Lund Observatory

department of Astronomy and Theoretical Physics

Seminars at Lund Observatory

Astronomy seminars are given in English. They are open to all, but aimed at an audience with basic knowledge in astrophysics. Unless otherwise noted, seminars take place on Thursdays 14:15 in Lundmarksalen.

Autumn 2018

Licenciate thesis defence
Thursday 09:00
Noemi Schaffer
Dust dynamics in protoplanetary disks
2018-09-20 Steven Longmore
Liverpool John Moores University
Star formation in the Galactic Centre
Abstract: The unknown physics of star formation and feedback represent the main bottleneck in connecting the observable galaxy population to cold dark matter cosmology. Both physical processes are expected to vary strongly with galactic environment and across cosmic history. I will discuss recent progress in understanding the physics of star formation and feedback in the inner few hundred pc of the Milky Way - the Central Molecular Zone (CMZ) - an environment with gas properties very similar to those in starbursts and high-z galaxies, in which most stars in the Universe formed. Within our lifetime, the CMZ is the only such environment for which it will be possible to simultaneously resolve the gas properties down to the size scales of individual (forming) stars, while also tracing galactic-scale processes, making it a critical benchmark for studies of star and planet formation, feedback, and the interstellar medium across cosmic time. I will focus on recent work seeking to explain a puzzling observational paradox: the vast majority of gas in the CMZ is underproducing stars by 1-2 orders of magnitude compared to empirical star formation relations and theoretical predictions, and yet at the same time a very small fraction of the gas is producing the most violent star formation events in the Galaxy. I will discuss the implications of these findings for environmentally (in)dependent star and planet formation relations/theories and the environment into which supernovae explode. I will finish by outlining the details of a model linking the emerging, multi-scale picture of star formation and feedback to a more general understanding of the mass flows and energy cycles in (extra) galactic nuclei.
Friday 10:30
Steven Longmore
Liverpool John Moores University
Using machine learning to identify animals from drones
Abstract: The World Wildlife Fund for Nature (WWF) estimates that up to five species of life on our planet become extinct every day. This astonishing rate of decline has potentially catastrophic consequences, not just for the ecosystems where the species are lost, but also for the world economy and planet as a whole. Indeed, biodiversity loss and consequent ecosystem collapse is commonly listed as one of the 10 foremost dangers facing humanity, and most pressingly in the developing world. There is a fundamental need to routinely monitor animal populations over much of the globe so that conservation strategies can be optimized with such information. The challenge faced to meet this need is considerable. To date most monitoring of animal populations is conducted manually, which is extremely labour-intensive, inherently slow and costly. Building on technological and software innovations in astronomy and machine learning, we have developed a drone plus thermal infrared imaging system and an associated automated detection/identification pipeline that has the potential to provide a cost-effective and efficient way to overcome this challenge. I will describe the current status of the system and our efforts to enable local communities in developing countries with little/no technical background to run routine monitoring and management of animal populations over large and inhospitable areas and thereby tackle global biodiversity loss.
2018-09-27 Jeremy Fensch
European Southern Observatory
Gas fraction of galaxies and impact of mergers across cosmic times
Abstract: The recent acceleration in millimeter astronomy with ALMA has shown that the gas mass fraction of galaxies is an increasing fonction of redshift, until at least z=3 (Combes et al., 2013). In particular, the bulk of star-forming galaxies at z = 2, the peak of the cosmic star formation history, typically have a molecular gas mass fraction above 50% of their total baryonic mass. These gas-dominated galaxies present different physical properties from local disk galaxies, such as a high gas turbulence (~ 40 km/s) and a clumpy UV morphology (see e.g. Guo et al., 2014, 2015). We use parsec-scale hydrodynamical simulations of isolated and interacting galaxies with different gas fractions to study the impact of the gas fraction parameter on the conditions of star formation on galactic scales. We first show that the high gas fraction major mergers do not show a high star formation rate enhancement, contrarily to local gas-poor major mergers. This is mainly due to a saturation of the turbulence, whose initially high level can barely be increased by the interaction. This provides an explanation for the observed decreasing efficiency of merger-driven starburst with redshift (Rodighiero et al., 2011). We also show that that mergers of gas-dominated galaxies do not trigger much gas fragmentation, which suggests that major mergers are not a major channel of formation of star clusters at z > 2. Last but not least, detailed simulations of disk instabilities during interactions of intermediate-redshift type gas fraction disks (gas mass fraction of 30%, typical of z=0.7) show the formation of massive young stellar clumps, similar to the ones observed in isolated z=2 type galaxies. This work in progress could provide an explanation to the increased clumpiness observed for starbursting galaxies at this redshift in the COSMOS field (Calabro et al., in prep.).
ATP talk
Wednesday 15:15
Oscar Agertz
The edge of galaxy formation
2018-10-04 Katarina Kraljic
Galaxy evolution in the metric of the cosmic web
Abstract: The strikingly anisotropic large-scale distribution of matter, the so-called cosmic web, is made of an extended network of voids delimited by sheets, themselves segmented by high-density filaments, within which matter flows towards compact nodes where they intersect. Do the properties of galaxies, such as e.g. their morphology, retain a memory of these large-scale cosmic flows from which they emerge? And what are the signatures of this environment at different locations within the cosmic web? In this talk, I will address these questions using the set of observed and virtual galaxies, from the spectroscopic survey GAMA and large-scale hydrodynamical simulation HORIZON-AGN, respectively. I will argue that on top of stellar mass and large-scale density, the traceless component of the tides from the anisotropic large-scale environment also shapes galactic properties. I will show that these results can be qualitatively explained in terms of anisotropic assembly bias by an extension of excursion theory.
