Upcoming Talks

Protoplanetary discs serve as the cradle for planetary formation and evolution. It is then fundamental to study their evolution to gain a comprehensive understanding of exoplanetary system formation. These discs can be studied using two distinct approaches.

On one side, they can be analysed as a set of single sources, allowing for a detailed analysis of the mechanisms behind the diversity of observed morphologies using gas and dust tracers such as rings, gaps and asymmetries.

On the other side, it is crucial to study star-forming regions, understanding which physical processes are governing the global disc evolution.

In this talk, I will firstly describe results from the modelling of single sources, underlining the information we can obtain by comparing multi-wavelengths observations with results from the hydrodynamical models of specific sources (e.g., HD169142 , PDS70, GG Tau A). In particular, I will focus on how simulations can help in constraining the mass and position of the candidate proto-planets that may be responsible for the ALMA and SPHERE observational results, as well as how they can support future observational strategies.

I will then summarize some of the results obtained by testing disc evolution models by comparing them with the Lupus star forming region. In these works, we tested the secular evolution of the observed dust and gas radius of disc populations and their ratio, to test the efficiency of radial drift and the viscous evolution theory.

• Speaker: Claudia Toci (ESO)
• Tuesday 27 February 2024, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Emily Sandford.

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The Square Kilometre Array (SKA) will be the largest interferometric radio telescope to date, with unprecedented resolution and sensitivity to study various phenomena of the universe. In data processing pipelines for radio telescopes, real time calibration, such as beam former and pointing offset calibration, are crucial for obtaining high-quality interferometric data from the observations. As an example, I will discuss the design and ongoing implementation of the pointing offset calibration pipeline within SKA ’s data processing software, describing the steps carried out to integrate the pipeline into telescope execution control and data queue system, as well as outlining challenges and greater implications on the data processing algorithm and software within the radio astronomy community.

• Speaker: Dr. Ying-He Celeste Lü (Cavendish Astrophysics)
• Tuesday 27 February 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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CubeSats stand at the forefront of the New Space revolution, a paradigm shift in space exploration characterised by reduced launch costs and increased accessibility to space. These miniature satellites, defined by their standardised dimensions and modular design, have emerged as a pivotal technology with some implications of research in astronomy. With their standardised dimensions and modular design, these small satellites enable a wide range of experiments that were previously the domain of larger, more costly missions. In my talk, I aim to introduce you to valuable opportunities that can emerge by leading a CubeSat project with special interest in payloads dedicated to astrophysics research. As a cost-effective space instrument, CubeSats unlock observational windows across the ultraviolet, far-infrared, and low-frequency radio spectra, which are inaccessible from Earth’s surface. Beyond their technical capabilities, these satellites enable sustained observations of celestial bodies over extended periods, free from the scheduling constraints of larger telescopes.

• Speaker: Dolev Bashi
• Tuesday 05 March 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Dolev Bashi.

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Abstract not available

• Speaker: Jean-Luc Lehners (MPI for Gravitational Physics, Potsdam)
• Monday 13 May 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

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The Square Kilometre Array (SKA) will be the largest interferometric radio telescope to date, with unprecedented resolution and sensitivity to study various phenomena of the universe. In data processing pipelines for radio telescopes, real time calibration, such as beam former and pointing offset calibration, are crucial for obtaining high-quality interferometric data from the observations. As an example, I will discuss the design and ongoing implementation of the pointing offset calibration pipeline within SKA ’s data processing software, describing the steps carried out to integrate the pipeline into telescope execution control and data queue system, as well as outlining challenges and greater implications on the data processing algorithm and software within the radio astronomy community.

• Speaker: Celeste Lu (Cavendish Astrophysics)
• Tuesday 27 February 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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It has been suggested that the effects of renormalization significantly reduce the amplitude of the inflationary spectra at scales measurable in the cosmic microwave background. Via a gauge-invariant analysis, we compute the renormalized scalar and tensor power spectra and follow their evolution in an inflating universe that undergoes a transition to an FRW phase with a growing horizon. For perturbations originating from Minkowski vacuum fluctuations, we show that the standard prediction for the spectrum on superhorizon scales is a late-time attractor, while it is UV finite at all times. Our result is independent of the equation of state after inflation, showing that the standard prediction is fully robust.

