With One Hand Waving Free


29th October - 4th November 2017, Port Douglas, Queensland, Australia

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List of Abstracts

Tyrone Woods, Monash University

Supernova Archaeology: Unveiling the origin of Type Ia supernovae

About half of the iron in our blood was born in the thermonuclear explosion of a white dwarf—a Type Ia supernova (SN Ia). However, we still do not know why a white dwarf would undergo such an explosion. Evolutionary models can be grouped into either "accretion" or "merger" scenarios, with accretion models typically implying a hot, luminous phase prior to explosion. These objects are significant sources of ionizing radiation; therefore, the environment surrounding nearby SN Ia remnants should be strongly ionized, and traced by faint nebular emission. Such "relic" nebulae should extend out to tens of parsecs and linger for roughly the recombination timescale in the ISM (~100,000 years). Here we report deep upper limits on the temperatures and luminosities of the progenitors of several young Galactic and Magellanic SN Ia remnants based on the absence of such extended nebulae in their vicinity. For Tycho's supernova, we exclude any luminous accreting progenitor in the last 100,000 years.

Jeffrey Simpson

GALAH Survey: Chemical tagging confirmation of very wide binary star systems

We present the confirmation using data from the GALAH survey of seven very wide (>2 pc) pairs of stars that have the same chemical abundances and the same Galactic orbits. We also find that six claimed co-moving pairs are not truly co-orbiting. All pairs were initially identified using proper motions and parallaxes from Gaia DR1 but the confirmation of their true sibling nature relied on high resolution HERMES spectra to provide precise radial velocities and abundances. Stars such as these, wide binaries and co-orbiting debris of past star-formation episodes, are a crucial way to explore the limits of chemical tagging in the Milky Way. Of particular interest is one pair, which was found on a relatively eccentric and inclined orbit. A comparison of nearby stars with similar orbits showed that none had the same abundance pattern, in particular an enhancement in magnesium and a depletion in sodium.

Tomaz Zwitter (University of Ljubljana, Faculty of Mathematics and Physics)

Galah, RAVE, and Gaia-ESO surveys: from radial velocities to physical parameters of stars and the interstellar medium

Synergies between these ground based spectroscopic surveys and Gaia open new possibilities to explore radial velocities and chemistry of stars and the interstellar medium. I will compare current results for the matching objects and outline what we may expect when Gaia's second data release or its end-of-mission results are available.

Hans Van Winckel

The chemical diversity of Post-AGB stars

The atmospheres of Post-Assymptotic Giant Branch (post-AGB) stars display the outcome of chemical enrichments from internal nucleosynthesis and dredge-up processes which occurred during the entire stellar evolution. Spectra of post-AGB stars are dominated by atomic transitions rather than molecular transitions and this allows abundance determinations of a wide range of elements. Furthermore, the photospheres of post-AGB stars are convenient to study as the spectral types tend to cluster in a range where model atmosphere analysis in the optical is the most reliable. Post-AGB stars are, however, chemically much more diverse than anticipated. Some objects are among the most enriched objects in neutron capture (s-process) elements, while others are not enhanced at all and might even display s-process deficiencies. In this contribution I will give an overview of this chemical diversity and focus on the challenges to explain this diversity.

Gregor Traven

SB2 systems and stars in short-lived evolutionary phases explored by t-SNE reduction of spectral information

Peculiar spectra and objects to which they belong are relatively abundant among targets of general all-sky surveys such as RAVE, Gaia-ESO, and GALAH. Detection of such objects is important because the automatic evaluation of their stellar and chemical properties might turn out to be very challenging and therefore introduces a complication in obtaining new scientific insights into e.g. stellar evolution. On the other hand, the nature of peculiar objects can be quite intriguing and might include cataclysmic variables, symbiotic stars, stars with massive outflows or inflows, stars exhibiting chromospheric emission, different binary systems, and others. We employ the novel dimensionality reduction technique t-SNE (t-Distributed Stochastic Neighbor Embedding) to alleviate the discovery and overview of distinct morphological types of spectra which enables us to perform classification of stars from aforementioned surveys/datasets. Our classification results will be presented together with a user-friendly utility called t-SNE Explorer, which provides a convenient overview of the results of our method. Additionally, we aim to present the detected double-lined spectroscopic binary systems (SB2s) and their physical properties along with stars which are experiencing short-lived phases in stellar evolution and displaying features like complex H$\alpha$ emission profiles.

