Início » Ciência » Webinars » Apresentações » 2022
15/12 - 11:00 am
Cullan Howlett
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Cullan Howlett
Title
Cosmology and cosmography with galaxy peculiar velocity surveys (University of Queensland)
Abstract
Direct measurements of galaxy peculiar velocities, i.e., their motions with respect to us beyond that expected from just the expansion of the Universe, are undergoing a resurgence. Five years ago, individual surveys were limited to a few thousand galaxies and to within the z~0.05 Universe. With the newest state-of-the-art, the number of galaxies, and the cosmological volume they cover, will increase by more than an order of magnitude. In this talk I will present the motivation and mechanisms for carrying out these measurements, focusing on both how they can be used to provide more precise tests of General Relativity on large scales than are possible with just galaxy redshifts, and how they can be used to create detailed cosmographic maps of hidden structures in the nearby Universe. As an example, I will discuss the construction and new cosmological results from my recently released Sloan Digital Sky Survey peculiar velocity catalogue. I will finish the talk by highlighting the exciting upcoming results we expect from the next generation of peculiar velocity surveys being carried out with the Dark Energy Spectroscopic Instrument (DESI) and 4-Metre Multi-Object Spectroscopic Telescope (4MOST).
Slides not available
08/12 - 11:00 am
Claudia Maraston
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Claudia Maraston
Title
Stellar population models and clues to galaxy evolution (University of Portsmouth)
Abstract
Evolutionary population synthesis models describing the energetic emission and stellar mass distribution of galaxies and star clusters are the essential interpretative tool in astrophysics and cosmology. They are used to infer key properties of stellar systems (age, chemical composition, stellar mass, dark matter fraction) from data, to predict the spectral energy distribution of simulated galaxies, to trace galaxy ages as a function of cosmic time for constraining cosmology, to predict the number, mass and location of stellar remnants rooting gravitational waves. Given their widespread use, the accuracy of population synthesis models directly affect our understanding of galaxy formation and evolution in a cosmological context. I shall review progress and difficulties and discuss key applications of these models over cosmic time.
Slides not available
01/12 - 11:00 am
Ana Chies Santos
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Ana Chies Santos
Title
Globular cluster systems as probes of the build-up of galaxies and their environments (Federal University of Rio Grande do Sul)
Abstract
Globular clusters (GCs) are found in galaxies spanning a large range of masses, from giants to dwarfs, and because of their high surface brightnesses, they can be readily identified up to distances z~0.2 with the Hubble Space Telescope. The properties of GC systems are intrinsically connected to the assembly histories of their host galaxies, and they can be used as tracers of the total mass of their parent halos. Moreover, GCs are not only found in the bodies of their host galaxies but also free-floating in galaxy clusters, not necessarily bound to a host galaxy. In this talk, I will review the main properties of globular cluster systems across a range of masses and environments and present recent works from our group on the topic. I will show our current efforts to map GC systems through multi-band imaging around the surprisingly neglected nearby spiral galaxies, relic galaxies, and low surface brightness galaxies. I will finish by showing prospects for the field in the coming years with the new generation of ground-based surveys and space facilities.
Slides not available
17/11 - 11:00 am
Sebastian Bocquet
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Sebastian Bocquet
Title
Cluster Cosmology with the South Pole Telescope (Ludwig-Maximilians-University of Munich)
Abstract
Cluster Cosmology with the South Pole Telescope
Slides not available
10/11 - 01:00 pm
Pablo Santos-Sanz
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Pablo Santos-Sanz
Title
Unveiling the trans-Neptunian belt through thermal data and stellar occultations (Instituto de Astrofísica de Andalucía)
Abstract
Physical knowledge of trans-Neptunian objects (TNOs) and Centaurs has improved in recent years thanks to more sensitive observations of their thermal emission with the Spitzer and Herschel space telescopes. Thermal emission from TNOs/Centaurs has also been measured with ALMA, WISE, and other ground- and space-based radio facilities. These data allow, by means of thermal or thermophysical models, to obtain the diameters and albedos of these bodies with uncertainties of ~10% in diameters and ~20% in albedos. Thermal properties such as thermal inertia or surface roughness can also be obtained. In total, we have thermal measurements for ~180 TNOs/Centaurs, for which we have obtained equivalent diameters, albedos, and thermal properties. On the other hand, stellar occultations produced by TNOs and Centaurs are a very direct and elegant way to obtain sizes (with a few kilometers of uncertainty), shapes, and albedos of these bodies from the timing of a star disappearing and reappearing behind the object’s limb. In the last decade, it has been possible to predict and observe stellar occultations by TNOs/Centaurs thanks to the better knowledge of their orbits and the improvement of stellar positions from the available stellar catalogs. To date, stellar occultations produced by ~50 TNOs/Centaurs have been observed, obtaining an accurate determination of their sizes and albedos. Thermal emission is available for most of these ~50 objects. There is a clear synergy between thermal measurements and stellar occultations and it is possible to combine the results of both techniques to obtain a better physical and thermal characterization of these bodies.
