Title: The role of binarity in Wolf-Rayet central stars
of planetary nebulae
Abstract: Around 10% of central stars of planetary nebulae show spectra that mimic the appearance of massive Wolf-Rayet stars. While much progress has been made in identifying close binary central stars of planetary nebulae, with around 50 systems now known, only two are known to have Wolf-Rayet components. I'll give an overview of recent results in this area and report on some preliminary results from SALT spectroscopic monitoring of Wolf-Rayet central stars.
Antonino P. Milone & Anna F. Marino
Title: Multiple stellar populations in Globular
Abstract: For half a century, globular clusters (GCs) have been considered as prototype of simple stellar populations and their color-magnitude diagrams (CMDs) were believed to be the proxy of an isochrone. Recent work has resulted in one of the most exciting and unexpected developments in stellar-population studies in recent years: the discovery that the CMDs of many GCs are made of two or more intertwined sequences that can be followed continuously from the hydrogen-burning limit to the last stages of the stellar evolution. These findings, together with the discovery that multiple sequences correspond to distinct stellar populations with different helium and light-element abundance, have dramatically changed the traditional picture of these seemingly simple stellar systems.
Among the open issues are the still-eluding second-parameter problem of the horizontal-branch morphology and the formation mechanisms that build the Galactic halo. Multiple populations may correspond to different generations of stars and prove that GCs, similarly to dwarf galaxies, have experienced a very complex star-formation history. As an alternative, they can be the product of exotic phenomena that have taken place in the proto-GC environment only.
The recently-discovered multiple populations in GCs thus provide unique inside on the cluster formation and on their role in the assembly of the Galaxy. In this talk we provide the modern picture of Galactic and extragalactic GCs by using both high-resolution ground-based spectroscopy and Hubble-Space-Telescope photometry. We use these new results to constrain the series of events that led from massive clouds in the high-redshift Universe to the clusters we see today
Title: Searching for pulsars in radio continuum surveys
Abstract: While pulsars are primarily detected and observed with high time resolution in order to resolve their narrow pulses, the phase averaged emissions of pulsars can be detected in radio continuum surveys. More importantly, continuum surveys are equally sensitive to all pulsars, not affected by the dispersion measure smearing, scattering or orbital modulation of spin periods, and therefore allow us to search for extreme pulsars, such as sub-millisecond pulsars, pulsar-black hole systems and pulsars in the Galactic Centre.
Next-generation radio continuum surveys, such as the ASKAP Evolutionary Map of the Universe (EMU), will map a large sky area at different radio frequencies with high sensitivities. Such surveys allow a search over the full field of view while avoiding the need for expensive pixel-by-pixel high time resolution searches.
In this talk, I will show you how to detect pulsars in radio continuum surveys and how to distinguish them from other compact radio sources. I will demonstrate a technique called variance imaging, which allows us to detect pulsars with interstellar scintillation, and show you how many new pulsars we can find with EMU.
Title: Anisotropies in the gravitational wave
background as a probe of the cosmic string network
Abstract: Cosmic strings are one-dimensional topological defects, which arise naturally in scenarios of the early Universe, such as inflation based on string theory as well as phase transitions in field theories. Pulsar timing array is the powerful tool to search for the existence of cosmic strings through detection of gravitational waves, and could provide us with insights on those high energy theories.
In this talk, I will present how pulsar timing arrays can be used to search for cosmic strings and what types of information we can obtain if we detect gravitational wave background from them. Furthermore I will show that we can extract more information on the cosmic string network by analyzing anisotropies in the gravitational wave background.
Title: Multi-fluid Shock
Waves in Molecular Clouds, A Submitted Thesis
Abstract: The formation of stars occurs in the dense molecular cloud phase of the interstellar medium. Strong magnetic field gradients decouple the ionized component of molecular clouds from the neutral fluid. Similar decoupling occurs between gas and aerodynamic dust grains. Multi-fluid treatments are therefore required to accurately model the ubiquitous shock waves found in dynamic, violent molecular clouds. In this talk, I summarise my recently submitted thesis which focused on low-velocity turbulence driven magnetohydrodynamic shocks and dusty gas shocks in protoplanetary discs.
Title: How cosmological simulations can inform
observational surveys and fundamental cosmology
Abstract: I will show two important ways in which cosmological simulations of galaxy formation can be used to inform astronomy and cosmology. Firstly, as part of the SAMI project, I have used a synthetic pipeline to produce mock SAMI datacubes of galaxies in simulations. In particular, I will show how synthetic galaxies have been "observed" with proposed designs for the Hector instrument.
Secondly, cosmological simulations can be used to investigate early-universe cosmological theories. Theories of cosmological inflation often predict that cosmic conditions will vary from place to place in the universe as a whole. In particular, the value of the cosmological constant can plausibly explained by a combination of environmental variation and its effect on galaxy formation.