2018-10-11 Giovanna Tinetti
University College London
A chemical survey of planets in our galaxy
Abstract: Thousands of exoplanets have now been discovered with a broad range of masses, sizes and orbits: from rocky Earth-size planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. Work in exoplanet spectroscopy with current instruments has thus far been very piecemeal and mainly focused on gaseous planets. The launch of the James Webb Space Telescope next year will permit for the first time the remote exploration of smaller planets: super-Earths and sub-Neptunes. However, progress with the science questions spelled out above demands a very large, unbiased spectroscopic survey of exoplanets. In the next decade new dedicated space missions, such as the ESA's next medium-class science mission ARIEL, have been conceived to conduct such a survey and to explore the nature of exoplanet atmospheres and, through this, the key factors affecting the formation and evolution of planetary systems in our galaxy.
2018-10-18 Melvyn B. Davies
The Astrophysics of Stellar Clusters
Abstract: Stellar clusters are common. Globular clusters contain some of the oldest stars, whilst the youngest stars are found in OB associations or in other clusters associated with recent star formation. Such crowded places are hostile environments: a large fraction of stars will collide or undergo close encounters. I will explain how stellar clusters are factories for producing exotic objects, including back hole binaries which spiral together and merge as they emit gravitational waves. I will consider how supermassive black holes may form and grow within the nuclear stellar clusters located at the very centres of galaxies. I will also discuss how planetary systems similar to our own solar system are vulnerable within stellar clusters due to interactions with other stars.
2018-10-25 Chris Belczynski
Nicolaus Copernicus Astronomical Center, Warzaw
Gravitational-wave Astrophysics: BH-BH/NS-NS mergers with LIGO/Virgo
Abstract: I will discuss the astrophysical importance of the recent LIGO/Virgo direct detections of gravitational-waves. Despite the fact that massive BH-BH dominance in gravitational-wave signal was predicted prior the detections, it is not at all clear which one of the several formation scenarios produces these massive mergers. This inhibits astrophysical information inference from LIGO/Virgo observations, as conclusions are different within each formation scenario. There is quite an opposite problem with the recent detection of NS-NS merger in an old elliptical host galaxy. None of the formation channels that can reproduce basic properties of the detected BH-BH mergers, can recover the NS-NS merger rate estimated by LIGO/Virgo. Despite the fact that the exact origin of LIGO/Virgo sources is not yet known, several astrophysical implications are beginning to emerge.
ATP talk
Wednesday 15:15
Victor Olariu
Multi-scale dynamical modelling of early T-cell precursor commitment
2018-11-01 Andrew Cameron
University of St Andrews
Why doomed hot Jupiters are most easily found when young.
Abstract: Massive planets in close orbits around their host stars undergo tidal orbit decay at a rate that increases with planet mass and proximity to the host star. The upper left-hand corner of the mass-separation diagram is visibly depleted as a result. By modelling the underlying population it's possible to calibrate the strength of the tidal interaction from the location of the boundary. The model has some curious features. The probability of seeing a planet today depends on how much its migration has sped up since birth, as well as the probability density for its birth location. Batches of planets formed recently at a given location haven't yet been spread out by the accelerating flow, whereas older batches from further upstream have a more thinly-spread probability density. I'll show how this explains some curious features of the hot-Jupiter population and their host stars.
2018-11-08 Ravit Helled
University of Zurich
Understanding Jupiter, the Solar System's Gas Giant
Abstract: Giant planets are thought to have cores in their deep interiors, and the division into a heavy-element core and hydrogen-helium envelope is applied in both formation and structure models. I will briefly discuss the standard model for giant planet formation, and will show that the primordial internal structure of giant planets depends on their formation location and growth history. I will present a new formation scenario for Jupiter that is consistent with cosmochemical constraints, and discuss the expected primordial internal structure of Jupiter from recent formation and evolution models (fuzzy core, inhomogeneous interior). Finally, I will discuss the importance of these results for interpreting the measurements of the Juno (NASA) mission, and for giant exoplanets characterization.
2018-11-15, 13:30 Brian Thorsbro
Licenciate thesis defence
ATP talk
Wednesday 15:15
Stefan Prestel
Precision calculations in HEP event generators
2018-11-29 Gregor Traven
Binary stars in the era of data-driven astronomy
Abstract: Binary stars offer exceptional insight to star formation and evolution, establishing distances across the Galaxy and beyond, providing critical tests in asteroseismology, and furnishing benchmark systems with accurate fundamental stellar properties. The list goes on, and although no one disputes the astrophysical importance of multiple systems, they are often overlooked simply because their nature can be quite effectively concealed in observational data. However, the advances in machine learning, and the unprecedented volume of stellar spectra from modern surveys, enable us to devise new approaches for discovery and characterisation of these fascinating associations of stars. I will present some efforts towards a better understanding of large samples of binary stars in the GALAH spectroscopic survey. The discussion will range from efficient discovery of double-lined spectroscopic binaries with the help of a general dimensionality reduction technique t-SNE, to deriving the basic stellar parameters of both stars in a binary system. The latter is mostly based on a data-driven technique The Cannon, complemented by a Bayesian analysis of an ensemble of available photometric and astrometric data, fournishing reliable estimates of another fundamental property, the stellar radius. I'll show how the derived parameters can be used to explore the initial properties of analysed binary systems using a fast binary evolution algorithm BSE.
2018-12-06 Benjamin Ragan-Kelley
Jupyter: facilitating interactive, open, and reproducible science
ATP talk
Wednesday 15:15

