Fri 24 May 11:30: The Extremes of Resolved Stellar Spectroscopy
The study of local star clusters and galaxies with existing spectroscopic instruments and techniques has reached the point of diminishing returns. Breakthroughs require new instruments or innovation in spectral analysis. I will describe the measurement of radial velocities and abundances of individual stars at the threshold of spectral resolution and signal-to-noise ratio. First, I will address measurements from Keck/DEIMOS and KCWI . I will discuss the “backsplash” galaxy Andromeda XVIII (at 1.33 Mpc!), neutron-capture abundances in Milky Way satellites, and the “fundamental” stellar mass-stellar metallicity relation of low-mass field galaxies. New spectrograph innovations, like the upgrade to DEIMOS and the Subaru Prime Focus Spectrograph, will lead stellar spectroscopy into the future.
- Speaker: Evan Kirby (Notre Dame)
- Friday 24 May 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Tue 21 May 11:15: Diffusion meets Nested Sampling
Sampling techniques are a stalwart of reliable inference in the physical sciences, with the nested sampling paradigm emerging in the last decade(s) as a ubiquitous tool for model fitting and comparison. Parallel developments in the field of generative machine learning have enabled advances in many applications of sampling methods in scientific inference pipelines. This work explores the synergy of the latest developments in diffusion models and nested sampling. I will review the challenges of precise model comparison in high dimension, and explore how score based generative models can provide a solution. This work builds towards a public code that can apply out of the box to many established hard problems in fundamental physics, as well as providing potential to extend precise inference to problems that are intractable with classical methods. I will motivate some potential applications at the frontiers of inference that can be unlocked with these methods.
- Speaker: David Yallup (University of Cambridge)
- Tuesday 21 May 2024, 11:15-12:00
- Venue: Coffee area, Battcock Centre.
- Series: Hills Coffee Talks; organiser: David Buscher.
Tue 21 May 13:00: Exploring the atmospheric structure of water-rich sub-Neptunes
Population studies and planetary formation models predict a class of water-rich sub-Neptunes consisting of a rocky core overlain by a water-rich envelope. Characterising such planets is difficult since differing interior structures often lead to degenerate mass and radii. Recent JWST observations aim to break some of these degeneracies by retrieving atmospheric composition, however accurate atmospheric models are required to interpret data. For example, separate analyses of the JWST transmission spectrum of water world candidate TOI -270 d predicted different interior structures – a “Hycean world” scenario with a liquid water surface and a “miscible sub-Neptune” where the water in the envelope is in a supercritical state. To distinguish these scenarios, I have developed a radiative-convective model specifically designed to model water-rich sub-Neptunes. In particular, the model accounts for the inhibition of convection due to mean molecular weight gradients induced by the condensation of water vapour in a less dense background gas. I show that this can warm a liquid water surface significantly, moving the traditional habitable zone of the planet outwards and disfavouring the presence of water oceans for sub-Neptunes with Earth-like instellations. Following on from this, I will explore the possible equilibrium states of a sub-Neptune with a supercritical water envelope. Lastly, I will discuss attempts to decipher whether sub-Neptunes have surfaces using atmospheric chemistry and the implications this has on interpreting present and future observations.
- Speaker: Hamish Innes (Freie Universität - Berlin)
- Tuesday 21 May 2024, 13:00-14:00
- Venue: Hoyle Committee Room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.
Tue 21 May 13:00: Exploring the atmospheric structure of water-rich sub-Neptunes
Population studies and planetary formation models predict a class of water-rich sub-Neptunes consisting of a rocky core overlain by a water-rich envelope. Characterising such planets is difficult since differing interior structures often lead to degenerate mass and radii. Recent JWST observations aim to break some of these degeneracies by retrieving atmospheric composition, however accurate atmospheric models are required to interpret data. For example, separate analyses of the JWST transmission spectrum of water world candidate TOI -270 d predicted different interior structures – a “Hycean world” scenario with a liquid water surface and a “miscible sub-Neptune” where the water in the envelope is in a supercritical state. To distinguish these scenarios, I have developed a radiative-convective model specifically designed to model water-rich sub-Neptunes. In particular, the model accounts for the inhibition of convection due to mean molecular weight gradients induced by the condensation of water vapour in a less dense background gas. I show that this can warm a liquid water surface significantly, moving the traditional habitable zone of the planet outwards and disfavouring the presence of water oceans for sub-Neptunes with Earth-like instellations. Following on from this, I will explore the possible equilibrium states of a sub-Neptune with a supercritical water envelope. Lastly, I will discuss attempts to decipher whether sub-Neptunes have surfaces using atmospheric chemistry and the implications this has on interpreting present and future observations.
- Speaker: Hamish Innes (Freie Universität - Berlin)
- Tuesday 21 May 2024, 13:00-14:00
- Venue: Hoyle Committee Room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.