In such models, it is crucial that we understand how quickly and efficiently the onset of accelerating expansion shuts down accretion of matter into dark matter haloes and galaxies. I will show simulations, based on the cosmological galaxy formation code of the Eagles collaboration that investigates this effect.
Title: Zen and the art of building
astronomical instruments... (in Chile!)
Abstract: In this seminar I will report on the work done at the Center of Astro Engineering of Pontificia Universidad Catolica de Chile in the area of astronomical instrumentation. In particular I will present our results in spectroscopy from the early steps to the recent installation of the high resolution spectrograph FIDEOS at the ESO 1m telescope of La Silla and the participation of our team in the project MOONS for the ESO VLT. Building astronomical instruments in a developing country is an interesting and challenging task, the purpose of the seminar is to share this experience in the broadest possible context.
toolkit of the 21st century astronomer
Abstract: I will cover some methods for tasks astronomers face daily: (1) measuring a quantity of an astrophysical object (e.g. luminosity) under uncertainty (2) Combining multiple such uncertain objects for understanding the distribution of the population, sometimes under censorship. (3) comparing complex models of physical effects. New algorithms and easy-to-use implementations, including (Py)MultiNest and Stan, today make powerful tools available for analysing real problems with sufficient complexity.
Briefly, I will also give an overview of my X-ray astronomy research, which includes AGN obscuration, SMBH growth over cosmic time, GRBs and the analysis of cosmological hydrodynamic simulations.
Title: The Ancient Star Formation History of the Disc and Halo of M31
Abstract: More than two decades of observations with the Hubble Space Telescope have demonstrated the exquisite insight on galaxy assembly that can be gained from analysing the resolved stellar populations in very local galaxies. Deep colour-magnitude diagrams enable precision star formation histories and age-metallicity relations to be derived back to early epochs and provide a means to probe the stellar mass build-up in individual galaxies that is unrivalled by any other technique and that is directly complementary to high redshift observations. I will present some recent results from the analysis of the disc and halo of M31 and discuss how these compare to inferences from the Milky Way and more distant galaxies. I will conclude by briefly mentioning the exciting prospects offered by JWST for extending this type of work.
path to ASKAP: faint things and curvy things
Abstract: During my thesis, I studied two classes of AGN: Infrared-Faint Radio Sources (IFRSs) and Gigahertz-Peaked Spectrum (GPS) / Compact Steep Spectrum (CSS) sources. IFRSs are recently discovered objects, whose nature was unconfirmed. We found a population of >1300 brighter IFRSs and measured the first spectroscopic redshifts, which showed they were high-z radio galaxies at z > 2 that might extend out to z ~ 7 and significantly increase the number of known high-redshift galaxies. We observed the faintest population of GPS/CSS sources to date, consisting of ~140 sources, using high-resolution ATCA observations. We observed the most compact of these with the LBA, determined their linear sizes and used many radio observations spanning 70 MHz - 34 GHz to model their radio spectra and spectral ages. We find evidence that low-luminosity GPS/CSS sources are similar to brighter samples, which are young and evolving GPS and CSS sources that may experience frustration and intermittent activity.
This study of young and distant radio sources led to working on the scientific validation of ASKAP continuum data, an important step both for commissioning the instrument and assessing its performance, and for beginning to develop the framework for the automated quality control and scientific verification that will be necessary for EMU. I will discuss the automated pipeline I have developed to produce a science validation report of ASKAP continuum data, the current results and the next steps.
Title: Star Formation near
the Supermassive Black Hole Sgr A*
Abstract:The environment of Sgr A* provides a window for close-up study of star formation under extreme physical conditions. A critical question regarding star formation near supermassive black holes (SMBHs) is whether tidal shear in the vicinity of SMBHs is able to completely suppress or induce star formation. There are currently two modes of star formation that are considered to explain the origin of young stars near Sgr A*. One is the standard cloud-based mode of star formation. The other mode is disk-based, which explains the disk of stars orbiting Sgr A*.
I will present recent multi-wavelength observations taken with the VLA and ALMA and discuss these modes of star formation applied to the region within 0.5 pc of Sgr A* and beyond the nuclear cluster. In addition, I will describe a viable mechanism to explain the origin of the Fermi bubble resulting from gas accretion onto Sgr A* around the same time that young OB stars were formed near the black hole.
Gas in Galaxies Near and Far
Abstract: While the stellar populations of galaxies gives insight into their past, determining their gas content is vital to understand their future growth. In the nearby universe HI observations have shown us the gas distribution of galaxies far outside their optical disk, yet becomes difficult to detect in the distant Universe. Here I will talk about determining the total gas mass in galaxies near and far, and concentrate on on how we can determine their gas mass at all redshifts through a common associate, dust.
