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Mon 17 Mar 14:00: TBD

Next External Talks - Fri, 24/01/2025 - 10:53
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Mon 10 Mar 14:00: TBD

Next External Talks - Fri, 24/01/2025 - 10:53
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Mon 09 Jun 13:00: Title to be confirmed

Next External Talks - Thu, 23/01/2025 - 09:56
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Mon 16 Jun 13:00: Title to be confirmed

Next External Talks - Fri, 17/01/2025 - 11:21
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Mon 12 May 13:00: Title to be confirmed

Next External Talks - Fri, 17/01/2025 - 11:20
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Mon 24 Mar 13:00: Title to be confirmed

Next External Talks - Thu, 16/01/2025 - 09:44
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Thu 13 Mar 16:00: Reconstructing the History of the Milky Way Galaxy Using Stars

Next Colloquia - Wed, 15/01/2025 - 14:15
Reconstructing the History of the Milky Way Galaxy Using Stars

Astronomy of the Milky Way Galaxy has entered a transformative era. The Gaia mission and an ensemble of ground-based spectroscopic surveys are delivering element abundances and velocities for millions of stars. These data provide both an opportunity to deepen our understanding of galaxy formation and to test the “limits of knowledge.” There have been several surprises that have come out of the large stellar surveys and data-driven methodologies built to analyse them. We have learned that up to 1 in 100 stars in the disk are “abundance doppelgangers” – chemically identical but unrelated – limiting the prospect of reconstructing the disk’s star cluster building blocks. Furthermore, for stars in the disk, most of the element abundances measured for most of the stars can be predicted to a precision of better than 10 percent given only two key abundances. However, this is not the case for stars in the stellar halo. These findings frame how we can most effectively work with the data to turn photons into a quantified description of Galactic history and provide strong constraints on the star formation and mixing processes that have set the Galactic environment.

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Mon 17 Mar 13:00: Title to be confirmed

Next External Talks - Tue, 14/01/2025 - 09:47
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Mon 28 Apr 13:00: Title to be confirmed

Next External Talks - Fri, 10/01/2025 - 15:54
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Wed 14 May 16:00: To be confirmed

Next External Talks - Fri, 20/12/2024 - 09:37
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Wed 04 Dec 13:15: Abiotic Ozone in the Observable Atmospheres of Venus-like Planets

Next Wednesday Seminars - Thu, 28/11/2024 - 17:54
Abiotic Ozone in the Observable Atmospheres of Venus-like Planets

Ozone is a potential exoplanet biosignature due to its association with photosynthetically produced oxygen and strong absorption in the mid-infrared. However, the existence of ozone in Venus’s observable atmosphere, a planet with no known life, raises the possibility of ozone biosignature false-positives on Venus-like exoplanets. We use a photochemical model of Venus’s atmosphere to investigate the origin of its mesospheric ozone layer, and how similar ozone layers would manifest for Venus-like exoplanets. Our model shows that the hypothesis that Venus’s ozone forms on the nightside due to a flux of O radicals from the dayside, cannot generate enough ozone to match observed levels. Furthermore, we show that sufficient ozone cannot be produced by varying the surface chemistry, atmospheric thermal structure, or stellar flux in our model of Venus’s atmosphere, implying that a presently unknown chemical pathway is responsible for the ozone in Venus’s mesosphere. Until the origin of Venus’s ozone is understood, we cannot rule out that ozone production will be common on abiotic Venus-like worlds, a possibility that limits the usefulness of ozone as a biosignature.

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Wed 04 Dec 13:40: Linking the low surface brightness Universe and galactic growth

Next Wednesday Seminars - Thu, 28/11/2024 - 17:54
Linking the low surface brightness Universe and galactic growth

In hierarchical models of galaxy formation and evolution, galaxies grow through gas accretion and merger events. The tidal debris produced during these mergers serves as a fossil record of a galaxy’s assembly history, with characteristics that depend on the nature of the merger. Exploring these faint Low Surface Brightness (LSB) structures around galaxies of varying masses and environments is essential to fully understanding galactic evolution. Advances in dedicated instruments and data reduction pipelines from past, ongoing, and future surveys have significantly expanded our ability to explore the LSB Universe. In this talk, I will discuss how LSB features can be leveraged to investigate galactic growth, using deep imaging data from the Canada-France-Hawaii Telescope (CFHT) and ESA ’s Euclid space telescope, combined with an innovative online annotation tool.

