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Exoplanet adventures the 2020s and beyond

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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When black holes are born from collapsing stars, they emit a short-lived jet that may slow down the black hole’s rotation to nearly a standstill

Uncovering Long-Period Transiting Exoplanets with TESS and CHEOPS

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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Dark matter-deficient galaxies (DMDGs) discovered in the survey of ultra-diffuse galaxies (UDGs), in apparent conflict with standard CDM, may be produced by high-velocity galaxy-galaxy collisions, the $\textit{Mini-bullet}$ scenario. Recent observations of an aligned trail of $7-11$ UDGs near NGC1052, including DMDGs DF2 and DF4, suggesting a common formation event, $\sim8.9\pm1.5$ Gyr ago, provide a test. Hydro/N-body simulations, supplemented by galaxy orbit integrations, demonstrate that satellite-satellite collisions outside the host-galaxy virial radius can reproduce the observed UDGs in the NGC1052 group. A trail of $\sim10$ DMDGs is shown to form, including two massive ones that replicate the observed motions of DF2 and DF4. The linear relation, $v=Ax+v_{0}$, conjectured previously to relate positions ($x$) and velocities ($v$) of the aligned DMDGs as a signature of the collision event, is approximately obeyed, but individual DMDGs can deviate significantly from it. The progenitors whose collision spawned the trail of DMDGs survive the collision without, themselves, becoming DMDGs. We predict one progenitor is located at the end of the trail, testable by observing the difference between its stars, formed pre-collision, from those of the DMDGs, formed post-collision. By contrast, stellar ages and metallicities of the DMDGs are nearly identical. We further offer a hint that the tidal field of host NGC1052 may contribute to making DMDGs diffuse. $\Lambda$CDM simulation in a 100 cMpc box finds our required initial conditions $\sim10$ times at $z

High-contrast eclipsing binaries with low mass M-dwarf secondaries are precise benchmark stars to build empirical mass-radius relationships for fully convective low-mass ($\rm M_{*}

The Gaia-ESO Survey is an European Southern Observatory (ESO) public spectroscopic survey that targeted $10^5$ stars in the Milky Way covering the major populations of the disk, bulge and halo. The observations were made using FLAMES on the VLT obtaining both UVES high ($R\sim47,000$) and GIRAFFE medium ($R\sim20,000$) resolution spectra. The analysis of the Gaia-ESO spectra was the work of multiple analysis teams (nodes) within five working groups (WG). The homogenisation of the stellar parameters within WG11 (high resolution observations of FGK stars) and the homogenisation of the stellar parameters within WG10 (medium resolution observations of FGK stars) is described here. In both cases, the homogenisation was carried out using a bayesian Inference method developed specifically for the Gaia-ESO Survey by WG11. The WG10 homogenisation primarily used the cross-match of stars with WG11 as the reference set in both the stellar parameter and chemical abundance homogenisation. In this way the WG10 homogenised results have been placed directly onto the WG11 stellar parameter and chemical abundance scales. The reference set for the metal-poor end was sparse which limited the effectiveness of the homogenisation in that regime. For WG11, the total number of stars for which stellar parameters were derived was 6,231 with typical uncertainties for Teff, log g and [Fe/H] of 32~K, 0.05 and 0.05 respectively. One or more chemical abundances out of a possible 39 elements were derived for 6,188 of the stars. For WG10, the total number of stars for which stellar parameters were derived was 76,675 with typical uncertainties for Teff, log g and [Fe/H] of 64~K, 0.15 and 0.07 respectively. One or more chemical abundances out of a possible 30 elements were derived for 64,177 of the stars.

