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The WEAVE-TwiLight Survey: Implementing and Testing a New Low Field Density Observing Mode

Bright exoplanet host stars provide highly precise stellar and planetary parameters, as well as chemical abundances. However, modern multi-object spectroscopic surveys often neglect stars brighter than 11 visual magnitudes due to their relatively low on-sky number density, resulting in significant observational overhead. The WEAVE -TwiLight Survey (WTLS) will address this gap by employing a groundbreaking observing mode, that allows for observations of low-density/bright star fields, without compromising survey efficiency. With an input catalogue derived primarily from the northern PLATO long-duration phase field, WEAVE -TwiLight will result in a highly homogeneous spectral dataset, characterizing approximately 6,000 future PLATO targets, including 68 confirmed planet hosts. In this talk, I will present the progress made in implementing the new observing mode, alongside preliminary results from test observations obtained in late summer 2024, using WEAVE ’s high-resolution setup. Full-scale science operations for WEAVE -TwiLight are expected to begin in Q2 of 2025.

• Speaker: Thomas Hajnik / IoA
• Wednesday 05 February 2025, 13:15-13:40
• Venue: The Hoyle Lecture Theatre + Zoom .
• Series: Institute of Astronomy Seminars; organiser: Xander Byrne.

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Animals, Sediments, Slime, Muck and Goo: The Record of Earth’s Early Animals and their Environments with Implications for Discovering Life Elsewhere

Patterns of origination and evolution of early complex life on this planet are interpreted largely from the fossils of the Precambrian soft-bodied Ediacara Biota. Excavation and reconstruction of beds of the Ediacara Member of the Rawnsley Quartzite at the Nilpena Ediacara National Park fossil site in the Flinders Ranges area of South Australia has exposed nearly 400 square meters of fossiliferous bedding planes. As a result, the taphonomy and sedimentology of the succession are well-constrained, rendering it possible to disentangle ecological from environmental and taphonomic signals. The excavation and reconstruction of beds at Nilpena yields an exceptional and unique opportunity to examine not only the taxonomic composition of Ediacara communities but also their ecological character at various stages of development and the nature of the complex and diverse organic mat structures. Preserved ecological ‘snapshots’ of fossil assemblages range from immature communities of small-bodied individuals, associated with poorly developed organic mats to communities characterized by a high diversity of macrofaunal taxa, wide range of body sizes and the presence of dense textured organic surfaces. Animals of the Ediacara Biota had an intimate relationship with the organic mats which acted as a food source for early motile organisms and as a place of attachment for sessile organisms living in high energy conditions. Mapping of fossil beds has revealed ecological interactions such as self-thinning and commensalism as well as new body plan – most recently, the oldest ecdysozoan and evidence of chirality. Together with data from other fossil sites around the world, it is very clear that the dawn and early evolution of the animal life is recorded in the Ediacaran Period.

• Speaker: Mary Droser, University of California, Riverside (Department of Earth and Planetary Sciences)​
• Wednesday 05 March 2025, 16:00-17:00
• Venue: Martin Ryle Seminar Room, Kavli Institute.
• Series: LCLU Seminars; organiser: Selen Etingü.

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arXiv:2501.14408v1 Announce Type: new Abstract: The Euclid mission is generating a vast amount of imaging data in four broadband filters at high angular resolution. This will allow the detailed study of mass, metallicity, and stellar populations across galaxies, which will constrain their formation and evolutionary pathways. Transforming the Euclid imaging for large samples of galaxies into maps of physical parameters in an efficient and reliable manner is an outstanding challenge. We investigate the power and reliability of machine learning techniques to extract the distribution of physical parameters within well-resolved galaxies. We focus on estimating stellar mass surface density, mass-averaged stellar metallicity and age. We generate noise-free, synthetic high-resolution imaging data in the Euclid photometric bands for a set of 1154 galaxies from the TNG50 cosmological simulation. The images are generated with the SKIRT radiative transfer code, taking into account the complex 3D distribution of stellar populations and interstellar dust attenuation. We use a machine learning framework to map the idealised mock observational data to the physical parameters on a pixel-by-pixel basis. We find that stellar mass surface density can be accurately recovered with a $\leq 0.130 {\rm \,dex}$ scatter. Conversely, stellar metallicity and age estimates are, as expected, less robust, but still contain significant information which originates from underlying correlations at a sub-kpc scale between stellar mass surface density and stellar population properties.