Joss Bland-Hawthorn, U Sydney

Near field cosmology: the age of massive stellar surveys

This is a veritable golden age for galactic archaeology with many outstanding surveys now under way to map the properties of millions of stars across the Galaxy. Here we review the main science goals which motivate these surveys, and look to what the future may hold. The observations extend far beyond what numerical simulations can reasonably explain. The Galaxy is extremely complex and no simple model or feedback prescription will do justice to the richness of our data. It is crucial to describe accurately what we observe and fully understand the selection processes in those observations. If we get this right, in all likelihood, we will make important new discoveries about the state of galaxies today, and their connection to processes in the distant past.

Robert Malaney, UNSW

Stars, Quasars and Quantum Entanglement

In this talk I review recent developments in the cross-disciplinary area of astronomy, quantum mechanics and quantum communication. Einstein's famous quip "spooky action at a distance," based on the famous 1935 EPR paper that argued quantum mechanics was incomplete, led John Bell to propose his equally famous Inequality Test in 1964. All subsequent tests have led to a violation of Bell's Inequality, therefore supporting the notion that spooky action at a distance in the form of quantum entanglement is the true reality - as opposed to a "local realism" solution touted by Einstein. Indeed, over the past decade, quantum communication tests based on entanglement have flourished with the most recent event being this year's quantum-enabled satellite experiment that fully supported the premise that quantum entanglement exists at least up 1000km. However, "niggling" loopholes remain which still allow for a local realism solution. One of these loopholes is the "freedom-of-choice" loophole - the allowance for external influences on the random number generators used in quantum-entanglement experiments. Very recently this loophole has been made substantially smaller by experiments which couple stellar photon measurements to the random number generating processes. Future experiments will close the loophole even further by using quasar sources as the random photonic input. In this talk I will review these fundamental experiments and discuss the possibilities for closing the Bell violation loopholes completely via astronomical sources.

Michael A. Dopita (1) & A. Ali (2)

(1) Research School of Astronomy & Astrophysics, The Australian National University
(2) Cairo University, Giza, Egypt & King Abdulaziz University, Jeddah, Saudi Arabia)

Probing Planetary Nebula Evolution through WiFeS Integral Field Spectroscopy

A continuing integral field spectroscopy study using the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope is revealing new details of post-AGB stellar evolution in the Planetary Nebula (PNe) phase. I will describe how, in conjunction with theoretical photoionisation modelling using the MAPPINGS 5.2 code, this work provides chemical abundances, stellar temperatures, stellar luminosities, nebular distances and nebular ages. We will show how the so-called Weak Emission Line Star (WELS) classification is fundamentally flawed, since the emission lines used for this classification generally arise in the nebula, rather than in the star. In the particular case of IC 418, we present 3400-9000Å spectra with a dynamic range of ~10^6, and we model the emission line spectrum over five orders of magnitude of intensity, demonstrating that the previously reported abundance discrepancy between recombination lines and forbidden lines does not exist, once fluorescent pumping is taken into account. For this radiation pressure dominated PNe, the properties of the fast stellar wind shocked region are modelled, and the age of the nebula is determined to be only ~200 yr. Finally, we present an extensive integral field study of the spectacular PNe He 2-111, which demonstrates expansion velocities possibly as large as 800 km/s. For this object, a chemo-dynamic analysis reveals that N-rich "bullets" are plowing through a previously ejected PNe bipolar nebular shell. We hypothesise that this is the result of a recent nova explosion on a white dwarf companion of the PNe central star; a nova within a PNe!

Dennis Stello

A cornet of goodies from asteroseismology

In this talk I will present recent asteroseismic results arisen from NASA's Kepler and K2 missions, and show what we can expect from TESS. We have come incredibly far in the past decade in terms of directly probing the physics of stellar interiors. This includes (1) our ability to `see' which stars are burning helium in their cores, (2) measurements of radial differential rotation, (3) and the detection of strong magnetic fields in the cores of red giant stars. Due to the large numbers of stars for which asteroseismic inference can now be made, the field has branched out to answer questions not only about stellar physics, but also the physics that has governed the formation and evolution of the Milky Way.

