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IoA Institute of Astronomy Talk Lists

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This is a List of Talks Lists that is a List of all IoA Seminars, Colloquia, Extra talks, IoA Stellar Pops and Extragalactic Gathering, etc. It is used as a feed for the IOA website and Digital Display screens. Individual Talks should NOT be added to this Talk lists. They should be added to one of the series that feed this list.
URL: https://talks.cam.ac.uk/show/index/13724
Updated: 54 min 45 sec ago

Fri 24 May 11:30: The Extremes of Resolved Stellar Spectroscopy

Thu, 16/05/2024 - 19:20
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.

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Tue 21 May 13:00: Exploring the atmospheric structure of water-rich sub-Neptunes

Thu, 16/05/2024 - 10:48
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.

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Fri 17 May 11:30: Machine Learning enhanced Bayesian Workflows for Galaxies

Wed, 15/05/2024 - 00:45
Machine Learning enhanced Bayesian Workflows for Galaxies

Abstract not available

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Thu 13 Jun 16:00: Title to be confirmed

Tue, 14/05/2024 - 09:22
Title to be confirmed

Abstract not available

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Fri 12 Jul 11:30: Title to be confirmed

Mon, 13/05/2024 - 08:50
Title to be confirmed

Abstract not available

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Fri 06 Sep 11:30: Title to be confirmed

Mon, 13/05/2024 - 08:26
Title to be confirmed

Abstract not available

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Wed 15 May 13:15: Prototyping a Sparse-Aperture, Segmented, Parabolic Primary Mirror Telescope for SUPERSHARP

Sun, 12/05/2024 - 21:46
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.

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Tue 25 Jun 11:30: Do we understand cosmic structure growth? Insights from new CMB lensing measurements with the Atacama Cosmology Telescope

Fri, 10/05/2024 - 11:08
Do we understand cosmic structure growth? Insights from new CMB lensing measurements with the Atacama Cosmology Telescope

One of the most powerful tests of our cosmological model is to verify the predicted growth of large-scale structure with time. Intriguingly, many recent measurements have reported small discrepancies in such tests of structure growth (“the S8 tension”), which could hint at systematic errors or even new physics. Motivated by this puzzling situation, I will present new determinations of cosmic structure growth using CMB gravitational lensing measurements from the Atacama Cosmology Telescope (ACT). These ACT DR6 CMB lensing measurements allow us to directly map the dark matter distribution in projection out to high redshifts; new cross-correlations of CMB lensing with unWISE galaxies also allow us to probe the matter tomographically. I will discuss the implications of our lensing results for the validity of our standard cosmological model as well as for key cosmological parameters such as the neutrino mass and Hubble constant.

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Tue 14 May 13:00: Attractor reconstruction of active stellar light curves

Fri, 10/05/2024 - 10:47
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.

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Fri 14 Jun 11:30: Title to be confirmed

Thu, 09/05/2024 - 09:07
Title to be confirmed

Abstract not available

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Wed 08 May 10:00: EuCAIFCon recap

Tue, 07/05/2024 - 09:37
EuCAIFCon recap

Discussion of recent EU Conference for AI in fundamental physics

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Fri 10 May 11:30: Halpha filaments in Massive Ellipticals: the roles played by Turbulence and type Ia Supernovae

Fri, 03/05/2024 - 22:22
Halpha filaments in Massive Ellipticals: the roles played by Turbulence and type Ia Supernovae

Massive elliptical galaxies are often quiescent in star formation, despite hosting large amounts of -10 million K gas in their ISM , which can cool in a few 100 Myr and fuel star formation. Many of these elliptical galaxies also host massive kpc-scale filaments of cooler atomic (10^4 K) and molecular gas (~10 K) which coexist with the hot ISM .

Two of the outstanding problems related to these systems are – (1) when and how do these cold filaments form? and (2) what keeps the rest of the ISM of the elliptical galaxies hot?

In the first part of this presentation, I will discuss the results of our latest local patch simulations with gravity, turbulence, and radiative cooling physics included. I will present a new condensation criterion to form cold gas from the hot ISM , which takes the effect of turbulence, cooling, and buoyancy into account. (https://arxiv.org/abs/2302.09380)

In the inner few kilo-parsecs (kpc) of the elliptical galaxies, the net heating due to type 1a supernovae (SNIa) is comparable to the net radiative cooling rate and can help maintain the ISM hot. In the second part of the talk, I will present the results from our 1 kpc ISM -patch simulations with individually resolved type SNIa bubbles. I will discuss how these SNIa heat the ISM and drive turbulence in it. Finally, I will compare our results against more commonly implemented smooth heating models in previous theoretical studies. (arxiv: https://arxiv.org/abs/2402.03613)

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Fri 10 May 11:30: Halpha filaments in Massive Ellipticals: the roles played by Turbulence and type Ia Supernovae

Fri, 03/05/2024 - 21:26
Halpha filaments in Massive Ellipticals: the roles played by Turbulence and type Ia Supernovae

Massive elliptical galaxies are often quiescent in star formation, despite hosting large amounts of -10 million K gas in their ISM , which can cool in a few 100 Myr and fuel star formation. Many of these elliptical galaxies also host massive kpc-scale filaments of cooler atomic (10^4 K) and molecular gas (~10 K) which coexist with the hot ISM .

Two of the outstanding problems related to these systems are – (1) when and how do these cold filaments form? and (2) what keeps the rest of the ISM of the elliptical galaxies hot?