Spring 2018


PhD seminars

2018-01-25 Mirek Giersz
Black holes in stellar clusters
2018-02-01 Jayne Birkby
New frontiers in exoplanet characterisation
Exoplanet characterization is undergoing a rapid evolution, especially in the study of exoplanet atmospheres. I will discuss the very latest results from both space and ground-based observations and highlight how they are helping us to understand exoplanet origins and diversity. I will focus part of my talk on high-resolution spectroscopy, which is a robust and powerful tool in exoplanet characterization. It uses changes in the Doppler shift of a planet to disentangle its spectrum from the glare of its host star. The technique is sensitive to the depth, shape, and position of a planet’s spectral lines, and thus reveals information about the planet’s composition, atmospheric structure, mass, global wind patterns, and rotation. I will present MEASURE: the MMT Exoplanet Atmosphere SURvEy. This 40 night survey is the largest high-resolution study of exoplanet atmospheres to date. It contains spectra of exoplanets from hot Jupiters to warm Neptunes, both transiting and non-transiting, observing both their dayside and nightside thermal emission. I will describe the survey and present some of its exciting preliminary results. The survey not only enables a homogenous dataset to perform comparative exoplanetology, but provides complementary high-resolution spectra for exoplanets observed with HST and Spitzer. The combination of high- and low-resolution spectroscopy can provide stringent constraints on planet metallicity and C/O ratios, and signifies the next step in the detailed characterization of exoplanet atmospheres.

