Prof. Farhad Yusef-Zade
Title: The Massive Black Hole at the Centre of the Galaxy
The processes occurring in the nuclear disk of our own Galaxy are interesting because this region can potentially provide a template for the study of more distant galactic nuclei. There are several sources of activity in this unique region of the Galaxy. One is the underluminous supermassive black hole (Sgr A*) at the dynamical centre. Sgr A* exhibits flares which occur a few times a day, arising from the inner ten Schwarzschild radii of the 4 million solar mass black hole. The other is the nuclear stellar cluster, which consists of a population of evolved stars and a young population of stars in a disk orbiting within 0.5 pc of Sgr A*. On a scale of milli-pc, a three earth mass gas and dust cloud (G2) is on a collision course with Sgr~A*. VLT observations indicate that the G2 cloud approaches pericentre in mid-2013 and it will be disrupted and portions will likely be accreted by the massive black hole residing there.
In this talk, I will describe what we have learned from studying Sgr A*, how stars are formed near Sgr A* and what we expect to learn by monitoring the light from the interaction of the G2 cloud and Sgr A*.
Title: Improving the precision of wide-field ground-based Exoplanet surveys
Transiting planet surveys have become increasingly popular since the first detection of a planetary primary eclipse around HD209458 using a small and inexpensive wide-field telescope. Motivated by this result, The SuperWASP project was founded in 2002, consisting of 2 robotic telescopes aimed at surveying the night sky in search of planetary transits. This is currently the most successful exoplanet survey of its kind, having detected almost 100 planets to date. However, it has under-achieved with respect to the initial detection predictions, which suggested thousands of planets would be found. As with most ground based surveys, systematic noise is a limiting factor in precision and a good understanding of this noise is vital to any potential improvement.
I present a study of the SuperWASP detector maps as a diagnostics method, highlighting some key features, investigating their causes and suggesting potential improvements.
I will also mention the successor to this project, the Next Generation Transit Search, currently on the final stages of development. This instrument is due to start observing in early 2014 from a single large facility at ESO’s Paranal Observatory.
Title: Contribution of Magnetic Turbulence to Gas accretion in Circumplanetary Disks
During the creation of gas giant planets, gaseous disks form around them. These disks are called circumplanetary disks, and are believed to be the formation sites of satellites. Although an understanding of disk evolution is required for developing theories of satellite formation, gas accretion rates of circumplanetary disks are very uncertain. The most promising mechanism of gas accretion is thought to be magnetic turbulence which is driven by magnetorotational instability (MRI), and recent studies of MRI have shown that even thin MRI-active layers can drive mass accretion. We investigate the sizes of MRI-active regions in circumplanetary disks of various surface densities by calculating the ionization degree of the disk gas. If there are no dust grains, thin active layers may appear at large radii; however, we find that there are not even thin active layers in regions of satellite formation with sufficient small dust grains. Our results suggest that gas accretion mechanism other than MRI should be taken into account.
European Southern Observatory
Title: A biased view of the Canis Majoris “dwarf” galaxy
Abstract:There has been a debate on the presence (or not) of a cannibalized dwarf galaxy in Canis Major. I will present arguments in favour of a Galactic origin of this stellar over-density.
Title: The extra-planar ISM of Spiral Galaxies
Abstract:In recent years it has become clear that the gas circulation above the plane of spiral galaxies plays a crucial role in their evolution. Studies of the extra-planar hydrogen can improve our understanding of this disk-halo interaction and continued star formation as well as accretion from the IGM. Kinematical information is of particular interest since it provides clues to the origin of the gas and helps to disentangle projection effects. Such kinematical studies have shown that the rotational velocities of the gas in massive spiral galaxies decline with increasing distance to the mid-plane, the so-called lag. In several cases, apart from the main disk, a large diffuse second component is observed in the vertical distribution of the gas. However, in which manner these thick disks and lags relate to each other as well as their origins remain open questions. Currently large multi-wavelength surveys are undertaken to obtain the properties of the extra-planar gas for large samples of galaxies. One of these surveys is the WSRT Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) Survey. This survey will, for the first time, provide us with the data to correlate the extra-planar gas properties with global galaxy properties and provide us with a consensus of cold gas accretion in the nearby Universe. Additionally, the search for extra-planar gas has recently been expanded to early type galaxies.
