaurusA group
The CenA/M83 group is a nearby dense complex (~4Mpc) dominated by a
giant elliptical and a giant spiral, hosting more than 60 dwarf
companions with a variety of morphological types and stellar contents.
My aim is to constrain galaxy evolution processes through the study of
resolved stellar populations of galaxies in this group. Firstly, for
dwarf members I characterize the recent star formation histories and
metallicity content (by using optical and near-infrared data from
ACS/HST and ISAAC/VLT), and compare them to what is known for Local
Group dwarfs, underlining similarities and differences. My results
probe the fundamental interplay between nature (mass) and nurture
(environmental effects) in shaping the evolution of dwarfs in groups
of galaxies. I furthermore present results from the first deep survey
of resolved stellar populations in the remote outer halo of our
nearest giant elliptical, CenA (VIMOS/VLT optical data). Tracing its
halo structure (radial profile, extent and metallicity) out to a
remarkable ~14 Reff and comparing the halo stellar populations to
those of CenA’s dwarf companions enables me for the first time to
constrain the mechanisms that contributed to the build-up of CenA in
the context of cosmological galaxy formation models.
Esko Gardner
Comparing N-Body Simulations to the Boxy Bulge of the Milky Way
The Boxy Bulge of the Milky Way is an observationally recently studied feature. I will make a comparison of the Bulge of the Milky Way to N-body simulations. The comparisons show where and what kinds of clear signatures of the Boxy Bulge can be found, in both the kinematic and morphological domains.
Rok Roskar
Radiation Feedback in Cosmological Spiral Galaxy Formation
State-of-the-art fully cosmological simulations of spiral galaxies have over the
past few years began to yield systems that are increasingly consistent with
observational constraints. Typically, modelers rely on various flavors of
‘feedback’ processes in order to modulate the growth of baryons to avoid the
problems associated with overcooling, which prevent the formation of extended
late-type disks. However, in Milky Way-size halos, even strong supernova
feedback prescriptions are often unable to unbind sufficient quantities of
baryons to match the semi-empirical stellar mass-halo mass relations, resulting
in systems that contain several times too many stars given their halo mass. I
will present our attempts to mitigate some of these issues by using a new
feedback model that tries to mimic the impact of stellar radiation on the ISM
around star-forming regions.
Andreea Font
Milky Way gas-dynamical simulations for Gaia
Our understanding about how Milky Way has formed and evolved will be revolutionised in the next few years thanks to the advent of a new generation of space instruments such as Gaia, an European Space Agency space mission which will be launched later this year. Gaia will provide an a plethora of data about our Galaxy, including an accurate 3D map of about 1 billion stars in the disc, bulge and the halo. It is expected that these data will ultimately unravel the formation history of the Milky Way and thus achieve an important milestone not only in Galactic studies but also in the wider field of galaxy formation and evolution.
However, to fully make sense of the intricacy of this panoramic view of our Galaxy, ultimately one needs to resort to physically motivated simulations of galaxy formation. The current generation of gas-dynamical cosmological simulations is gearing up to meet the challenge of comparisons with the upcoming data. In this talk, I will present our progress in creating realistic simulations of Milky Way-like galaxies in the context of Lambda CDM cosmology and I will discuss some of the still outstanding problems in theoretical models of galaxy formation.
17th July: CARD: Planet formation by disc fragmentation
By Dr Dimitris Stamatellos, JHI, UCLan
17th July 2013
I will discuss the role that disc fragmentation plays in the formation of gas giant and terrestrial planets, and how this relates to the formation of brown dwarfs and low-mass stars, and ultimately to the process of star formation. Protostellar discs may fragment, if they are massive enough and can cool fast enough, but most of the objects that form by fragmentation are brown dwarfs. It may be possible that planets also form, if the mass growth of a proto-fragment is stopped (e.g. if this fragment is ejected from the disc), or suppressed and even reversed (e.g by tidal stripping). I will discuss if it is possible to distinguish whether a planet has formed by disc fragmentation or core accretion, and mention of a few examples of observed exoplanets that are suggestive of formation by disc fragmentation.
Slipping magnetic reconnection: observations
and theory
Dr Jaroslav Dudik, Univ. of Cambridge
We present SDO/AIA observations of an eruptive X-class flare of July 12,
2012, and compare its evolution with the predictions of a 3D numerical
simulation. In particular, we focus on the dynamics of flare loops that
are seen to undergo slipping reconnection during the flare. In the AIA
131A filter, footpoint portions of 10 MK flare loops are seen to move
with velocities of several tens of km/s along the developing flare
ribbons. DEM analysis shows that the flare loops have temperatures up to
the formation Fe XXIV. In the early stages of the flare, the ribbons
observed in AIA 171A, 304A and 1600A consist of compact, localized
bright features that are the transition-region emission from the flare
loops footpoints. A portion of the flare loops, including a series of
very long, S-shaped loops are also seen to erupt, leading to a CME
observed by STEREO. The observed dynamics are compared with the
evolution of magnetic structures in the “standard solar flare model in
3D”. This model matches the observations well, reproducing both the
evolution of slipping flare loops, non-potential S-shaped long loops and
the evolution of flare ribbons. All of these processes are explained via
3D reconnection mechanisms resulting from the expansion of the
torus-unstable flux rope. The magnetic configuration of the flaring
region is described via quasi-separatrix layers (QSLs). Comparisons with
observations show that the flare involves a complex topology not only
due to polarities associated with the ribbons, but also the large-scale
magnetic structure, as inferred from the extrapolation of photospheric
magnetic field. Comparisons between AIA observations and the numerical
model are completed with radio observations in the metric and decimetric
ranges that show many bursts appearing in a broad range of frequencies.