• Speaker: Silvia Pla Garcia (King's College London)
• Monday 26 February 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

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Field theoretic descriptions are a powerful tool to capture the emergent, collective behaviour of strongly correlated many body systems on large scales. Gauge field theories in particular are of special interest in modern physics, due to their connection to topological behaviour and fractionalisation. Through this modelling, the original dense system of strongly interacting degrees of freedom can be interpreted as an emergent vacuum with quasiparticle excitations whose properties are closely related to the nature of the emergent gauge fields. This change in perspective affords us an unprecedented insight into the properties of these systems and in predicting new behaviour. We will review some of these concepts in a model and material that has become a paradigmatic case in point: spin ice. We shall further discuss how microscopic details can lead to surprisingly important effects in the cooperative dynamics of these systems, which becomes underpinned by near-fractal structures.

• Speaker: Claudio Castelnovo (Cavendish)
• Wednesday 21 February 2024, 14:00-15:00
• Venue: MR2.
• Series: Theoretical Physics Colloquium; organiser: Hannah Banks.

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In a recent paper we presented pop-cosmos, a state-of-the-art stellar population synthesis (SPS) framework. We described the details of how we fitted this framework to a large, deep, flux-limited (r < 25) sample of galaxies from the Cosmic Evolution Survey (COSMOS), enabling investigation of the full web of dependencies between different galaxy properties for the first time. In this talk I will present my recent work investigating the star formation histories (SFHs) of galaxy populations up to z=4 utilising the pop-cosmos model. I will begin by summarizing the details of our model and the SFH prescription employed in it. I will then present key galaxy evolution results such as the mean stellar mass assembly histories of galaxy populations through cosmic time. Further, by defining star-forming and quiescent subpopulations based on recent star formation activity (i.e. last 100 Myr), these relations will highlight how these subpopulations build up their stellar mass.

• Speaker: Sinan Deger
• Wednesday 21 February 2024, 13:40-14:05
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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European Space Agency recently adopted the Laser interferometry space antenna (LISA) to launch it in the 2030s to observe Gravitational waves (GWs) in the millihz frequency band. LISA ’s primary sources are massive black hole binaries (MBHBs) of 104-108 solar masses due to the merger of galaxies, stellar-mass BHs coalescence into their galactic central MBH , and numerous white dwarf binaries that exist in the Milky Way. I focus on MBH Bs that usually require an environment consisting mainly of gas and stars to merge within the Universe’s lifetime. I primarily consider the effects of a gas accretion disc for a sub-pc separation as it can significantly torque the binary to affect the initial binary parameters in the LISA band, especially orbital eccentricity. While gas perturbations become sub-dominant to GWs a few years before the merger of MBH Bs, they can still cause detectable phase shifts and excite observable eccentricities for reasonable disc properties that hint toward their history before reaching the millihz band. I will use analytical and numerical techniques to show the minimum measurable eccentricity of an MBHB that LISA will measure in a vacuum and gas. To be robust, I consider a high-order post-Newtonian gravitational waveform model, LISA ’s motion in its orbit around the Sun, and the time delay interferometery to enhance astrophysical signal over the dominant laser noise. I also explore if a weak gas effect can be mimicked by a small eccentricity and vice versa to motivate synergies between LISA and electromagnetic observations to unlock mysteries of the MBHB evolution.

• Speaker: Mudit Garg (University of Zurich)
• Friday 23 February 2024, 13:00-14:00
• Venue: Potter room/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Xi Tong.

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Measurements of the clustering of large scale structure can place strong constraints on our understanding of cosmology. However, many of our predictions of non-linear structure formation are based on gravity only (i.e. dark matter only) N-body simulations because the simultaneous modelling of lengths scales from a few parsecs for star formation to 100s of megaparsecs for the cosmic web is a prohibitively expensive process. In order to address any potential systematics arising from the neglect of baryons, we have performed a suite of cosmological, fully hydrodynamic simulations called the FLAMINGO simulations. Using these simulations, we have created realistic mock catalogues for the SDSS DR12 CMASS galaxy sample, a sample that is often used to derive cosmological constraints. From these catalogues we measure the projected correlation function, monopole and quadrupole correlation functions and compare these to observations to provide a bound on the impact of baryons on large scale structure cosmology. We further investigate the effect of assuming different models for AGN feedback and star formation.