Title: Magnetic fields in giant planet formation
Abstract: Over 700 planets around other stars have been discovered – almost all of which are roughly Jupiter-sized. During the final growth phase of these giant planets, their accretion is controlled by a surrounding circumplanetary disk. Current accretion theories rely on magnetic turbulence for viscosity within the disk. However, whether the disk is able to interact sufficiently with the magnetic fields to produce this turbulence remains a key question. Here I apply methods developed for disks around young stars to examine the effectiveness of magnetic coupling in circumplanetary disks. I present radial midplane temperature, ionisation, and magnetic diffusivity profiles, calculated assuming the standard alpha-disk model. I demonstrate that thermal ionisation couples the disk midplane out to only 25 Jupiter radii, beyond which accretion cannot proceed. I present an alternative scenario in which the entire midplane is ionised, and discuss the effectiveness for cosmic ray surface ionisation and electric discharge as additional ionising sources.
Title: Estimating the fraction of binary central stars of planetary nebulae using the IR-excess method
Abstract:There is no quantitative theory to explain why a high 80% of all planetary nebulae are non-spherical. The Binary Hypothesis states that a companion to the progenitor of a central star of planetary nebula is required to shape the nebula and even for a planetary nebula to be formed at all. A way to test this hypothesis is to estimate the binary fraction of central stars of planetary nebulae and to compare it with that of the main sequence population. Preliminary results from photometric variability and the infrared excess techniques indicate that the binary fraction of central stars of planetary nebulae is higher than that of the main sequence, implying that PNe could preferentially form via a binary channel.
I will show very fresh results resulting from the recent analysis of a CSPN sample observed at the NOAO 2.1m telescope in 2011.
Title:The Past, Present and Future of High Redshift Radio Galaxies
High redshift radio galaxies are unique markers of the coeval formation of massive galaxies and their central black holes within the of peaks of dark matter over-densities in the early Universe. As such they are important laboratories for studying the formation of massive galaxies containing active galactic nuclei and how AGN activity affects the host galaxy and environment. I shall present results from ‘Project HeRGE’, a systematic study of 71 high redshift radio galaxies (z>1, L_500MHz>10^26 W/Hz) using Spitzer and Herschel photometry. From these data we are able to constrain the stellar mass, the AGN power and the SFR of these sources and, hence obtain a measure of the overall evolutionary state of the system. By comparing the current state of the system with the radio emission and environment we are able to evaluate models of massive galaxy formation, feedback and cluster growth.
Orsola De Marco
Title:The progenitors of planetary nebulae
We can safely assume that pre-planetary nebulae will turn into planetary nebulae, once the gas is ionised by the heating cental star.
However, not all planetary nebulae have gone through a pre-planetary nebula phase. Similarly, not all asymptotic giants will go through a pre-planetary nebula phase. Each of these classes of objects seems instead to arise only when a specific set of circumstances is in place. In this review (which was recently written for the ESO conference on “The Death of Stars and the lives of Galaxies”) I will highlight some of the key problems and open questions on the evolution of intermediate mass stars. I will show how the familiar paradigm needs substantial revisions.
Title:LMC PNe as astrophysical tools to explore the PNLF bright-end cut-off and LMC kinematics
Reid & Parker have now extended the original PN survey of the LMC’s central 25 deg2 (Reid & Parker 2006ab) to a larger >80deg2 region covering the entire outer LMC. I will show multi-wavelength images and spectroscopic confirmation of our newly discovered PN candidates and previously known PN in this larger region. A large fraction of new LMC PNe are ~3× fainter than those previously known, tripling numbers accrued from all surveys over the last 80 years. These data have led to significant advances in our understanding of the kinematical sub-structure of the central LMC including improved determination of LMC rotation, inclination and transverse velocity as well as better elucidation of the old stellar population and a significantly improved PNLF. Both the Magellanic Cloud Emission-line Survey (MCELS) and our priority access to the SHS H-alpha/Short Red survey of the Magellanic Clouds has provided the candidates for spectroscopic identification.
Up until now, PNe kinematics in the outer LMC was unknown. We are currently using PNe to trace out the progression of thetamax and its elliptical structure across the whole LMC in order to unravel its true kinematical structure. The candidate positions and subsequent measured spectroscopic velocities are now being used to map the outer kinematic structure of the LMC to refine the warps, velocity structures and system rotation uncovered in the inner regions. Velocities of ~5km/s for PNe in the LMC’s central bar have enabled us to investigate PNe population kinematics and their interaction with the tidal forces and the HI disk.