Gary Da Costa (on behalf of SkyMapper EMP-star team); RSAA, ANU

The SkyMapper Search for Extremely Metal-Poor Stars in the Galactic Halo

The filter system employed in the SkyMapper survey of the southern sky incorporates a narrow ‘v’ filter that covers the Ca II K-line at 3933Ang, facilitating the identification of extremely metal-poor (EMP) stars in the photometric dataset. A initial survey carried out during telescope commissioning resulted in the discovery of the most iron-poor star known in the Galactic halo (SMSS J0313-6708). In this contribution we present updated results from a new search for Galactic halo EMP stars based on SkyMapper Survey DR1 data. We will discuss the selection process, possible biases, outcomes from the on-going low resolution spectroscopic follow-up program with the ANU 2.3m telescope at Siding Spring Observatory, and initial results from high-dispersion follow-up observations of promising candidates at the Magellan 6.5m telescope.

Trevor Ireland & Janaína Ávila, Planetary Science Institute and Research School of Earth Sciences, Australian National University

Diamonds and dirt: Where is the r-process in presolar grains?

Presolar grains have given us a lot of insight in to s-process nucleosynthesis occurring in He-burning stars. Abundance levels of heavy element isotopes (e.g. Ba-Hf) can be modelled fairly well with current AGB stellar models [1], and likely can be extended up to Pb and Bi. On the other hand, we don’t seem to be picking up the r-process carriers. In modelling the solar system abundances, the r-process is commonly attributed to what is left over from solar system abundances once the s-process is subtracted.
The density of free neutrons required for the r-process points to explosive environments such as core-collapse (type II) supernovae where pre supernova stars of at least 8 solar masses evolve quickly to form an Fe-Ni-rich core. Implosion of the core produces rapid neutronisation of all heavy elements and is followed by a more relaxed epoch of beta decay back to the valley of stability. The presence of U and Th in the solar system and in presolar grains attests to r-process production being ongoing in the galaxy. But where are the carriers?
Hibonite grains carry the memory of highly neutronised material. They show large variations (tens of percent) in the heavy isotopes 48Ca and 50Ti, which have been ascribed most likely to SNI-style nucleosynthesis. Still it appears that these very refractory grains have been processed in the solar system. The recent measurement of extremely small grains (order 50 nm) with large 54Cr anomalies [2] may be direct condensates from such a neutron-rich environment, but once these small grains are analysed there is little left for follow up work.
SiC X grains have C, N, and Si isotope compositions that appear to relate them directly to SN nucleosynthesis. Limited analyses of Sr and Ba show significant effects but excesses and depletions are apparent in r-process nuclides in different grains [3]. Fe and Ni isotope anomalies are present in SiC X grains, but they do not appear consistent, or related to r-process but rather to pre-supernova evolution [4]. The Mo isotopic signature observed in SiC X grains is also not consistent with r-process nucleosynthesis as they do not show the expected large 100Mo excess. The Mo isotopic pattern can be explained by a short intense neutron burst instead [5]. The nano diamonds derived by chemical digestion of chondrites show large anomalies in Xe. This is the so-called HL component that shows anomalies (up to a factor of 2 relative to solar) in the heaviest and lightest isotopes. Contributions appear to have been derived from r-process-rich and a p-process-rich xenon. However, despite much effort, the two components have not been able to be separated. Nanodiamonds are small and the Xe concentration relates to one Xe atom per million nanodiamonds. And, the C isotopic composition of bulk nano diamonds is close to solar [6]. As such, separation of a concentrated r- or p-process component by physical or chemical separation of diamonds will be difficult. The r-process is well represented in solar system material but we are having difficulty in isolating any distinct carriers.
Dust condensation is apparent in images of SN. This may simply be a result of the differential velocity between the SN dust and aggregating molecular clouds. At the high interaction speeds, dust will be ablated and it may be that distinct r-process carriers are simply too small for us to see at this stage.

