Join us for the traditional presentation of this year Nobel Prize laureates.

Accretion disks are usually modelled to be axisymmetric. However, whenever a misaligning torque is applied to the accretion disk, this can break in separate annuli, leading to a peculiar evolution. In the last two years, an unexpectedly large number of observations have revealed that this physical mechanism indeed occurs in astrophysical environments. Observational evidence range from quasi-periodic modulation of X-rays binaries, photometric dippers in young stellar object, and in particular high resolution images of protoplanetary disks. The misaligning torque can be different in nature, e.g. a binary system, a misaligned magnetic field, or a misaligned spin of the central black hole. In this discussion, I will show recent results on this topic in different astrophysical scenarios, and discuss the implications focusing in particular on the planet forming disks.

During 2018, the fellows and students of ESO (Garching and Vicatura), have been leading a project in 8 ESO member states and Chile. The goals have been to: (1) promote science opportunities for young researchers; (2) take the Supernova experience to the people and (3) raise general awareness of ESO with a focus on the ELT. Overall we had 52 ambassadors carrying out these activities in the member states, including many without an ESO affiliation but were still enthused to help fulfil the aims of the project. In this informal discussion we will give an overview of the project, summarise our experiences, assess the impact that we have had and present the lessons we learnt. There will also be an opportunity to try out some of the hands-on activities that we took to science festivals and donated to educational centres.

Comets are considered to be leftover planetesimals from the epoch of planet formation. As such, they are believed to still preserve information about the physical conditions in the protoplanetary disc. However, the current comet population also bears the signatures of the dynamical processes during the epoch of planetary migration ~4 billion years ago. Moreover, active comets are known to experience dramatic changes in the current epoch due to sublimation close to perihelion. These considerations imply that many of the primordial properties of comets might have been significantly altered. Therefore, in order to use comets to study the early Solar System, we need to disentangle the signatures of each stage of their evolution.

The complicated history makes comets some of the most interesting and most complex objects in the Solar System and has motivated a number of recent space missions. The latest mission to a comet was ESA/Rosetta which followed comet 67P/Churyumov–Gerasimenko along its orbit between 2014 and 2016 and provided unprecedented continuous observations of the comet nucleus. Rosetta answered many long-standing questions in cometary science but it also fueled anew the debate of how pristine comet nuclei are.

In this discussion, I will begin with a brief introduction on the current understanding of comet evolution in the Solar System. I will then proceed to highlight some of the most puzzling discoveries from Rosetta. Finally, I will present the open questions in cometary science which I aim to answer with the help of telescope observations.

The star cluster population of the Milky Way provides a unique window to study the formation history of our Galaxy. The conditions of the epochs when the Milky Way built up most of its stellar mass are preserved in the star clusters we observe to date. However, the physics governing the formation of star clusters are still not entirely understood. For example, ancient globular clusters show subtle differences in the chemical compositions of their stars which appear to be absent in the clusters forming today. Does this suggest that cluster formation varies with mass or cosmic age? In my presentation, I want to show how we can use the stellar dynamics of the clusters to answer such questions. Thanks to satellites such as Hubble or Gaia and powerful spectrographs we can nowadays study the motions of representative samples of stars in clusters of all ages. Using data from the MUSE spectrograph, we could already show that rotation played a crucial role in the formation of globular clusters and that they harbour larger populations of black holes than previously thought. We are further using the data to search for differences in the kinematics of their stellar populations. If detected, such differences put stringent constraints on the mechanisms that led to the formation of multiple populations in globular clusters.

I introduce an algorithm that simultaneously map the photometry, astrometry, and PSFs of multiple images to study differential changes. The algorithm employs the most general delta-function convolution kernel. It is coded in Fourier space which makes it adaptable to GPUs for fast data processing. I will discuss problems associated with difference imaging, especially correlated errors generated during image combination and methods to de-correlate background errors. I will show examples of such operations and the limitations of de-correlated images. Differential comparisons of images are widely used in supernova search, exoplanet transit search, and imaging polarimetry.

The ELT telescope is under construction. In this informal discussion we offer a Question and Answer session on the telescope system. Do you have questions about how the primary mirror works, how the segments are made, the shape of the other mirrors, why is M4 deformable, what does M5 do, how many guide probes do we use, what is a phasing station, is the dome really that big, how much does the telescope weigh, how will we point the telescope? Or more?