Confirmation of faint PNe candidates to V=21 has also provided the most complete and accurate spectroscopically confirmed PNLF across a whole galaxy ever assembled with which to accurately predict the number of stars in the PN evolutionary stage in each luminosity bin compared to the luminosity and mass of the whole galaxy. Establishing the consistent shape of the entire function has provided a basis for estimating the number of PNe in any galaxy, when only PNe in the brightest 3 or 4 mag are detectable. Our LMC PNLF extends down just over 10 mag and has a distinct turnover, not associated with incompleteness, at only 6 mag below the brightest providing a unique probe into the LMC’s chemical and dynamical evolution.
Title:A radio continuum study of MASH Planetary Nebulae
Accurate radio continuum observations of Planetary Nebulae (PNe) are important tool for determining reliable physical parameters for these objects. The radio flux is used for the determination of interstellar extinctions towards PNe and as an evolutionary tracer via distance independent parameters like brightness temperature, infrared excess or turnover frequency. Since it is produced by the electron gas it gives the overall density structure of the ionised nebula (providing adequate resolving power) and with a knowledge of reliable distance it can be used for the estimate of the total ionised mass. Finally the negligible extinction at cm wavelengths pinpoints the radio continuum data, in combination with NIR data, as the main tool for finding candidates for the “missing” PN population in regions of the high interstellar extinction.
In this talk I will present observational results from ATCA survey of PNe from the MASH catalogue. It is one of the largest and most sensitive radio continuum survey on Galactic PNe bringing to the table a large data set for some of the most distant and highly evolved objects.
Title:Properties of the planetary systems
Kepler has detected hundreds of extra solar planets around wide variety of stars. These extra solar planetary systems throw new light on the disc-planet interaction. I shall compare and contrast the properties of the solar and extra solar planetary systems. Further, I shall briefly touch upon the planet migration theory that tends to explain the close proximity of Jupiter like planets to the star in the extra solar planetary system.
Title:So what does star formation have to do with turbulence in galaxies?
High redshift galaxies are not only typically highly star forming, but integral-field spectroscopy has revealed that they also have high gas velocity dispersions or turbulence. Observations of early galaxies are informing much of our understanding of galaxy evolution because their properties are often so varied from more nearby galaxies—modern star forming galaxies typically have more modest star formation and turbulence. Our basic theories of star formation suggest that turbulence and star formation are intimately linked, and observations reflect this link for galaxies across all redshifts. Therefore, (potentially rare) local galaxies with similar properties to high-redshift galaxies could provide an even better means for understanding galaxy evolution because so many more astronomical tools can be brought to bear on the problem. I will discuss a sample of galaxies where my collaborators and I have been able to do just this: apply powerful tools to local galaxies and see the same processes which are common at high redshift. I’ll finish by outlining the consensus that is beginning to form around some aspects of galaxy formation from all of the new data in the past few years.
University of Canterbury
Title:Spectral matching for elemental abundances of evolved stars of omega Centauri
In order to understand the origin of globular clusters, large samples of their stars need to be observed and analysed for their chemical composition. This is especially true for the complex, multimetallic cluster omega Centauri with its large range of iron, carbon, nitrogen, oxygen, sodium and barium abundances. In order to accomplish this, an automated spectral matching pipeline was developed to determine these abundances for hundreds of stars. My research makes use of photometry and low resolution spectroscopy to analyse the chemical composition of evolved stars in three clusters: omega Centauri, 47 Tuc and NGC 6752. The latter two clusters are monometallic and selected due their similar metallicities to the metal-rich and metal-poor stars in omega Centauri. This allowed them to be used as test-cases for the spectral matching pipeline.
Subsequent to the abundance analysis, k-means clustering analysis was used to group the stars in omega Centauri into four groups based upon these abundances. These groups suggest that there were at least four main periods of star formation in the cluster. The exact order of these star formation events is not yet understood, with some models predicting the groups formed from iron-poorest to iron-richest, while others suggest the potential for iron-poorer groups to form after iron-rich groups.
These results compare well with those found from higher resolution studies and show the value of more extensive lower resolution spectral surveys. They also highlight the need for large samples of stars when working with a complex object like omega Centauri.