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Wed 04 Dec 13:15: Abiotic Ozone in the Observable Atmospheres of Venus-like Planets

Next Wednesday Seminars - Wed, 27/11/2024 - 10:22
Abiotic Ozone in the Observable Atmospheres of Venus-like Planets

Ozone is a potential exoplanet biosignature due to its association with photosynthetically produced oxygen and strong absorption in the mid-infrared. However, the existence of ozone in Venus’s observable atmosphere, a planet with no known life, raises the possibility of ozone biosignature false-positives on Venus-like exoplanets. We use a photochemical model of Venus’s atmosphere to investigate the origin of its mesospheric ozone layer, and how similar ozone layers would manifest for Venus-like exoplanets. Our model shows that the hypothesis that Venus’s ozone forms on the nightside due to a flux of O radicals from the dayside, cannot generate enough ozone to match observed levels. Furthermore, we show that sufficient ozone cannot be produced by varying the surface chemistry, atmospheric thermal structure, or stellar flux in our model of Venus’s atmosphere, implying that a presently unknown chemical pathway is responsible for the ozone in Venus’s mesosphere. Until the origin of Venus’s ozone is understood, we cannot rule out that ozone production will be common on abiotic Venus-like worlds, a possibility that limits the usefulness of ozone as a biosignature.

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Wed 27 Nov 13:40: Tracing velocity substructures in the planet-forming disks of exoALMA

Next Wednesday Seminars - Sun, 24/11/2024 - 17:43
Tracing velocity substructures in the planet-forming disks of exoALMA

The measurement of rotation curves led to big discoveries in astronomy, like the proposition of dark matter halos around galaxies. With the emergence of ALMA , it is now similarly possible to measure the rotation of gas in protoplanetary disks, which are several orders of magnitude smaller than galaxies. While the overall motion of the gas around newborn stars is Keplerian, with high spectral resolution molecular line observations, we can trace small-scale velocity perturbations caused by local pressure variations in the disk, possibly due to embedded planets. In the talk, I will discuss how we can observe gas rotation in planet-forming disks and what we can learn from studying the deviations from Keplerian rotation. In particular, I will present results from the rotation curve study for the disks of the exoALMA Large Program. We find that substructures in the deviation from Keplerian rotation are ubiquitous in our sample, on both small and large scales, and can reach up to 15 percent in the most extreme cases. Interestingly, the majority of the dust continuum rings and gaps are co-located with pressure maxima and minima, respectively. Finally, I will compare the presented results with the predictions from the theory and put them into the bigger picture of planet formation.

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Wed 27 Nov 13:15: Toward a Self-Consistent Evaluation of Gas Dwarf Scenarios for Temperate Sub-Neptunes

Next Wednesday Seminars - Sun, 24/11/2024 - 17:42
Toward a Self-Consistent Evaluation of Gas Dwarf Scenarios for Temperate Sub-Neptunes

Sub-Neptunes—planets intermediate in size between Earth and Neptune—are a major focus in exoplanet science. Despite having no Solar System counterparts, they are the largest known class of exoplanets. They exhibit an unexpected bimodal size distribution, the larger portion of which has a density inconsistent with an Earth-like rocky composition. This has led to hypotheses about their internal composition, including “gas dwarfs” (rocky planets with hydrogen-rich envelopes) and “volatile-rich” scenarios (water-rich planets with thin hydrogen atmospheres). Interest has grown with suggestions that some volatile-rich planets could be potentially habitable “hycean” worlds. Notably, JWST observations of the temperate sub-Neptune K2-18 b have been variously interpreted: as confirming its hycean candidate status, supporting a gas-dwarf scenario with a magma ocean, or classifying it as a mini-Neptune. In this seminar, I will present an integrated framework we have developed to model gas dwarf scenarios—with and without magma oceans—on temperate sub-Neptunes and to predict their unique observable features. I will then discuss how we applied this framework to K2-18 b, and compare our predictions with available observations to draw conclusions about its likely internal structure.