The recent second release (DR2) of the Gaia catalog has allowed researchers in several fields of astronomy to gain new insights in their work, and to immediately obtain unforeseen results. In order to give an idea of the numbers and on the variety of these results, several ESO staff have agreed to give a very quick (5 min) introduction to their results obtained using Gaia DR2 data.

The program will be as follows:

10:45     Welcome and introduction

10:50     Tereza Jerabkova: What’s up with Gaia photometry: the case of the Orion Nebula Cluster

10:55     Giacomo Beccari: A sextet of clusters in the Vela OB2 region revealed  by Gaia

11:00     Carlo Manara: Gaia DR2 view of the Lupus V–VI clouds: The candidate diskless young stellar objects are mainly background contaminants

11:05     Christian Hummel: GAIA parallaxes of SB2s with interferometric orbits

11:10     Michael Hilker: Mean proper motions, space orbits and velocity dispersion profiles of Galactic globular clusters derived from GAIA DR2 data

11:15     Preben Grosbol: Spiral Potential of the Sagittarius arm

11:20     Richard Anderson: Milky Way Cepheid Standards for Measuring Cosmic Distances and Application to Gaia DR2: Implications for the Hubble Constant

11:25     Palle Moeller: Resolving the longstanding quasar selection bias with DR2

The upcoming LISA mission is the only experiment that offers the opportunity to study the Milky Way through gravitational wave radiation, exploiting the signals from Galactic double white dwarf (DWD) binaries. I will show that the large number of DWD detections will allow us to use these systems as tracers of the Milky Way potential. Furthermore, in the coming years, a large number of DWDs can be simultaneously detected in both electromagnetic (e.g. with Gaia and LSST) and gravitational wave radiation. This will provide a unique opportunity to perform a multi-messenger study of the Galaxy. Finally, I will talk about prospects of observing extra-galactic DWDs in the Local Group.

Modified Newtonian Dynamics (MOND) is an alternative to non-baryonic dark matter, proposed by Israeli physicist Moti Milgrom. Back in July, we discussed the general predictions of this paradigm and how they fare with astronomical observations. In this second part, we will discuss some specific examples of non-relativistic MOND theories, which can be derived from a Lagrangian formulation. These MOND theories satisfy the usual conservation laws (energy, momentum) but violate other principles, like the strong equivalence principle in the case of modified gravity or locality in the case of modified inertia. Even if you did not attend the first part of this informal discussion, you should be able to actively participate in this second part.

Open access to scientific results is rapidly gaining importance over the entire spectrum of scientific research. In particular for astrophysics, an important part of the research process includes the development of source codes.

Journal articles detail the general logic behind new results and ideas, but often the source codes that enable these results remain hidden from public view. In this presentation, I will discuss our recent study on the availability of source codes used for published astro research and how this affects the transparency and reproducibility of this research. The Astrophysics Source Code Library (ASCL, ascl.net) was started in 1999 to encourage software availability and thus improve research transparency. I will cover what the ASCL is, how to submit software to the resource, and the benefits of doing so.

I will share how ASCL enables links between literature and software entries, in ADS and how an ASCL ID can be used for citing your code. I will also cover good and bad ways to cite software, avenues for publishing software, and how journals are changing to include and recognize the contribution software makes to our discipline.

Low-mass stars form via gravitational collapse of molecular cloud cores.  Although their formation has received considerable attention in the last few decades, the rate at which a star gains most of its mass and the physics that drives the main phase of stellar growth is still not understood. Most protostars have luminosities significantly fainter than the luminosity expected from steady accretion over the protostellar lifetime.   The solution to this problem may lie in episodic mass accretion -- prolonged periods of very low accretion punctuated by short bursts of rapid accretion.  In this informal discussion, I will describe these challenges and initial constraints on protostellar variability from the East Asia Observatory JCMT/SCUBA2 sub-mm monitoring program of eight nearby star forming regions, the first large sub-mm variability program.