• Speaker: Juliana Kwan (DAMTP)
• Monday 19 February 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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Radio observations of the neutral hydrogen signal from the Cosmic Dawn and Epoch of Reionisation have helped to provide constraints on the properties of the first stars and galaxies. Since this global 21-cm cosmological signal from the Cosmic Dawn is effectively constant on observing timescales and since effects resulting from systematics will vary with time, the effects of these systematics can be mitigated without the need for a model of the systematic. In this talk I will present a method to account for unmodelled time-varying systematics in 21-cm radio cosmology experiments using a Gaussian process method to account for correlations between time bins in a fully Bayesian way. I will finally present a further method using Gaussian process regression to calculate a mean fit to the residuals over time, providing a basis for producing a model of the time-varying systematic.

• Speaker: Christian Kirkham (University of Cambridge)
• Wednesday 21 February 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.

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In our quest to find other Earths, we’ve uncovered an extraordinarily diverse set of outcomes of the star-planet formation process, far beyond our imagination, and yet we have still barely scratched the surface of what we can learn about this eclectic zoo of other worlds. While exoplanet hunters continue the search for the nearest Earth twins, our last decade of study has pushed to understand the atmospheres of these new planets, and how their climate physics and chemistry respond to the environment created by their parents stars. In this talk, I will demonstrate how new instrumentation, high in resolution, precision, and contrast is pushing our understanding of exoplanet atmospheres to increasing detail. I’ll discuss studies of gas giants as well as the crucial preparation we are doing to find biosignatures on nearby rocky worlds with the Extremely Large Telescopes. Finally, I will demonstrate our recent work on techniques to map out storms in giant exoplanet atmospheres, and end by discussing the next phase of exoplanet observations that aim to reveal the surface interactions of rocky exoplanets.

• Speaker: Jayne Birkby (University of Oxford)
• Thursday 15 February 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

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Long-period transiting exoplanets are incredibly important, allowing us to study planets with temperatures similar to those in our own solar system. However, due to its observing strategy, the Transiting Exoplanet Survey Satellite (TESS) is heavily biased towards the discovery of short-period planets. To increase the yield of long-period planets, I am using TESS “duotransits” – planet candidates with two observed transits separated by a large gap, typically two years. From the two non-consecutive transits, the period of the planet is unknown, but there exists a discrete set of period aliases. As a member of the CHaracterising ExOPlanet Satellite (CHEOPS) Duotransit Program, I perform targeted follow-up of TESS duotransits to recover their true periods. To identify the best targets for CHEOPS follow-up, I developed a specialised pipeline to discover TESS duotransits. In this seminar, I will present my pipeline, its five discoveries and the sample of small, long-period planets being uncovered by TESS and CHEOPS , including the Neptune-mass planet TOI -5678 b and the bright multi-planet system HD 15906 .

• Speaker: Amy Tuson (Cavendish)
• Tuesday 20 February 2024, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Emily Sandford.

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We present the first effective-one-body model for generic-spins quasicircular black-hole–neutron-star (BHNS) inspiral-merger-ringdown gravitational waveforms (GWs). Our model is based on a new numerical-relativity (NR) informed expression of the BH remnant and its ringdown. It reproduces the NR (ℓ, m ) = ( 2, 2 ) waveform with typical phase agreement of ≲0.5 rad ( ≲1 rad) to merger (ringdown). The maximum (minimum) mismatch between the (2, 2) and the NR data is 4% (0.6%). Higher modes (HMs) (2, 1), (3, 2), (3, 3), (4, 4), and (5, 5) are included, and their mismatch with the available NR waveforms are up to (down to) a 60% (1%) depending on the inclination. Phase comparison with a 16 orbit precessing simulation shows differences within the NR uncertainties. We demonstrate the applicability of the model in GW parameter estimation by performing the first BHNS Bayesian analysis with HMs (and nonprecessing spins) of the event GW190814 , together with new (2, 2)-mode analysis of GW200105 and GW200115 . For the GW190814 study, the inclusion of HMs gives tighter parameter posteriors. The Bayes factors of our analyses on this event show decisive evidence for the presence of HMs, but no clear preference for a BHNS or a binary black hole source. Similarly, we confirm GW200105 and GW200115 show no evidence for tidal effects.