Arizona State University
Title:How will the James Webb Space Telescope measure First Light, Reionization, and
Galaxy Assembly: Science and Project Update as of 2013.
We review how the 6.5 meter James Webb Space Telescope (JWST) — after its launch planned for 2018 — can measure the epochs of First Light, Reionization, and Galaxy Assembly, building on recent results from the Hubble Wide Field Camera 3. Significant technical progress has been made on the design and fabrication of JWST: more than 80% of its launch mass has been built, passed final design, or is being built as of Spring 2013. All JWST’s 18 flight mirrors have been gold-coated with an optical performance that meets or exceed specs. Two of JWST’s scientific instruments were delivered to NASA GSFC in 2012, with the last two to follow in 2013. I will briefly summarize the path from today till launch, now planned for Fall 2018.
We show what combination of area, depth, and wavelength coverage are needed for JWST to detect a sufficient number of First Light objects, and to measure their evolving luminosity function (LF). JWST will map the epoch of First Light through Pop III-star dominated objects at redshifts z=8–20, and its transition to the first Pop II stars in dwarf galaxies at z^<9. JWST will measure the evolution of the steep faint-end of the dwarf galaxy LF at z=6–15, which likely provided the UV-flux needed to start and finish cosmic Reionization.
I will also discuss: 1) simulations of deep JWST images, using lower redshift rest frame UV–optical HST images as templates; (2) if ultradeep JWST images will run into the instrumental or natural confusion limits; (3) to what extent gravitational lensing bias from foreground object halos may affect the search for First Light objects at redshifts z>8–10. A new generation of algorithms may be needed to automatically detect, measure and classify objects in very crowded, ultradeep JWST fields; and (4) the optimum mix of random deep JWST fields, and lensing fields centred on foreground clusters or groups.
Université de Strasbourg
Title:The Virgo Cluster in the area of large surveys –
An overview with a focus on the Next Generation Virgo cluster Survey (NGVS and NGVS-IR)
Telescopes have been pointed at galaxies in the Virgo Cluster for decades, uncovering numerous effects of dynamical and hydrodynamical harassment on the evolution of galaxies. The Virgo Cluster covers more than 100 square degrees on the sky – it takes the latest generation of wide field survey cameras to replace pointed observations with deep and homogeneous contiguous images. The NGVS (Next Generation Virgo cluster Survey, Ferrarese et al. 2012) has almost completed a deep, high resolution survey of the cluster in the u,g,r,i,z filter system, using Megacam on the Canada France Hawaii Telescope. It allows a completely renewed view of the low end of the galaxy mass function, where both compact galaxies and extended low surface brightness objects still challenge galaxy evolution models. With a surface brightness limit of 29 mag/arcsec^2 in g, it highlights the numerous signatures of interactions that affect the outer parts of galaxies. The survey also addresses foreground (Solar System, Milky Way halo) and background science (baryonic structure out to z~1.5, mass concentrations traced by gravitational lensing).
Numerous surveys from X-rays to the far-IR provide additional information on the SEDs of Virgo galaxies, that will help us establish the history of Virgo. I will focus on NGVS-IR, a near-IR follow-up survey in the J and Ks bands. One of the most immediate results of the combination of NGVS and NGVS-IR is an excellent color-based classification of objects. In particular, the numerous globular clusters in Virgo can be separated from stars and background galaxies much better than with ugriz colours alone. This photometric classification tool opens an avenue for future studies of globular cluster systems in environments of all sorts.
Acknowledgement: The French PIs and co-Is of several of the above-mentioned surveys are supported by the VIRAGE project (VIRgo: Alterations of Galaxies in dense Environments).
Observatoire de Strasbourg
Title:The Virtual Observatory – Enabling Science
The Virtual Observatory is a global endeavour that aims to provide efficient and interoperable access to astronomy data and simulations.
The International Virtual Observatory Alliance (IVOA) coordinates some 20 VO projects with the mission to “facilitate the international coordination and collaboration necessary for the development and deployment of the tools, systems and organizational structures necessary to enable the international utilization of astronomical archives as an integrated and interoperating virtual observatory.” I will describe the current status of the Virtual Observatory with an emphasis on how interoperating tools and services are bringing new scientific capabilities to astronomers
Swinbourne University/ESO Santiago
Title:Metallicity effects on globular cluster evolution
While it has been known for a long time that the sizes of globular clusters within our galaxy correlate to their galactocentric distances, more recently it has also been found that blue, metal-poor clusters are on average larger than red, metal-rich clusters in nearby galaxies. This has generated a debate on the origin of these size differences: is it intrinsic or external? Using direct N-body simulations of globular clusters with different metallicities, one can distinguish between structural and apparent (i.e. mass versus light) differences and I will show that metallicity does not significantly affect the cluster structure, while metallicity alone can produce apparent size differences as observed.