arXiv:2407.10845v2 Announce Type: replace Abstract: We propose and implement a novel test to assess deviations from well-established concordance $\Lambda$CDM cosmology while inferring dark energy properties. In contrast to the commonly implemented parametric forms of the dark energy equation-of-state (EoS), we test the validity of the cosmological constant on the more fundamental scale factor [$a(t)$] which determines the expansion rate of the Universe. We constrain our extended `general model' using the late-time observables. The posterior of the dark energy EoS is mainly constrained to be quintessence-like naturally excluding physically unviable regions such as phantom crossings or exponential growth.

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• Speaker: Malcolm Druett (Sheffield)
• Monday 17 March 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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TBD

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• Speaker: Paul Barrere (Geneva)
• Monday 10 March 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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arXiv:2501.13575v1 Announce Type: new Abstract: AU Mic is a very active M dwarf with an edge-on debris disk and two transiting sub-Neptunes with a possible third planetary companion. The two transiting planets exhibit significant transit-timing variations (TTVs) that are caused by the gravitational interaction between the bodies in the system. Using photometrical observations taken with the CHaracterizing ExOPlanet Satellite (CHEOPS), our goal is to constrain the planetary radii, the orbital distances and periods of AU Mic b and c. We aim to determine the superperiod of the TTVs for AU Mic b and to update the transit ephemeris for both planets. Based on the observed TTVs, we study the possible presence of a third planet in the system. We conducted high precision photometric observations with CHEOPS in 2022 and 2023. We used Allesfitter to fit the planetary transits and to constrain the planetary and orbital parameters. We combined our new measurements with results from previous years to determine the periods and amplitudes of the TTVs. We applied dynamical modelling based on TTV measurements from the 2018-2023 period to reconstruct the perceived variations. The orbital distances and periods for AU Mic b and c agree with the results from previous works. However, the values for the planetary radii deviate slightly from previous values, which we attribute to the effect of stellar spots. AU Mic c showed very strong TTVs, with transits that occurred ~80 minutes later in 2023 than in 2021. Through dynamical analysis of the system, we found that the observed TTVs can be explained by a third planet with an orbital period of ~12.6 days and a mass of 0.203+0.022-0.024 M_E. We explored the orbital geometry of the system and found that AU Mic c has a misaligned retrograde orbit. Due limited number of observations the exact configuration and planetary parameters could not be determined. Further monitoring with CHEOPS may improve these results.

arXiv:2501.13152v1 Announce Type: new Abstract: From $>1000$ orbits of HST imaging, we present deep homogeneous resolved star color-magnitude diagrams that reach the oldest main sequence turnoff and uniformly measured star formation histories (SFHs) of 36 dwarf galaxies ($-6 \ge M_V \ge -17$) associated with the M31 halo, and for 10 additional fields in M31, M33, and the Giant Stellar Stream. From our SFHs we find: i) the median stellar age and quenching epoch of M31 satellites correlate with galaxy luminosity and galactocentric distance. Satellite luminosity and present-day distance from M31 predict the satellite quenching epoch to within $1.8$ Gyr at all epochs. This tight relationship highlights the fundamental connection between satellite halo mass, environmental history, and star formation duration. ii) There is no difference between the median SFH of galaxies on and off the great plane of Andromeda satellites. iii) $\sim50$\% of our M31 satellites show prominent ancient star formation ($>12$ Gyr ago) followed by delayed quenching ($8-10$ Gyr ago), which is not commonly observed among the MW satellites. iv) A comparison with TNG50 and FIRE-2 simulated satellite dwarfs around M31-like hosts show that some of these trends (dependence of SFH on satellite luminosity) are reproduced in the simulations while others (dependence of SFH on galactocentric distance, presence of the delayed-quenching population) are weaker or absent. We provide all photometric catalogs and SFHs as High-Level Science Products on MAST.