The extremely metal-poor stars (EMP) hold in their atmospheres the fossil record of the chemical composition of the early phases of the Galactic evolution. The chemical analysis of such objects provides important constraints on the early chemical enrichment of the Galaxy.  EMP stars are very rare objects; to dig them out the analysis of large amounts of data is necessary. I will present how these most metal poor stars can be found and present the methods which allow to determine their chemical composition.

So far most of what we have learned about the stellar content of Early-Type Galaxies come from the visible, particularly for detailed spectroscopic studies. New observational facilities and new modeling means allow us to start exploiting the near-IR spectral range. Good fitting solutions should work out for both the Near-IR and the optical ranges. I will show you new results, but most importantly, will discuss with you the potential of this spectral range for constraining the SFHs, IMF and abundance ratios of these galaxies.

Type Ia supernovae originate from the explosion of carbon-oxygen white dwarfs in binary systems,but the exact nature of their progenitors remains elusive. Recent studies have found that theX-ray bulk properties of Type Ia supernova remnants, such as the radius and the Fe Kalpha centroid energy and luminosity, can discriminate between progenitor energetics and circumstellar environments.Using Chandrasekhar, and for the first time, sub-Chandrasekhar models for the chemical composition of Type Ia supernova ejecta, we model the dynamical and thermal evolution of supernova remnants up to 5000 years for several uniform ambient media in one dimension. We generate synthetic X-ray spectra from these models with updated atomic data and compare these bulk properties for different expansion ages with X-ray observations from the Chandra and Suzaku telescopes. We find an overall agreement between our models and the observational data. We also find that the ambient medium density and the expansion age are the main contributors to the X-ray diversity of these bulk properties, not the progenitor scenario. Detailed X-ray fittings that determine chemical abundances or flux ratios are needed to discriminate between Chandrasekhar and sub-Chandrasekhar progenitor scenarios.

Modified Newtonian Dynamics (MOND) is an alternative to non-baryonic dark matter, proposed by Israeli physicist Moti Milgrom in 1983. It aims to explain the mass discrepancies observed in the Universe by changing the laws of dynamics instead of postulating new particles. MOND is a general paradigm that includes different physical theories, such as modified gravity and modified inertia. I will start with a brief review of the general paradigm and its predictions. If time allows, I will also illustrate some non-relativistic MOND theories and possible relativistic extensions. In general, MOND is successful on galaxy scales, it has problems on galaxy cluster scales, and it's almost entirely mute on cosmological scales (CMB, large scale structure). In this regard, MOND is diametrically opposed to LCDM in terms of explaining/predicting power, so it is generally difficult to properly compare the two paradigms.

It is now well established that the star formation rates (SFRs) of galaxies are reduced by their passage through a dense environment.  However, the processes responsible for this suppression are uncertain, as are the timescales over which they act.  Some observational constraints have provided evidence for fast (<~ 500 Myr) suppression while others support a long timescale (2-5 Gyr).  A successful model for resolving this discrepancy is a “delay+rapid” quenching model, in which galaxies enter a cluster and are unaffected for a period of time, the “delay” period, followed by a rapid quenching event.  While this model is successful at explaining many aspects of quenching in clusters, it is unknown what happens to galaxies in the “delay” period.  I will discuss a set of completed and in prep. papers from the Local Cluster Survey that address this issue. We use spatially resolved observations of star formation tracers in star-forming galaxies in 9 nearby clusters to understand how the star-forming disks of cluster galaxies are affected by their environment.  We find that spatially resolving the star formation is a crucial ingredient to understanding environmental transformation and I will present our results on the relative size and shrinking timescales of star-forming disks inside and outside the clusters.  I will also discuss the implication that this has for understanding how the spatially integrated SFRs of galaxies are modified as they enter dense environments.

Every globular cluster (GC) host stars with different light element abundances. These can be broadly classified in two populations: the first population (P1) has the same abundance as field stars of similar [Fe/H], while a second population (P2) shows abundance variations of some specific light elements like He, C, N, O, Na, Al and Mg. Here I’ll introduce the main idea behind the origin of the anomalous abundances of GC stars, and the challenges they face in the light of new evidence that have come up in the last two years.

Almost forgotten, in the era of GPS/GLONASS/GALILEO, the art of astronomical navigation is still being practiced. I will introduce the tools: the sextant, the "Nautical Almanach", paper, preferably with polar coordinates and pocket calculator, a slide rule could do as well.