Mon 20 May 14:00: A large-scale dynamo via MRI-driven alpha Omega dynamo in binary neutron star mergers
We challenge the magnetar scenario for short gamma-ray bursts by performing a high-resolution neutrino magnetohydrodynamics numerical relativity simulation of a binary neutron star merger. We find the alpha Omega dynamo mediated by the magnetorotational instability generates the large-scale magnetic field in the merger remnant. The resultant large-scale field is efficiently wrapped and drives a relativistic Poynting-flux dominated outflow from the merger remnant.
- Speaker: Kenta Kiuchi (Max Planck Institute for Gravitational Physics)
- Monday 20 May 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Tue 21 May 12:00: The dynamics of parsec-scale eccentric stellar disks around SMBHs in galactic nuclei: disk disruption mechanisms, tidal disruption events and milliparsec stars
We study the dynamics of eccentric parsec-scale stellar disks around supermassive black holes (SMBHs) in galactic nuclei using our novel post-Newtonian N-body code BIFROST . The simulated eccentric disks (Mdisk
- Speaker: Antti Rantala (Max Planck Institute for Astrophysics)
- Tuesday 21 May 2024, 12:00-13:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Thomas Jannaud.
Fri 17 May 11:30: Machine Learning enhanced Bayesian Workflows for Galaxies
Abstract not available
- Speaker: Harry Bevins (KICC)
- Friday 17 May 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Thu 13 Jun 16:00: Title to be confirmed
Abstract not available
- Speaker: Georges Maynet (Geneva)
- Thursday 13 June 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: eb694.
Ray Dolby Professorship of Theoretical and Experimental Physics
The Board of Electors to the Ray Dolby Professorship of Theoretical and Experimental Physics invite applications for this Professorship from persons whose work falls within the general field of the Professorship to take up appointment as soon as possible.
Candidates will have an outstanding research record of international stature in the broader field of quantum phenomena and technologies, including but not limited to development of novel quantum devices, precision measurements at the quantum level, and investigations of topological and layered materials and devices. The candidate will also have the vision, leadership, experience and enthusiasm to build on current strengths in maintaining and developing a leading research presence. They will hold a PhD or equivalent postgraduate qualification.
Standard professorial duties include teaching and research, examining, supervision and administration. The Professor will be based in Cambridge. A competitive salary will be offered.
Click the 'Apply' button below to register an account with our recruitment system (if you have not already) and apply online.
Further information is available at: http://www.hr.admin.cam.ac.uk/professorships or contact the Human Resources, University Offices, The Old Schools, Cambridge, CB2 1TT, (email: professorships@admin.cam.ac.uk).
Applications, consisting of a letter of application, a statement of current and future research plans, a curriculum vitae and a publications list, along with details of three referees should be made online no later than 12 September 2024.
Informal enquiries may be directed to Professor Mete Atat¿re, Head of Department of Physics and Convenor of Board of Electors.
Please quote reference KA41639 on your application and in any correspondence about this vacancy.
The University actively supports equality, diversity and inclusion and encourages applications from all sections of society.
The University has a responsibility to ensure that all employees are eligible to live and work in the UK.
Fri 12 Jul 11:30: Title to be confirmed
Abstract not available
- Speaker: Suhail Dhawan (KICC)
- Friday 12 July 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Fri 06 Sep 11:30: Title to be confirmed
Abstract not available
- Speaker: Mark Krumholz (ANU)
- Friday 06 September 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Wed 15 May 13:15: Prototyping a Sparse-Aperture, Segmented, Parabolic Primary Mirror Telescope for SUPERSHARP
The motivation for my research comes from the SUPERSHARP mission concept for large, unfolding, lightweight space telescopes which take advantage of unfolding segmented optics and a sparse aperture primary mirror to generate powerful observations while maintaining limited cost, mass, and volume requirements. The original motivation for the SUPERSHARP design comes from the ongoing search for life in the universe, but the technology has wider applications in both space and Earth observation. Prototyping of the optical system is integral to ensuring technological readiness of key aspects of the telescope design – in particular, the active control and maintenance of optics alignment. In this talk, I will present the work I have done designing and building a prototype of a sparse-aperture, segmented, parabolic primary mirror telescope using two mirror segments. I will also outline the immediate improvements and next steps required for the prototype to more accurately model an effective imaging system.
- Speaker: Zoe Horvath
- Wednesday 15 May 2024, 13:15-13:40
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: .
Fri 17 May 13:00: Non-smooth horizons in Kerr black hole mergers
Dynamical black holes are known to develop non-smooth structures on their horizon. We begin by reviewing a classification of all generic non-smooth structures that may appear on black hole horizons in four-dimensional spacetimes. Introducing a time function, we describe how two of these features – namely creases and caustics – evolve, and in particular discuss processes known as ‘perestroikas’, where the non-smooth structure on a horizon cross-section changes qualitatively. We then study the merger of two Kerr black holes in the extreme mass ratio limit, and focus on the creases and caustics that are present on the horizon. We explain how our results differ from an older analysis of the same system by Emparan et al., and show that these novel results are consistent with the properties of creases expected generically. This talk is based on work done with Harvey Reall and Robie Hennigar.