• Speaker: Alejandra González (FSU Jena)
• Friday 16 February 2024, 13:00-14:00
• Venue: Potter room/Zoom.
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

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Type Ia supernovae (SNe Ia) can be standardised to provide distance estimates to put constraints on cosmological parameters. When building a sample for this, astrophysical selection effects mean that we are biased towards detecting SNe Ia with certain characteristics. The most famous example is Malmquist bias, meaning surveys are more likely to detect brighter SNe towards the edge of their limiting magnitudes. This disproportionally bright sample at high redshifts leads to an underestimation of distances on the Hubble diagram. If we fit for cosmological parameters naively without accounting for this effect, we will bias our constraints on fundamental parameters. In this presentation I will cover some of the existing methods to correct for Malmquist bias. I will then outline our own method that combines simulation-based inference and hierarchical Bayesian modelling. Simple simulations will be used to demonstrate our method can match analytical solutions. I will conclude by discussing plans to show the generalisation of our flexible method to real survey selection effects where analytical solutions are intractable.

• Speaker: Ben Boyd
• Wednesday 14 February 2024, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: .

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Abstract not available

• Speaker: Silvia Pla Garcia (King's College London)
• Monday 26 February 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

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The Cosmic Dawn marks the first star formations and preceded the Epoch-of-Reionization, when the Universe underwent a fundamental transformation propelled by the radiation from these first stars and galaxies. Interferometric 21-cm experiments aim to probe redshifted neutral hydrogen signals from these periods, constraining the conditions of the early Universe. The SKA -LOW instrument of the Square Kilometre Array telescope is envisaged to be the largest and most sensitive radio telescope at m and cm wavelengths. In this talk we present a data analysis pipeline that was used in the SKA Science Data Challenge 3a: Epoch of Reionisation (SKA SDC3a) to process the novel data products expected from the SKA . To determine whether a successful 21-cm detection is possible with the envisaged SKA , we implement predictive foreground and Bayesian Gaussian Process Regression models alongside a foreground avoidance strategy to isolate the 21-cm signal from that of the astrophysical radio frequency (RF) foregrounds.

• Speaker: Yuchen Liu & Oscar O'Hara (Cavendish Astrophysics)
• Tuesday 13 February 2024, 11:15-12:00
• Venue: Coffee area, Battcock Centre.
• Series: Hills Coffee Talks; organiser: Charles Walker.

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The cosmic history of galaxy formation is the history of star formation writ large. While the contents of the universe are mostly invisible and interact with baryons only weakly, a wide array of physical processes affect evolution of the observable baryons. Some of the most important processes involve coupling between stellar and gaseous components, since massive stars are the primary energy source in the interstellar medium (ISM), circumgalactic medium (CGM), and intergalactic medium (IGM). The majority of stellar energy — including UV radiation, winds, and supernovae — is returned rapidly after a given population of stars forms, and is therefore collectively termed “star formation feedback.” Because the state of the ISM determines the star formation rate, and stellar feedback determines the ISM state, quantifying how this co-regulation works is crucial to theoretical modeling. The need to quantify feedback responses also extends to galaxy formation theory on larger scales, where galactic winds driven by feedback heat and add metals to the CGM , thereby regulating the accretion that replenishes the ISM , and where escaping stellar UV ionizes the IGM . Because the observational characterization of galaxies — both near and far — relies on emission lines and infrared continuum from gas and dust subject to photoheating and photochemistry from starlight, quantitative interpretation of observations also relies on calibration using physical models that accurately represent radiative transfer in complex environments. In this lecture, I will review current theory of the physics of feedback, showcasing results from state-of-the-art, high-resolution numerical radiation-magnetohydrodynamic simulations that directly follow multiphase ISM evolution including the effects of UV radiation, stellar winds, and supernovae. These simulations, on both scales of individual star-forming molecular clouds, and scales of galactic disks, show star formation efficiencies and rates that are consistent with detailed observations in the nearby universe, and also indicate strong sensitivity to environment. At high densities and where dust and metal abundances are high, stellar radiation does not propagate as far, and cooling rates are enhanced. As a result of the reduced effectiveness of feedback in maintaining the ISM pressure (turbulent, thermal, and magnetic), star formation rates and efficiencies are expected to increase in high-density environments. Results from suites of resolved star-forming ISM simulations have been used to calibrate new subgrid models, and incorporation of these new results in galaxy formation models may potentially significantly change predictions for star formation at high redshift.

• Speaker: Eve Ostriker (Princeton University)
• Tuesday 12 March 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy (and online - details to be sent by e-mail).
• Series: The Kavli Lectures; organiser: Steven Brereton.

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Abstract not available

• Speaker: Claudio Zanni (INAF Turin)
• Monday 17 June 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

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Abstract not available

• Speaker: Chris Osborne (Glasgow)
• Monday 10 June 2024, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.

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