The Dynamical Universe for ALL

2018-02-08 Beibei Liu
Understanding the formation and evolution of super-Earth planets
Disk migration theory predicts that super-Earth planets would end up at resonance. However, the Kepler mission has found that the period ratios of these planets do not show strong pile-ups near mean motion resonances (MMRs). Here I explain a mechanism, magnetospheric rebound that can rearrange the orbits of the resonant planets during the disk dispersal phase. We conduct N-body simulations of two-planet systems and investigate under which conditions planets can escape resonances. Meanwhile, I will present a possible scenario for the formation of TRAPPIST-1. The system contains a 0.08 solar-mass star and 7 Earth planets within 0.1AU. In our scenario, planetesimal is formed at the snow line by streaming instabilities. Further mass growth is lead by efficient accretion of mm to cm-size pebbles that drifted from the outer disk. In this way, the disk solid mass is able to efficiently transferred into the planet masses.
2018-02-15 Ariel Goobar
Cosmic transparency and the dimming of standard candles
Accurate accounting for the dimming of light along the line of sight for distant sources is of great importance in astronomy. Furthermore, it is an essential step in the measurements of cosmological distances used to probe the cosmic composition. In spite of the great success in the last two decades in the use of Type Ia supernovae to measure the properties of the accelerating universe, understanding the wavelength dependence of the extinction in the supernova host galaxies has remained elusive. I will explain why this has been a puzzle and present a possible solution. A measurement of the transparency of the intergalactic medium will be discussed
2018-02-22 Marie Martig
Liverpool John Moores University
The structure of galactic thick disks
ATP talk
Wed. 15:15
Johanna Larsson
How does the culture of physics affect physics teacher education?

COMPUTE Winter meeting

2018-03-08 Fabio Antonini
University of Surrey
Nuclear clusters and (supermassive) black holes
ATP talk
Wed. 15:15
Johan Thoren
Colors in QCD
2018-03-15 Hiranya Peiris
Towards fundamental physics from cosmological surveys
Wed. 14:15
Gillian Nave
Spectra of Th/Ar and U/Ne hollow cathode lamps for spectrograph calibration
PhD defence, 09:00
Asli Pehlivan Rhodin
Experimental and computational atomic spectroscopy for astrophysics
COMPUTE seminar Mon. 14:15
Martin Turbet
Exploring the diversity of planetary atmospheres with Global Climate Models
More than 50 years ago, scientists created the first Global Climate Models (GCMs) to study the atmosphere of the Earth. Since then, the complexity and the level of realism of these models (that can now include the effect of oceans, clouds, aerosols, chemistry, vegetation, etc.) have considerably increased. The large success of these models have recently motivated the development of an entire family of GCMs designed to study extra-terrestrial environments in our solar system (Venus, Mars, Titan, Pluto) and even beyond (extrasolar planets).
I will first show various GCM applications on Venus, Mars, Titan and Pluto. Solar system GCMs successes and sometimes failures teach us useful lessons to investigate and possibly predict the possible climates on planets where no (or almost no) observations are available. I will then present several examples of studies recently performed using a 'generic' Global Climate Model developed at the Laboratoire de Météorologie Dynamique in Paris, designed to explore the possible atmospheres and the habitability of ancient planets or extrasolar planets.
Wed. 14:15
Ivan Minchev
AIP, Potsdam
Semi-empirical estimation of stellar birth radii and the time evolution of the Milky way ISM abundance gradients
Licenciate defence, Thursday 10:00
Iryna Kushniruk
Searching for kinematic structures in the Solar neighbourhood
ATP talk
Wed. 15:15
Holly Capelo
Fluid instability in the particle stream of a dilute-gas flow: experiments in connection with planetesimal formation
Abstract: For the past half century, the origin of planetary precursor bodies - planetesimals- has remained an open and challenging question. Breakthrough theoretical studies have established that particle-gas-drag induced fluid instabilities are an efficient way to concentrate solid particles in the process of planet formation. I will introduce an experimental facility that was designed to provide the first empirical tests of whether such fluid instabilities exist and if they are as robust as numerical simulations suggest that they should be. I will present experimental results demonstrating evidence for a fluid instability in a low-pressure dust-gas mixture.