Black holes in the centre of globular clusters on the other hand can affect their half-light radii, and I will compare models and observations to illustrate this.
Title:Detecting and Characterising Exoplanet at the Highest Angular Resolution
High angular resolution observations of known exoplanet systems enables false-positives to be identified and a study of planet frequency as a function of stellar multiplicity. When high-resolution of AO imaging is combined with high-contrast techniques such as kernel-phase, radiation from young exoplanets themselves can be detected. As part of a deep multi-year non-redundant aperture mask infrared imaging campaign observing transition disks, I present multi-epoch monitoring of the resolved emission seen within the disk gap of LkCa 15. Orbital motion of both the central source and extended lobes as presented in Kraus and Ireland (2012) is clearly detected at the level of 4 degrees/year (deprojected), in both K and L’-bands. Based on these data as well as single-epoch H and M bands epochs, I present a model for the central source as thermal emission, eliminating scattering as the emission mechanism. The physical cause of the extended emission remains a mystery, but the luminosity is inconsistent with non-planetary explanations. Finally, I will briefly describe what the future holds for direct exoplanet detection in the era of the Gemini Planet imager and the Giant Magellan Telescope.
Title:Understanding the evolving galaxies in the Local Universe
The Local Universe provides an excellent high-resolution laboratory for studying the detailed processes of star formation and galaxy evolution. In this seminar, I will present some highlights from multiwavelength star formation studies of nearby HI-selected galaxies from HIPASS as well as results on galaxies in transition. I will show that: (i) selecting galaxies via their HI content is a good way of selecting a large variety of star-forming galaxies regardless of size/stellar luminosity; (ii) the upper mass end of the stellar IMF may not be uniform; (iii) nearby post-starburst galaxies occupy the low-mass end of the green valley and represent a population of galaxies which are quickly going from the blue cloud to the red sequence; and (iv) unlike strong gravitational interactions, ram pressure does not strongly induce star formation.
Title:Star formation in the vicinity of the supermassive black hole at the Galactic Centre
The supermassive black hole Sgr A* at the centre of the Galaxy is surrounded by a sub-parsec-scale counter-rotating disk of young, massive stars. The surface density of stars increases as 1/r^2 but is truncated within 0.04 pc of Sgr A*. I explore the origin of these stars in a scenario in which star formation took place in a disk of gas created through the partial capture of a molecular cloud as it swept through the inner few parsecs of the galaxy and temporarily engulfed Sgr A*.
Cancellation of angular momentum during circularisation naturally gives rise to a steep disk surface density profile, so that in stark contrast to standard disk models, self-gravity becomes increasingly important at small rather than large radii. However, between 0.04 and 0.01 pc from Sgr A* the resulting disk is so optically thick that, although gravitationally unstable, it cannot fragment because of inefficient cooling. Instead, it forms a gravito- or magnetoturbulent accretion disk that accretes onto Sgr A* in a few million years. Meanwhile, fragmentation of the gas beyond the central 0.04 pc hole creates the observed young stellar disk. Interestingly, the S-stars lying within 0.01 pc of Sgr A* may also be created during this event because grains sublimate in the inner disk and the disk can again cool rapidly enough to permit fragmentation.
The estimated stellar ages imply that this capture event occurred about 10 Myr ago, and such events occurring over the life time of the Galaxy could significantly contribute to the current mass of Sgr A* and the nuclear star cluster.
Title:Simulating astrophysical jets
Astrophysical jets are highly collimated flows coming from a wide range of astrophysical objects, including protostars, black holes, neutron stars, and planetary nebulae. Jets have a wide range of velocities depending on the source, from slow (100 km/s) to ultrarelativistic. It is not known what mechanism is responsible for making jets, nor if it is the same mechanism for all the different kinds of jets. In this talk I will present the results of 3-dimensional simulations of a wind from an accretion disk threaded by large scale magnetic fields. This magnetic field can explain both the launching, acceleration, and collimation of the jet. I will then illustrate that this same mechanism may explain both parsec-scale jets from protostars and megaparsec-scale jets from supermassive black holes in the centre of active galaxies.