Slides not available
20/10 - 11:00 am
Renu Malhotra
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Renu Malhotra
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Pluto near the edge of strong chaos (University of Arizona)
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Slides not available
13/10 - 11:00 am
Tessa Baker
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Tessa Baker
Title
Beyond standard sirens: gravitational wave cosmology without electromagnetic counterparts. (Queen Mary University of London)
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Slides not available
06/10 - 11:00 am
Sebastian Grandis
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Sebastian Grandis
Title
Towards robust cluster cosmological inference (University of Innsbruck)
Abstract
Number counts of galaxy clusters are a well established cosmological probe, which infers the cosmological model by measuring the abundance of clusters as a function of their mass and cosmic age. We review first the key ingredients for cluster cosmological inference, identifying two main regions of systematic uncertainty: cluster mass measurements and cluster selection modelling. Based on recent work for the South Pole Telescope and the Dark Energy survey cluster cosmological analyses, we present how to tackle these issues via a combination of Bayesian population modelling, cosmological volume hydrodynamical simulations and multi-wavelength observations. Finally, we outline how these new methods will lead to robust cluster cosmological inference in the age of the next generations surveys like eROSITA, Rubin, Euclid, and CMB-Stage IV.
Slides not available
29/09 - 10:00 am
Elisa Maria Alessi
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Elisa Maria Alessi
Title
Natural perturbations as allies to design deorbiting solutions to mitigate the space debris problem. (Istituto di Matematica Applicata e Tecnologie Informatiche)
Abstract
The aim of this presentation is to introduce the problem of space debris and the actions that the worldwide community is taking to mitigate it. I will focus in particular on the role of end-of-life disposal strategies and how natural perturbations and advanced mathematical tools can help to design orbital solutions to preserve the orbital regions around the Earth.
15/09 - 11:00 am
Vincent Desjacques
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Vincent Desjacques
Title
Dynamical friction on circular orbits (Technion)
Abstract
The gravitational field of a massive object moving in a discrete or continuous medium induces a density wake in that medium. Dynamical friction is the gravitational force exerted on the perturber as a result of the induced density fluctuation. The pioneering study of Chandrasekhar (1943) considered a perturber linearly moving in a collisionless medium. In this talk, I will present an analytic approach to the dynamical friction acting on circularly moving point masses in a gaseous medium. I will show how it can be extended to axion dark matter backgrounds. Some astrophysical implications will also be discussed.
Slides not available
08/09 - 11:00 am
Joel Johansson
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Joel Johansson
Title
Type Ia supernovae in the Infrared (Stockholm University)
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Slides not available
01/09 - 11:00 am
Pierluca Carenza
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Pierluca Carenza
Title
A glimpse of axion phenomenology in astrophysics (Stockholm University)
Abstract
The old and successful idea of using astrophysical systems as laboratories for fundamental physics is becoming extremely popular nowadays. Axions are a remarkable example of Feebly Interacting Particles playing an important role in astrophysical phenomena. It is well-known that stars are powerful axion factories, giving strong constraints on their properties. Aspects of the axion phenomenology in horizontal-branch stars and supernovae are reviewed.
25/08 - 11:00 am
Monica Valluri
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Monica Valluri
Title
Effects of coeval formation of supermassive back holes on box/peanut bulges (University of Michigan)
Abstract
Stellar bars are found in over 60% of disk galaxies in the local Universe and supermassive black holes (SMBH) are ubiquitous in most massive galaxies. Since bars can transport angular momentum outwards they have long been favored as a means to feed and grow SMBH. A previous generation of N-body simulations found that if a black hole grows in a barred galaxy after the bar forms and attains equilibrium, the SMBH weakens the bar. We find, on the contrary, that if an SMBH forms prior to the formation of the bar, or coevolves with it, it can strengthen both the bar and the boxy/peanut/X (BP/X) shaped bulge. We uses frequency analysis to uncover the role of resonances in the growth of the BP/X shape. We concluded that an SMBH that coevolves with the bar influences the dynamics well outside its nominal sphere-of-influence.