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Thu 21 Nov 13:40: Tracing velocity substructures in the planet-forming disks of exoALMA

Next Wednesday Seminars - Thu, 21/11/2024 - 13:00
Tracing velocity substructures in the planet-forming disks of exoALMA

The measurement of rotation curves led to big discoveries in astronomy, like the proposition of dark matter halos around galaxies. With the emergence of ALMA , it is now similarly possible to measure the rotation of gas in protoplanetary disks, which are several orders of magnitude smaller than galaxies. While the overall motion of the gas around newborn stars is Keplerian, with high spectral resolution molecular line observations, we can trace small-scale velocity perturbations caused by local pressure variations in the disk, possibly due to embedded planets. In the talk, I will discuss how we can observe gas rotation in planet-forming disks and what we can learn from studying the deviations from Keplerian rotation. In particular, I will present results from the rotation curve study for the disks of the exoALMA Large Program. We find that substructures in the deviation from Keplerian rotation are ubiquitous in our sample, on both small and large scales, and can reach up to 15 percent in the most extreme cases. Interestingly, the majority of the dust continuum rings and gaps are co-located with pressure maxima and minima, respectively. Finally, I will compare the presented results with the predictions from the theory and put them into the bigger picture of planet formation.

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Wed 13 Nov 13:40: The dynamic circumstellar environment around white dwarfs

Next Wednesday Seminars - Mon, 11/11/2024 - 13:26
The dynamic circumstellar environment around white dwarfs

Evidence for the survival of outer planetary systems to the white dwarf phase comes from observations of planetary material polluting the atmospheres of white dwarfs. These observations uniquely reveal the chemical composition of exo-planetary material. Studies of circumstellar dust and gas close to white dwarfs help trace how planetary bodies are perturbed and accreted onto these stars. This scattering process is thought to be stochastic, with the potential for variability observable on human timescales. Indeed, some white dwarfs show variability in their dust and gas, but we are yet to have a comprehensive understanding of these dynamic circumstellar environments. I will present findings from recent studies on circumstellar gas and dust around white dwarfs polluted with planetary material, including the first detection of simultaneous dust and gas emission from a white dwarf disc, advancing us towards a holistic picture of these systems.

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Wed 13 Nov 13:40: TBD

Next Wednesday Seminars - Mon, 11/11/2024 - 09:08
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Wed 13 Nov 13:15: Tagging and Tracing Globular Cluster-Origin Stars from the Early Milky Way with Gaia

Next Wednesday Seminars - Sun, 10/11/2024 - 14:40
Tagging and Tracing Globular Cluster-Origin Stars from the Early Milky Way with Gaia

Globular clusters (GCs) are sites of extremely efficient star formation, and recent studies suggest they significantly contributed to the early Milky Way’s stellar mass build-up. Although their role has since diminished, GCs’ impact on the Galaxy’s initial evolution can be traced today by identifying their most chemically unique stars—those with anomalous nitrogen and aluminum overabundances and oxygen depletion. While they are a perfect tracer of clusters, be it intact or fully dissolved, these high-[N/O], high-[Al/Fe] GC-origin stars are extremely rare within the current Galaxy. To address the scarcity of these unusual, valuable former GC members, we train a neural network (NN) to identify high-[N/O], high-[Al/Fe] stars using low-resolution Gaia BP/RP spectra. Our NN achieves a classification accuracy of approximately 99% and a false positive rate of around 7%, identifying 878 new candidates in the Galactic field. We validate our results with several physically-motivated sanity checks, showing, for example, that the incidence of selected stars in Galactic GCs is significantly higher than in the field. Moreover, we find that most of our GC-origin candidates reside in the inner Galaxy, having likely formed in the proto-Milky Way, consistent with previous research. The fraction of GC candidates in the field drops at a metallicity of [Fe/H]=-1, approximately coinciding with the completion of spin-up, i.e. the formation of the Galactic stellar disk.

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Wed 12 Mar 16:00: To be confirmed

Next External Talks - Thu, 07/11/2024 - 11:00
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