Title:Star Clusters as Chronometers of Star Formation
Galaxies evolve through a number of processes, some of which can be studied through their recent star formation record. In that sense, studying the past billion-or-so years of star formation activity is key to understanding (at least some of) the processes that drive galaxy evolution. While resolved stellar populations provide the most accurate toolkit for such studies, they are limited by current instrumentation to only a handful of nearby systems. Star clusters receive the baton past a few Mpc, groupings of stars of roughly the same age and metal content, referred to as ‘simple’ stellar populations. Bright as they are, they extend the boundary of galactic archaeology studies.
I will discuss a couple of projects that explore the utility of star clusters as chronometers of star formation, and focus primarily on the Snapshot Hubble U-band Cluster Survey. SHUCS is based on this principle, and has observed a pilot sample of ten galaxies with the Hubble Space Telescope. By including the UV band (at the fringe of the ultraviolet regime) it enables the detection and age-dating of extragalactic star clusters, and therefore the derivation of the star formation history of the host systems.
Title:A deeper view of the mass, metallicity, SFR, and HI relationships
We demonstrate that the space formed by the star formation rate (SFR), gas-phase metallicity (Z), and stellar mass can be reduced to a plane. We study three different approaches to find the best representation of this 3D space, using a principal component analysis (PCA), a regression fit, and binning of the data. The PCA shows that this 3D space can be adequately represented in only two dimensions, i.e., a plane. We find that the plane that minimizes the ?2 for all variables, and hence provides the best representation of the data, corresponds to a regression fit to the stellar mass as a function of SFR and Z, Mass= f(Z, SFR). We find that the distribution resulting from the median values in bins for our data gives the highest ?2. The fact that we can represent stellar mass as a linear combination of SFR and metallicity suggests that the stellar mass of a galaxy can be thought of as the rate at which a galaxy is currently forming stars (SFR), plus a measure of the star formation history, here represented by the metallicity, corresponding to the amount of reprocessing of the gas by past stellar generations. The SF history and current SFR of a galaxy are closely linked to the stellar mass.
Finally, using data from SDSS, GAMA, ALFALFA and GASS surveys, we generate a model based on the Z-SSFR relation that shows that at a given stellar mass, depending on the amount of gas, galaxies will follow opposite behaviours.
Title:Ionization in the Central Molecular Zone
The Central Molecular Zone (CMZ) contains a twisted elliptical ring of dense molecular gas orbiting the galactic centre. This region is known to have atypical values of the parameters important in star forming processes, e.g. elevated temperatures, stronger magnetic fields, high gas densities and stronger turbulence. Despite the high densities, there is evidence of suppressed star formation and a top heavy initial mass function, making this region an interesting testbed for star formation theories.
In this talk, I focus on the ionization rate as a critical parameter involved in many aspects of star formation. Abundances of H3+ and HCO+ ions in the CMZ suggest the ionization rate may be orders of magnitude higher in this region compared to the galactic disk. I consider the diffusion of Cosmic-ray electrons through molecular gas for different sources of accelerated particles. The implications of this process are explored and observational diagnostics suggested.
Leibniz-Institut für Astrophysik Potsdam (AIP)
Title:Constraining the formation and evolution of galactic discs through numerical modelling
Abstract:I will discuss various galactic dynamics problems related to our understanding of the formation and evolution of disc galaxies. It will be demonstrated that if radial migration is indeed responsible for the formation of extended galactic discs, then they must be kinematically hot because of the approximate conservation of stellar radial and vertical actions. While contributing to disc thickening in the disc outskirts, radial migration will be shown to have minimal effect at intermediate radii (R
Title:Exploring Transient Astrophysical Phenomena with The Dark Energy Survey
Abstract:The Dark Energy Camera achieved first light just over a year ago, and is now engaged in a large-scale long-duration survey on the Blanco 4m telescope at Cerro Tololo Interamerican Observatory. The Dark Energy Survey comprises multi-epoch observations in five filters (grizY), covering 5000 square degree of the Southern sky. Its primary goal is to constrain the time-dependent and time-independent parameters of the equation of state of dark energy using four independent probes: large scale structure, galaxy clustering, weak gravitational lensing, and supernovae. We describe the features of the Dark Energy Camera, and we provide details of the primary scientific goals of the Dark Energy Survey.