References
[1] Ireland T. R., et al. (2017) Rare Earth Element abundances in presolar SiC. Geochim. Cosmochim Acta, in press.
[2] Nittler L., et al. (2017) Extreme chromium isotope anomalies in Orgueil nano-oxides: Presolar Type IA supernova condensates? Abstract, 80th Annual Meteoritical Society Meeting, #6330.
[3] Stephan T., et al. (2017) Strontium and barium isotopes in presolar silicon carbide grains measured with CHILI—two types of X grains. Geochim. Cosmochim Acta, in press.
[4] Kodolányi J., et al. (2017) Iron and nickel isotope compositions of presolar silicon carbide grains from supernovae. Geochim. Cosmochim Acta, in press.
[5] Meyer B. S., et al. (2000) Molybdenum and zirconium isotopes from a supernova neutron burst. The Astrophy. Journal 540:L49.
[6] Lewis J.B., et al. (2017) Origin of nanodiamonds from Allende constrained by statistical analysis of C isotopes from small clusters of acid residue by NanoSIMS. Geochim. Cosmochim Acta, in press.

Ken Freeman

Observational Aspects of Thick Disk Formation

I will review observational properties of the thick disk of the Milky Way and other nearby disk galaxies. I will also discuss some related properties of high redshift disk galaxies. The goal is to identify observational properties that may help us to understand the processes that led to the formation of thick disks, and to understand the role of the thick disk in galaxy formation.

Simon Campbell, Monash

Attempts at 3D Models of Stellar Interiors

Whilst 1D stellar models have been very successful in reproducing many observables, some of their success is based on parameterisation and calibration, as opposed to good physical models or understanding. This is especially true for phases in which the structure is dominated by convection, and, in particular, the extent of convection, as delineated by convection boundaries. Here we present some of our initial attempts at modelling stellar interior convection zones, for a core helium burning model, and for an oxygen burning shell. We summarise some basic lessons we have learned from our foray into the field so far.

David Yong, ANU

Chemical abundances in globular clusters and metal-poor stars

Measurements of chemical abundances in stars enable us to probe the physics underpinning stellar nucleosynthesis, nuclear astrophysics and Galactic evolution. Ancient stars in the Galactic halo and globular clusters offer an observational window into the early epochs of the universe. In this talk, I will discuss some highlights in these areas and how those data keep theorists like Lattanzio honest.

Andrew R. Casey (Monash) et al.

The Lithium-rich Giant Puzzle

Theoretical models of stellar evolution predict that most of the lithium in a star will be destroyed as it ascends the red giant branch. However, observations reveal that ~1% of red giants are peculiarly rich in lithium, often exceeding the interstellar medium or big bang nucleosynthesis predictions. With only 151 lithium-rich giants discovered in the past four decades, and no common observables other than lithium enhancement, the origin of lithium-rich giant stars is one of the oldest fundamental problems outstanding in stellar astrophysics. In this talk I will report the discovery of 2,232 lithium-rich giant stars, and use these data to rule out internal and external phenomena proposed to explain the origin of lithium-rich giant stars.

Sarah Martell (UNSW), Jeffrey Simpson (AAO), Kate Henkel (Monash), Graeme Smith (UC Santa Cruz)

Thermohaline mixing at the extremes of the metallicity distribution function

Thermohaline mixing is a standard part of red giant branch evolution, cycling material from a star's surface through its hydrogen burning shell and causing continuous changes in the surface light-element abundances. While deep mixing is ubiquitous and predictable in low-mass red giants, it is difficult to model numerically. Treating thermohaline mixing as a diffusion process, we have only recently been able to simultaneously match the evolution of carbon and lithium abundance in a globular cluster. I will describe an observational project to expand the range of deep mixing measurements in globular cluster stars to lower and higher metallicity, and discuss how well the observed carbon depletion rate can be reproduced by a thermohaline mixing model.