- Speaker: Maxime Gadioux, DAMTP, University of Cambridge
- Friday 17 May 2024, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Tue 14 May 13:00: Attractor reconstruction of active stellar light curves
Stellar activity is notoriously difficult to model, being neither periodic nor purely stochastic. In light curves, the interplay between the stellar rotation period and the birth and death of spots and faculae gives rise to quasi-periodic modulation over time scales of hours to weeks. Despite the complexity of this interplay, the resulting light curves bear strong qualitative resemblance to systems known to exhibit low-dimensional dynamical chaos, such as the Rössler attractor.
In the 1980s and 1990s, a suite of techniques for nonlinear dynamical analysis, called attractor reconstruction, evolved to study exactly this type of system. Attractor reconstruction works by embedding a 1-dimensional time series, such as stellar light curve, in a higher-dimensional phase space capable of capturing its full dynamical behavior: too low a dimensionality, and the system’s trajectory will self-intersect and tangle, which we know to be physically unrealistic given the non-periodicity of the observed signal. This technique has been used successfully to model the historical sunspot record and the light curves of variable stars (both simulated and observed) and to recover important features of their underlying dynamics, including their dimensionality and the time scales over which they can be meaningfully forecast into the future. Here, I discuss the application of attractor reconstruction to the light curve of the Sun over Solar cycles 23-25, as observed by the Solar and Heliospheric Observatory.
- Speaker: Emily Sandford (Cavendish)
- Tuesday 14 May 2024, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.
Tue 14 May 13:00: Attractor reconstruction of active stellar light curves
Stellar activity is notoriously difficult to model, being neither periodic nor purely stochastic. In light curves, the interplay between the stellar rotation period and the birth and death of spots and faculae gives rise to quasi-periodic modulation over time scales of hours to weeks. Despite the complexity of this interplay, the resulting light curves bear strong qualitative resemblance to systems known to exhibit low-dimensional dynamical chaos, such as the Rössler attractor.
In the 1980s and 1990s, a suite of techniques for nonlinear dynamical analysis, called attractor reconstruction, evolved to study exactly this type of system. Attractor reconstruction works by embedding a 1-dimensional time series, such as stellar light curve, in a higher-dimensional phase space capable of capturing its full dynamical behavior: too low a dimensionality, and the system’s trajectory will self-intersect and tangle, which we know to be physically unrealistic given the non-periodicity of the observed signal. This technique has been used successfully to model the historical sunspot record and the light curves of variable stars (both simulated and observed) and to recover important features of their underlying dynamics, including their dimensionality and the time scales over which they can be meaningfully forecast into the future. Here, I discuss the application of attractor reconstruction to the light curve of the Sun over Solar cycles 23-25, as observed by the Solar and Heliospheric Observatory.
- Speaker: Emily Sandford (Cavendish)
- Tuesday 14 May 2024, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.
Mon 13 May 14:00: Convection, waves and mixing in stars: insights and challenges from numerical simulations
The lifecycle of stars is profoundly shaped by the internal transport and mixing of chemical elements. Within most stars, regions of convective motions and stable stratification coexist, separated by so-called convective boundaries. While convective regions are very efficient at mixing chemical species, stably stratified regions mostly inhibit the vertical transport of elements. Current models suggest that mixing beyond convective regions is needed to explain observed stellar properties. Waves, excited by convection at convective boundaries, could play a crucial role by providing additional mixing in the vertical direction.
In this talk, I will highlight results from recent numerical simulations with the MUSIC code on the study of waves, convection, and mixing in stars. I will discuss challenges in measuring vertical mixing and transport by waves in numerical simulations, and present some prospects for improving our understanding of mixing mechanisms through numerical experiments.
- Speaker: Thomas Guillet (Exeter)
- Monday 13 May 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Fri 14 Jun 11:30: Title to be confirmed
Abstract not available
- Speaker: Sergio Martin Alvarez (Stanford)
- Friday 14 June 2024, 11:30-12:30
- Venue: Ryle seminar room + online.
- Series: Galaxies Discussion Group; organiser: Sandro Tacchella.
Fri 14 Jun 13:00: TBC
TBC
- Speaker: William Biggs, DAMTP, University of Cambridge
- Friday 14 June 2024, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 07 Jun 13:00: TBC
TBC
- Speaker: Amelia Drew, DAMTP, University of Cambridge
- Friday 07 June 2024, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.
Fri 31 May 13:00: TBC
TBC
- Speaker: Iain Davies, DAMTP, University of Cambridge
- Friday 31 May 2024, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Xi Tong.