Recent Talks

The Astrophysics Research Institute (ARI) was established at LJMU in 1992. Today the Institute comprises around 70 staff and research students working on topics ranging from stellar evolution to cosmology. In this talk I will give an overview and some highlights of the work undertaken in recent years on Classical and Recurrent novae by the nova group of the ARI. This involves multi-frequency observations of both Galactic novae and those in Local Group galaxies and includes topics such as the exploration of their potential links to the progenitors of Type Ia supernovae. Along the way, I will briefly describe the work of the Liverpool Telescope on La Palma, one of whose primary science drivers is the efficient and effective observation of transient objects such as these, and look forward to our plans for the development of an even larger and faster-reacting robotic telescope at ORM - currently codenamed 'LT2".

What can the shape and size of a galaxy tell us about how it has evolved across cosmic time? Which evolutionary mechanisms are important, or relevant, and which not? How do galaxies form in the early Universe? As we enter a new era of big-data astronomy, our capacity to further pursue answers to these questions is increasingly limited not by Human ingenuity but by our use of 20th century data analysis techniques. In this talk, I will summarise my work with the Galaxy And Mass Assembly (GAMA) Survey in measuring the multi-wavelength light profile and stellar mass properties of ~200,000 galaxies in the local Universe. I will show how the stellar mass function may be broken down by morphology and structural component, and the implications this has for our understanding on which evolutionary mechanisms are important in shaping the galaxies around us over the course of the last 1 billion years. 

Adaptive optics systems rely on a real-time control system which is responsible for receiving wavefront sensor information and computing and applying the necessary correction to the deformable mirrors. Historically, real-time control systems have relied on customised hardware comprised of multiple FPGA and DSP systems, which high complexity. More recently it has been demonstrated that conventional PCs are now sufficiently powerful to to perform this task. In this talk, I will present an open-source real-time control system, DARC, discuss its implementation on the CANARY AO system at the William Herschel Telescope, and cover the algorithms available. Extension to ELT-scale operation will be discussed, including hardware and detector considerations. The internal architecture of this modular system will be presented, with a case being made for its suitability for implementation on any AO system type, on any telescope.

Dwarf galaxies are the most common type of galaxy in the Universe andinclude the most dark-matter-dominated objects known. They offerintriguing insights into evolutionary processes at low halo masses and low metallicities. Moreover, as survivors of a once much more numerous population of building blocks of larger galaxies, they are key to understanding very early star formation processes. The Local Group and particularly the Milky Way's dwarf galaxy entourage offer us the unique possibility to compare in detail dwarf and Galactic populations. This is an important step towards quantifying the magnitude and time scales of dwarf contributions to the build-up of the Milky Way and allows us to test predictions of cosmological theories and hierarchical structure formation.

Over the past two decades, advances in infrared instrumentation have allowed us to identify a vast and previously unseen population of low-temperature stars, brown dwarfs and free-floating extrasolar planets, collectively called ultracool dwarfs. These sources, with surface temperatures reaching below 0ºC, encompass three new spectral classes and include some of the nearest systems to the Sun. Research in this field is now concentrating on the physical characterization of the ultracool dwarf population and application to Galactic studies. In this talk, I will summarize the recent observational advances in ultracool dwarf research, including the recent discovery of the Y dwarf spectral class. I will then describe our ongoing IRTF/SpeX survey, which has measured the low-resolution, near-infrared spectra of over 1500 late M, L and T dwarfs and uncovered new subpopulations of young (5-30 Myr) brown dwarf, metal-poor halo brown dwarfs and short-period spectral binaries.

Modern imaging surveys provide a fundamental tool in order to study the morphological
properties of galaxy populations in the nearby and the distant Universe. In order to
process a complete set of survey images, we designed GALAPAGOS-C. GALAPAGOS-C
unifies the detection of sources (via source extractor), postage stamp cutting, object
mask preparation, sky background estimation and complex two-dimensional light profile
Sérsic modeling (via GALFIT) in one automatic program. GALAPAGOS-C is designed
around the concept of MPI-parallelization, allowing the processing of large data sets
in a quick and efficient manner. Further, GALAPAGOS-C is capable of fitting multiple-
Sérsic profiles to each galaxy, each representing distinct galaxy components (e.g. bulge,
disc, bar), in addition to the option to fit asymmetric distortions with a Fourier mode
expansion to the axis-symmetric single-Sérsic isophotes. The modeling reliability of our
core single-Sérsic fitting capability and the optional Fourier mode expansion are tested
thoroughly using image simulations.
GALAPAGOS-C is applied to a sample of 2063 galaxies in the A901/902 galaxy cluster
(z ∼ 0.165) from the Space Telescope A901/902 Galaxy Evolution Survey (STAGES) and
an additional sample of 2876 field galaxies from the Galaxy Evolution From Morphology
And SEDs Survey (GEMS). We measure the distribution of Sérsic indices as a function of
local object density in the A901/902 cluster sample to provide one of the first measures
of the Sérsic index–density relation. In addition, we measure the distribution of lopsided
galaxies in the A901/902 cluster sample and quantify the intensity of lopsidedness in
the galaxies in the field since z ∼ 0.9 in order to study the evolution of lopsidedness as
a function of redshift. In each application, we study the correlations of the measured
parameters with other intrinsic and structural variables, e.g. the stellar mass, the color
or the presence or absence of a disk. Our results provide further clues on the evolution
of galaxy structure with cosmic time and the dependence on environment.