Starting from posing the problem, say how to sail from Tenerife to the Caribic, beauty and pitfalls of working with the sextant will be explained, including the artificial horizon. The measured altitude of celestial bodies then needs to be converted into crossing bearing lines. This leads to the graphic solution introduced as late as 1875 by French navy captain Marcq Saint-Hilaire. The method, btw. is a master piece how to design a highly efficient and numerically stable algorithm.

As a side issue, time permitting, the astronomical correction of the magnetic compass will shortly be touched.

Which mechanisms are mainly driving AGN activity is a major unsettled question. Thereby, the role of galaxy mergers is heavily debated, from both an observational as well as from a theoretical point of view. I will discuss different contradictory observational and theoretical results and present a study in which we investigated the statistical relevance of galaxy mergers for driving AGN activity, using large-scale cosmological hydrodynamic simulations from the Magneticum Pathfinder set. Our simulations predict that for luminous AGN at z=2, more than 50 per cent of their host galaxies have experienced a merger in the last 0.5 Gyr, consistent with a number of observational studies. These high merger fractions, however, merely reflect the intrinsically high merger rates of massive galaxies at z=2, in which luminous AGN preferentially occur. Apart from that, our simulations suggest that merger events are not the statistically dominant fuelling mechanism for nuclear activity over a redshift range z=0-2. Despite the statistically minor relevance of mergers, at a given AGN luminosity and stellar mass, the merger rates of AGN hosts can be up to three times higher than that of inactive galaxies. Such elevated merger rates still point towards an intrinsic connection between AGN activity and mergers, consistent with our traditional expectation.

The current epoch holds science in high esteem. The belief that science and its methods have something particular seems to be very much shared. Qualifying a statement or a reasoning as scientific gives it sort of a merit or shows that we give it a particular trust. But, if science has something particular, what is it then?

(‘What is this thing called Science?’, Alan Chalmers, my translation)

To try and grasp the subtlety of this question, I will present and discuss the basis of three different science philosophies, which all have had a tremendous impact on how people considered the scientific activity at the time:

1/ ‘Induction’ promulgated by Sir Francis Bacon, the first modern science philosopher.

2/ ‘Falsificationism’, created by Sir Karl Popper to attack induction.

3/ I will conclude by presenting the structuralist theory of science by Thomas Kuhn, who created and popularized the now widely used term ‘paradigm shift’.

The governance of file formats, protocols, and standards has recently emerged as a site of interest for both computer science and social science. Governed by an International Astronomy Union working group since 1982, over the last four decades, the FITS file format has become the de facto standard for sharing, analyzing and archiving astronomy data. FITS was widely adopted by the astronomical polity in the early 1980’s because of its ability to overcome the problem of incompatibilities between operating systems. Using the FITS format, an astronomer could share image files across operating systems using FITS as a common substrate. On the back of the original intent of FITS, astronomical data became both backwards compatible and easily shared.

However, new advances in astronomy instrumentation, computational technologies and analytic techniques have resulted in new data that do not work well within the traditional FITS format. Tensions have arisen between the desire to update the format to meet new data and analytic challenges and adherence to the original edict for FITS files to be backwards-compatible. The future of FITS is caught between the demands of rapidly changing technology and the insistence upon the stability of a rarely-changed format. We examine three inflection points in the governance of FITS: a) initial development and success, b) widespread acceptance and governance by the working group, and c) the challenges to FITS in a new era of increasing data and computational complexity within astronomy.

The characterization of the local double white dwarf (DWD) population is crucial to our understanding of multiple questions, from stellar evolution, through the progenitors of Type-Ia supernovae, to gravitational wave sources. From a spectroscopic sample of 439 WDs from the ESO-SPY survey, we measure the maximal changes in radial-velocity (DRVmax) between epochs, and model the observed DRVmax statistics via Monte-Carlo simulations, to constrain the population characteristics of DWDs. We then combine the results with those of a complementary sample from the SDSS to obtain new and precise information on the DWD population and on its gravitational-wave-driven merger rate. We find that ~10% of WDs are in DWD systems in the separation range ~<4AU within which the data are sensitive to binarity. The Galactic WD merger rate per WD is ~1e-11 per year. Integrated over the Galaxy lifetime, this implies that 8.5-11% of all WDs ever formed have merged with another WD. If most DWD mergers end as more-massive WDs, then some ~10% of WDs are DWD-merger products, consistent with the observed fraction of WDs in the 'high-mass bump' in the WD mass function, now possibly seen in Gaia DR2. The implied Galactic DWD merger rate is 4.5-7 times the Milky Way's specific type-Ia supernova (SN Ia) rate. If most SN Ia explosions come about from the mergers of some DWDs then ~15% of all WD mergers must lead to a SN Ia.