Geoffrey C. Clayton
Title: Studying dust in the Universe with JWST
Abstract: The James Webb Space Telescope (JWST) is about to become a reality. It is scheduled to launch next year and the first round of proposals are due in August. The suite of instruments will do imaging and spectroscopy in the near- and mid-IR at a spatial resolution similar to that seen with Hubble Space Telescope. These instruments are ideal for the study of circumstellar and interstellar dust in a wide range of environments. I plan to discuss the capabilities of JWST and some of the exciting studies of dust that are being planned.
LEDA: Towards Detection of Cosmic Dawn using the Owen’s Valley LWA
Abstract: The LEDA Project is being conducted at the Harvard-Smithsonian Centre for Astrophysics, using an LWA-like telescope at Owens Valley in California. Its intention is to measure the 21cm HI signal at high redshift, thus providing information about the early development of the Universe. I will give an overview of 21cm cosmology, the telescope being used, and discuss the status of the project. This will include some recent results on measuring the global 21cm signal, and new work beginning on measurements of 21cm power spectrum. I will mention some of the issues that we face in obtaining the desired measurements and some technical aspects of the telescope hardware and software that support the project.
Van Hiep Nguyen
Title: Shinning Light on the
Dark Milky Way: Probing our Galaxy’s Hidden Gas
Abstract: Many studies have proved the existence of the “dark gas” which is not detected by traditional radio emission from atomic hydrogen (HI) and carbon monoxide (CO) molecules. To probe this gas component, interstellar dust has been used as a proxy for total gas column density NH. By comparing the thermal dust data from Planck satellite and Sloan Digital Sky Survey with archival HI and OH data from the Millennium Survey along sightlines where neither CO nor OH is detected, we confirm the tight linear correlations between optical depth τ353, dust radiance R, reddening E(B−V) and NH. From our own dust opacity σ353 and dust specific luminosity LH obtained in low-to-moderate NH range, we confirm that the variation of σ353 in Planck Collaboration 2014 is due to the evolution of dust grains in the interstellar medium and the change in their LH may come from the presence of the dark gas.
We also estimate the molecular hydrogen column densities NH2 from these linear relationships and hence the OH/H2 abundance ratio X_OH, for which few literature measurements exist. The XOH ratios derived from the three NH proxies are consistent and vary in the range from 10^-8 to 20×10^-8 with the mean value around 5×10^-8. Since these results are obtained in a wide ranges of longitude l and latitude b with some sightlines through the Galactic plane, it suggests that OH main lines at 1665MHz and 1667MHz are excellent tracers of molecular gas in the ISM.
Title: Cold gas in the ISM -
Measuring the temperature of the Riegel-Crutcher cloud
Abstract: An important question of galaxy evolution is, how the neutral atomic gas transitions into the essential molecular gas for star formation. A key to this is mapping the temperature and density variations of the cold neutral medium (CNM) component of the inter stellar medium (ISM). Neutral hydrogen (HI) self absorption (HISA) clouds are ideal places to study the CNM. They are found throughout the Galaxy where cold HI clouds are located in front of warmer HI emission and they reveal the spatial structure of the CNM.
However, to get a good handle on the physical properties of the cold gas HI absorption measurements against bright background sources are needed. To do this, we mapped the Riegel-Crutcher cloud, one of the most famous HISA regions located in front of the Galactic Centre, in HI absorption. I will present our HI absorption survey against ~40 background continuum sources and discuss what we can learn from these observations.
Title: Characterisation of
high-z dusty galaxies in Herschel cosmological surveys
Abstract: The abundance of dusty galaxies at high-redshifts tests our theories about early galaxy formation. However, due to limited samples the contribution of dusty galaxies to the cosmic star formation rate density (SFRD) at z > 4 is still incomplete. One of widely used methods to detect potentially z>4 dusty galaxies is to select Herschel sources with thermal SED peak shifts to wavelengths longer than 500 microns (so-called "FIR-risers"). The method was successful to identify the most distant dusty starburst galaxies known to date (Riechers et al. 2013).We aim to build statistically significant sample of "FIR-risers" and to fully inspect selection biases. We consider one of the largest Herschel surveys, the Herschel Virgo Cluster Survey (HeViCS) centred at the heart of famous Virgo cluster. Since detection of "FIR-risers" is very challenging process due to the high source confusion, we implemented a new selection technique to find these sources, combining de-blending and SED fitting of sources (Donevski et al. 2017, to be submitted). We made a final sample of 133 "FIR-risers" reaching a good agreement with evolutionary models (e.g. Bethermin et al. 2012, 2017, Schreiber et al. 2016). It challenges previous studies in other Herschel fields (e.g. Asboth et al. 2016) which concluded to a significant under-prediction of the number of "FIR-risers" by the models. We further analyse mechanisms that could drive a galaxy to such prodigious infrared luminosities at early cosmic times.
