CSH-CEH Virtual Seminar Series

Note: This talk series is triggered by the current coronavirus crisis, which has forced the cancellation of the regular CSH Colloquium and Seminar series. To keep the intellectual momentum, the CSH has partnered with the Centre for Exoplanets & Habitability (CEH) of the University of Warwick to co-host a joint virtual seminar series. Hosted jointly by Kevin Heng (CSH) and Dave Armstrong (CEH).

Day & Time: Every Wednesday from 14:00-15:00 (Central European Time)
British Time: 13:00-14:00
U.S. East Coast Time: 08:00-09:00

Format and Ground Rules:
- 45 minutes of talk time.
- Participants are categorised as Host, Panelist (video+voice rights) or Attendee. By default, anyone entering the Zoom Webinar is an Attendee. The Hosts may promote Attendees to Panelists at their discretion.
- If you wish to ask a question during the talk, we recommend using the Q&A function of Zoom Webinar. It is a button located on your interface. Using the Q&A function allows the questions to be logged and visible for all participants.
- 15 minutes of discussion and Q&A. If you wish to have an extended exchange with the speaker, please indicate this in the chat window and one of the Hosts will promote you to Panelist. Otherwise, please use the Q&A function.

25/03/20 (Wed): Prof. Richard Dawid (University of Stockholm)
Title: The Significance of Non-Empirical Confirmation in Fundamental Physics
Abstract: In the absence of empirical confirmation, scientists may judge a theory’s chances of being viable based on a wide range of arguments. We will discuss Dawid's view that a considerable degree of trust in an empirically unconfirmed theory could be generated based on 'non-empirical theory confirmation’ (Dawid 2013).
Moderator: Dr. Vera Matarese (CSH Fellow in Philosophy of Science)
NOTE: This is a discussion led by the philosophers (Dawid, Matarese), rather than a regular talk.

01/04/20 (Wed): Prof. Jonathan Tan (Chalmers University)
Title: A Light in the Dark - Massive Star Birth Through Cosmic Time
Abstract: Massive stars have played a dominant role in shaping our universe since its earliest times, but there is still no consensus on the mechanism by which they form. I review the physics that is important for massive star formation and the connection this process may have with star cluster formation. I then focus on a particular theoretical model, Turbulent Core Accretion, which assumes the initial conditions are massive, turbulent, magnetized cores of gas and dust that are reasonably close to virial equilibrium. Our group has been exploring this scenario via analytic models and numerical simulations of the physics and chemistry of the interstellar medium, ranging from the earliest pre-stellar core phase to protostellar cores being impacted by strong self-feedback. Crucially, these models can now be tested in detail with ALMA, SOFIA and other facilities, and I present the latest results from multiple projects that are zooming in to massive star birth in the darkest shadows of giant molecular clouds. Extension of this work has the potential to also determine how the full stellar initial mass function is established across different Galactic environments. Finally, I discuss an application of massive star formation theory to the early universe: how massive were the first stars and could they have been the progenitors of supermassive black holes?

08/04/20 (Wed): Dr. Jo Barstow (Open University)
Title: Modelling transit spectra for cloudy exo Jupiters
Abstract: Abstract: For a large fraction of transiting hot Jupiters, spectroscopic observations contain evidence of aerosol in their atmospheres. Generally, transit spectra are interpreted using retrieval methods, which combine simple parameterised atmospheric models with a comparison algorithm such as MultiNest. The physical processes that produce cloud and haze are complex; however, in a retrieval model these phenomena must be represented using a minimal number of parameters. I will discuss the challenges of exoplanet atmosphere retrieval, with an emphasis on the different approaches to modelling cloud on hot Jupiters, and how these influence our understanding of their atmospheres.

15/04/20 (Wed): Prof. Bence Kocsis (Universities of Eötvös and Oxford)
Title: On the Origin of Gravitational Wave Sources observed by LIGO/VIRGO
Abstract: With the detection of gravitational waves emitted during black hole and neutron star mergers, LIGO has recently opened the field of gravitational wave astrophysics. In this talk I will review the astrophysical processes that may be responsible for the formation of the observed events. The event rate distribution with mass, spins, eccentricity and redshift may be used to discriminate among different processes that lead to black hole mergers. I will show that the currently known standard astrophysical merger channels are already in tension with LIGO/VIRGO observations. New ideas may be needed to explain the origin of the detected sources.