In addition to reaching its key science goals, the Survey will provide a wealth of data that will be useful in answering myriad other open questions in astrophysics. We focus on how the DES can contribute to one specific aspect of this additional science: the understanding of transient phenomena such as gamma-ray bursts. Several Macquarie Uni students are involved in this effort; we describe the algorithm they have developed to process automatic notices of GRB detections, and to provide relevant Dark Energy Survey results in near-real-time to those interested in performing follow-up observations of these transients.
Title:Estimating the binary fraction of Central Stars of Planetary Nebulae
Abstract:There is no quantitative theory to explain why a high 80% of all planetary nebulae are non-spherical. The Binary Hypothesis states that a companion to the progenitor of a central star of planetary nebula is required to shape nebulae whose shapes are not spherical or mildly elliptical, implying that many single post-AGB stars do not make a PN at all. A way to test this hypothesis is to estimate the binary fraction of central stars of planetary nebula and to compare it with that of the main sequence population. Preliminary results from the infrared excess technique indicate that the binary fraction of central stars of planetary nebula is higher than that of the main sequence, implying that PNe could preferentially form via a binary channel. I will present new results from a search of red and infrared flux excess in an extended sample of central stars of planetary nebula and compare the improved estimate of the PN binary fraction with that of main sequence stars.
Title:A new population of planetary nebulae candidates towards the Galactic bulge
Abstract:A new population of up to 300 planetary planetary nebulae (PNe) candidates have been discovered serendipitously in deep [OIII] imaging of the Galactic Bulge taken with the Mosaic II wide-field CCD imager on the Cerro Tololo Inter-American Observatory’s 4 m Blanco telescope. This imaging was taken to determine accurate [OIII] fluxes for known Bulge PNe, but, through careful examination, is also yielding significant numbers of new PNe candidates. These new candidates range from compact but still relatively faint sources, through to very extended, low surface brightness PNe. The new population will be summarised, discovery techniques reviewed and preliminary confirmatory spectroscopy presented.
Title:Searching for Planets with Single-mode Spectrographs
Abstract:In my thesis, I am building a compact high-resolution spectrograph with a new calibration source, which will move astronomical precision radial velocity technology from just a few major observatories to many small telescopes. This shift is necessary in order to overcome the limitations of stellar radial velocity noise. Existing methods to calibrate radial velocity spectrographs have many limitations, especially not providing enough bright lines throughout the visible spectrum. To solve this, I constructed a novel and inexpensive photonic wavelength reference based on an optical fibre Mach-Zehnder interferometer. After the wavelength reference is fully characterized I will utilize this in a single-mode spectrograph I am currently designing.
Title:How old is the Sco-Cen association?
Abstract:OB associations provide a glimpse into a group of stars directly after formation. The nearest OB association to the sun is the Sco-Cen association, and is also the nearest region of massive star formation. Sco-Cen provides a rich laboratory for the study of the output of star formation. Despite the relatively complete high-mass membership, the G to M-type PMS membership is highly incomplete. Sco-Cen has been used extensively as an age-calibrated sample of young stars for the study of star formation, planets search and evolution, circumstellar disk evolution and multiplicity. The Classical age of Sco-Cen has long been considered to be quite young based on photometry and isochrone fitting (5-20 Myr, depending on region), however, recent work has hinted that the youngest part of the association is potentially significantly older at ~11 Myr. If the new age is correct, this has interesting implications for our understanding of the evolution of stars and disk evolution. Using binary orbits, we can determine ages of individual stars in the Sco-Cen association to significantly better accuracy than what can be achieved using photometric techniques. Knowledge of a binary orbit provides an indirect measurement of the system dynamical mass, which adds a new orthogonal dimension to fitting an age to a given system. I will present age estimates using binary orbits of a number of K/M-type Sco-Cen stars and 2 high mass B-type stars, and give a preliminary age estimate of the youngest part of Sco-Cen.