Bayes Day meeting

Nik Piskunov
How to get a transmission spectrum of an exoplanet from observations?
Abstract: Extracting a transmission spectrum from observations is not easy. The projected area of a planetary atmosphere on its host star is small while the S/N of individual observations is limited by the planet motion. I will present possible methodology and a few numerical and real data tests supporting feasibility of such measurements with soon-available ground- and space-based instruments.
Lennart Lindegren
Gaia DR2
Wed. 10:30
Christine Borgman
The durability and fragility of knowledge infrastructures: lessons learned from astronomy
Abstract: Infrastructures are not inherently durable or fragile, yet all are fragile over the long term. Durability requires care and maintenance of individual components and the links between them. Astronomy is an ideal domain in which to study knowledge infrastructures, due to its long history, transparency, and accumulation of observational data over a period of centuries. This talk draws upon a long-term study of scientific data practices to ask questions about the durability and fragility of infrastructures for data in astronomy. Methods include interviews, ethnography, and document analysis. As astronomy has become a digital science, the community has invested in shared instruments, data standards, digital archives, metadata and discovery services, and other relatively durable infrastructure components. Several features of data practices in astronomy contribute to the fragility of that infrastructure. These include different archiving practices between ground- and space-based missions, between sky surveys and investigator-led projects, and between observational and simulated data. Infrastructure components are tightly coupled, based on international agreements. However, the durability of these infrastructures relies on much invisible work – cataloging, metadata, and other labor conducted by information professionals. Our research in astronomy seeks general lessons for science in the stewardship of data and the sustainability of knowledge infrastructures.
COMPUTE seminar Tue 10:30
Alice Quillen
Astro-viscoelastodynamics or Soft Astronomy: Tidal encounters, tidal evolution and spin dynamics
Abstract: Mass spring models, originally developed for graphics and gaming applications, can measure remarkably small deformations while conserving angular momentum. By combining a mass spring model with an N-body simulation, we simulate tidal spin down of a viscoelastic moon, directly tying simulated rheology to orbital drift and internal heat generation. I describe a series of applications of mass spring models in planetary science. Close tidal encounters among large planetesimals and moons were more common than impacts. Tidal encounters can induce sufficient stress on the surface to cause large scale brittle failure of an icy crust. Strong tidal encounters may be responsible for the formation of long chasmata in ancient terrain of icy moons such as Dione and Charon. The new Horizons mission discovered that Pluto and Charon’s minor satellites Styx, Nix, Kerberos, and Hydra, are rapidly spinning, but surprisingly they have spin axis tilted into the orbital plane (they have high obliquities). Simulations of the minor satellites in a drifting Pluto-Charon binary system exhibit rich resonant spin dynamics, including spin-orbit resonance capture, tumbling resonance and spin-binary resonances. We have found a type of spin-precession mean-motion resonance with Charon that can lift obliquities of the minor satellites in the Pluto/Charon system.
ATP talk
Wed. 15:15
Najmeh Abiri
"Nothing" better exists with deep learning

Kallen symposium: Exoplanets towards the future

Master seminar
Mon. 09:15
Erik Dahlof
Master seminar
Mon. 11:15
Linn Eriksson
Master seminar
Mon. 14:15
Maria Lomaeva
Master seminar
Tue. 13:15
Sofia Savvidou
Master seminar
Tue. 15:15
Eric Andersson
Dave Armstrong
Circumbinary planets: detection and populations
Jon Holtzman
New Mexico State University
Chemical Cartography of the Milky Way Disk with SDSS/APOGEE
Abstract: The SDSS Apache Point Observatory Galactic Evolution Experiment (APOGEE) has collected high resolution near-IR spectra of several hundred thousand stars across the Milky Way. I'll describe some observational results about the spatial variation of chemical abundances as a function of Galactocentric radius and distance from the midplane, discussing mean abundances, metallicity distribution function, and the variation of abundance ratios of multiple elements. Additional information related to stellar ages can be obtained from [C/N] for red giant stars. Several lines of evidence suggest that radial migration has had a significant impact on the Galactic disk.
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