In the first part of this presentation, I will discuss the results of our latest local patch simulations with gravity, turbulence, and radiative cooling physics included. I will present a new condition criterion to form cold gas from the hot ISM , which takes the effect of turbulence, cooling, and buoyancy into account. (https://arxiv.org/abs/2302.09380)

In the inner few kilo-parsecs (kpc) of the elliptical galaxies, the net heating due to type 1a supernovae (SNIa) is comparable to the net radiative cooling rate and can help maintain the ISM hot. In the second part of the talk, I will present the results from our 1 kpc ISM -patch simulations with individually resolved type SNIa bubbles. I will discuss how these SNIa heat the ISM and drive turbulence in it. Finally, I will compare our results against more commonly implemented smooth heating models in previous theoretical studies. (arxiv: https://arxiv.org/abs/2402.03613)

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Wed 08 May 13:40: Type Ia supernovae: Constraining thermonuclear explosion physics with machine learning

Fri, 03/05/2024 - 11:32
Type Ia supernovae: Constraining thermonuclear explosion physics with machine learning

Type Ia supernovae are thermonuclear explosions of white dwarfs in binary systems. They play an important role in many areas of astrophysics, from providing chemical enrichment for galaxies to acting as cosmological distance probes. In spite of this, we still fundamentally do not know how or why some white dwarfs explode as thermonuclear supernovae. Multiple explosion mechanisms have been proposed, but the computational expense associated with developing realistic explosion simulations and the difficulty in observing key diagnostic signatures mean that providing robust constraints on the explosion physics is challenging. In this talk, I will provide a general overview of thermonuclear explosion physics and discuss the main explosion scenarios suggested in the literature. I will present my recent work focused on using machine learning to automatically fit spectral sequences of type Ia supernovae in a much more quantitative and efficient way than existing methods. With automated fitting we can test different explosion scenarios against observations and statistically determine which scenario provides the best overall agreement. As spectroscopic samples of supernovae continue to grow, automated fitting tools will become increasingly important to maximise the physical constraints that can be gained in a quantitative and consistent manner.

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Wed 08 May 13:15: The cometary delivery of prebiotic feedstock molecules to the early-Earth and rocky exoplanets

Thu, 02/05/2024 - 10:12
The cometary delivery of prebiotic feedstock molecules to the early-Earth and rocky exoplanets

The delivery of prebiotic feedstocks molecules, such as hydrogen cyanide (HCN), during cometary impacts may have significantly influenced prebiotic chemistry on the early Earth, motivated by the discovery of a rich diversity of CHN - and CHS -bearing molecules on solar system comets. Numerical experiments have demonstrated that HCN survival during cometary impacts is however only possible in oblique impacts at very low velocities. In this talk I will discuss the effects of stellar mass, and planetary architecture on minimum cometary impact velocities onto rocky exoplanets. Using both an analytical model and numerical N-body simulations, we show the lowest impact velocities occur for low-mass planets in tightly-packed planetary systems around high-mass (i.e., Solar-mass) stars, enabling the intact delivery of prebiotic feedstock molecules. I will finish by discussing a specific origins scenario, proposed to achieve favourable conditions for subsequent prebiotic chemistry, which invokes the arrival of a secondary impactor in the same location. We consider the atmospheric fragmentation of cometary impactors, and use the lunar crater record to quantitatively evaluate the likelihood of these `double impact’ scenarios on the early-Earth. These scenarios are found to be extremely unlikely settings for the initial stages of prebiotic chemistry, unless there was a particularly high impact rate on the early-Earth, and global environmental conditions conducive to successful cometary delivery.

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Thu 13 Jun 16:00: Title to be confirmed

Tue, 30/04/2024 - 17:01
Title to be confirmed

Abstract not available

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Thu 13 Jun 16:00: Title to be confirmed

Tue, 30/04/2024 - 17:01
Title to be confirmed

Abstract not available

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Thu 09 May 16:00: Insights into cosmological simulations from modified initial conditions

Tue, 30/04/2024 - 16:51
Insights into cosmological simulations from modified initial conditions

I will discuss the GMGalaxies programme, which is pursuing a new ‘hybrid’ approach to cosmological galaxy formation simulations combining the best of cosmological zooms and idealised approaches of the past. By customising (‘genetically modifying’) our initial conditions, we can construct controlled tests of structure formation within a fully cosmological environment. This approach has allowed us to obtain new and unique insights into ultra-faint dwarf galaxy formation, AGN -driven galaxy quenching, large scale structure formation and — in soon-to-be-released ultra-high-resolution simulations — the Milky Way fossil record seen by Gaia. In this talk, I will summarise some of these results but focus especially on recent insights into dwarf galaxy formation.

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Thu 06 Jun 16:00: Black hole accretion in the TDAMM Era

Tue, 30/04/2024 - 12:40
Black hole accretion in the TDAMM Era

Most of the power from an Active Galactic Nucleus is released close to the black hole, and thus studying accretion at event horizon scales—at the intersection of inflow and outflow—is essential for understanding how much matter accretes and grows the black hole vs. how much matter is ejected, thus effecting the black hole’s large-scale environments. In the past decade, we have had a breakthrough in how we probe the inner accretion flow, through the discovery of X-ray Reverberation Mapping, where X-rays produced close to the black hole reverberate off inflowing gas. By measuring reverberation time delays, we can quantify the effects of strongly curved space time and measure black hole spin, which is key for understanding how efficiently energy can be tapped from the accretion process. In this talk, I will give an overview of this field, and will show how extending these spectral-timing techniques to extreme, transient (and possibly multi-messenger) accretion events like Tidal Disruption Events and Quasi Periodic Eruptions can help us understand the growth and impact of black holes in galactic centers.

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Fri 05 Jul 11:30: Title to be confirmed

Tue, 30/04/2024 - 10:26
Title to be confirmed

Abstract not available

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