Slides not available
18/08 - 11:00 am
Diego Pallero
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Diego Pallero
Title
The quenching history of cluster galaxies in Hydrodynamical Simulations (Pontificia Universidad Católica de Chile)
Abstract
One of the fundamental problems in modern astrophysics is the understanding of the role that the environment plays in the galaxy evolution. Many works, both theoretical and observational, have focused on this topic. Nevertheless, it is not clear yet which are the main physical mechanisms that lead to the cessation of star formation, or quenching, in galaxies that reside in dense environments. State-of-the-art hydrodynamical simulations are perfect tools to study the evolution of galaxies in extremely dense environments such as galaxy clusters. Using both theoretically- and empirically- based definitions to select star-forming and passive (quenched) galaxies, we separate our sample into galaxies that suffer the largest effects on their star formation histories either inside or outside the cluster. We find that > 70% of galaxies are processed before they are accreted onto the clusters regardless of the cluster mass. However, most galaxies reach their quenching state in dense environments, several gigayears after this processing event, indicating that pre-processing plays an important role in establishing the time scales and the history of star formation quenching in massive structures. On the other hand, the definitive cease of star formation is mainly driven by an environmental effect; we find that there is a minimum threshold in the gas density of the ICM, of ρ(ICM) > 10^-28 gr cm^-3 to quench the star formation of galaxies. At this density, ram pressure becomes the dominant, and galaxies rapidly get depleted from their gas component. Typically, this threshold takes place near the cluster R200, regardless of cluster\\\'s M200.
Slides not available
11/08 - 02:00 pm
Andrea Buccino
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Andrea Buccino
Title
Magnetic activity cycles in solar-type stars and beyond (Universidad de Buenos Aires)
Abstract
The Mount Wilson survey is the most extended database to explore the long-term chromospheric activity in F to K stars. However, activity in southern late-type stars and beyond the convective limit (~M3.5) has not been extensively explored by this program. Over the last decade, new interest in M dwarfs has emerged. They are prime targets for current and upcoming exoplanet searches and characterization efforts, due to their ubiquity in the solar neighborhood and high occurrence rates of small exoplanets in the habitable zone. However, these stars can be very active and their activity signatures can hinder the detection of orbiting planets. To analyze the long-term activity in late-type stars near and beyond the convective limit, since 1999 the HKα Project has been operating in the Argentine CASLEO (Complejo Astronómico El Leoncito) observatory. We systematically observe more than 150 main-sequence southern stars from F3 to M5.5. To date, we have more than 6000 mid-resolution spectra, ranging from 389 to 669 nm, which constitute an ideal dataset to study long-term activity in cool stars. In this talk I will revise the main results of the HKα Project. First, I show evidence of cyclic activity for M dwarfs, including fully-convective stars. Then, I concentrate on multiple cycles in solar-type stars and the interpretation from the dynamo theory.
04/08 - 11:00 am
Marla Geha
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Marla Geha
Title
The SAGA Survey: Exploring Satellite Galaxies Around Milky Way Analogs (Yale University)
Abstract
The Milky Way\'s satellite galaxies provide critical clues to how low mass galaxies form and the nature of dark matter. Yet the Milky Way itself is a single realization of a Milky Way-mass galaxy halo. I will review recent studies of the Milky Way\'s satellite population and work to put the Milky Way\'s satellite galaxies in context, highlighting the SAGA Survey. The SAGA Survey aims to measure the distribution of satellite galaxies around 100 systems analogous to the Milky Way down to the luminosity of the Leo I dwarf galaxy. I will discuss results on the quenched fraction of satellites, luminosity functions, radial distributions and more, comparing to the Milky Way itself and predictions from simulation.
28/07 - 11:00 am
Sabrina Stierwalt
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Sabrina Stierwalt
Title
The Baryon Cycle in Dwarf-Dwarf Mergers: Fueling Hierarchical Assembly (Occidental College)
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Both cosmological simulations and observations of the ultraviolet luminosity function suggest dwarf galaxies are the dominant population at high redshifts and that the galaxy merger rate per unit volume is dominated by low mass galaxies. However, dwarf-dwarf interactions have not yet been subject to systematic study, even in the nearby universe. I will report on our efforts to do just that: TiNy Titans is the first systematic study of a sample of isolated interacting dwarf galaxies and the mechanisms governing their star formation. How much of what we know about massive galaxy mergers - triggering of starbursts, significant rearranging of gas & dust, AGN growth - occur in the shallower gravitational potential wells of dwarf galaxies? Do we observe these low mass mergers at the rate predicted by cosmological simulations? Do groups of only dwarf galaxies exist? I will also highlight our most recent results investigating the age and mass distributions of the star cluster populations in dwarf mergers as observed with high resolution Hubble imaging.