22/04/20 (Wed): Dr. Antonija Oklopcic (Harvard-CfA/Amsterdam)
Title: Probing the Dynamics and Magnetic Fields of Extended Exoplanet Atmospheres
Abstract: Atmospheric escape is an important process in the evolution of exoplanet atmospheres, especially those orbiting very close to their host stars. However, many aspects of atmospheric escape remain poorly understood, in part due to a limited number of direct observations of this process. Recently, the high-resolution transmission spectroscopy in the helium line at 1083 nm has been established as a powerful new diagnostic tool for studying the extended and escaping exoplanet atmospheres, providing valuable insights into the dynamics of the upper atmospheres. I will discuss how these observations may lead to a better understanding of the physical processes that drive atmospheric escape. In the second part of the talk, I will describe how radiation polarization in the helium 1083 nm line can be used as a probe of magnetic fields in exoplanet atmospheres. Linear and circular polarization signals in the helium line arise in the presence of a magnetic field due to atomic level polarization induced by anisotropic stellar radiation, and the combined action of the Zeeman and Hanle effects. Assuming magnetic fields with strengths comparable to the magnetic fields observed in solar system planets, polarization signals in the helium 1083 nm line could be detectable with current and next-generation high-resolution spectropolarimeters operating at NIR wavelengths.

29/04/20 (Wed): Prof. Jason Steffen (University of Nevada at Las Vegas)
Title: New measurements of water ice and its implications for exoplanets
Abstract: I present new measurements of the water equation of state under high pressure. These measurements applied new experimental techniques that mitigate against key systematic effects. Analysis of these data show a new phase of water ice between the molecular-bonded Ice-VII and ionic-bonded Ice-X, and a sharp increase in the bulk modulus at the transition to Ice-X. For water-rich, Earth-mass planets, this new phase likely contributes to a significant fraction of the planetary structure and the increased bulk modulus implies larger planets for a given mass.

06/05/20 (Wed): Prof. Konstantin Batygin (Caltech)
Title: Formation of Giant Planet Satellites
Abstract: Recent analyses have shown that the concluding stages of giant planet formation are accompanied by the development of large-scale meridional flow of gas inside the planetary Hill sphere. This circulation feeds a circumplanetary disk that viscously expels gaseous material back into the parent nebula, maintaining the system in a quasi-steady state. Here we investigate the formation of natural satellites of Jupiter and Saturn within the framework of this newly outlined picture. We begin by considering the long-term evolution of solid material, and demonstrate that the circumplanetary disk can act as a global dust trap, where s ~ 0.1-10 mm grains achieve a hydrodynamical equilibrium, facilitated by a balance between radial updraft and aerodynamic drag. This process leads to a gradual increase in the system's metallicity, and eventually culminates in the gravitational fragmentation of the outer regions of the solid sub-disk into R ~ 100 km satellitesimals. Subsequently, satellite conglomeration ensues via pairwise collisions, but is terminated when disk-driven orbital migration removes the growing objects from the satellitesimal feeding zone. The resulting satellite formation cycle can repeat multiple times, until it is brought to an end by photo-evaporation of the parent nebula. Numerical simulations of the envisioned formation scenario yield satisfactory agreement between our model and the known properties of the Jovian and Saturnian moons.

13/05/20 (Wed): Dr. René Kiefer (University of Warwick)
Title: Asteroseismic Insights into Magnetic Activity (Cycles) - From Dwarfs to Giants
Abstract: The properties of stellar oscillation eigenmodes change with the level of magnetic activity. This has been measured with data from CoRoT and Kepler, where signatures of magnetic activity have been found in the seismic parameters of a few dozen main-sequence and sub-giant stars. However, as of yet, no detection of temporal variations in the oscillation frequencies of more evolved stars have been reported.

In this talk, I will first review the progress in the exploration of seismic signatures of magnetic activity (cycles) that has been achieved over the last two decades. To understand the observed variations of mode frequencies of stars stretching from the main-sequence to the asymptotic giant branch, it is first necessary to understand their sensitivity to magnetic perturbations. We used MESA stellar evolutionary models to obtain a set of new scaling relations for these mode sensitivities. Finally, I will present some recent results, which show the first detections of seismic signatures of magnetic activity for several hundred giant stars and I will discuss how these detections compare with the predictions made with our new scaling relations.

20/05/20 (Wed): Dr. Maximilian N. Günther (MIT)
Title: Selected TESS Highlights: Small Planets, Big Flares and Allesfitter
Abstract: The Transiting Exoplanet Satellite Survey (TESS) has now almost completed its primary mission. Over the past two years, TESS has observed nearly the entire sky, photometrically monitoring all bright and nearby stars. On its journey, TESS has detected and confirmed dozens of small exoplanets, discovered thousands of further candidates, and unveiled information about stellar flares on M-dwarfs. In this talk I will showcase a series of TESS highlights that I have worked on. I will focus on small planets orbiting small stars and the impact of stellar flares on their habitability, while also including examples like TESS' first exoplanet, first Earth-sized planet, first habitable zone planet, TTV systems, exoplanet phase curves, as well as super-Earths and sub-Neptunes spanning the photo-evaporation gap. In this context, I will also introduce our allesfitter software, which was key to the analysis of some of these systems and is publicly available.