In the early stages of the flare, slipping reconnection is associated
with a noise storm in the metric range. Dm-drifting pulsation structures
occur during the eruption and indicate both the plasmoid ejection and
the onset of fast magnetic reconnection.
Milky Way gas-dynamical simulations for Gaia
Dr Andreea Font, Liverpool JMU
Our understanding about how Milky Way formed and evolved will be revolutionised in the next few years thanks to the advent of a new generation of space instruments such as Gaia, an European Space Agency space mission which will be launched soon this year. Gaia will provide a plethora of data about our Galaxy, including an accurate 3D map of about 1 billion stars in the disc, bulge and the halo. It is expected that these data will ultimately unravel the formation history of the Milky Way and thus achieve an important milestone not only in Galactic studies but also in the wider field of galaxy formation and evolution.
However, to fully make sense of the intricacy of this panoramic view of our Galaxy, ultimately one needs to resort to physically motivated simulations of galaxy formation. The current generation of gas-dynamical cosmological simulations is gearing up to meet the challenge of comparisons with the upcoming data. In this talk, I will present our progress in creating realistic simulations of Milky Way-like galaxies in the context of Lambda CDM cosmology and I will discuss some of the still outstanding problems in theoretical models of galaxy formation.
Simulating Galaxy Formation: Numerical and Physical Uncertainties
Dr Debora Sijacki, Cambridge
Hydrodynamical cosmological simulations are one of the most powerful tools to
study the formation and evolution of galaxies in the fully non-linear
regime. Despite several recent successes in simulating Milky Way look-alikes,
self-consistent, ab-initio models are still a long way off. In this talk I will
review numerical and physical uncertainties plaguing current state-of-the-art
cosmological simulations of galaxy formation. I will then present global
properties of galaxies as obtained with novel cosmological simulations with
the moving mesh code Arepo and discuss which feedback mechanisms are needed to
reproduce realistic stellar masses and galaxy morphologies in the present day
Universe.
A Narrow-band View of Star Formation in the SXDS-UDS Field
Dr Alyssa Drake, Liverpool JMU
I will present new results on the cosmic star formation history in the SXDS-UDS field out to z=1.6. We have compiled narrow-band data from the Subaru Telescope and the Visible and Infrared Survey Telescope for Astronomy (VISTA) to make a selection of 5725 emission-line galaxies in 12 redshift slices, using 11-band photometry from SXDS-UDS to determine reliable photometric redshifts. We use the maximum-likelihood technique to determine an Halpha, [0III] or [0II] luminosity function in each redshift slice and model the selection effects inherent in any narrow-band selection statistically. Narrow-band data are sensitive to very low star formation rates (SFRs) and select galaxies irrespective of stellar mass, allowing an accurate evaluation of the faint end slope of the Schechter function. We find that is particularly sensitive to the assumed faintest broadband magnitude of a galaxy capable of hosting an emission line, and propose that this limit should be empirically motivated. We compute the integrated SFR density, SFR, and find our results to be in good agreement with the literature confirming a steep decline in star formation activity since z=1.6. We next determine stellar masses for galaxies in the 4 highest redshift slices of the deep Subaru data at z=0.63, z=0.83, z=1.19 and z=1.46. We apply our maximum likelihood method to determine luminosity functions in a series of mass bins at each redshift, and determine values of SFR as a function of mass. We use two different prescriptions for extinction as a function of stellar mass to determine dust extinction at H, and use the Cardelli Clayton and Mathid (1989) reddening law to extrapolate values for each at [0III] and [OII]. We calculate metallicities for objects in each mass bin, and correct the SFR accordingly where necessary. We highlight the importance of these corrections for the shape of the overall SFR as a function of mass, and its normalisation with redshift.
A Narrow-band View of Star Formation in the SXDS-UDS Field
Dr Alyssa Drake, Liverpool JMU
I will present new results on the cosmic star formation history in the SXDS-UDS field out to z=1.6. We have compiled narrow-band data from the Subaru Telescope and the Visible and Infrared Survey Telescope for Astronomy (VISTA) to make a selection of 5725 emission-line galaxies in 12 redshift slices, using 11-band photometry from SXDS-UDS to determine reliable photometric redshifts. We use the maximum-likelihood technique to determine an Halpha, [0III] or [0II] luminosity function in each redshift slice and model the selection effects inherent in any narrow-band selection statistically. Narrow-band data are sensitive to very low star formation rates (SFRs) and select galaxies irrespective of stellar mass, allowing an accurate evaluation of the faint end slope of the Schechter function. We find that is particularly sensitive to the assumed faintest broadband magnitude of a galaxy capable of hosting an emission line, and propose that this limit should be empirically motivated.