arXiv:2501.13082v1 Announce Type: new Abstract: Recent observations from JWST have revealed an abundant population of active galactic nuclei (AGN) and so-called ``Little Red Dots'' (LRDs) at $2\lesssim z \lesssim 11$, many of which are characterized by V-shaped UV-to-optical continua with turnovers around the Balmer limit. The physical nature of these LRDs is unclear, and it remains debated whether the peculiar spectral shape originates from AGN, compact galaxies, or both. We present the analysis of new NIRSpec-IFU data from the BlackTHUNDER JWST Large Programme and archival NIRSpec-MSA data of a lensed LRD at $z=7.04$. The spectra confirm the presence of a smooth Balmer break and a broad H$\beta$ tracing the Broad Line Region (BLR) of an AGN. The small velocity dispersion of the H$\beta$ narrow component indicates a small dynamical mass of the host galaxy of $M_{\rm dyn}<4 \times 10^8~M_{\odot}$, which implies that the stellar population cannot contribute more than 10% to the optical continuum. We show that the Balmer break can be well described by an AGN continuum absorbed by very dense ($n_{\rm H}\sim 10^{10}~{\rm cm^{-3}}$) and nearly dust-free gas along our line-of-sight (possibly gas in the BLR or its surrounding). The same gas is expected to produce H$\beta$ absorption, at a level consistent with a tentative detection ($3\sigma$) in the high-resolution spectrum. Such a non-stellar origin of the Balmer break may apply to other LRDs, and would alleviate the issue of extremely high stellar mass surface densities inferred in the case of a stellar interpretation of the Balmer break. We note that this is a rare case of a black hole that is overmassive relative to both the host galaxy stellar and dynamical masses. We finally report indications of variability and the first attempt of AGN reverberation mapping at such an early epoch.

Title to be confirmed

Abstract not available

• Speaker: Etienne Camphuis
• Monday 09 June 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Louis Legrand.

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arXiv:2406.07030v2 Announce Type: replace Abstract: The direct observation of cold and temperate planets within 1 to 10 AU would be extremely valuable for uncovering their atmospheric compositions but remains a formidable challenge with current astronomical methods. Ground-based optical interferometry, capable of high angular-resolution imaging, offers a promising avenue for studying these exoplanets, complementing space-based observations. Our objective is to explore the fundamental limits of dual-field interferometry and assess its potential for characterizing exoplanets in reflected light using the Very Large Telescope Interferometer (VLTI). We developed analytical expressions to describe the performance of dual-field interferometry and integrated these with simulations of atmospheric wavefronts corrected by extreme Adaptive Optics. An analytical solution for optimal phase apodization was formulated to enhance starlight rejection when injected into a single-mode fibre. This framework was applied to determine the detectability of known exoplanets in reflected light across various wavelength bands for both the current VLTI and a proposed extended version. Our results indicate that employing shorter wavelengths improves detectability, enabling at least seven Jupiter-mass exoplanets to be observed in the J band with current VLTI's baselines. Adding new baselines with lengths beyond 200 meters significantly enhances VLTI's capabilities, increasing the number of detectable exoplanets and revealing potential habitable zone candidates such as $\tau$ Ceti e and Proxima Centauri b. To substantially improve the VLTI's exoplanet characterization capabilities, we recommend developing instrumentation at wavelengths shorter than 1$\,\mu$m, as well as the addition of a fifth Unit Telescope (UT5).