In this informal discussion we want to talk about the question of which results should be published where. We will give you an overview of the journals available for astronomers to publish their results. In particular we will present the recently reinvented AAS research notes, a journal for fast publication of small results, work in progress or null results. Furthermore, we will give an overview of the ESO publication guidelines. We will end with an introduction to open access journals and compare them with traditional journals.

The recent surge on neural-network based data modelling shows one thing: large data sets with Gaussian properties can be efficiently and scalably represented. How can we understand these models, why are they efficient, and why are we still no-where close to solving machine learning? What can and what cannot we do yet? I will try to sort some lines of thoughts, and goal discussing personal research topics which try to address the ‘cannot’s. And unfortunately lack the time to touch upon reinforcement learning and quantum computing, since those are even less solved.

In the nearby Universe, double-barred galaxies account for 20% of all disc galaxies, this fraction being a lower limit due to the difficulties inherent to the detection of inner bars embedded within the central regions of structurally complex galaxies. Forming and sustaining two coexistent non-axisymmetric structures in a galaxy is a challenging problem not well understood yet with simulations nor with observations. The TIMER project (Time Inference with MUSE in Extragalactic Rings) is a well-designed survey of barred galaxies with noticeable central structures, such as inner bars and nuclear rings, which are considered as footprints of secular evolution. The current TIMER sample is composed by 24 galaxies, two of them being confirmed double-barred systems. In this Informal Discussion I will tell you about the effort we are making to retrieving the star formation histories of the TIMER galaxies, as well as the unprecedented results on the formation and stellar properties of double-barred galaxies.

I will review our recent results on the intrinsic three-dimensional  (3D) shape of bulges and bars in a statistically significant sample of galaxies from the CALIFA survey. Our work, based on the outcome of accurate multi-component structural decompositions of the galaxies, allow us to derive a probabilistic estimation of the 3D shape of individual structures, and it provides a new look at the secular evolution processes taking place in nearby galaxies.

We would like to share our manifold impressions and experiences from our recent trip to Ghana with you.

We will summarize our workshop with 40 Ghanaian students held at the University of Cape Coast, as well as the outreach activities we conducted in a fishing village and at the Ghana Planetarium in Accra (the only planetarium in sub-Saharan Africa outside of South Africa).

Furthermore, we would like to discuss the way forward for this initiative.

I will discuss the formation and dissipation of circumstellar disks around B-type emission line stars, and what we can learn from that in a wider context. A forming disk comes with a unique photometric signature constraining the absolute gas density and density law in the disk. When the time evolution of this signature is undisturbed by additional events, it allows to measure the viscosity in the disk, as it builds up and decays, as well as to constrain the mass and angular momentum losses from the star during such an event. Considering that Be stars are near critical rotators, the angular momentum loss from the star must be driven by the angular momentum transport from the evolving stellar core to the surface, and in this way Be stars may be used to calibrate stellar internal mixing theory well beyond its current limits.

We present the area of theoretical computer science called formal methods. We survey several ways how formal methods can help to ensure correctness of software. Further, we describe techniques for analysis of systems featuring probabilistic phenomena, where we do not rely only on simulations but rather on rigorous analysis and discuss their potential advantages.