E. Chiosi (1), S. Pasetto (2), C. Chiosi (3)

(1) INAF-Osservatorio Astronomico di Padova, Vicolo dell'Osservatorio 5, 35122 Padua, Italy
(2) Uiversity College London, Department of Space & Climate Physics, Mullard Space Science Laboratory, Holmbury St. Mary, Dorking Surrey, United Kingdom
3) Department of Physics & Astronomy, "`Galileo Galilei"', University of Padua, Vicolo dell'Osservatorio 2, Padova, Italy

Theory of stellar convection III: boundary conditions for the SFC theory

In a recent paper, Pasetto et al (2014, MNRAS.445.3592P) developed a fully self-consistent, scale-free theory of stellar convection, named the SFC theory, in which the convective elements simultaneously move radially and expand/contract under the action of the buoyancy force and the inertia of the displaced fluid. The more complete treatment of the dynamics compared to the classical Mixing Length (ML) theory provides all the properties of stellar convection as a function of the environment physics, with no need of the ML parameter. Subsequently, Pasetto et al (2016, MNRAS.459.3182P) introduced suitable boundary conditions at the surface of the external convection in a star and presented the first stellar models and evolutionary tracks on the Hertzsprung-Russell Diagram (HRD). The new stellar models with the SFC theory are very similar to those based on the ML theory. In this paper we go further on investigating the physical meaning of the boundary conditions. The work focuses on the critical layers just below the surface of the star in which the adiabatic gradient falls because of the ionization. Here we propose a new set of boundary conditions that better describe the physical situation in the layers just beneath the stellar surface, and derive the analog of the ML parameter also for the SFC theory. This allows us to describe the results of the SFC theory using the same language of the classical ML theory.

Peter Wood, ANU

Explaining the period-luminosity sequences of red giant variables

I will present our current understanding of the causes of the period-luminosity sequences of red giant variables. This includes a revision of the pulsation mode assignments which brings two divergent past interpretations into alignment. The mysterious sequence-D variables are still not understood. The binary star sequence is discussed, along with what we can learn from it.

Janaina Avila & Trevor Ireland, Research School of Earth Sciences and Planetary Science Institute, The Australian National University

The end of s-process nucleosynthesis: Pb isotopic compositions in presolar grains

Similar to the majority of stable isotopes with atomic mass higher than iron, lead is synthesized by both slow (s-) and rapid (r-) neutron capture processes. However, the mass region between Pb and Bi is particularly interesting as most of the reaction flow is trapped at 208Pb and 209Bi (the last stable isotopes in the neutron capture chain of the s-process) because of the small neutron capture cross sections of these neutron magic nuclei. The s-process flows through 204Pb to 208Pb. Further neutron captures on 209Bi feeds the short-lived ground state of 210Bi (t1/2 = 5.01 days), which decays to 210Po (t1/2 = 138.4 days), as well as the isomer 210mBi, which is unstable with a long half-life (t1/2 = 3 x 10^6 yr). The s-process flow is then recycled back to 206,207Pb via -decays from 210,211Po and 209Bi. In this termination region, 204Pb is the only isotope of pure s-process origin due to shielding from r-process by its isobar 204Hg. Its final s-process abundance is therefore determined by the branching at 204Tl, which is interesting because of the pronounced temperature dependence of its half-life.
The main sites of production of s-process Pb in the Solar System are attributed to low-mass asymptotic giant branch (AGB) stars, with the main component being produced by AGB stars with about half of the solar metallicity, and the strong component, which is responsible for large amounts of 208Pb, the result of s-processes in early generation, low-metallicity AGB stars. Although the production of Pb is dominated by s-process, the r-process still produces a substantial proportion of it through a series of -decay reactions from extremely neutron-rich (unstable) nuclei. 206Pb, 207Pb, and 208Pb have substantial radiogenic components, as they are the final products of a complex chain of decay reactions that started at 238U, 235U, and 232Th, respectively.
Lead abundances have been successfully measured for a number of stars enriched in elements made by the s-process. However, isotopic determinations are more difficult to obtain. An indirect way to measure Pb isotopic compositions in stars is by analysing stardust grains. These grains condensed directly from the gas phase present in ancient stellar outflows or stellar ejecta, and thus became part of the interstellar medium from which our Solar System formed about 4.56 Gyr ago. SiC grains interpreted to have condensed in the outflows of C-rich TP-AGB stars, were analysed for their Pb isotopic compositions. The grains isotopic signature shows the typical feature of the s-process, which is enrichment in the s-only 204Pb. This is not unexpected, since previous analyses of heavy elements in AGB SiC grains have shown that these grains are strongly enriched in s-process nucleosynthetic products. The spread in Pb isotopic ratios is, however, much larger than that predicted by s-process models.