Title: Radionuclides: from
Cosmochronology to Habitability
Abstract: Radionuclides with half-lives between 0.1 and 100 million years were present at the time of the birth of the Sun, as inferred from high-precision meteoritic analysis. Their abundances allows us to measure time intervals related to the birth of the Sun. Among these nuclei, aluminium-26 generated enough heat to contribute to the melting of ice and loss of water in ice-rich planetesimals in the early Solar System, with crucial implications on the amount of water delivered to the terrestrial planets in the habitable zone. However, the origin of aluminium-26 is still an open question and we do not know how common its presence may be in other planetary systems in the Galaxy.
Title: The diverse origins
of compact Elliptical galaxies
Abstract: Compact elliptical galaxies (cEs) are rare in the local Universe, with only about two hundred reported to date. With very compact sizes (100-1000kpc) and intermediate stellar masses (10^8-10^10Msun), they have very high densities that resemble those seen in the cores of massive ellipticals or disks. This suggest that cEs could be, in fact, the remnant of a larger, more massive galaxy that lost its stars via a stripping process. Other evidences support this claim, like the fact that they are typically found near a massive galaxy in dense environments or the fact that some have been caught in the act of stripping. However, some other recently found isolated cEs and cosmological models challenge this view, showing properties that demand another mechanisms of formation. Therefore, as it usually happens in nature, things are not simply white or black, and many factors come into play. Determining the origin and evolutionary stage of these rare cEs is not an easy task, but in this talk I will present a set of tools that can help discriminate between the possible formation mechanisms for cEs.
Title: Australian-ESO partnership: instruments and applying time
Abstract: Australian astronomers got access to the Paranal and La Silla facilities including the 8m class telescopes after signing the decadal Strategic partnership with the European Southern Observatory (ESO). I as being the ex-ESO fellow and a support astronomer at Paranal will provide more insights to successfully apply for the ESO time. My talk will coverÂ instruments available at Paranal and La Silla facilities. This will particularly give a good start to the users applying first time for the ESO night time. Hands on stuff, practical procedures, and phases for observing with ESO telescopes will be shown.
Wei Siang Tan
Title: SURVEY FOR C-BAND HIGH SPECTRAL
LINES WITH THE ARECIBO TELESCOPE
Abstract: High-mass stars have masses greater than 8 solar masses and are the main source of heavy elements such as iron in the interstellar medium. This type of stars form in giant molecular clouds. Studying the molecular environment in star-forming regions is crucial to understand the physical structure and conditions that lead to the formation of high-mass stars. We present observations with the 305m Arecibo Telescope in Puerto Rico toward twelve high-mass star forming regions. Every source was observed in multiple spectral lines including transitions of CH3OH, H2CS, and OH lines, and radio recombination lines. The observations were conducted with the C-Band High receiver of the Arecibo Telescope in the frequency range of 6.0 to 7.4 GHz. The goals of the observations were to investigate the detectability of different molecular species and obtain high sensitivity observations of the 6.7 GHz CH3OH line to detect absorption and use it as a probe of the kinematics of the molecular material with respect to the ionized gas. Among of the results of the observations, we report detection of 6.7 GHz CH3OH masers toward nine regions, OH masers toward five sources, 6.7 GHz CH3OH absorption toward four sources, and detection of H2CS toward the star forming region G34.26+0.15. The 6.7 GHz CH3OH and 6278.65 MHz H2CS absorption lines were modeled using the radiative transfer codes RADEX and Molpop to investigate the physical conditions of the molecular clouds responsible for the absorption lines. Our analysis of the absorption lines supports the interpretation that the spectral lines are tracing molecular envelopes of HII regions. In the case of 6.7 GHz CH3OH absorption, our results and data from an extensive literature review indicate that absorption is rare, but that a population of 6.7 GHz CH3OH absorbers may be present at levels below 100mJy. In the case of the 6278.65 MHz H2CS absorption in G34.26+0.15, the data are consistent with infalling gas onto the HII region, which supports the key principle of gravitational collapse of molecular clouds during the process of star formation.
Title: Passive Galaxies in Massive Clusters - a Journey from z=1.27 to the Present
Abstract: Mapping galaxy evolution through observations of similar galaxies as a function of redshift can be used to constrain models of their formation and evolution. Here we focus on passive galaxies in dense cluster environments. We investigate possible size evolution, test the usability and limitations of a simple passive evolution model and establish how ages, metallicities and abundance ratios depend on galaxy velocity dispersion and on redshift. The data come from the Gemini/HST Galaxy Cluster project, covering 14 clusters with deep ground-based optical spectroscopy and HST imaging.