Title:Citizen Science and Radio Galaxy Zoo
Abstract:Citizen science is a method of conducting scientific research using amateur or nonprofessional scientists. In astronomy, citizen science came to light in 2006 when Kevin Schawinski and Chris Lintott devised a method to use the public to help them visually classify galaxies from the Sloan Digital Sky Survey; calling their project Galaxy Zoo. With the success of Galaxy Zoo, the Zooniverse was created to handle a variety of citizen science projects from space research to humanities research. With the next generation radio telescopes beginning to come online, the large data volumes will require new ways to handle the data. The Evolutionary Map of the Universe, an Australian Square Kilometer Array Pathfinder study, will detect 70 million radio sources in the southern sky. A large number of these sources will be handled by computer algorithms, however, 10% will fail our algorithms. Radio Galaxy Zoo is a project that we have begun to handle these 7 million radio sources. In this talk I will present Radio Galaxy Zoo, the new Zooniverse project and the science we will achieve from this citizen science project.
Title:AGN jets and their magnetic fields from pc to kpc scales
Abstract:Substantial progress in our understanding of AGN jets has been made in recent times, particularly in our knowledge of the three-dimensional jet magnetic field structure as well as the jet particle composition. I will review our current understanding of jets before presenting new radio observations providing the first robust determination of the circular polarization spectrum of a AGN jet. I will show how these multi-frequency full-Stokes radio observations provide important constraints on the 3-D jet magnetic field structure as well as its particle composition. Finally, I will show recent results on the Faraday rotation associated with the most extended regions of the radio galaxy Centaurus A and the implications for the jet particle composition and magnetic field structure of AGN on the largest scales.
Title:Common envelope numerical simulations: What are we missing?
Abstract:The common envelope (CE) interaction is a very fast astrophysical process (it lasts about a year) whereby a close binary star temporarily becomes one large star. What happens next is anybody’s guess. The two stars may merge, explode or transform into a compact binary. The main way to study this phenomenon are numerical simulations, but nowadays the works that have been made in this direction fail to explain various important questions about the CE.
By carrying out 3-dimensional simulations of the CE interaction using a 3D hydrodynamic plus gravity code, we are trying to push the simulations a step further. We are adding additional ingredients that could be relevant to solve those important questions, in particular we are analysing the effects of the tidal interaction preceding the CE on the CE itself and of the stellar rotation.
Title:On-chip, narrowband spectral filtering of multimode devices
Abstract:The photonic lanterns with multi-notch waveguide Bragg
gratings were fabricated using the femtosecond direct-write technique
in boro-aluminosilicate glass. Our results demonstrate efficient and
symmetrical performance of each of the gratings in the photonic
University of Sydney
Title:Resolving the Mass-Anisotropy Degeneracy of the Spherically Symmetric Jeans Equation
Abstract:A widely used method for the estimation of mass of stellar systems with apparent spherical symmetry is dynamical modelling with the use of the spherically symmetric Jeans equation. Unfortunately this approach suffers from a degeneracy between the assumed mass density and the second order velocity moments. This degeneracy can lead to significantly different predictions for the mass content of the system under investigation; thus it poses a barrier for accurate estimates of dark matter and therefore of our understanding of the $\Lambda$CDM model. We present an algorithm that removes this degeneracy and reconstructs a unique kinematic profile for each assumed mass density. Our algorithm can be applied in systems with constant or variable mass-to-light ratio. The essence of our method lies in using smoothing B-spline functions for representation of some terms in the spherically symmetric Jeans equation. Then we compare theoretical functions with observables to recover the form of kinematic profile of second order radial and tangential velocity moments. We explore parameter space with Markov Chain Monte Carlo methods to see if there exists inherent degeneracy in the dynamical modelling process. We demonstrate our algorithm through applications to synthetic data with $10\%$ and $20\%$ error on the reference values of the true profile. In all cases we recover excellent fits of theoretical functions to observables and unique solutions.
Our algorithm is simple, easy to apply and efficient for the reconstruction of the kinematic profile through the use of spherically symmetric Jeans equation. It removes the mass anisotropy degeneracy and allows for unbiased mass estimates. The efficiency of our method depends on the wealth of available kinematic data.
Astronomy Australia Ltd
Title:Astronomy Australia Ltd: Update on current activities and future plans
Abstract:Astronomy Australia Ltd (AAL) is an independent not-for-profit company established in 2007 to advance its vision that astronomers in Australia will have access to the best astronomical research infrastructure. AAL’s members comprise every institution in Australia with a significant astronomy research program. The goals of AAL are to implement the infrastructure priorities of the Decadal Plan, advise the Government on new astronomy infrastructure investments, and manage some of those investments. This talk gives an update on AAL’s current activities and projects, and plans for the future.