One of the challenges in solar astronomical observations is the lack of high resolution observations over a wide FOV. Adaptive optics (AO) systems, which are routinely used in current solar telescopes, can only provide successful correction over a narrow FOV. Multi-conjugate adaptive optics (MCAO) systems attempt to address this issue and provide correction over a much wider FOV. It will become a key technology in the next generation of solar telescopes, such as the EST and DKIST. At this time, there is no fully operational solar MCAO system in operation. Work is under way at several solar facilities like the NST (Ø1.6m, BBSO) and GREGOR (Ø1.5m, KIS) to build prototype solar MCAO
systems. There is also a significant investigative effort at the IAC to study the design and operation of a solar MCAO system (proper location of the DMs and WFS, appropriated sensing for an extended object,
communication between different WFS, convenient reconstruction method). This talk will provide a review of the current state of solar MCAO, concentrating on solar MCAO simulation efforts under development
at the National Solar Observatory.

Microvariations probe the physics and internal structure of quasars. Unpredictability and small flux variations make this phenomenon elusive and difficult to detect. Variance based probes such as the C and F tests, or a combination of both, are popular methods to compare the light-curves of the quasar and a comparison star. Recently, detection claims in some studies depend on the agreement of the results of the C and F tests, or of two instances of the F-test, in rejecting the non-variation null hypothesis. However, the C-test is a non-reliable statistical procedure, the F-test is not robust, and the combination of tests with concurrent results is anything but a straightforward methodology. A priori Power Analysis calculations and post hoc analysis of Monte-Carlo simulations show excellent agreement for the Analysis of Variance test to detect microvariations, as well as the limitations of the F-test. Additionally, combined tests yield correlated probabilities that make the assessment of statistical significance unworkable. However, it is possible to include data from several field stars to enhance the power in a single F - test or ANOVA nested designs, increasing the reliability of the statistical analysis. These would be the preferred methodology when several comparison stars are available. These results show the importance of using adequate methodologies, and avoid inappropriate procedures that can jeopardize microvariability detections. Power analysis and Monte-Carlo simulations are useful tools for research planning, as they can reveal the robustness and reliability of different research approaches.

The ultra-deep multiwavelength HST Frontier Fields coverage of the Abell Cluster 2744 is used to derive the stellar population properties of its intra-cluster light (ICL). The restframe colors of the ICL of this intermediate redshift (z=0.3064) massive cluster are bluer (g-r=0.68 ±0.04; i-J=0.56±0.01) than those found in the stellar populations of its main galaxy members (g-r=0.83±0.01; i-J=0.75±0.01). Based on these colors, we derive the following mean metallicity Z=0.018±0.007 for the ICL. The ICL age is 6±3 Gyr younger than the average age of the most massive galaxies of the cluster. The fraction of stellar mass in the ICL component comprises at least 6% of the total stellar mass of the galaxy cluster. Our data is consistent with a scenario where the bulk of the ICL of Abell 2744 has been formed relatively recently (z<1). The stellar population properties of the ICL suggest that this diffuse component is mainly the result of the disruption of infalling galaxies with similar characteristics in mass (M*~ 3x10^10 Msolar) and metallicity than our own Milky Way. The amount of ICL mass in the central part of the cluster (<400 kpc) is equivalent to the disruption of 4-6 Milky Way-type galaxies.

We have learned a great deal about the universe from measurements ofthe cosmic microwave background (CMB). Most of what we have learned so far has been based on the temperature anisotropy combined with measurements of the polarization at angular scales of roughly 10 degrees. We are entering a new era in which the polarization of the CMB will be measured to high accuracy especially at degree angular scales and smaller. With the polarization we can, for example,  measure or limit the presence of gravitational radiation from the early universe and determine the sum of the neutrino masses. The polarization will also give us a new way to determine the cosmological parameters. We review recent results on the CMB polarization with anemphasis on those from the Atacama Cosmology Telescope (ACT) project.