arXiv:2410.11077v2 Announce Type: replace Abstract: Carbon-rich (C-rich) stars can be found at all metallicities and evolutionary stages. They are often the result of mass-transfer from a companion, but some of the most metal-poor C-rich objects are likely carrying the imprint of the metal-free First Stars from birth. In this work, we employ a neural network to predict metallicities and carbon abundances for over 10 million stars with Gaia low-resolution XP spectra, down to [Fe/H] = -3.0 and up to [C/Fe] $\approx$ +2. We identify ~2000 high-confidence bright (G<16) carbon-enhanced metal-poor (CEMP) stars with [Fe/H] < -2.0 and [C/Fe] > +0.7. The majority of our C-rich candidates have [Fe/H] > -2.0 and are expected to be binary mass-transfer products, supported by high barium abundances in GALAH and/or their Gaia RUWE and radial velocity variations. We confirm previous findings of an increase in C-rich stars with decreasing metallicity, adopting a definition of $3\sigma$ outliers from the [C/Fe] distribution, although our frequency appears to flatten for -3.0 < [Fe/H] < -2.0 at a level of 6-7%. We also find that the fraction of C-rich stars is low among globular cluster stars (connected to their lower binary fraction), and that it decreases for field stars more tightly bound to the Milky Way. We interpret these last results as evidence that disrupted globular clusters contribute more in the inner Galaxy, supporting previous work. Homogeneous samples like these are key to understanding the full population properties of C-rich stars, and this is just the beginning.

Title to be confirmed

Abstract not available

• Speaker: Timothy Hallatt (MIT)
• Tuesday 17 June 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Title to be confirmed

Abstract not available

• Speaker: Felix Sainsbury-Martinez (Leeds)
• Tuesday 10 June 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Title to be confirmed

Abstract not available

• Speaker: Anibal Sierra (UCL)
• Tuesday 03 June 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Title to be confirmed

Abstract not available

• Speaker: Lev Tal-Or (Ariel)
• Tuesday 20 May 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Title to be confirmed

Abstract not available

• Speaker: Olja Panic (Leeds)
• Tuesday 13 May 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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Title to be confirmed

Abstract not available

• Speaker: Craig Walton (ETH)
• Tuesday 18 March 2025, 13:00-14:00
• Venue: Ryle seminar room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Dolev Bashi.

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arXiv:2410.13935v2 Announce Type: replace-cross Abstract: Quasinormal modes (QNMs) are usually characterized by their time dependence; oscillations at specific frequencies predicted by black hole (BH) perturbation theory. QNMs are routinely identified in the ringdown of numerical relativity waveforms, are widely used in waveform modeling, and underpin key tests of general relativity and of the nature of compact objects; a program sometimes called BH spectroscopy. Perturbation theory also predicts a specific spatial shape for each QNM perturbation. For the Kerr metric, these are the ($s=-2$) spheroidal harmonics. Spatial information can be extracted from numerical relativity by fitting a feature with known time dependence to all of the spherical harmonic modes, allowing the shape of the feature to be reconstructed; a program initiated here and that we call BH cartography. Accurate spatial reconstruction requires fitting to many spherical harmonics and is demonstrated using highly accurate Cauchy-characteristic numerical relativity waveforms. The loudest QNMs are mapped, and their reconstructed shapes are found to match the spheroidal harmonic predictions. The cartographic procedure is also applied to the quadratic QNMs -- nonlinear features in the ringdown -- and their reconstructed shapes are compared with expectations based on second-order perturbation theory. BH cartography allows us to determine the viewing angles that maximize the amplitude of the quadratic QNMs, an important guide for future searches, and is expected to lead to an improved understanding of nonlinearities in BH ringdown.

Title to be confirmed

Abstract not available

• Speaker: Hendrik Hildebrandt (Ruhr University Bochum)
• Monday 16 June 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Louis Legrand.

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