Slides not available
21/07 - 11:00 am
Rebecca Bowler
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Rebecca Bowler
Title
Galaxy evolution at high-redshifts (University of Manchester)
Abstract
Studying galaxies at ultra-high redshifts (z > 6) provides a unique insight into the early stages of galaxy formation and evolution. I will give an overview of how star-forming ‘Lyman-break’ galaxies are selected in the first few billion years, and what is known about their properties from multi-wavelength follow-up (e.g. from ALMA, Hubble). I will then show how samples of these objects can constrain the astrophysics at play in early galaxy formation through the observed shape and evolution of the luminosity function. I will end by looking forward to upcoming wide-area surveys from the Vera Rubin Observatory and Euclid, which, when combined with detailed follow-up (e.g. from JWST, ALMA) will provide a revolution in the understanding of early galaxy formation.
Slides not available
23/06 - 11:00 am
Danielle Leonard
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Danielle Leonard
Title
Understanding intrinsic galaxy alignments for weak lensing cosmology (Newcastle University)
Abstract
Weak gravitational lensing measurements are a key cosmological observable of current and upcoming large-scale imaging surveys. We typically measure weak lensing via the statistical correlations it induces in projected galaxy shapes and orientations. However, similar correlations can also be induced by other, local effects including tidal forces and galaxy evolution history. Though these correlations, known as intrinsic alignments, are generally subdominant to lensing, the incredible precision of upcoming surveys such as Euclid and the Rubin Observatory\'s LSST demands their careful treatment in order to avoid biasing cosmological results. In this talk, I will first review some basics of intrinsic alignments, then discuss ongoing work towards ensuring cosmological analyses are robust to this effect in current and upcoming surveys.
09/06 - 11:00 am
Susana Barros
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Susana Barros
Title
Tidal deformation and tidal decay of WASP-103c (Instituto de Astrofísica e Ciências do Espaço)
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Tidal forces between short-period planets and their host stars are extreme. These lead to the deformation of the planet and the shrinkage of the planet’s orbit. Using the new ESA mission CHEOPS we are attempting to measure both these effects for a sample of exoplanets. Measuring the tidal deformation of the planet would allow us to estimate the second degree fluid Love number and gain insight into the planet\\\\\\\'s internal structure. Measuring the tidal decay timescale would allow us to estimate the stellar tidal quality factor, which is key to constraining stellar physics. WASP-103 was our first since it had the largest estimated signature of the tidal deformation. I will present the first detection of the tidal deformation of a planet directly from its light curve. This allowed us to measure the Love number of WASP-103b. We also found a hint that the orbital period of WASP-103b is increasing contrary to what is expected from tidal decay. I will explore the scenarios that could explain these observations.
02/06 - 02:00 pm
Somayeh Khakpash
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Somayeh Khakpash
Title
Microlensing in the era of large surveys (University of Delaware)
Abstract
Microlensing can be used to discover exoplanets of a wide range of masses with orbits beyond ~1 AU and even free-floating planets. The Roman space mission will use microlensing to discover approximately ~1400 planets by monitoring ~100 million stars to find ~50000 microlensing events. Modeling each microlensing event, especially the ones involving two or more lenses, is typically complicated and time-consuming, and analyzing thousands of microlensing events is possibly infeasible using the traditional methods. In this presentation, I will introduce two large surveys including the Roman space mission and the Rubin LSST, and discuss their synergies and the tools under development to utilize the uniqueness of these two surveys.