Assembling the Puzzle of Barred Galaxies
Dr Jairo Mendez-Abreu, IAC/St Andrews
Bars are elliptical-like structures present in most of disk galaxies. Despite their importance to understand galaxy evolution in general, several observational aspects regarding bars are still not well settled. In this talk I will review our recent results on two major observational bar characteristics: the evolution of their pattern speed and the role of environment in bar formation. I will discuss our recent findings in the context of bar formation and evolution and compare them with numerical simulation predictions.
Cross-field transport of energetic particles early in a solar event
Timo Laitinen
Solar energetic particles (SEPs) have been observed to have access to a
wide range of heliographic longitudes, suggesting strong SEP propagation across
the mean Parker spiral field. An often-used diffusion approach fails to describe
such wide spreading of particles without resorting to extremely large
cross-field diffusion coefficients. We use full-orbit simulations of a energetic
particles in a turbulent magnetic field, superposed on a constant background
field, to study to what extent the spread across the mean field is due to
particles following the meandering field lines rather than to diffusion in the
turbulent fields. We compare the full-orbit code results to solutions of a
Fokker-Planck equation including spatial and pitch angle diffusion, and of one
including also propagation of the particles along random-walking magnetic field
lines. The diffusion parameters for the latter models are consistent with the
full-orbit simulations, with a parallel scattering mean free path 0.3 AU. We
find that the cross-field spread of the particles at 1 AU is consistent with
deterministic propagation of particles along meandering field lines in the
beginning of the simulated event. The mean square width of these particles an
hour after the injection of the beam is an order of magnitude larger than that
given by the diffusion model, indicating that the diffusion description is
invalid for the early phase of particle propagation in SEP events. We conclude
that modelling SEP events must take into account the spreading of particle
propagation along meandering field lines for the first 20 hours of the event.
Chemodynamics of a Simulated Disk Galaxy: Structures in Abundance Space
Dr Christopher Few, Exeter
Numerical simulations are powerful tools allowing us to combine the disparate elements of galaxy formation and evolution
into a single model and to test the predictions of those models. In this talk I present a simulation code that traces chemical
evolution within the framework of hydrodynamical processes and a fully cosmological assembly history. I use this code to
examine how the assumptions of chemical evolution models manifest in the elemental composition of an L* field galaxy
and how the influence of cosmological assembly can be seen even in the present-day abundance ratios.
Emission measure distributions of solar eruptive events
Iain Hannah, Univ. of Glasgow
The current wealth of temperature sensitive solar observations presents a
unique opportunity to study energy release in solar eruptive events (flares and
CMEs). Data from SDO and Hinode gives an unprecedented view of dynamical heating
in the solar atmosphere but to fully exploit this resource the underlying
thermal properties of the emitting plasma (Emission Measure Distribution, EDM)
needs to be recovered. This is difficult as it is an ill-posed inverse problem
and, in the case of SDO/AIA, there is an overwhelming amount of data. Our
recently implemented regularized inversion method (Hannah & Kontar A&A 2012,
2013) can quickly and robustly find the EMD solution (and its uncertainties),
with the resulting EM maps allowing the temperature and density evolution to be
studied both spatially and temporally. I will present EMDs of flares,
microflares and eruptions, discussing the thermal and heating properties, as
well as comparing this to the non-thermal energy input derived from RHESSI hard
X-ray observations.
The Formation and Evolution of the Milky Way Disc: Constraints from Numerical Simulations
Dr Ivan Minchev, AIP
I will present a new chemo-dynamical model for the Milky Way, consistent with a large range of observations, and will outline some predictions for forthcoming large-scale spectroscopic surveys. I will discus a new chemo-kinematic relation involving stellar velocity dispersions, metallicity and α-enhancement, found in two independent large data sets: RAVE giants and SEGUE G-dwarfs. Using simulated data, I will show that these results may offer a way to recover the entire merger history of the Milky Way disk.
The Formation and Evolution of the Milky Way Disc: Constraints from Numerical Simulations
Dr Ivan Minchev, AIP
Tales from the Zooniverse: Science with 800,000 volunteers
Dr Chris Lintott, Oxford University
The Zooniverse is the world’s largest and most successful scientific crowdsourcing platform, engaging more than 800,000 volunteers in tasks including classifying galaxies, discovering planets and mapping star formation in the Milky Way. This talk will present highlights from the last six years, including the serendipitous discovery of galaxy-scale light echoes, and explain how an unusual set of bulgeless spiral galaxies identified by Galaxy Zoo volunteers is informing models of galaxy formation and feedback. The talk will also set out the future for this massively distributed effort in the world of future facilities such as the LSST and SKA.