The cold gas reservoir in galaxies determines their star formation rates over cosmic time. However, measuring the amount of cold gas in a large sample of galaxies was difficult in observation. Lack of observation constraints, the understanding of gas evolution from simulations and semi-analytic modeling is strongly limited. Fortunately, an alternative method of using dust continuum as an indirect proxy for cold gas has been developed during the last few years, and can be applied to thousands of galaxies that have (sub-)millimeter observations. Here I introduce our A3COSMOS project: mining the ALMA Archive Automatically in the COSMOS field. We exploited the full public ALMA archive in COSMOS in a systematic and automated way, with detailed photometry and extensive Monte Carlo simulation verifications. A3COSMOS aims at obtaining ALMA continuum photometry for each star-forming galaxy that falls into public ALMA pointings in COSMOS, and also detect any galaxy that is not in optical/near-infrared/radio prior catalogs. This pipelined exploitation will be regularly updated with ingesting more data as it becomes available. With ~650 currently well-constrained galaxies from 800+ high confidence ALMA detections, I present the properties of these galaxies and the newly measured evolution of gas fraction (gas-to-stellar mass ratio) and depletion time (=Mgas/SFR). I will demonstrate how galaxies’ spectral energy distributions and photometric redshifts can be much improved with our ALMA photometry, and how galaxies’ gas masses can be differed due to conversion methods, as well as how our new results can more tightly constrain the gas evolution compared to literature works.

Jan Hendrik Oort:  75 years of passion for astronomy

Jan Hendrik Oort’s (1900-1992) professional life is part of the astronomical world heritage.

Part II will tell the most exciting stories of Oort’s research - the rotation of the Galaxy, the Crab nebula, the solar-system cloud of comets, and the boot strapping of radio astronomy - and delineate the links of his work to that of other famous astronomers of his time.

A long-standing question in galaxy evolution is how "red-and-dead" elliptical galaxies have been assembled. Thanks to the advancement of sensitive, wide-field near-infrared instruments in the past decade, we now know that such galaxies were already in place when the Universe was only a few billion years old. Their high stellar masses and low current star formation rates imply that they must have formed their stars very efficiently at z>2, and its star formation was rapidly shut down (“quenched”) thereafter. What is the physical process that quenches star formation at z~2? Active galactic nuclei feedback is the most commonly accepted interpretation, but its role in galaxy star formation remains controversial.

In this talk, I will review the evidence for early quenching in massive galaxies and the various quenching mechanisms proposed in literature. To address this decade-old puzzle, I will present new results from our multi-wavelength campaign of a sample of z~2 quiescent galaxies with ALMA, VLA and VLT, providing strong constraints on their stellar populations and interstellar medium.

Jan Hendrik Oort:  75 years of passion for astronomy

Jan Hendrik Oort’s (1900-1992) professional life is part of the astronomical world heritage.

Part I outlines Oort’s professional life with his seminal roles as founding father of radioastronomy in Europe and of a joint European optical observatory (ESO) as outstanding highlights.  It also gives an overview of the half dozen scientific fields which he influenced in a lasting fashion. These topics are nearly fully unrelated to one another, ranging from the solar system to the dynamics of the Milky Way and on to the large-scale structure of the Universe.  Oort’s achievements are interwoven into a unique network of 20th century astrophysics.  Very few people have similarly inspiringly combined unfiltered scientific curiosity with a firm, focused instinct for what is relevant and how it can be made bear fruit.

The rotation curve of the Galaxy is generally thought to be flat.However, using radial velocities of interstellar molecular clouds, which is common in rotation curve determination, seems to be incorrect and may lead to incorrectly inferring the shape of the rotation curve is flat. Tests, using photometric and spectral observations of bright stars as the rotation tracers are affected by motions of stars around local gravity centers and pulsation effects, seen in such early type objects, are difficult to betaken into account unless a lot of observing work is involved. I propose a method of studying the kinematics of the thin disc of our Galaxy outside the solar orbit in a way that avoids these problems. The proposed test is based on observations of interstellarCaII H and K lines which allow to determine both radial velocities and distances. The test was implemented using stellar spectra of thin disc stars at galactic longitudes of 135deg and 180deg. Using this method, I constructed the rotation curve of the thin disc of the Galaxy. The test leads to the obvious conclusion that the rotation curve of the thin gaseous galactic disk, represented by the CaII lines, is Keplerian outside the solar orbit rather than flat.

I will talk about a novel theory of dark matter superfluidity that matches the success of LCDM model on cosmological scales while simultaneously reproducing the MOND phenomenology on galactic scales.

I will introduce some results and on-going project of observing multiple transition isotopic lines of dense gas tracers toward nearby galaxies, which can help us to determine optical depth of dense molecular gas and other parameters.