Klemen Cotar, Tomaz Zwitter and the GALAH team, Faculty of mathematics and physics, University of Ljubljana, Slovenia

Identification of stellar associations using hierarchical clustering

Detailed chemical abundance measurements provide a possibility to identify stellar structures whose members were formed together in the same molecular cloud. This theoretical idea has so far not yielded much practical success in large surveys. One of the problems for this are presumably noisy measurements and low dimensionality of chemical abundance space. To overcome this we are using abundances determined by The Cannon procedure applied to the GALAH spectroscopic survey. Its aim is to observe up to 1 million stars and determine up to 30 individual abundances.
First step in our approach is to clusters stellar objects into a tree-like structure, that gives us a rough idea about the chemical relations between the object. Construction of the tree can be done by a hierarchical clustering algorithm or phylogenetic neighborhood joining method that are both based on the determination of distances between objects in our dataset. Multiple different combinations of clustering and distance (manhattan, canberra etc.) algorithms were assessed based on clustering results for repeated observations of the same objects and known members of stellar clusters. Here we looked into if those observations were clustered into the same region and what is the separation between them.
The next step is the identification of possible stellar structures (clusters, streams etc.) from the clustering results. The tree structure is traversed from the the leaves (chemically identical objects) to its root. At every node of the tree, the descendant objects are further analyzed including their stellar position and kinematics information from two different auxiliary datasets; Gaia-TGAS (only for limited subset of our objects) and UCAC5. To preform the identification of possible stellar structures, we begin by finding pairs of objects with similar kinematics, that were previously clustered together in the chemical abundance space. After obtaining the list of pairs, we look for over-densities in positions of the object in that list that might represent significant stellar structure.
In the current version of our algorithms we are looking for new members of known clusters, close co-moving stellar pairs, and possible new, previously unidentified open stellar clusters. In our presentation we will present the result of the proposed analysis. To verify the performance of our algorithm we use auxiliary reference data set where we matched known cluster stars with GALAH observations. Therefore we can say that the proposed algorithm is able to recover known stellar associations without any prior knowledge.

A. Wallner

Supernova-60Fe detected on Earth - can we also link 244Pu to an r-process site?

The Interstellar Medium (ISM) is continuously fed with new nucleosynthetic products. The solar system moves through the ISM and collects dust particles. Therefore, direct detection of freshly produced radionuclides on Earth, before decaying, provides insight into recent and nearby nucleosynthetic activities. Indeed, a pioneering work at TU Munich, using AMS for ocean crust-samples, showed an enhanced $^{60}$Fe signal of extraterrestrial origin.
Within an international collaboration we have continued to search for ISM radionuclides trapped in deep ocean archives. We have analyzed sediments, crusts and nodules for extraterrestrial $^{60}$Fe (t$_{1/2}$=2.6 Myr), $^{26}$Al (0.7 Myr) and $^{244}$Pu (81 Myr) complemented by independent work at Munich. We demonstrated that multiple events happened in our galactic neighbourhood and left their fingerprint on Earth. A global $^{60}$Fe influx is evidence for exposure to recent ($\le${10} Myr) supernova explosions.
Unknown is still the site where the heaviest elements are made in nature. The low concentrations measured for $^{244}$Pu suggest an unexpectedly low abundance of interstellar $^{244}$Pu. It signals a rarity of actinide r-process nucleosynthesis which is incompatible with the rate and expected yield of supernovae as the predominant actinide-producing sites.
I will present new results for $^{60}$Fe measured at the ANU and $^{244}$Pu at ANSTO with unprecedented sensitivity. These data provide new insights into their concomitant influx and their ISM concentrations over a time period of the last 11 Myr.

George Angelou (MPA, MPS), Achim Weiss (MPA)

The Aarhus Challenge - A comparison of Stellar Evolution Codes

We present results from the Aarhus Challenge - A comparison between stellar evolution codes in order to identify the minimum level of systematic and numerical differences in low-mass Red Giant Branch models.