Correcting for Malmquist Bias in Type Ia Supernova Cosmology

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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We extend our model of magnetic braking (MB) from fully convective M-dwarfs (FCMDs) to explain the surface and internal spin $P_\mathrm{spin}$ evolution of partly convective dwarfs (PCDs) starting from disc-dispersal stage to main-sequence turnoff. In our model, the spin of the core is governed by shear at the core-envelope boundary while the spin of the envelope is governed by MB and shear. We show that (1) the most massive FCMDs experience a stronger spin-down than PCDs and less massive FCMDs; (2) the stalled spin-down and enhanced activity of K-dwarfs and the pileup of G-dwarfs older than a few Gyr are stellar-structure- and MB-dependent, and weakly dependent on core-envelope coupling effects; (3) our empirical expression of the core-envelope convergence time-scale $\tau_\mathrm{converge}(M_\ast,\,P_\mathrm{spin})$ between a few 10 to 100 Myr is strongly dependent on stellar structure and weakly dependent on MB strength and shear, where fast and massive rotators achieve corotation earlier; (4) our estimates of the surface magnetic fields are in general agreement with observations and our wind mass loss evolution explains the weak winds from the solar analog $\pi^1$ UMa; (5) the massive young Sun theory as a solution to the faint young Sun problem, which states that the early Sun was sufficiently more massive to maintain liquid water on Earth when the Sun's luminosity would have been about 30 percent lower, can likely be ruled out because the maximum mass lost by winds from our Sun with our model is about $0.001M_\odot$, an order of magnitude smaller than required to solve the problem with this theory.

For most of humanity’s existence, we have observed the universe using light, but these days photons aren’t the only game in town, says Chanda Prescod-Weinstein

The eROSITA X-ray telescope’s survey of the night sky has revealed extreme and violent processes in the universe, including inexplicably strange stars and erupting black holes

In 1905, Einstein discovered a paradox in the predicted behaviour of mirrors travelling at impossible speeds, but it may now have been resolved

Dual-field interferometric observations with VLTI/GRAVITY sometimes require the use of a "binary calibrator", a binary star whose individual components remain unresolved by the interferometer, with a separation between 400 and 2000 mas for observations with the Units Telescopes (UTs), or 1200 to 3000 mas for the Auxiliary Telescopes (ATs). The separation vector also needs to be predictable to within 10 mas for proper pointing of the instrument. Up until now, no list of properly vetted calibrators was available for dual-field observations with VLTI/GRAVITY on the UTs. Our objective is to compile such a list, and make it available to the community. We identify a list of candidates from the Washington Double Star (WDS) catalogue, all with appropriate separations and brightness, scattered over the Southern sky. We observe them as part of a dedicated calibration programme, and determine whether these objects are true binaries (excluding higher multiplicities resolved interferometrically but unseen by imaging), and extract measurements of the separation vectors. We combine these new measurements with those available in the WDS to determine updated orbital parameters for all our vetted calibrators. We compile a list of 13 vetted binary calibrators for observations with VLTI/GRAVITY on the UTs, and provide orbital estimates and astrometric predictions for each of them. We show that our list guarantees that there are always at least two binary calibrators at airmass

Nature, Published online: 07 February 2024; doi:10.1038/d41586-024-00345-9

The sea within Saturn’s satellite Mimas formed within the last 25 million years, a blink of the eye in geologic terms.

Nature, Published online: 07 February 2024; doi:10.1038/s41586-023-06975-9

An analysis of the orbital motion of Saturn’s moon Mimas shows that a recently formed global subsurface ocean lies beneath its cratered icy shell and that this ocean is probably still evolving.

Nature, Published online: 07 February 2024; doi:10.1038/d41586-024-00194-6

The shifting orbit of one of Saturn’s moons indicates that the satellite has a subsurface ocean, contradicting theories that its interior is entirely solid. The finding calls for a fresh take on what constitutes an ocean moon.

Close measurements of Mimas’s orbit suggest there could be an ocean 30 kilometres deep beneath the small moon’s icy exterior

A type of distant planet long thought to have water oceans on its surface may be too hot for liquid water, and magma oceans might be more likely

Star Formation, Feedback, and Cosmic Evolution: A Modern Primer

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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Star Formation, Feedback, and Cosmic Evolution: A Modern Primer

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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Title to be confirmed

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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