26/05 - 02:00 pm
Sierra Villarreal
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Sierra Villarreal
Title
Extreme Scale Image Simulation Workflows for LSST DESC (Argonne National Laboratory)
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19/05 - 09:00 am
Véronique Buat
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Véronique Buat
Title
Dust and stars: an unavoidable and complex interplay (Laboratoire d’Astrophysique de Marseille)
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12/05 - 02:00 pm
Laure Ciesla
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Laure Ciesla
Title
Rewind: recovering the star formation histories and past properties of galaxies (Laboratoire d’Astrophysique de Marseille)
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Slides not available
28/04 - 11:00 am
Ummi Abbas
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Ummi Abbas
Title
Differential Astrometry with Gaia (INAF - Osservatorio Astronomico di Torino)
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07/04 - 11:00 am
Ana Carolina Lourenço
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Ana Carolina Lourenço
Title
Are there more jellyfish galaxies in merging clusters? (University of Valparaiso)
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31/03 - 11:00 am
Raffaella Margutti
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Raffaella Margutti
Title
Transient Sky in the New Era of Time Domain Multi-Messenger Investigations (University of California Berkeley)
Abstract
Astronomical transients are signposts of catastrophic events in space, including the most extreme stellar deaths, stellar tidal disruptions by supermassive black holes, and mergers of compact objects. Thanks to new and improved observational facilities we can now sample the night sky with unprecedented temporal cadence and sensitivity across the electromagnetic spectrum and beyond. This effort has led to the discovery of new types of astronomical transients, revolutionized our understanding of phenomena that we thought we already knew, and enabled the first insights into the physics of neutron star mergers with gravitational waves and light. In this talk I will review some very recent developments that resulted from our capability to acquire a truly panchromatic view of transient astrophysical phenomena. I will focus on two key areas of ignorance in the field: (i) What are the progenitors of stellar explosions and what happens in the last centuries before death? (ii) What is the nature of the compact objects produced by these explosions and what happens when compact objects merge? The unique combination of Discovery Power (guaranteed by planned transient surveys like LSST, combined with efforts in the realm of artificial intelligence) and Understanding (enabled by multi-messenger observations) is what positions time-domain astrophysics for major advances in the near future.
17/03 - 11:00 am
Niel Brandt
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Niel Brandt
Title
A Good Hard Look at Cosmic Supermassive Black-Hole Growth (The Pennsylvania State University )
Abstract
The 7 Ms Chandra X-ray Observatory exposure on the Chandra Deep Field-South (CDF-S) has provided the most sensitive extragalactic X-ray survey by a wide margin. About 1050 X-ray sources have been detected, primarily distant active galactic nuclei (AGNs) and starburst/normal galaxies. The unmatched deep multiwavelength coverage for these sources allows superb follow-up investigations, revealing the details of supermassive black-hole growth over most of cosmic time. I will briefly describe the sources in the 7 Ms CDF-S and highlight some exciting science results. The latter will include (1) measurements of long-term black-hole growth informed by galaxy morphological and physical measurements; (2) constraints upon black-hole growth in the first galaxies as revealed by direct detection and stacking; and (3) the discovery of representatives of a new population of faint, fast X-ray transient sources. Finally, I will discuss some future prospects for X-ray surveys of AGNs in the distant universe, including the recently completed 5 Ms XMM-SERVS survey of the LSST Deep Drilling Fields and new X-ray missions.
Slides not available
10/03 - 02:00 pm
Kyle Dawson
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Kyle Dawson
Title
The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Cosmological Implications from two Decades of Spectroscopic Surveys at the Apache Point observatory (University of Utah)
Abstract
The Extended Baryon Oscillation Spectroscopic Survey (eBOSS) concluded observations of the cosmic distance scale and the growth of structure in February, 2019. The three dimensional clustering in all samples from the Sloan Digital Sky Survey (SDSS) was used to make 15 distinct, high precision measurements of Baryon Acoustic Oscillations (BAO) to an effective redshift z<2.4 and six measurements of redshift space distortions (RSD) to z<1.5. With this redshift coverage and sensitivity, the SDSS experiment is unparalleled in its ability to explore models of dark energy. Using available cosmological samples, we provide new constraints on the cosmological model with an emphasis on the role of the final BAO and RSD clustering measurements in advancing the cosmological model. In this talk, I will give a brief overview of the BAO and RSD measurements and present the highlights of the advances in modeling dark energy, the local expansion rate, tests of general relativity, neutrino masses, and the overall cosmological model.
10/02 - 11:00 am
Michelle Lochner
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Michelle Lochner
Title
Anomaly Detection in Astronomical Data using Machine Learning (University of the Western Cape)
Abstract
The next generation of telescopes such as the SKA and the Vera C. Rubin Observatory will produce enormous data sets, far too large for traditional analysis techniques. Machine learning has proven invaluable in handling large data volumes and automating many tasks traditionally done by human scientists. In this talk, I will discuss how machine learning for anomaly detection can help automate the process of locating unusual astronomical objects in large datasets thus enabling new cosmic discoveries. I will introduce Astronomaly, a general purpose framework for anomaly detection in astronomical data using active learning and overview some recent results.